Phospholipid, Sterol Composition and Ethylene Production in Relation to Choline-Induced Chill-Tolerance in Mung Bean (Vigna radiataL. Wilcz.) During a Chill-Warm Cycle

Mung bean (Vigna radiata L. Wilcz. cv. Berken) seedlings were raised hydroponically in 0, 5 and 15 mol m−3 choline. Fourteen-day-old plants were chilled at 5°C (under light conditions) for 24 h and then returned to warm conditions for a further 24 h. Primary leaf lamina tissue was used for the determination of phospholipid, mole ratio of sterol to phospholipid (ST/PL), sterol composition, and ethylene-forming enzyme (EFE) activity for the various choline-temperature treatments employed. Chilling caused an irreversible loss of lipid in the absence, of choline. Differential loss of lipid resulted in an increase in ST/PL and a decline in the mole ratio of sitosterol to stigmasterol (S/S). There was no recovery of EFE activity following chilling in the absence of choline. Choline (5 and 15 mol m−3) enhanced phospholipid and sterol levels prior to chilling and maintained lipid levels throughout the chill-warm cycle, without any significant change in ST/PL. At 5.0 mol m−3 choline, the chilling-induced decline in S/S was reduced, while at 15 mol m−3 S/S increased following chilling. Choline treatment, though reducing EFE activity prior to chilling, allowed recovery of EFE activity following transfer of plants from chilling to warm conditions.