Received 12 Jan. 2005 Accepted 12 Jul. 2005Publication of this paper is supported by Science Publication Foundation of the Chinese Academy of Sciences and the National NaturalScience Foundation of China (30424813).*Author for correspondence. Tel: + 92 41 920 0312; Fax: + 92 41 920 0764; E-mail: <iqbaluaf@yahoo.com>.

Journal of Integrative Plant BiologyFormerly Acta Botanica Sinica 2005, 47 (11): 1315−1325

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Presowing Seed Treatment with Cytokinins and Its Effect on Growth,Photosynthetic Rate, Ionic Levels and Yield of Two Wheat

Cultivars Differing in Salt ToleranceMuhammad IQBAL* and Muhammad ASHRAF

(Department of Botany, University of Agriculture, Faisalabad 38040, Pakistan)

Abstract: The effects of presowing seed treatment with different concentrations of cytokinins (kinetin andbenzylaminopurine; 100, 150, and 200 mg/L) on growth, photosynthetic capacity, and ion homeostasis wereinvestigated in two spring wheat (Triticum aestivum L.) cultivars, namely MH-97 (salt sensitive) and Inqlab-91 (salt tolerant). Primed and non-primed seeds were sown in a field in which NaCl salinity of 15 dS/m wasdeveloped. Of the different concentrations of priming agents tested, the effect of a moderate concentrationof kinetin (150 mg/L) was very pronounced, particularly in improving growth and grain yield, in bothcultivars. In addition, priming with kinetin alleviated the adverse effect of salt stress on gaseous exchangecharacteristics (net CO2 assimilation rate and water use efficiency) in both cultivars. Seed priming with amoderate concentration of kinetin also altered the pattern of accumulation of Na+ and Cl– in the shoots,irrespective of the wheat cultivar, under conditions of salt stress. However, all other priming agents at thedifferent concentrations tested did not show any consistent effect on ion levels, except hydropriming,which increased K+ levels in the shoots of both cultivars under salt stress. In conclusion, a moderateconcentration of kinetin showed a consistent effect in altering the growth and grain yield of both wheatcultivars, which was related to the beneficial effects of kinetin priming on water use efficiency and photo-synthetic rate under conditions of salt stress.Key words: growth; hormonal priming; photosynthesis; pre-treatment; salt stress; yield.

Cytokinins (CKs) generally decline in response tosalinity (Zhang and Zhang 1994; Wang et al. 2001).The quantitative and qualitative responses of plants tod i f f e ren t CKs , such a s k ine t in (Kin ) andbenzylaminopurine (BAP), may differ considerably.Thomas et al. (1975) and Biddington and Thomas(1976) demonstrated that BAP is more active than anyother CK in germination, as well as in breaking the dor-mancy of celery and lettuce seeds. The possible in-volvement of CKs in responses to adverse environmen-tal conditions has also been suggested (Hare et al. 1997;Brault and Maldiney 1999).

Recen t ly , p resoak ing seeds wi th op t imal

concentrations of phytohormones has been shown tobe beneficial to the germination, growth, and yield ofsome crop species grown under saline conditions(Gadallah 1999; Debez et al. 2001), possibly by in-creasing nutrient reserves through increased physiologi-cal activities and root proliferation (Darra et al. 1973).There are reports that seed priming with CKs alleviatesthe inhibitory effect of salinity on germination andgrowth (Kaur et al. 2002; Khan et al. 2004).

The beneficial effects of CKs on the germinationand growth of plants grown under saline conditionsare attributed to many physiological and biochemicalchanges induced by pretreatment with the CKs. For

Journal of Integrative Plant Biology (Formerly Acta Botanica Sinica) Vol. 47 No. 11 20051316

example, Kin application reduced Na+, Ca2+, and Cl–

accumulation, and improved K+ uptake, in wheat un-der conditions of salt stress (Gadallah 1999). In addition,seed soaking in 10 mg/L Kin increased the plant growthof pigeon pea (Cajanus cajan L.; Verma and Srivastava1998). These authors suggested that damage causedto the apparatus involved in protein synthesis by salin-ity can be prevented by pretreatment with Kin, enablingbetter plant growth. In another experiment, exogenousapplication of Kin (5 mg/L) increased the transpirationrate and the chlorophyll a and b content in wheat plants(Malibari 1993).

In view of the reports cited above, it was hypoth-esized that presowing treatment with CKs would beable to alleviate the depression in growth and yield in-duced by salt stress in wheat plants. Therefore, theprimary aim of the present study was to determine theeffects of presowing seed treatment on some of thephysiochemical attributes responsible for adequatephysiological adaptation of wheat plants to salt stress.In addition, how far hormonal priming is able to inducesalt tolerance in wheat cultivars differing in salt toler-ance was examined.

1 Materials and Methods

The seeds of two spring wheat (Triticum aestivumL.) cultivars, namely MH-97 (salt sensitive) and Inqlab-91 (salt tolerant; Hollington 2000), were obtained fromthe Wheat Section, Ayub Agricultural Research Institute(Faisalabad, Pakistan). Solutions of 100, 150 and 200mg/L Kin and BAP were used for seed priming. Distilledwater (DW) was used for hydropriming. Healthy wheatseeds (17 g for each treatment) were primed separatelyin 100 mL of the Kin and BAP solutions, as well as DW,for 12 h at room temperature in plastic cups (250 mL).After presoaking, seeds were surface dried on filter pa-per and then allowed to air dry for 12 h at roomtemperature. Air-dried seeds (primed seeds) and untreatedseeds (non-primed seeds) were used for fieldexperiments.

Field experiments were conducted at the BotanicalGarden, University of Agriculture, Faisalabad (UAF).

Eight blocks, 365.76 cm×137.16 cm×45.72 cm(length×width×depth), lined with polythene sheets werefilled with thoroughly mixed sandy loam soil (pH 7.56;electrical conductivity of the saturation paste extract2.84 d S/m; saturation percentage 25.5). In order todevelop 15 dS/m NaCl salinity, the calculated amountof NaCl was dissolved in water required for completesaturation of the soil in four blocks (replicates). Thus,the soil was completely saturated with salt solution (150mmol/L) so as to homogenize soil salinity. The otherfour blocks served as controls (salinity 2.84 dS/m).After 3 weeks, when the soil moisture content was12%–14%, the primed seeds of each treatment groupand the non-primed seeds were sown in rows, keepingthe row to row spacing at 15 cm. All presowing seedtreatments were randomized in each block. The ex-periments were laid out in a split-split plot design.

At the boot stage, 12 plants from each treatment(three plants per replicate) were uprooted and washedwith DW. After being dried with filter paper, the rootswere removed carefully and data on the fresh weightof shoots were recorded. Samples were dried in anoven at 65 °C for 2 weeks and the dry weight of shootwas recorded. At maturity, grain yield per plant (in g)was recorded.1.1 Determination of ions in shoots and roots

Oven-dried shoots and roots were ground finely soas to pass through a 2-mm sieve. The dried material(0.1–0.5 g) was digested in a digestion mixture (sulfuricacid-hydrogen peroxide) according to the methods ofWolf (1982). The amount of Na+, K+, and Ca2+ in thedigests was determined using a flame photometer(PFP7; Jenway). For chloride determination, the groundshoot or root material (0.1–0.5 g) was extracted in 10mL DW at 80 °C for 6 h. The Cl– content was deter-mined using a chloride analyzer (model 926; SherwoodScientific, Cambridge, UK).1.2 Gas exchange characteristics

Measurements of net CO2 assimilation rate (A), tran-spiration (E), and stomatal conductance (gs) were madeat the boot stage on a fully expanded third leaf (fromthe top) of each plant (four plants per treatment),

Muhammad IQBAL and Muhammad ASHRAF: Presowing Seed Treatment with Cytokinins and Its Effect on Growth, Photosynthetic Rate, Ionic Levels and Yield of Two Wheat Cultivars Differing in Salt Tolerance 1317

using an open system LCA-4 ADC portable infraredgas analyzer (Analytical Development Company,Hoddesdon, UK). These measurements were made from10:00 to 15:00 h with the following specifications/adjustments: leaf chamber area was fixed at 11.35 cm2,ambient CO2 concentration (Cref) was (342.5 ± 4.8)µmol/mol, sub-stomatal CO2 concentration (Ci) was235 µmol/mol, leaf chamber temperature (Tch) was (39± 3.9) °C, leaf chamber gas flow rate (V) was (389.5± 3.3) mL/min, molar flow of air per unit leaf area (Us)was (222.8 ± 1.6) mol.m−2.s−1, ambient pressure (P)was (99.8 ± 0.7) kPa, and light intensity at the leaf

surface (Qleaf) was up to (1 025 ± 72) µmol.m−2.s−1.1.3 Data analysis

Analysis of variance (ANOVA) of pooled data of 2years (2000–2001 and 2001–2002) for all attributes wascomputed using a COSTAT computer package (CoHortSoftware, Monterey, CA, USA). Means were comparedwithin the COSTAT computer package using Duncan’snew multiple range (DMR) test.

2 Results

Salt stress caused a significant reduction in the plantheight of both cultivars (P < 0.01). Different priming

Table 1 Growth attributes of two cultivars of hexaploid wheat at 2.84 dS/m (control) or 15 dS/m NaCl when the seeds wereprimed with solutions of cytokinins

Pre-sowing seed MH-97 Inqlab-91

treatments

2.84 (dS/m) 15 (dS/m) 2.84 (dS/m) 15 (dS/m)Plant height (cm)

100 81.04cd 69.75m 80.78cde 60.54oBAP (mg/L) 150 79.09efgh 60.55o 78.83fgh 57.24q

200 77.38hi 68.78m 75.91ij 54.33r100 88.85a 78.47gh 77.61ghi 65.05n

Kin (mg/L) 150 82.02bc 74.11k 81.26c 59.91op200 79.33defg 74.85jk 80.53cdef 57.97q

Distilled water 83.48b 71.69l 80.53cdef 58.46pqUntreated 75.42jk 57.16q 77.61ghi 49.97s

LSD 5 % = 1.637Fertile (tillers/plant)

100 1.79fghi 1.54hijk 2.19de 1.88efghBAP (mg/L) 150 1.70ghij 1.13lm 2.11def 1.37jklm

200 2.09def 1.46ijkl 2.29cd 1.37jklm100 2.95ab 2.67bc 2.61bc 1.37jklm

Kin (mg/L) 150 3.18a 1.83efghi 2.62bc 1.54hijk200 2.64bc 2.29cd 2.36cd 1.37jklm

Distilled water 1.79fghi 1.21klm 2.13def 1.37jklmUntreated 2.09def 1.00m 2.04defg 1.08lm

LSD 5 % = 0.327Shoot dry biomass (g/plant)

100 4.24fg 3.07l 6.69ab 3.39hijklBAP (mg/L) 150 4.51f 3.03l 6.84a 3.36ijkl

200 4.21fg 2.917l 5.29e 3.39hijkl100 5.37de 3.32jkl 6.52abc 3.88fghijk

Kin (mg/L) 150 5.96cd 4.07fgh 5.98cd 4.03fghi200 5.24e 3.62ghijkl 6.18abc 4.25fg

Distilled water 5.17e 3.39hijkl 6.27abc 3.99fghijUntreated 4.30fg 2.96l 6.09bc 3.22kl

LSD 5 % = 0.595BAP, Benzyladenine (Benzylaminopurine); Kin, Kinetin. Means with the same letters do not differ significantly at P < 0.05 within eachattribute (n = 4).

Journal of Integrative Plant Biology (Formerly Acta Botanica Sinica) Vol. 47 No. 11 20051318

agents overall improved plant height under conditionsof salt stress. Of the CKs tested, Kin (100 mg/L) provedto be a very effective priming agent, increasing the plantheight of both cultivars under conditions of salt stress(Table 1). Although all concentrations of both CKs (Kinand BAP) tested increased plant height compared withplants raised from untreated seeds under conditions ofsalt stress, higher concentrations of BAP decreasedplant height in both cultivars, particularly the alt-toler-ant Inqlab-91 cultivar, under non-saline conditions.Overall, the improvement in plant height (78.47 cm)due to priming agents, particularly 100 mg/L Kin, wasgreater in MH-97 compared with Inqlab-91 (65.05 cm)under conditions of salt stress.

Soil saline significantly affected the number of fer-tile tillers per plant in both cultivars (P < 0.01). Thecultivars did not differ significantly with respect to thisattribute. The effects of the priming agents were sig-nificantly different with respect to the number of fer-tile tillers per plant (P < 0.001). The number of fertlietillers per plant in plants grown under saline conditionswas increased in MH-97 plants by 100 mg/L Kin and inInqlab-91 plants by 100 mg/L BAP (Table 1). Overall,the different priming agents were more effective in MH-97 than in Inqlab-91 plants in terms of increasing thenumber of fertile tillers per plant under saline condi-tions (1.00–2.67 vs 1.08–1.88, respectively).

The saline medium caused a reduction in the dryweight of the shoots of plants of both cultivars (P <0.001). Application of CKs improved shoot dry biom-ass in both cultivars under conditions of salt stress (Table2). Of the different concentrations of CKs tested, 200mg/L Kin in Inqlab-91 plants and 150 mg/L Kin in bothcultivars were found to be effective in increasing theshoot dry biomass under saline conditions.

A significant reduction in the number of grains perear in both cultivars was observed as a result of saltstress (P < 0.01). As shown in Table 1, MH-97 plantsraised from seeds treated with Kin (200 mg/L) had agreater number of grains per ear under saline condi-tions compared with those raised from seeds presoakedin different concentrations of other priming agents. In

contrast, in Inqlab-91 plants, priming with lower con-centrations of Kin (100–150 mg/L) was very effectivein increasing the number of grains per ear.

Salt stress imposed through the growth mediumcaused a significant reduction in the grain yield of bothcultivars (P < 0.01). All concentrations of Kin increasedgrain yield under conditions of salt stress in bothcultivars. However, priming of MH-97 and Inqlab-91seeds with 100 and 150 mg/L Kin, respectively, wasslightly more effective in enhancing grain yield underconditions of salt stress (Table 2). In contrast,presowing seed treatment in 150 mg/L BAP showedsome toxic effects and, thus, decreased grain yield inMH-97 plants compared with plants raised from un-treated seeds under conditions of salt stress.

Grain weight (100-grain weight) of both cultivarswas significantly reduced under saline conditions (P <0.05). Priming agents also significantly affected the 100-grain weight (P < 0.001). Compared with non-priming,the change in 100-grain weight due to priming was notsignificant in plants of both cultivars under saline ornon-saline conditions (Table 2).

A marked reduction in A was found in both culti-vars as a result of salt stress (P < 0.01). Of all thepriming agents tested, 150 mg/L Kin in Inqlab-91 plantsand 200 followed by 100 mg/L Kin in MH-97 plantswere the most effective concentrations in improving Aunder saline conditions (Fig. 1). However, pretreatmentwith a higher concentration of BAP (200 mg/L) slightlydecreased A under saline conditions in Inqlab-91 plants.

Stomatal conductance (gs) of both cultivars de-creased significantly as a result of salt stress (P <0.01). The priming agents significantly altered gs in bothcultivars (P < 0.001). The application of 100 mg/L BAPwas the most effective in Inqlab-91 plants in increas-ing gs under saline conditions (Fig. 1). In contrast, 200mg/L BAP and 100 mg/L Kin improved gs in MH-97plants under conditions of salt stress. Hydroprimingwas ineffective in increasing gs in both cultivars com-pared with plants raised from untreated seeds underboth saline and non-saline conditions.

Salt stress had a significant effect on instantaneous

Muhammad IQBAL and Muhammad ASHRAF: Presowing Seed Treatment with Cytokinins and Its Effect on Growth, Photosynthetic Rate, Ionic Levels and Yield of Two Wheat Cultivars Differing in Salt Tolerance 1319

water use efficiency (WUE; calculated as A/E), al-though there was no significant difference between thecultivars. The differences among different primingagents were significant (P < 0.001). Of the primingagents tested, 150 mg/L Kin was the most effective inimproving WUE in both cultivars under saline condi-tions (Fig. 1). In contrast, higher concentrations ofKin and BAP, as well as hydropriming, decreased WUEin both cultivars under saline conditions.

Soil salinity caused a significant increase in shootNa+ levels in both cultivars (P < 0.01). All priming

agents (compared with non-priming) were found to beeffective in reducing leaf Na+ levels in Inqlab-91 plantsunder saline conditions (Table 3). In contrast, pretreat-ment with 150 mg/L Kin and 100 mg/L BAP increasedshoot Na+ levels in MH-97 plants compared with un-treated plants under saline conditions. Priming of seedswith either lower concentrations of Kin and BAP (100mg/L; Inqlab-91 ) or higher concentrations of 200mg/L Kin (MH-97) was the most effective in loweringshoot Na+ levels under saline conditions.

Soil salinity significantly reduced shoot K+ levels in

Table 2 Grain yield and yield components of two cultivars of hexaploid wheat at 2.84 dS/m (control) or 15 dS/m NaCl whenthe seeds were primed with solutions of cytokinins

Pre-sowing seed MH-97 Inqlab-91

treatments

2.84 (dS/m) 15 (dS/m) 2.84 (dS/m) 15 (dS/m)Number of grains/ear

100 56.80 de 49.45hijk 54.53defgh 50.33ghijBAP (mg/L) 150 53.78efgh 44.48klm 54.78defgh 47.93ijkl

200 53.95defgh 45.40jklm 63.55bc 45.53jklm100 66.20ab 51.73efghi 68.23ab 56.18def

Kin (mg/L) 150 67.92ab 50.65fghij 68.15ab 57.25de200 67.83ab 55.75defg 70.93a 54.50defgh

Distilled water 59.65cd 42.85lmn 55.80defg 47.58ijklUntreated 55.75defg 38.65n 57.00de 40.45mn

LSD 5% = 4.78Grain yield (g/plant)

100 3.19gh 2.22jkl 3.60ef 2.27ijkBAP (mg/L) 150 3.05h 1.99l 3.76de 2.33ijk

200 3.21gh 2.36ijk 3.98bcd 2.46ij100 3.97bcd 3.24gh 3.98bcd 3.11h

Kin (mg/L) 150 4.11abc 3.11h 3.93cd 3.17gh200 4.29a 3.11h 4.21ab 3.00h

Distilled water 3.60ef 2.35ijk 3.58ef 2.52iUntreated 3.43fg 2.12kl 3.57ef 2.25ijkl

LSD 5% = 0.239100-grain weight (g)

100 2.93 2.70 3.60 3.35BAP (mg/L) 150 2.78 2.63 3.53 3.35

200 2.90 2.73 3.65 3.48100 3.03 2.83 3.70 3.55

Kin (mg/L) 150 3.08 2.90 3.83 3.45200 3.00 2.83 3.78 3.50

Distilled water 2.80 2.70 3.73 3.60Untreated 2.68 2.58 3.30 3.20

(S × V × T = ns)BAP, Benzyladenine (Benzylaminopurine); Kin, Kinetin. Means with the same letters do not differ significantly at P < 0.05 within eachattribute (n = 4).

Journal of Integrative Plant Biology (Formerly Acta Botanica Sinica) Vol. 47 No. 11 20051320

both cultivars (P < 0.001). Of the priming agents tested,some proved to be effective in increasing shoot K+ lev-els in both cultivars. All priming agents, except DW(hydropriming), lowered shoot K+ levels in MH-97plants compared with plants raised from untreated seedsunder saline conditions (Table 3). In contrast, Inqlab-91 plants raised from seeds presoaked in all primingagents had the highest shoot K+ levels compared with

plants raised from untreated seeds under salineconditions. However, hydropriming followed by soak-ing in a moderate concentration of Kin (150 mg/L) in-creased shoot K+ levels in Inqlab-91 plants under con-ditions of salt stress.

Although shoot Ca2+ levels decreased significantlyas a result of salt stress in both cultivars, there wereslight changes in shoot Ca2+ levels following primingtreatments (Table 3). The most effective priming agentin increasing shoot Ca2+ in MH-97 compared with plantstreated with other priming agents under saline condi-tions was Kin (200 mg/L). In contrast, all other prim-ing agents exacerbated the marked effect of salt stresson shoot Ca2+ in Inqlab-91 plants.

Generally, salt stress significantly increased theconcentration of Cl– in the shoots of both cultivars (P< 0.001). All priming agents increased shoot Cl– levelsin MH-97 (Table 5). In contrast, Inqlab-91 plants raisedfrom seeds treated with 150 mg/L Kin had a lower shootCl– concentration compared with plants raised fromnon-primed seeds or seeds primed with the othertreatments.

Although salt stress caused a considerable increasein root Na+ in both cultivars, some priming agents wereeffective in reducing root Na+ levels in both cultivarsunder saline conditions. Application of a lower con-centration of Kin (100 mg/L) to Inqlab-91 seeds and ahigher concentration of BAP (200 mg/L) to MH-97seeds was most effective in decreasing root Na+ levelsunder saline conditions (Table 4).

A saline substrate significantly altered root K+ con-centration in plants of both cultivars (P < 0.05).However, most of the priming agents caused a reduc-tion in root K+ levels, irrespective of the cultivars, ex-cept for 100 mg/L BAP in Inqlab-91 plants under salineconditions (Table 4). In contrast, all priming agentsdecreased root K+ levels in MH-97 plants under saltstress.

Although root Ca2+ decreased significantly in bothcultivars as a result of salt stress, the effect of primingagents was not very evident, because only some prim-ing agents caused an increase in root Ca2+ levels (Table

Fig. 1. Gas exchange characteristics of two cultivars ofspring wheat (means ± SE, n = 4) at 2.84 dS/m (control) or15 dS/m NaCl (salt) when the seeds were primed with solu-tions of cytokinins. A, net CO2 assimilation rate; BAP,Benzylaminopurine; gs, stomatal conductance; HP,hydropriming; INQ, Inqlab-91; Kin, Kinetin; MH, MH-97;UT, untreated; WUE, water use efficiency (A/E); 1, 2 and3, (100, 150 and 200 mg/L, respectively).

Muhammad IQBAL and Muhammad ASHRAF: Presowing Seed Treatment with Cytokinins and Its Effect on Growth, Photosynthetic Rate, Ionic Levels and Yield of Two Wheat Cultivars Differing in Salt Tolerance 1321

4). Application of a moderate concentration of BAP (150mg/L) to Inqlab-91 seeds and in a lower concentration(100 mg/L BAP) to MH-97 seeds was most effectivein increasing root Ca2+ levels under saline conditions.

Root Cl– levels increased significantly in both culti-vars as a result of salt stress (P < 0.001). A markedeffect of priming agents was observed in decreasingthe Cl– levels in roots, except for 100 mg/L BAP forInqlab-91 plants grown under saline conditions (Table4). The greatest decrease in root Cl– concentrations inplants grown under saline conditions was observed

following the application of a moderate concentration(150 mg/L) of BAP to MH-97 seeds and a higher con-centration (200 mg/L) to Inqlab-91 seeds.

3 Discussion

Presoaking seeds with optimal concentrations ofCKs has been shown to be beneficial to germination,growth, and the yield of some crop species grown undersaline conditions (Kaur et al. 2002; Khan et al. 2002).It is possible that in the presence of high saltconcentrations, the amount of natural occurring CKs

Table 3 Shoot Na+, K+ and Ca2+ concentration (mg/g DW) of two cultivars of hexaploid wheat at 2.84 dS/m (control) or15 dS/m NaCl when the seeds were primed with solutions of cytokinins

Pre-sowing seed MH-97 Inqlab-91

treatments

2.84 (dS/m) 15 (dS/m) 2.84 (dS/m) 15 (dS/m)Na+

100 6.96k 37.76a 9.02ijk 18.12hBAP (mg/L) 150 9.28ijk 30.36bcd 6.96k 26.79efg

200 6.70k 32.92b 8.77ijk 28.32def100 9.797ijk 30.36bcd 7.99ijk 16.59h

Kin (mg/L) 150 7.99ijk 39.55a 8.51ijk 24.24g200 8.77ijk 29.34cde 10.57ij 25.26g

Distilled Water 11.09i 26.28fg 9.797ijk 25.01gUntreated 7.73jk 31.64bc 9.02ijk 30.62bcd

LSD 5% = 2.68K+

100 33.44e 11.22pq 40.23b 12.76opBAP (mg/L) 150 24.56hi 9.19q 25.34gh 14.79lmno

200 20.38k 13.27nop 41.27b 17.09 100 32.65e 16.33lm 37.09c 13.78no

Kin (mg/L) 150 29.78f 14.29mno 42.32b 19.90k 200 36.57cd 15.56lmn 45.98a 14.54mno

Distilled water 36.05cd 36.23cd 32.65e 22.96ijUntreated 27.17g 20.92jk 34.48de 10.21q

LSD 5% = 2.23Ca2+

100 3.37e 2.63i 2.87g 2.53ijkBAP (mg/L) 150 3.08f 2.02m 2.74h 1.79n

200 3.08f 2.07m 3.34e 2.02m 100 2.85gh 2.25l 4.15b 2.07m

Kin (mg/L) 150 2.89g 2.25l 2.89g 2.19l200 3.37e 2.76h 4.49a 2.42k

Distilled water 3.63d 2.50jk 3.45e 2.45kUntreated 4.02c 2.58ij 3.11f 2.58ij

LSD 5% = 0.109BAP, Benzyladenine (Benzyl aminopurine); Kin, Kinetin. Means with the same letters do not differ significantly at P < 0.05 within eachattribute (n = 4).

Journal of Integrative Plant Biology (Formerly Acta Botanica Sinica) Vol. 47 No. 11 20051322

may be suppressed and presowing treatment inducestheir synthesis under saline conditions (Shah and Loomis1965). In addition, the quantitative and qualitative re-sponses of plants to different CKs may differ consid-erably under saline conditions, as was observed in thepresent study. Generally, presowing treatment withdifferent CKs alleviated the inhibitory effect of salt stresson both wheat cultivars investigated in the present study;Kin was the most effective priming agent that caused amaximum increase in shoot growth and improved grainyield irrespective of the cultivar. This increase in growth

and grain yield was found to be associated with in-creased photosynthetic rate and improved WUE, as wellas to an increased number of grains per ear under sa-line conditions. It was reported earlier that salt stresscan reduce CK export from the root to the shoot inmany plants (Rao and Rao 1985; Kuiper et al. 1990).However, an adequate CK supply is essential for nor-mal plant development (Schmülling et al. 1997; Takeiet al. 2002) and this may explain why the exogenousapplication of CKs in the present study overcame theeffect of salinity stress on the growth and grain yield

Table 4 Root Na+, K+ and Ca2+ concentration (mg/g DW) of two cultivars of hexaploid wheat at 2.84 dS/m (control) or 15dS/m NaCl when the seeds were primed with solutions of cytokinins

Pre-sowing seed MH-97 Inqlab-91

treatments

2.84 (dS/m) 15 (dS/m) 2.84 (dS/m) 15 (dS/m)Na+

100 17.61mn 44.81a 15.48p 29.85jBAP (mg/L) 150 17.88mn 38.78c 17.08no 36.93d

200 20.28 34.96fg 14.95pq 33.68gh100 16.01op 37.43d 13.88q 27.05k

Kin (mg/L) 150 17.88mn 43.63a 14.94pq 29.09j200 18.681m 36.44de 15.48p 32.66hi

Distilled water 17.88mn 35.21ef 15.74op 31.52iUntreated 20.55 40.83b 20.28l 34.19fg

LSD 5% = 1.342K+

100 14.37bcde 11.99hijk 9.40m 13.27defghBAP (mg/L) 150 14.89abc 14.03cdef 12.02hijk 12.25ghijk

200 12.80fghij 13.78cdefg 11.76hijk 12.50fghij100 12.80fghij 11.99hijk 14.63abcd 12.25ghijk

Kin (mg/L) 150 11.76hijk 11.23jkl 10.71klm 10.21lm200 12.80fghij 11.48ijkl 13.06efghi 11.23jkl

Distilled water 15.93a 13.27defgh 12.54fghij 13.01efghiUntreated 11.49ijkl 15.56ab 13.06efghi 12.25ghijk

LSD 5% = 1.313Ca2+

100 2.85c 2.12f 1.88g 1.61jklBAP (mg/L) 150 2.38de 1.38m 3.06a 2.17f

200 2.95b 1.84gh 1.38m 1.52l100 2.82c 1.84gh 1.93g 1.68ij

Kin (mg/L) 150 2.87bc 1.76hi 2.43de 1.76hi200 2.49de 1.63jk 2.32e 1.68ij

Distilled water 2.46d 1.66ijk 1.59jkl 1.40mUntreated 2.40de 1.38m 1.57kl 1.38m

LSD 5% = 0.099BAP, Benzyladenine (Benzyl aminopurine); Kin, Kinetin. Means with the same letters do not differ significantly at P < 0.05 within eachattribute (n = 4).

Muhammad IQBAL and Muhammad ASHRAF: Presowing Seed Treatment with Cytokinins and Its Effect on Growth, Photosynthetic Rate, Ionic Levels and Yield of Two Wheat Cultivars Differing in Salt Tolerance 1323

of both wheat cultivars under conditions of salt stress.The results of the present study are in agreement withthose of earlier studies (Salama and Awadalla 1987;Farida et al. 2003). In addition, the improvement inwheat productivity (grain yield) due to the increasedrate of translocation of photosynthates from leaves tograins caused by hormone pretreatment has been sug-gested (Ray and Choudhuri 1981; Aldesuquy andIbrahim 2001).

Plants of the salt-sensitive cultivar MH-97 raised fromseeds treated with both CKs showed maximum shootand root Na+ concentration under saline conditions. Incontrast, in the salt-tolerant cultivar, pretreatment withKin decreased Na+ and increased K+ in the shoots un-der saline conditions. Gadallah (1999) found that Kinapplication reduced the harmful effects of combinedsaline-anaerobic treatment through a reduction in theaccumulation of inorganic ions (Na+, Ca2+, and Cl–).In the present study, pretreatment with Kin caused

accumulation of Ca2+ only in the shoots of the salt-sensitive cultivar under saline conditions. Presowingtreatment with BAP caused Na+ accumulation in theshoots and K+ and Cl– accumulation in the roots ofboth cultivars under salt stress. This may have beenbecause BAP pretreatment increased the ability of plantsto accumulate ions for osmotic adjustment. Such anosmotic adjustment resulting from an increased abilityto take up mineral nutrients and translocate them to theleaves has already been reported in Lycopersiconpennellii under saline conditions (Perez-Alfocea et al.1993; Bolarin et al. 1995). Similarly, while workingwith soybean, Yang and Blanchar (1993) and Umezawaet al. (2000) found that salt tolerance was correlatedwith the accumulation of ions (Na+ or Cl–) in the roots.

Hydropriming increased the growth of both culti-vars compared with plants raised from untreated seedsunder saline conditions. In contrast, hydropriming didnot affect grain yield and photosynthesis in either

Table 5 Shoot and root Cl− concentrations (mg/g DW) of two cultivars of hexaploid wheat at 2.84 dS/m (control) or 15dS/m NaCl when the seeds were primed with solutions of cytokinins

Pre-sowing seed MH-97 Inqlab-91

treatments

2.84 (dS/m) 15 (dS/m) 2.84 (dS/m) 15 (dS/m)Shoot

100 15.99l 27.68cd 17.09k 30.13aBAP (mg/L) 150 15.84lm 26.28e 21.73h 26.73e

200 19.58i 28.98b 18.19j 28.53bc100 17.39jk 24.68g 18.14j 26.18ef

Kin (mg/L) 150 17.24k 28.23bcd 14.79n 25.38fg200 15.09mn 28.08cd 18.24j 26.18ef

Distilled water 14.54n 25.28g 16.84k 26.33eUntreated 14.44n 24.53g 15.69lm 27.63d

LSD 5% = 0.780Root

100 12.87ijk 24.29bc 11.31l 25.59aBAP (mg/L) 150 12.16k 23.14ef 14.68h 24.09cde

200 14.53h 24.14cd 13.42ij 21.79g100 12.62jk 23.79cde 12.57jk 22.74f

Kin (mg/L) 150 10.50lm 23.54cdef 13.67i 23.29def200 8.85n 25.74a 12.57jk 24.19cd

Distilled water 10.15m 23.29def 13.12ij 24.29bcUntreated 10.81lm 25.94a 13.27ij 25.14ab

LSD 5% = 0.837BAP, Benzyladenine (Benzyl aminopurine); Kin, Kinetin. Means with the same letters do not differ significantly at P < 0.05 within eachattribute (n = 4).

Journal of Integrative Plant Biology (Formerly Acta Botanica Sinica) Vol. 47 No. 11 20051324

cultivar under salt stress. Hydropriming has been shownpreviously to be ineffective in improving germinationand growth in wheat (Chaudhri and Wiebe 1968) andKentucky bluegrass (Poa pratensis; Pill and Necker2001). There are some studies reporting a consider-able effectiveness of hydropriming on germination andlater growth in different plant species under both salineand non-saline conditions, including in Acacia tortilis(Rehman et al. 1998) and wheat (Kamboh et al. 2000).However, hydropriming was most effective in increas-ing shoot K+ concentration in both cultivars under sa-line conditions. The higher uptake of beneficial mineralelements, such as K+, is an important mechanism ofsalt tolerance in most crop species (Greenway andMunns 1980; Ashraf 1994; Shannon and Grieve 1999).The effect of hydropriming on the distribution and ac-cumulation of other ions in the present study was notconsistent in either cultivar under conditions of saltstress.

In conclusion, of the different priming agents in-vestigated in the present study, Kin was found to bethe most effective in alleviating the adverse effect ofsalt stress on growth and grain yield in both cultivars.Kinetin-induced salt tolerance in spring wheat can beattributed, in part, to its beneficial effect on ion ho-meostasis under saline conditions. In addition, thispriming agent improved WUE and decreased the in-hibitory effect of salt stress on photosynthetic rate inboth cultivars. Moreover, its beneficial effects ongrowth and yield were consistent in both (salt-sensi-tive and -tolerant) wheat cultivars. Thus, presowingseed treatment with Kin can be recommended for wheatcultivars to alleviate the inhibitory effects of salt stresson growth and yield, when plants are grown under sa-line conditions.

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