Light influences transpiration and calcium accumulation in fruit of

kiwifruit plants (Actinidia deliciosa var. deliciosa)

Giuseppe Montanaro *, Bartolomeo Dichio, Cristos Xiloyannis,Giuseppe Celano

Dipartimento di Scienze dei Sistemi Colturali, Forestali e dell’Ambiente, University of Basilicata,

Viale dell’Ateneo Lucano, 10-85100 Potenza, Italy

Received 8 June 2005; received in revised form 6 October 2005; accepted 10 October 2005

Available online 2 November 2005

www.elsevier.com/locate/plantsci

Plant Science 170 (2006) 520–527

Abstract

Calcium (Ca) is an essential plant nutrient involved in determining fruit quality of several fruits, including kiwifruit. The objective of the present

study was to evaluate the influence of light intensity on transpiration and water flow into fruit of kiwifruit (Actinidia deliciosa var. deliciosa, C.F.

Liang et A.R. Ferguson) and the resulting effects on Ca accumulation. At fruit-set two light treatments were imposed on single canes. The exposed

treatment was maintained through summer pruning, while the shade treatment was imposed using shade cloth. Fruit transpiration was measured on

attached fruit using a portable photosynthesis system. The inflow of water into the fruit via the xylem was estimated from fruit transpiration and its

relationship with fruit Ca accumulation determined. The concentration of Ca was measured in xylem sap extracted using a Scholander pressure

chamber. Following the first 40–50 days after fruit-set (AFS) the cumulative xylem water inflow into the fruit increased exponentially in both

treatments, but by the end of the growing season the total influx was 30% higher in the exposed treatment than in the shaded treatment, reaching

140 g per fruit. The shade treatment influenced the concentration of Ca, causing accumulation in the fruit to be about 50% of that in the exposed

treatment. Our results suggest that transpiration is not the only factor controlling Ca transport, and that light also influenced the Ca concentration in

xylem sap. Taking into account that auxin is able to stimulate Ca uptake and that light promotes the biosynthesis of auxin protecting phenols

(hydroxycinnamic acids), a new working hypothesis is proposed: light, induces the biosynthesis of such phenols, indirectly decreases auxin

degradation, and therefore, increases Ca accumulation.

# 2005 Elsevier Ireland Ltd. All rights reserved.

Keywords: Exposure conditions; Calcium nutrition; Transport; Xylem; Water inflow

1. Introduction

Calcium (Ca) is an essential plant nutrient, whose role has

been well documented [1]. Ca is involved in several

biochemical and physiological processes [2], but the structural

role of apoplastic Ca is particularly important in fruit pro-

duction, because of its function in the cell wall and the resulting

influence on the shelf-life of several fruit [3] including

kiwifruit.

Low fruit Ca concentrations are generally associated with

physiological disorders in apple [4,5] avocado [6,7] tomato [8]

and kiwifruit [9,10]. Many authors have reported the dynamics

of Ca accumulation in kiwifruit during the growing season and

* Corresponding author. Tel.: +39 3293606252.

E-mail address: fruit@unibas.it (G. Montanaro).

0168-9452/$ – see front matter # 2005 Elsevier Ireland Ltd. All rights reserved.

doi:10.1016/j.plantsci.2005.10.004

have stressed that the amount of Ca in the fruit as early as 6–7

weeks after fruit-set (AFS) accounts for almost the whole

content of Ca at harvest time [11–13]. As for the mechanisms

determining such kinetics of Ca accumulation, there are a

number of hypotheses, but their relative importance has yet to

be determined. McLaughlin and Wimmer [14] have stressed

that Ca uptake and distribution at the whole-plant level is

influenced by water movement to transpiring organs and by the

relative rate of Ca use along the transport pathway. Numerous

environmental and internal factors can also affect Ca transport

into fruit. For example, fruiting position and leaf:fruit ratios are

a major source of variability in fruit mineral composition of

kiwifruit [9,10]. Also the reduced availability of soil water

causing a restricted flow through the xylem can significantly

increase the incidence of Ca-deficiency disorders [15]. In

addition, light influences water uptake and thus fruit mineral

composition [16]. The Ca content in the fruit at harvest, and

G. Montanaro et al. / Plant Science 170 (2006) 520–527 521

therefore, the quality of the fruit, thus depends on the

interaction of many factors.

Light is the environmental factor that has most influence on

yield quality of many tree crops, such as apple [17,18], grapes

[19] and kiwifruit [20–23]. However, little is known about the

mechanisms by which light influences the mineral composition

of fruit. Transport of Ca preferentially occurs in the apoplast

and xylem vessels, where the rate of transportation depends on

Ca2+ exchange adsorption on the xylem walls, on transpiration

rate [14,15,24] and on xylem functionality of the fruit [25].

A relationship between increased vascular development and

increased Ca concentration in kiwifruit exposed to light was

shown by Biasi andAltamura [23]. This suggests some influence

of light on the potential for transportation of nutrients to the fruit

through the transpiration stream.However, there has been limited

research on fruit trees that specifically examines the interactions

between canopy light environment, fruit transpiration and fruit

Ca accumulation, particularly on fruit in situ.

The objective of the present study was to evaluate the

influence of light on fruit transpiration and on water flow into

attached fruits in relation to their Ca accumulation. Reference

was also made to the effect of light on phenols biosynthesis in

kiwifruit, and the significance of these compounds for Ca

transport mechanisms was hypothesised.

2. Materials and methods

2.1. Experimental site and plant material

Trials were carried out during the 2001 growing season in

Southern Italy (Andriace, N 408200 E 168480) on mature own-

rooted kiwifruit plants (Actinidia deliciosa var. deliciosa, C.F.

Liang et A.R. Ferguson) (cultivar Hayward), trained on a

‘‘Pergola’’ system (625 plants ha�1) with E-SE row orientation

(1158 from theNorth), on sandy loamy soil. Thevines and the soil

were managed following local commercial practices. Fertiliser

was supplied through fertigationat a rateof115 kg ha�1 nitrogen,

approximately every 20 days fromApril to July. No phosphorous

and potassium were applied because the soil already had

sufficient amounts (400 ppm exchangeable K, 65 ppm available

P). Thevineswere regularlymicrojet-irrigated during the season,

on an approximately weekly basis in May, June, September, and

every 3 days during the periods of highest evaporative demand

(July,August).Waterwas suppliedbasedonevaporativedemand;

meteorological data were recorded throughout the study. Bloom

occurred during the last 10 days of May, and natural bee

pollination ensured normal and simultaneous fruit-set.

From June 3rd (fruit-set) and throughout the growing season,

2 light exposure levels were imposed on 20 canes with similar

leaf:fruit ratios, selected from five randomly chosen plants.

Each cane had seven to eight terminating shoots and

approximately 25 fruit.

The exposed treatment (>40% of above canopy Photo-

synthetic Photon Flux Density, PPFD, at 12:00 a.m.) was

maintained by summer pruning of shoots likely to shade the

chosen cane, while the shade treatment (<20% available PPFD

at 12:00 a.m.) was obtained using shade cloth (Arrigoni, CO,

Italy, mod. 2591WOOmbraverde 90) causing an 80% reduction

in incident light. The above canopy PPFD at 12:00 a.m. ranged

from 1950 to 1300 mmol m�2 s�1.

2.2. Light interception

Light measurements were carried out using 18 quantum

sensors (Model SKP 215, Skye Instruments LTD, Llandrindod

Wells, UK). Sensors were placed near fruit in three areas per

treatment (three sensors each) in the canopy, one sensor was

placed above the canopy to measure the incident PPFD. All

sensors were connected to a datalogger (CR10, Campbell

Scientific), which was programmed to monitor the PPFD at 60 s

intervals and to compute the averages at 15 min intervals. For

each sensor, daily PPFD was obtained by integrating the data

recorded every 15 min.

2.3. Fruit transpiration

Fruit transpiration was measured on attached fruit of the first

two terminating shoots near the base of the selected cane, using

a portable open system (ADC-LCA4) operated at a flow rate of

200 mmol s�1 (chamber model PLC-3) under the prevailing

environmental conditions. Measurements were taken in the 1st,

2nd, 3rd, 5th, 7th, 8th and 14th weeks AFS, five times per day

from 07:00 a.m. to 06:00 p.m. (approximately every 3 h) on 15

fruit per treatment randomly chosen from three vines.

For estimates of fruit surface area and transpiration rate per

unit surface area, in a preliminary experiment 70 fruit not

included in the trial were carefully peeled during the season and

their skin area measured using a portable area meter (Model Li-

3000, LI-COR). For the same fruit, estimated fruit surface area

(Es) was calculated as Es = LW 3.14, where L is the fruit length

and W, maximum fruit diameter. The fitted linear regression

(y = 1.0078 � Es + 0.798; R2 = 0.97) between estimated and

measured fruit surface area was then used in the field for

measurements of fruit transpiration.

By integrating the five transpiration measurements on each

measurement date the daily fruit transpiration per fruit was

estimated. Water resulting from the oxidation of sugars during

the respiration process was considered negligible (about

0.1 mL of water fruit�1 day�1) [11]. All daily transpiration

data were than analysed, by the integration of Lorentz function

and the cumulated fruit transpiration (CFT) throughout the

season was determined.

2.4. Estimating xylem fruit water inflow (XFWI)

To evaluate the influence of light on the transpiration, water

content and Ca content of the fruit, the contribution of xylem

water to total water flow into the fruit was estimated. The

amount of xylem fruit water inflow (XFWI) throughout the

season was determined as the difference between the sum of the

cumulative fruit transpiration (CFT) and the fruit water content

(FWC), and the cumulative phloem influx (PFWI)

XFWI ¼ CFTþ FWC� PFWI (1)

G. Montanaro et al. / Plant Science 170 (2006) 520–527522

Table 1

Values of the parameters of the dry matter accumulation function (Boltzman),

water content function (Double sigmoid) and daily transpiration function

(Lorentz) of kiwifruit grown in exposed and shaded position

A1 A2 X0 dx R2

Boltzman

Exposed �0.6252 20.414 62.142 23.012 0.99

Shaded �3.6829 19.281 60.864 36.409 0.98

A1 K1 T1 A2 K2 T2 R2

Double sigmoid

Exposed 121.35 0.10 23.44 70.41 0.06 89.19 0.99

Shaded 117.97 0.10 24.26 48.57 0.10 91.31 0.99

Y0 A Xc W R2

Lorentz

Exposed �0.3258 199.22 24.8 59.511 0.99

Shaded �0.1264 130.44 20.322 38.889 0.99

Fruit transpiration, dry matter (DM) and water content were

modelled as a function of time (x, days after fruit set) by fitting

curves to the measured data. For CFT throughout the season the

cumulative value of the following Lorentz function was used

y ¼ Y0 þ2A

p

W

4ðx� xcÞ2 þW2(2)

where A represents the total area below the curve; xc, the peak

point of the curve that parameterises the timing of the max-

imum value of the daily transpiration; W, the amplitude of the

curve; Y0, an off-set value. Values of the function parameters

are reported in Table 1.

For FWC the cumulative value from the following double

sigmoid function was used

y ¼ 1

2

�A2

1þ e�k1ðx�t1Þþ A1

1þ e�k2ðx�t2Þ

�(3)

where A1 and A2 are the first and the second upper asymptote of

the function, respectively; t1 and t2 parameterise the timing of

the inflection points of the first and second sigmoid curve,

respectively; k1 and k2, the reciprocal of the time constant

quantifying the duration of the rapid growth stage in the first

and second sigmoid curve, respectively. Values of the functions

parameters are reported in Table 1.

Phloem inflow was calculated from the fruit carbon budget

using a similar procedure to that adopted by Clark and Smith

[11]. The total carbon received by fruit during the growing

season (Ct) was estimated by assuming that the daily respiration

rate (Cr) for a kiwifruit berry decreased from 1.4 to 0.1 mmol

CO2 g�1 dry matter day�1 during the first 150 days AFS,

following an exponential decay pattern (Eq. (5)) and by

assuming that the carbon remaining in fruit dry matter was

approximately 48% [26,27]

Ct ¼ DMð0:48þ CrÞ (4)

Cr ¼ ð0:10635 þ 1:31078 eð�x=29:13114ÞÞ (5)

For Cr calculation in shaded fruit a coefficient of 1.5 was

used as reported by Bebete and Lakso [28].

DM was modelled by fitting the following Boltzman

sigmoid equation to the experimental data

y ¼ A1 � A2

1þ eðx�x0Þ=dxþ A2 (6)

where A1 is the lower asymptote of the accumulation function;

A2, the upper asymptote (the final DM of the fruit); x0, the

inflection point of the curve that parameterises the timing of the

maximum rate of accumulation; dx, a time constant quantifying

the duration of the rapid accumulation stage (x0 � dx, x0 + dx).

Values of the function parameters are reported in Table 1.

The concentration of carbon in phloem sap received by sun

and shade fruit was assumed to be the same [29]. To estimate

PFWI the carbon concentration of phloem sap was assumed to

be 70 mg C mL�1 and the contribution to the overall fruit

carbon budget from xylem sap (<1%) was ignored according to

Clark and Smith [11], i.e. for both treatments PFWI = Ct/

70 mg mL�1.

2.5. Dry matter and water content of fruit

For each treatment, twenty fruit were sampled every 10–

15 days in the early 7 weeks after fruit-set, subsequently

every 20–25 days, at the same time of day (10:00 a.m.) from

the terminating shoots near the base of the cane of the five

selected vines. Fruit were weighed (fresh weight) immedi-

ately; fruit dry matter (DM) (skin plus flesh) was determined

after 48 h drying (60 8C) using a ventilated oven (WTB-

Binder, mod. FED 400, Germany). Water content was

calculated as the difference between fresh weight and dry

weight.

2.6. Collection and analysis of xylem sap

Xylem sap was obtained from fruit by applying a

pneumatic pressure using a Scholander pressure chamber

pressurized with nitrogen. The pressure applied was 1.3 MPa

for 15 min. The stalk was carefully ring-barked by removing a

strip of bark of 1 cm wide from the proximal part using a

sharp knife. The samples (discarding the first drops) were

collected through a tube connected to the stalk and stored in a

1.5 mL Eppendorf tube at �20 8C until analysis. Xylem sap

was collected on days 18, 41 and 60 AFS between 10:00 and

midday. On each occasion, 9 fruits per treatment were

sampled and sap from groups of three fruit combined before

storage.

Ca was analysed directly in the xylem sap by atomic

absorption in a Varian AA-40 spectrophotometer (l = 422.7

nm; air-acetylene flame).

G. Montanaro et al. / Plant Science 170 (2006) 520–527 523

Fig. 2. Fruit transpiration per unit of fruit surface area of exposed (*) (con-

tinuous line) and shaded (*) (dotted line) kiwifruit during the experiment (each

point is the mean� S.E. of 15 fruit recorded at midday (12:30 a.m.–01:30 p.m.).

2.7. Fruit calcium analysis

Fruit were always sampled from the basal shoots of cane.

Samples were collected every 15–20 days until 50 days AFS

and every 20–25 days until the end of the growing season. Fruit

(9 per treatment) were immediately dried (48 h, 60 8C), threebulk samples (three fruits each) per treatment were prepared.

For each sample, Ca concentration (skin plus flesh) was

measured on the acid digested samples (H2SO4 + HNO3) using

a spectrophotometer (Varian, AA-40; l = 422.7 nm; air-

acetylene flame).

2.8. Data analyses

Data processing and curve fitting were by Origin1 6.1

(OriginLab Corporation, USA).

3. Results

3.1. Light conditions

During the experimental period, the daily available light in

the exposed treatment was 68% of the above canopy PPFD,

decreasing from 33 mol m�2 day�1 in the early part of season

to 13 mol m�2 day�1 at the end of experiment (Fig. 1). In the

shaded treatment, the daily available light was only 1–3% of

above canopy PPFD.

3.2. Fruit growth

Eq. (6) was fitted to the measurements of dry matter through

the season (R2 = 0.99 exposed; R2 = 0.98 shaded) (Table 1). The

final DM value per fruit was not influenced by light, reaching

19.21 � 0.57 g (S.E.) and 20.16 � 0.6 g per fruit in exposed and

shaded fruit, respectively (Student’s t-test, P = 0.05).

The increase in fruit water content exhibited a double

sigmoid pattern (see Eq. (3)) (Table 1). Radiation significantly

affected FWC only in the final stage of fruit growth (Student’s t-

test, P = 0.05), 70 days after fruit-set. At the end of season,

Fig. 1. Daily available light (PPFD) during the experiment. Each line represents

the mean of nine quantum sensors (Skye) placed in three areas per treatment.

water retained by fruit was 94.4 � 3.9 g (S.E.) and 81.8 � 3.4 g

in exposed and shaded fruit, respectively.

3.3. Fruit transpiration

Fruit transpiration per unit of fruit area had a maximum value

of 2.06 � 0.1 (S.E.) mmol m�2 s�1 and 2.29 � 0.08

mmol m�2 s�1 in exposed and shaded fruit, respectively, in

the first days AFS (Fig. 2). During the following 2 weeks

transpiration rapidly decreased by 65% compared to the initial

values. In the subsequent 30 days it reached very low values,

approximately 10% of the initial rate (Fig. 2).

An example of diurnal fruit transpirationmeasurement on day

37thAFS is given in the inset of Fig. 3 and shows a pattern similar

to leaf transpiration, reaching a maximum value at midday.

Fig. 3. Daily fruit transpiration (g H2O fruit�1 day�1) during the experiment of

kiwifruit grown in exposed (*) and shaded (*) fruiting canes, each point is the

mean � S.E. of fifteen daily fruit transpiration values. Lines are the Lorentz

function, parameters of which are given in Table 1. Note the maximum

displacement of curve in exposed fruit (continuous line) was about 10 days

larger than that in shaded one. In the inset, diurnal fruit transpiration

(mmol m�2 s�1) at day 37 after fruit-set.

G. Montanaro et al. / Plant Science 170 (2006) 520–527524

Fig. 4. Cumulative transpiration (g fruit�1) of exposed (continuous line) and

shaded (dotted line) fruit. The last measurements were made at time indicated

by arrow, thereafter fruit transpiration was about zero and thus cumulated

transpiration was considered constant.

Fig. 5. Calcium concentrations (%DM) of fruit sampled from exposed (*) and

shaded (*) canes during the season. Nutrient values (means � S.D.) were

determined from three bulks (three fruits each) and include skin and seed tissue

(means separation by Student’s t-test; (*) significant at P = 0.05).

The diurnal fruit transpiration measurements where inte-

grated, and thus total fruit transpiration was obtained for each

day of measurement (Fig. 3). Eq. (2) was then fitted to the daily

transpiration data (R2 = 0.99, Fig. 3).

In the first 25 days AFS, a considerable increase in daily fruit

transpiration was observed in both treatments. Avalue of 2 g of

water per fruit per day was reached. Subsequently, fruit

transpiration decreased but much more markedly in shaded

fruit. In fact, at 43 day AFS, the reduction in fruit transpiration

per day with respect to the peak value observed was 65% in

shaded fruit and 36% in exposed fruit. At 93 day AFS, fruit

transpiration was almost zero in both treatments (Fig. 3).

A very rapid increase in cumulative fruit transpiration

(Eq. (2)) was recorded in the first 30–40 days AFS (Fig. 4). In

the subsequent days, the increase was slower and differed

between the two treatments. In fact, in the whole period

following 40 days AFS, cumulative fruit transpiration increased

only 20% in shaded fruit, whereas, the increase was 43% in

exposed fruit. These differences caused the CFT in exposed

fruit to be 12 g more per fruit than the shaded ones at the end of

the experimental period.

3.4. Measurement of calcium in xylem sap

The concentrations of Ca in sap samples taken from fruit on

three sampling dates are given in Table 2. Essentially the results

Table 2

Calcium of xylem sap (mmol mL�1) collected by pressure method from fruit

subjected to different light condition

Sap collection data (days after fruit-set)

18 41 60

Exposed 5.50 � 1.21 6.09 � 1.28 6.12 � 1.41

Shaded 3.65* � 1.32 4.27 � 1.45 5.04 � 1.54

Each value is the mean (�S.E., n = 3) of three analyses.* Significant at P = 0.05, Student’s t-test.

obtained for each treatment were similar on each date. Ca

concentrations in xylem sap of exposed fruit were higher than

those of shaded fruit, but the difference was significant only on

day 18 AFS (Student’s t-test, P = 0.05).

3.5. Fruit calcium accumulation

Light significantly affected Ca concentrations in the fruit

(Fig. 5), at 20 days AFS the values were 0.6 and 0.4% of DM in

exposed and shade fruit, respectively. In both treatments Ca

concentrations in fruit declined rapidly from fruit set. By 120

days AFS Ca concentrations were only 36% of the initial value

in exposed fruit and 32% in shaded fruit (Fig. 5).

Ca accumulation followed a typical sigmoid pattern in the

fruit of both treatments but in the exposed treatment the

increase in fruit Ca content during the first 40 days AFS was

much more rapid, reaching 15.7 � 0.58 (S.E.) mg fruit�1 on

Fig. 6. Calcium content (mg fruit�1) on eight dates during fruit growth from

exposed (*) and shaded (*) fruit. Each point represents the mean � S.E. of

three bulks (three fruits each) per treatment.

G. Montanaro et al. / Plant Science 170 (2006) 520–527 525

Fig. 7. Estimation of cumulative xylem fruit water inflow (XFWI) (g fruit�1) for

exposed (continuous line) and shaded (dotted line) fruit. Note that fruit calcium

content was about 75% and 95% of total for exposed and shaded fruit,

respectively, at time marked (*) (see Fig. 6).

day 24 AFS, while in the shaded fruit it was 8.6 �0.3 mg fruit�1. At the end of growing season, fruit Ca content

was 39.6 � 1.4 (S.E.) and 23.0 � 0.8 mg fruit�1 in the exposed

and shaded fruit, respectively (Fig. 6).

3.6. Fruit water inflow

Through measurements of the in situ transpiration and water

content of fruit, and calculation of the amount of water received

by fruit from the phloem stream, it was possible to estimate the

xylem fruit water inflow (XFWI) during the experiment.

An initial period could be clearly distinguished, correspond-

ing to the first 40 days AFS, during which XFWI was very high,

reaching 105 and 98 g per fruit in exposed and shaded fruit,

respectively (Fig. 7). Later, XFWI increased slowly in both

treatments but continued for longer in exposed fruit, reaching

final values of 140 g per fruit in exposed fruit and 100 g per fruit

Fig. 8. Relationship between the xylem fruit water (XFWI) (g fruit�1) and their

calcium content (mg fruit�1) during the 50 days after fruit-set in exposed (*)

and shaded (*) fruit.

in shaded fruit (Fig. 7). In the first 50 days AFS, there was a

close linear relationship between estimated xylem fruit water

inflow and the measured amount of Ca in exposed (R2 = 0.97)

and shaded (R2 = 0.91) fruit (Fig. 8).

4. Discussion

4.1. Fruit growth

In the present study, shading did not affect the total fruit DM

accumulation, confirming that phloem transported assimilates

can be readily transferred within the vine from unshaded parts

of the canopy [9,30–31]. In both treatments, the increment in

fruit water content even when fruit transpiration was close to

zero (Fig. 2), was consistent with the shift in water supply to the

fruit from the xylem to the phloem system [12] at the end of the

early growth stage of the fruit. At the end of the experiment,

water content in exposed fruit was approximately 15% more

than that in shaded one.

4.2. Fruit transpiration

In the present work, fruit transpiration was measured on

attached fruit. In the literature, the information on fruit

transpiration is poor and often refers to detached fruit [11,31–

33]. The rapid decrease of fruit transpiration observed during

the first 2 weeks AFS (Fig. 2) agrees with the findings of Smith

et al. [31] who measured the transpiration of detached fruit. The

substantial reduction in transpiration of fruit by week 8 (Fig. 2)

occurs at the same time as the permanent disfunction of the fruit

vascular system that occurs approximately 60 days AFS, as

reported by Dichio et al. [25]. The decrease in fruit transpiration

is associated with the collapse of the surface tissues of the fruit

and the development of a suberized periderm [13,31].

Clark and Smith [11] used measurements from detached

fruit and their mass-flow vascular transport model to calculate a

fruit transpiration during the early weeks AFS of 3.5 g of water

fruit�1 day�1. Their value is higher than the maximum daily

fruit transpiration observed in this study (Fig. 3), possibly

because of differences in environmental conditions between the

two studies.

The difference in cumulative fruit transpiration between the

exposed and shaded treatments was due almost totally to the

slower decline in transpiration of the exposed fruit in the period

following 30 days AFS (Figs. 3 and 4).

4.3. Calcium in xylem sap

Ca concentrations in the xylem sap 18 days AFS (3.65–

5.5 mmol mL�1, Table 2) were higher than the values of

approximately 2 mmol mL�1 reported by Ferguson et al. [34]

for sap samples collected from 1-year-old stems by vacuum

extraction at 20 days after flowering. These amounts of Ca

xylem sap seem to be in accord in the light of the gradients in

sap compositions that markedly occurred from the 1-year-old

shoots down the plant [34]. There are no published data on the

effects of light on the mineral composition of xylem sap in

G. Montanaro et al. / Plant Science 170 (2006) 520–527526

kiwifruit, however, the higher Ca concentration in sap from

exposed fruit is supported by indirect evidence from the

literature. It has been shown by Biasi and Altamura [23] that in

exposed fruit the cross-section area of xylem in fruit carpellary

bundles can reach 12,900 mm2, approximately 40% more than

that in shaded fruit. Ca2+ ions are thought to be exchanged

between the xylem sap and sites on the xylem cell walls [14].

Thus it is possible to hypothesise that increased radiation could

increase sap Ca concentration by increasing xylem area, the

mass flow of solutes (including Ca) and the number of sites for

ion-exchange between the cell walls and the sap.

4.4. Ca accumulation and XFWI

The pattern of Ca accumulation in the shaded fruit (Fig. 6)

agrees with what reported by others [11–13]. Six to seven

weeks AFS the Ca contained by fruit was 80% of the total Ca

content at harvest (Fig. 6). At the same point in time cumulative

fruit transpiration of shaded fruit was 84% of the total (Fig. 4)

and from 50 days AFS fruit transpiration rate was very low

(Fig. 3). It is, therefore, reasonable to conclude that the decrease

in fruit transpiration caused Ca accumulation to proceed more

slowly during the final stages of fruit development.

Very little is known about the possible effect of radiation on

fruit Ca kinetic accumulation through the growing season.

There was a difference in the initial slope of the fruit Ca

accumulation in response to different light condition (Fig. 6).

The faster Ca accumulation in the first 40 days AFS observed in

exposed fruit could be caused by higher PPFD availability

(Fig. 5).

In this experiment, at day 150 AFS the shading treatment

caused a Ca concentration in fruit to be 59% of that in exposed

one. Biasi and Altamura [23] reported a Ca concentration in

shade fruit that was 56% of that in sun fruit at day 140 after full

bloom. Light therefore appears to have a strong influence on

fruit calcium accumulation. Ca content in sun fruit was about

40 mg fruit�1 (Fig. 6), a similar value was found by Thorp et al.

[9] who reported that the calcium content of fruit from long

shoots near the base of canes could reach 50 mg per fruit.

The Ca accumulation trend in fruit is consistent with the

XFWI curve in both treatments. No differences were recorded

during the early 40 days AFS, while following day 40 AFS a

greater increase of XFWI was observed in the exposed fruit, and

this, was in agreement with the greater increase of Ca content in

exposed fruit (Figs. 6 and 7). Light appears to have prolonged

the inflow of water into fruit (Fig. 7). Thus, results suggest that

greater light availability both increases and prolongs the inflow

of xylem stream into the fruit, and, consequently, also Ca

accumulation. The higher XFWI of exposed fruit may also be

explained by the positive effect of higher PPFD availability on

the differentiation of vascular tissues [23]. Fig. 8 shows the

linear relationship between the inflow of xylem sap into fruits

and their Ca content in both treatments, but with differences in

slope due to the differences in Ca concentrations in xylem sap

as shown in Table 2.

It is generally accepted that transport of Ca depends on

transpiration and on mobility of Ca in the phloem sap

[24,35]. White and Broadley [1] have stressed that when the

Ca concentration in the xylem sap is high, there is a close

relationship between transpiration and Ca delivery to the

shoot. However, the data presented in this study indicate that

for fruit there is no simple proportional relationship between

Ca and transpiration in agreement with Bangerth [15]. The

difference in terms of transpiration between the fruit of the

two treatments only partly explains the difference in

accumulated Ca, confirming that correlations between the

rate of transpiration and movement of Ca are not always clear,

as has already been described for bean pods [36,37] and for

tomato fruit [24]. Special attention should be given to the

early growth stages of the fruit when different amounts of Ca

are cumulated although there are no differences in transpira-

tion. In this study, at day 20 from fruit-set, Ca in the shaded

fruit was 65% of that of the exposed fruit, whereas, no notable

differences in fruit transpiration and in XFWI were observed.

This is possibly due to the higher Ca concentration of xylem

sap in exposed fruit (Table 2). Differences in Ca concentration

may be explained by a regulation mechanism for Ca

distribution that is governed by phytohormones. The ability

of auxin to stimulate Ca uptake has been observed in avocado

[6], tomato [24,38] and apple [35,39]. Here, we suggest a new

working hypotheses to explain radiation induced Ca

accumulation, taking into account the widely documented

role of light in promoting the biosynthesis of phenolic

compounds [40–42]. In kiwifruit, fruit exposure to full sun

causes hydroxicinnamic acids concentration to be approxi-

mately 30% higher than that of shaded fruit (Treutter,

unpublished data). Hydroxycinnamic acids are auxin protec-

tors [43]. Thus, it is proposed that light, inducing the

biosynthesis of such phenols, indirectly decreases auxin

degradation, and increases Ca accumulation.

In the present paper, additional information is provided on

the involvement of radiation in water flow in- and out of

attached fruit in relation to Ca accumulation.

Acknowledgements

The authors thank Prof. Treutter D. (Technical University

Munich – Germany) for invaluable discussion during prepara-

tion of the manuscript and Dr. Clearwater M.J. (Horticulture

and Food Research Institute, New Zealand) for critical

comments and language corrections. Research financially

supported by the Italian Ministry for Education, University

and Research. Special grants Cofin2001 and PRIN2003.

References

[1] P.J. White, M.R. Broadley, Calcium in plants, Ann. Bot. 92 (2003) 487–

511.

[2] P.K. Hepler, R.O. Wayne, Calcium and plant development, Ann. Rev.

Plant Physiol. 36 (1985) 397–439.

[3] A.D. Bauchot, I.C. Hallet, R.J. Redgwell, N. Lallu, Cell wall properties of

kiwifruit affected by low temperature breakdown, Postharvest. Biol.

Technol. 16 (1999) 245–255.

[4] M.C. Saure, Reassessment of the role of calcium in development of Bitter

Pit in apple, Aust. J. Plant Physiol. 23 (1996) 237–243.

G. Montanaro et al. / Plant Science 170 (2006) 520–527 527

[5] I.B. Ferguson, C.B. Watkins, Bitter pit in apple fruit, Hort. Rev. 11 (1989)

289–355.

[6] J.G.M. Cutting, J.P. Bower, The relationship between basipetal auxin

transport a calcium allocation in vegetative and reproductive flushes in

Avocado, Sci. Hortic. 41 (1989) 27–34.

[7] G.W. Witney, P.J. Hofman, B.N. Wolstenholme, Mineral distribution in

avocado trees with reference to calcium cycling and fruit quality, Sci.

Hortic. 44 (1990) 279–291.

[8] L.C. Ho, P.J. White, A cellular hypothesis for the induction of Blossom-

End Rot in tomato, Ann. Bot. 95 (2005) 571–581.

[9] T.G. Thorp, I.B. Ferguson, L.M. Boyd, A.M. Barnett, Fruiting position,

mineral concentration and incidence of physiological pitting in ‘‘Hay-

ward’’ kiwifruit, J. Hortic. Sci. Biotechnol. 78 (4) (2003) 505–511.

[10] I.B. Ferguson, T.G. Thorp, A.M. Barnett, L.M. Boyd, C.M. Triggs,

Inorganic nutrient concentrations and physiological pitting in ‘‘Hayward’’

kiwifruit, J. Hortic. Sci. Biotechnol. 78 (4) (2003) 497–504.

[11] C.J. Clark, G.S. Smith, Seasonal accumulation of mineral nutrients by

kiwifruit. II. Fruit, New Phytol. 108 (1988) 399–409.

[12] I.B. Ferguson, Movement of mineral nutrients into the developing fruit of

the kiwifruit (Actinidia chinensis Planch.), N. Z. J. Agric. Res. 23 (1980)

349–353.

[13] C. Xiloyannis, G. Celano, G. Montanaro, B. Dichio, L. Sebastiani, A.

Minnocci, Water relations, calcium and potassium concentration in fruits

and leaves during annual growth in mature kiwifruit plants, Acta Hort. 564

(2001) 129–134.

[14] S.B. McLaughlin, R. Wimmer, Calcium physiology and terrestrial eco-

system processes, New Phytol. 142 (1999) 373–417.

[15] F. Bangerth, Calcium-related physiological disorders of plants, Ann. Rev.

Phytopathol. 17 (1979) 97–122.

[16] J.G. Buwalda, G.S. Smith, Acquisition and utilization of carbon, mineral

nutrients, and water by the kiwifruit vine, Hortic. Rev. 12 (1990) 307–347.

[17] J.E. Jackson, Light interception and utilization by orchard systems, Hort.

Rev. 2 (1980) 208–267.

[18] J.E. Jackson, J.W. Palmer, M.A. Perring, R.O. Sharples, Effects of shade

on the growth and cropping of apple trees. III. Effects on fruit growth,

chemical composition and quality at harvest and after shortage, J. Hortic.

Sci. 52 (1977) 267–282.

[19] M.E. Hopping, Effect of light intensity during cane development on

subsequent bud break and yield of ‘‘palimino’’ grape vines, N. Z. J.

Exp. Agric. 5 (1977) 287–290.

[20] W.P. Snelgar, G. Hopkirk, Effect of overhead shading on yield and fruit

quality of kiwifruit (Actinidia deliciosa), J. Hortic. Sci. 63 (4) (1988) 731–

742.

[21] R. Biasi, G. Costa, P.J. Manson, Light influence on kiwifruit (Actinidia

deliciosa) quality, Acta Hort. 379 (1995) 245–251.

[22] C. Xiloyannis, G. Celano, G. Montanaro, B. Dichio, Calcium absorption

and distribution in mature kiwifruit plants, Acta Hort. 610 (2003) 331–

334.

[23] R. Biasi, M.M. Altamura, Light enhances differentiation of the vascular

system in the fruit of Actinidia deliciosa, Physiol. Plant. 98 (1996) 28–35.

[24] G.S. Banuelos, F. Bangerth, H. Marschner, Relationship between polar

basipetal auxin transport and acropetal Ca transport into tomato fruits,

Physiol. Plant. 71 (1987) 321–327.

[25] B. Dichio, D. Remorini, A. Lang, Developmental changes in xylem

functionality in kiwifruit fruit: implications for fruit calcium accumula-

tion, Acta Hort. 610 (2003) 191–195.

[26] E.F. Walton, T.M. De Jong, Estimation of the bioenergetic cost to grow a

kiwifruit berry, Acta Hort. 276 (1990) 231–237.

[27] D.H. Greer, C. Cirillo, C.L. Norling, Temperature-dependence of carbon

acquisition and demand in relation to shoot and fruit growth of fruiting

kiwifruit (Actinidia deliciosa) vines grown in controlled environments,

Funct. Plant Biol. 30 (2003) 927–937.

[28] M. Bebete, A.N. Lakso, Apple fruit respiration in the field: relationships to

fruit growth rate, temperature, and light exposure, Acta Hort. 451 (1997)

319–326.

[29] K. Klages, H. Donnison, J. Wunsche, H. Boldingh, Diurnal changes in

non-structural carbohydrates in leaves, phloem exudate and fruit in

‘‘Braeburn’’ apple, Aust. J. Plant Physiol. 28 (2001) 131–139.

[30] E. Antognozzi, M. Boco, F. Famiani, A. Palliotti, A. Tombesi, Effect of

different light intensity on quality and storage life of kiwifruit, Acta Hort.

379 (1995) 483–490.

[31] G.S. Smith, K.U. Clages, T.G.A. Green, E.F. Walton, Changes in abscissic

acid concentration, surface conductance, and water content of developing

kiwifruit, Sci. Hortic. 61 (1995) 13–27.

[32] A. Lang, M.R. Thorpe, Xylem, phloem and transpiration flows in a grape:

application of a technique for measuring the volume of attached fruits to

high resolution using Archimedes’ principle, J. Exp. Bot. 40 (219) (1989)

1069–1078.

[33] F. Lescourret, M. Genard, R. Habib, S. Fishman, Variation in surface

conductance to water vapor diffusion in peach fruit and its effects on fruit

growth assessed by a simulation model, Tree Physiol. 21 (2001) 735–

741.

[34] A.R. Ferguson, J.A. Eiseman, J.A. Leonard, Xylem sap from Actinidia

chinensis: seasonal changes in sap composition, Ann. Bot. 51 (1983) 823–

833.

[35] F. Bangerth, A role for auxin and auxin transport inhibitors on the Ca

content of artificially induced parthenocarpic fruits, Physiol. Plant. 37

(1976) 191–194.

[36] H.V. Koontz, R.E. Foote, Transpiration and calcium deposition by uni-

foliate leaves of Phaseolus vulgaris differing in maturity, Physiol. Plant.

19 (1966) 313–321.

[37] K.W. Pomper, M.A. Grusak, Transpiration is not the only factor control-

ling calcium transport in green bean pods, Plant Physiol. 114 (3 (Suppl. S))

(1997) 513.

[38] M.M. Brown, L.C. Ho, Factors affecting calcium transport and basipetal

IAA movement in tomato fruit in relation to Blossom-end rot, J. Exp. Bot.

44 (264) (1993) 1111–1117.

[39] E.A. Stahly, N.R. Benson, Calcium levels of ‘‘Golden Delicious’’ apples

sprayed with 2,3,5-triidrobenzoic acid, J. Am. Hortic. Sci. 95 (1970) 726–

727.

[40] D.J. Kliebenstein, Secondary metabolites and plant/environment interac-

tions: a view through Arabidopsis thaliana tinged glasses, Plant Cell

Environ. 27 (2004) 675–684.

[41] C.J. Douglas, Phenylpropanoid metabolism and lignin biosynthesis: from

weeds to trees, Trends Plant Sci. 1 (1996) 171–178.

[42] J. Rozema, J. van de Staij, L.O. Bjorn, M. Caldwell, UV-B as an

environmental factor in plant life: stress and regulation, Trees 12

(1997) 22–28.

[43] O. Faivre-Rampant, J.P. Charpentier, C. Kevers, J. Dommes, H. van

Onckelen, C. Jay-Allemand, T. Gaspar, Cuttings of the non-rooting rac

tobacco mutant overaccumulate phenolic compounds, Functional Plant

Biol. 29 (2002) 63–71.