Contrasting photo‐ and thermoperiod‐induced changes in abscisic acid and lipid contents in leaves of mungbean seedlings

Abstract

Seedlings of Phaseolus aureus ROXB were grown under 12/12 h light/dark cycles with the light period at 32.5°C and darkness at 10°C (normal conditions N) or with light at 10°C and darkness at 32.5°C (inverse conditions, I). I‐conditions affected the level of chlorophyll and carotenoids (very low), monogalactosyldiacylgycerol (low) and phosphatidylinositol (high) in the leaves. Leaves of I‐seedlings showed a sharp and durable decline of relative water content during the low temperature phase. For the N‐seedlings, loss of water was restricted to the end of this period. The loss of water was accompanied by visible symptoms of wilting at specific times of day. Although the pigment content remained nearly unchanged, ABA content of leaves of both N‐and I‐seedlings increased during water stress. Upon return to the warm period, ABA level continued to increase after the leaves had regained turgor, this ‘after stress’increase being more pronounced in the leaves of I‐seedlings. Exogenous application of ABA induced a slight increase in the content of phospholipids in N‐ and I‐leaves and a decrease in free fatty acids, whereas monogalactosyldiacylglycerol content was significantly reduced in N‐leaves after application of ABA. Upon transfer of I‐plants to 20°C for 12 h during the light period, pigment and chloroplastic lipid content increased rapidly whereas upon a further exposure to 10°C in light, pigments and especially monogalactosyldiacylglycerol were lost. The control of pigment and lipid metabolism and the role of ABA during chilling stress are discussed.