PL A N T F U N C T I O N I N G U N D E R E N V I R O N M E N T A L S T R E S S P. 233-239

Cracow, 12th to the 15th September, 2012

THE IMPACT OF PLANT-DERIVED SMOKE ON SEED

GERMINATION IN THE CONTEXT OF SWAILING

Renata Bączek-Kwinta, Marcin MarkowiczUniversity of Agriculture in Krakow, Faculty of Agriculture and Economics,

Department of Plant Physiology, ul. Podłuzna 3, 30-239 Kraków, Poland

Corresponding author: : rrbaczek@cyf-kr.edu.pl

Abstract Smoke generated by wildfires have special ecological impact in various fire-prone

environment in Africa, Australia, and both Americas. However, in the countries of moderate

climate zones, swailing (controlled burning of meadows) is often, although illegally, prac-

ticed by farmers. Hence, the influence of smoke generated from plant debris on seed germi-

nation and radicle growth of 4 crops, popularly grown and 3 weed species, occurring in Cen-

tral Europe was studied. Smoke had stimulative effect on seeds germination of 6 from

7 studied species. There was no impact on germination of meadow cress seeds, but in this

case strong stimulation of radicle growth was noticed. The influence of smoke on germination

was the strongest in case of red cabbage, as the difference between smoke-treated and control

seeds was 60%, and the stimulation of growth of radicles was obtained. Summing up, plant-

derived smoke can stimulate seed germination and seedling vigour of some crop and weed

plants of moderate climate countries. Therefore, smoke generated by swailing can cause local

changes in both the natural and agricultural environments.

Key words: germination; seed; smoke; weed

Introduction

The role of fire-related cues (smoke and heat) in alterations of ecosystem prop-

erties in fire-prone areas such as chapparal, fynbos, kwongan or matorral, in Aus-

tralia, both Americas and Africa is obvious (Roche et al. 1997; Keeley and Foth-

eringham 1998, Brown et al. 2003; Crosti et al. 2006). Since the 1990s it has been

known that not only heat, but also smoke itself can affect seed germination (De

Lange and Boucher 1990), having both positive and negative impact (Drewes et al.

1995; Light et al. 2002; Daws et al. 2007). Physiologically active substances pres-

Renata Bączek-Kwinta, Marcin Markowicz

234

ent in smoke are mainly nitric oxides and butenolide derivatives. The latter have

wider physiological and ecological impact than nitric oxides (Flematti et al. 2004;

2005; Van Staden et al. 2005). They have been termed karrikinolides or karrikins

(KAR). The compound 3-methyl-2H-furo[2,3-c]pyran-2-one, obtained from plant-

derived smoke, has been referred to KAR1 (Chiwocha et al. 2009). Karrikins are

water soluble, thermostable, long lasting in solution and highly active at very low

concentration of 1-9 M in darkness (Flematti et al., 2004; Light et al 2005).

Physiologically active butenolide derivatives can be even synthesized in laboratory

conditions (Flematti et al. 2005; Light et al., 2005; Nagase et al 2008; Sun et al.

2008).

Physiological impact of smoke compounds on seeds of approx. 1200 species

proves their physiological and ecological role in various ecosystems. However, one

must remember that the number of 1200 is only 0.38% all known plant species

according to the International Union for Conservation of Nature and Natural Re-

sources (total 315 000, www.iucnredlist.org/documents/summarystatistics/2010

_1RL_Stats_Table_1.pdf]. Moreover, most of species can form various ecotypes,

and cultivars of crops are bred in the majority of the countries. Hence, the studies

on the impact of smoke and its compounds should not be restricted to fire-prone

environments. It was borne in mind that swailing (burning of meadows), often

practised by farmers n the areas of moderate climate, may also have an impact on

the local vegetation. Hence, the purpose of this work was to examine the influence

of smoke on seed germination and radicle growth of selected popularly grown

crops and some weed species occurring in Central Europe.

Materials and methods

Seed material. Seeds of seven species were used. Four crops: lettuce (Lactuca

sativa L., two cultivars having seeds insensitive to light: ‘Królowa Majowych’ and

‘Rozalka’), rapeseed (Brassica napus L., cv. ‘Mlochowski’), red cabbage (B. olera-

cea L. var. capitata f. rubra, cv. ‘Langedijker Polana’) and white cabbage (B. ole-

racea L. var. capitata f. alba cv. ‘Ditmarska’) were examined, as well as three

weed species: coltsfoot (Tussilago farfara L.), meadow cress (Cardamine pratensis L.)

and sorrel (Rumex acetosa L.). Lettuce and coltsfoot belong to the Asteraceae,

whereas cabbages and meadow cress to Brassicaceae, and sorrel belongs to Poly-

gonaceae family.

The source of smoke and smoke treatment. Two sets of seeds of each species

(and cultivar in case of lettuce) were placed in sealed boxes, in Petri dishes of

a diameter 4 cm, on a moistened blotting paper. Semi-dried plant debris (leaves and

stems of various grass species, 0.5 g FW), collected from a local meadow, was

burned in a glass dish, and smoke was directed to one of the boxes by a fan from

The impact of plant-derived...

235

a distance approx. 1 m, for 3 min. Burned and cooled ash was left in the box, to-

gether with the seeds, in an open dish, for 24 h. The treatment simulated the impact

of swailing, when not only smoke affects the environment, but also the volatiles

emitted from the burned debris. Control seeds were kept with similar dish filled

with unburned debris. Germination was performed in darkness for 5 days, the tem-

perature was 20/17ºC (day/night), relative humidity ca. 90%. Germination counts

were performed daily. Germination was considered when the radicle protruded 1 mm.

Statistical analysis

Each treatment consisted of four replicates of 10 seeds. The percentage of ger-

minated seeds of individual species and cultivar was arcsine transformed and the

data were compared among the species (also cultivar) and the treatment using one-

way analysis of variance (ANOVA at p<0.05). In case of the length of the radicles,

Student t-test was used to compare two means among the species, at p=0.05.

Results and discussion

The volatile compounds contained in smoke and/or burned plant debris had

stimulative effect on seed germination of all the studied species but meadow cress

(Table 1, Fig.1). Germination stimulation was noticed just on the 1st day in case of

lettuce, rapeseed, sorrel and coltsfoot (Table 1). Lettuce seeds are often used as

a germination model, also in smoke experiments (Jager at al. 1996), but the re-

sponse of seeds may greatly vary upon the cultivar due to its differentiated light-

sensitivity. In this work, performed on two cultivars having seeds insensitive to

light (unpublished results), genotypic differentiation was shown as different germi-

nation pattern of seed of both used cultivars (‘Rozalka’ seeds germinated faster,

Table 1), but their positive response to smoke was distinct (Table 1). Moreover,

growth of ‘Rozalka’ radicles was improved, as on the 4th day they were approx.

4 mm (20%) longer than in the control ones (Table 2). Sparg et al. (2005) dis-

cussed the role of smoke at the post-germination level, based on their results as

well as these obtained by Brown et al. (2003), and the improvement of seedling

vigour was raised.

Germination of seeds of rapeseed (Table 1) and both cabbage species was

stimulated by the treatment (Table 1, Fig. 1). The impact of smoke was stronger in

the case of red than white cabbage seeds, as the differences in percentages were 60

and 25%, respectively. Additionally, the effect of smoke on growth of red cabbage

radicles was distinct (Table 2), whereas there was no such response in case of white

cabbage (data not shown). Interestingly, smoke had no effect on germination of

seeds of meadowcress, which belongs to the same family as cabbage and rapeseed

Renata Bączek-Kwinta, Marcin Markowicz

236

(Brassicaceae), but triggered strong positive growth response in meadow cress

radicles, because their length was 160% of control upon the smoke treatment

(Table 2).

Table 1. The effect of smoke on seed germination during first 3 days.

Mean percentage of seeds germinated in four Petri dishes

(number of seeds in each dish = 10) ± standard deviation (SD) were given

Day of germination, % of germinated seedsClassification

Species,

cultivar

Treatment:

control (C),

smoke (S) 1. 2. 3.

C 5 ±7.07 a 90 ±0.00 b 100 ±0.00 bLettuce,

‘Królowa

Majowych’ S 15 ±7.07 a 95 ±7.07 b 100 ±0.00 b

C 50 ±7.07 a 80 ±7.07 b 90 ±7.07 bLettuce

‘Rozalka’ S 70 ±14.2 a 95 ±7.07 b 95 ±7.07 b

C 0.0 ±0.00 a 25 ±14.1 b 50 ±0.00 cRed cabbage

S 0.0 ±0.00 a 85 ±7.07 b 85 ±7.07 b

C 0.0 ±0.00 a 65±7.07 b 80 ±0.00 cWhite cabbage

S 0.0 ±0.00 a 90 ±14.1 b 95 ±7.07 b

C 25 ±35.4 a 95 ±0.00 b 100 ±0.00 b

Crops

RapeseedS 50 ±28.3 a 95 ±14.1 b 100 ±7.07 b

C 48 ±3.18 a 48 ±3.18 a 48 ±3.18 aColtsfoot

S 55 ±7.07 a 55 ±7.07 a 55 ±7.07 a

C 100 ±0.00 a 100 ±0.00 a 100 ±0.00 aMeadowcress

S 100 ±0.00 a 100 ±0.00 a 100 ±0.00 a

C 0 ±0.00 a 85 ±7.07 b 90 ±0.00 b

Weeds

SorrelS 10 ±0.00 a 90 ±14.1 b 95 ±7.07 b

Mean values with different letters (a–c) are significantly different (P\0.05)

Physiological basis for the mode of action of smoke compounds has not been

unraveled yet. Egerton-Warburton (1998) indicated that smoke acts as a scarifying

agent to the seed surface, but in the paper of Briggs and Morris (2008) it was

shown that the mechanism is not universal. On the other hand, most researchers

agree that smoke and its main physiologically active component, butenolide, inter-

acts with gibberellin, ABA and auxin pathways in seeds (Light et al. 2005; Chiwo-

cha et al. 2009). It can probably result in up-regulation of expansins, the proteins

disrupting the hydrogen bonds within the cell wall (Jain et al, 2008). Smoke com-

pounds, possessing their oxidative role, may also interfere with the cell redox status

(Light et al. 2009). All these circumstances lead to the supposition that the key

smoke compounds, butenolides, act as a new class of plant growth regulators

(Light et al. 2009).

The impact of plant-derived...

237

Red cabbage

Control Smoke

White cabbage

Control Smoke

Fig. 1. Germinated cabbage seeds, day 2. Samples representative for 4 replicates

(Petri dishes)

The results of the studies on the impact of smoke on germination can be appli-

cable in some cases, as the smoke extract can be used in case of late sowing to ac-

celerate germination (Light and Van Staden 2004), to overcome the light require-

ment for germination (Merrit et al. 2006) and to improve the vigour of some

indigenous plants (Sparg et al. 2005; Emery and Lacey 2010). Some papers also

emphasized the role of smoke compounds as conditioning agents in unfavourable

conditions (Jain et al. 2008). In case of seeds of persistent weed or invasive spe-

cies, such as Avena fatua L. (Kępczyński et al., 2010, 2012), the experiments can

Renata Bączek-Kwinta, Marcin Markowicz

238

explain the mechanism of germination stimulation and may improve new methods

for prevention. Other valuable application is the re-vegetation of degraded areas

(Light and Van Staden 2004).

Table 2. The effect of smoke on length of the radicles on the 4th day of germination

(only the significant differences were shown). Means of 4 Petri dishes ± SD were given.

The significance of differences between means was evaluated by Student’s t-test:

* - differentiation at P=0,05, ** - P=0,01, *** - P=0,001.

Species, cultivar

Treatment:

control (C),

smoke (S)

The length of the radicles [mm]

on the 4th day of germination

C 22.7 ± 0.90 **

Lettuce ‘Rozalka’S

27.2 ± 2.01

(120%)

C 11.5 ± 6.60*

Red cabbageS

18.5 ± 6.60

(161%)

C 24.4 ± 5.70***

MeadowcressS

38.9 ± 6.20

(159%)

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