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

Mung bean (Vigna radiata L. Wilcz. cv. Berken) seedlings wereraised hydroponically in 0, 5 and 15 mol m^–3 choline.Fourteen-day-old plants were chilled at 5°C (under lightconditions) for 24 h and then returned to warm conditions fora further 24 h. Primary leaf lamina tissue was used for thedetermination 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 increasein ST/PL and a decline in the mole ratio of sitosterol to stigmasterol(S/S). There was no recovery of EFE activity following chillingin the absence of choline. Choline (5 and 15 mol m^–3)enhanced phospholipid and sterol levels prior to chilling andmaintained lipid levels throughout the chill-warm cycle, withoutany significant change in ST/PL. At 5.0 mol m^–3 choline,the chilling-induced decline in S/S was reduced, while at 15mol m^–3 S/S increased following chilling. Choline treatment,though reducing EFE activity prior to chilling, allowed recoveryof EFE activity following transfer of plants from chilling towarm conditions. Key words: Chill sensitivity, choline, phospholipid, sterol ethylene forming enzyme, Vigna radiata