65] Polyunsaturation system from higher plants

Abstract

This chapter explains the preparation of polyunsaturation systems from higher plants. Polyunsaturated fatty acids, in particular, linoleic acid and a-linolenic acid are major components of most plant tissues. Mature spinach leaves contain <10% of their dry weight as lipid, of which 60%–75% is α-linolenate. Maximum rates of polyunsaturated fatty acid formation from the exogenous ∼4C-labeled fatty acids in cucumber cotyledons occurred at light intensities above 100 μEm −1 s −2 and after at least 10 hr of greening. Both [1- 14 C]oleate and [1- 14 C]linoleate desaturation were markedly stimulated by illumination, although the latter was more sensitive to light. It is shown that the activity of the oleate desaturating system declined slowly in the dark and not at all in continuous light for at least five days. The induction of linoleate desaturation closely parallels that of chlorophyll biosynthesis. Both activities rise sharply upon illumination and decline rapidly, if the tissue is returned to darkness and so may share common control mechanisms. Time-course studies showed that the rate of oleate desaturation leveled off after 4–6 h, but that linoleate desaturation increased up to 10 h.