PHOTOSYNTHETIC APPARATUS OF CHILLING-SENSITIVE PLANTS .32. PEROXIDATION OF FREE FATTY-ACIDS IN THYLAKOIDS OF CHILLING-SENSITIVE AND CHILLING-TOLERANT PLANTS

Peroxidation of free fatty acids (FFA) in thylakoids of chilling-sensitive (CS) bean and chilling-tolerant pea (CT) was measured by the formation of malondialdehyde (MDA) both under dark and light conditions. Illumination of pea and bean thylakoids did not essentially affect the initial rate of MDA formation, which was more effective in bean than in pea thylakoids and was related to the content of FFA. An increased level of FFA in thylakoids was achieved by chilling leaves or incubation of thylakoids with lipase, while washing of thylakoids with bovine serum albumin was applied for a decrease of FFA content. Release of FFA upon digestion with lipase was higher in pea than in bean thylakoids, but the rate of peroxidation was greater in bean thylakoids both in the presence and absence of lipase. The depletion of FFA by washing thylakoids with BSA was accompanied by a reduced rate of peroxidation, whereas the presence of Triton X-100 greatly enhanced the rate of MDA formation, probably by increasing access of FFA. Incubation of bean thylakoids in the presence of different detergents (cetavlon - CDAB, Tween 20, octylglucoside and Triton X-100) had similar effects on FFA level but different on initial rate of MDA formation. Triton X-100 was the most effective one in stimulation of peroxidation, while octylglucoside and Tween 20, respectively, were only 1/2 and 2/3 as effective as Triton X-100, and cetavlon was inhibitory. The data suggest that: (i) light is not obligatory for initiation of peroxidation and (ii) FFA are the main substrate for peroxidation in thylakoids.