THE DEVELOPMENT OF CAROTENOID-DEFICIENT MEMBRANES IN PLASTIDS OF BARLEY SEEDLINGS TREATED WITH NORFLURAZON

The effect of carotenoid (Car) deficiency on the formation of thylakoi d membranes in barley seedlings grown with norflurazon (NF) was invest igated. To exclude photodestruction during the growth of Car-deficient seedlings, the etiolated seedlings were illuminated for 24 h with 2.5 ms flashes every 12 min. The morphometric analysis of seven main ultr astructural parameters of plastids of control and NF-treated seedlings was carried out. The length of one partition and the number of partit ions per plastid section, which characterize the initial stages of sta cking, showed no difference in etiolated NF-treated and control seedli ngs. Compared with the control, the number of partitions was considera bly lower in those plastids of Car-deficient seedlings which, after fl ash illumination, were kept for 1.5 h in continuous light of low inten sity. The photobleaching of chlorophyll (Chi) in post-illuminated seed lings provides an indication of the photodestructive processes in Car- deficient seedlings exposed to low-intensity light. Chi bleaching did not appear in Car-deficient seedlings illuminated only with flashes; h owever, the stacking of the membranes was disturbed: the partition len gths and number of partitions per plastid section were higher in flash ed, non-treated seedlings than in Car-deficient seedlings. Although th e flashed control and NF-treated seedlings had an equal amount of Chi and the same polypeptide composition, no activity of photosystem II (P SII) and no PSII reaction centre complex were found in NF-treated seed lings. Car-deficient seedlings mainly contained photosystem I (PSI) wi th a ratio of Chi to P700 of 60 compared with 150 in the control. It i s therefore suggested that Car deficiency in flashed leaves, which may accumulate only a small amount of light-harvesting Chi alb protein, p revents the assembly of the PSII complex and membrane stacking.