The development of carotenoid-deficient membranes in plastids of barley seedlings treated with norflurazon

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The effect of carotenoid (Car) deficiency on the formation of thylakoid membranes in barley seedlings grown with norflurazon (NF) was investigated. 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 ultrastructural parameters of plastids control and NF-treated seedlings was carried out. The length of one partition and the number of partitions per plastids section, which characterize the initial stages of stacking, showed no difference in etiolated NF-treated and control seedlings. Compared with the control, the number of partitions was considerably lower in those plastids of Car-deficient seedlings which, after flash illumination, were kept for 1.5 h in continuous light of low intensity. The photobleaching of chlorophyll (Chl) in post-illuminated seedlings provides an indication of the photodestructive processes in Car-deficient seedlings exposed to low-intensity light. Chl bleaching did not appear in Car-deficient seedlings illuminated only with flashes; however, the stacking of the membranes was disturbed: the partition lengths and number of partitions per plastid section were higher in flashed, non-treated seedlings than in Car-deficient seedlings. Although the flashed control and NF-treated seedlings had an equal amount of Chl and the same polypeptide composition, no activity of photosystem II (PSII) and no PSII reaction centre complex were found in NF-treated seedlings. Car-deficient seedlings mainly contained photosystem I (PSI) with a ratio of Chl to P700 of 60 compared with 150 in the control. It is therefore suggested that Car deficiency in flashed leaves, which may accumulate only a small amount of light-harvesting Chl a b protein, prevents the assembly of the PSII complex and membrane stacking.