Chilling stressed chickpea seedlings: effect of cold acclimation, calcium and abscisic acid on cryoprotective solutes and oxidative damage

Chickpea (Cicer arietinum L.) is sensitive to chilling stress (< 15 degrees C). In the present study, hydroponically grown 14-day-old chickpea seedlings were subjected to temperatures ranging from 1 to 7 degrees C. Chilling injury was observed as electrolyte leakage (EL) and 2,3,5-triphenyltetrazolium (TTC) reduction activity. LT50 was noticed at 4 degrees C. Relative growth rate of the roots ceased at this temperature. Acclimation for 6 days at 10/7 degrees C lowered the LT50 by 2 degrees C. The growth rate of roots increased by 35% in cold-acclimated (CA) seedlings. Abscisic acid (ABA) content increased in cold-acclimated (CA) seedlings to 92 ng g(-1) fw in comparison to 61 ng g(-1) fw in non-acclimated (NA) seedlings. NA seedlings subjected to 4 degrees C in the presence of 1 mu M Ca2+ (as CaCl2; Ca) or 0.1 mu M abscisic acid (ABA) showed cold acclimation like response in terms of root growth, EL, TTC reduction, accumulation of cryoprotective solutes like total soluble carbohydrates, sucrose, glucose, fructose, trehalose and proline. Relatively, the increase was more in carbohydrates than proline. The oxidative damage as generation of lipid peroxides (malondialdehyde) and hydrogen peroxide (H2O2) was lesser in Ca or ABA treated NA and CA seedlings. Conversely, CA and NA seedlings growing in the presence of 10 mu M verapamil (calcium channel blocker) or fluridone (ABA biosynthesis inhibitor) showed substantial decrease in root growth, EL, TTC reduction, accumulation of solutes and increase in MDA and H2O2 content providing an indirect evidence that acclimation confers cold tolerance by involvement of cellular calcium and ABA. The beneficial effects of acclimation could not be fully substituted by either Ca or ABA. Calcium appeared to alleviate the chilling-induced primary effects like membrane damage through more effective diminution of oxidative damage while ABA probably acted through modulation of solute levels. The recovery process was facilitated more with calcium as compared to ABA treatment. (c) 2004 Elsevier B.V. All rights reserved.