Degradation of leaf polar lipids during chilling and post-chilling rewarming of Zea mays genotypes reflects differences in their response to chillingstress. The role of galactolipase

Degradation of leaf polar lipids [monogalactosyldiacylglycerol (MGDG), diga lactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and pho sphatidylglycerol (PG)] and chlorophyll (Chl) were studied in four Zen mays genotypes differing in chilling susceptibility following dark chilling and post-chilling rewarming at original growth conditions. Assessment of visua l chilling injury symptoms during post-chilling rewarming differentiated ma ize inbred lines into chiling-sensitive (CS) CM7 and Co151 lines and chilli ng-tolerant (CT) S215 and EP1 lines. Severity of chilling injury in CS and CT inbreeds were correlated with the extent of Chi and polar lipids degrada tion. Chilling for either 4 or 6 days followed by 4 days of rewarming caused more extensive degradation of total polar lipids content in CS than in CT lines . MGDG decreased mostly during chilling whereas DGDG dropped during rewarmi ng only. Chi content was not affected during chilling but its large decreas e, greater in CS than in CT lines, was observed upon rewarming. Extent of p olar lipids breakdown in CS and CT inbreeds during chilling and post-chilli ng rewarming is correlated with galactolipase activity in chloroplasts (Kan iuga et al., 1998) and visual assesment of chilling injury. In view of the data it is likely that contribution of galactolipase activit y induced during low-temperature stress of CS plants is an important factor responsible for thylakoid lipid degradation and development of chilling in jury as postulated previously (Kaniuga 1997). It is suggested that genetica lly engineered reduction of galactolipase activity or elimination of the fa ctors(s) involved in induction/stimulation of its activity during chilling might increase tolerance of CS species to chilling stress.