SUMMARY
The effect of light on Cucumis leaf pigments at 1 °C has been studied. Pigment degradation is a photo‐oxidative process. Kinetics of pigment degradation show a slow degradation rate (lag phase) followed by a fast one. The sensitivity to photo‐oxidation corresponds to the length of the lag phase. Carotene has the shortest lag phase and is most sensitive to photo‐oxidation, followed by xanthophyll, chlorophyll a, and chlorophyll b.
The lag phase decreases at 100% oxygen and disappears after boiling. Some possible factors causing the biphasic nature of chlorophyll degradation are discussed. It is suggested that carotene plays no primary role in the protection against photo‐oxidation during chilling.
The effect of pretreatment of cucumber (Cucumis sativus L.) roots with choline chloride or ethanolamine on leaf phospholipid composition and light-induced leaf damage during chilling was studied. Photooxidative chlorophyll degradation was similarly inhibited by both amino alcohols. The decrease of the chlorophyll a/chlorophyll b ratio and the increase of polyunsaturated-fatty-acid degradation during chilling in the light were equally inhibited by pretreatment with choline chloride or ethanolamine. Treatment with choline chloride and ethanolamine caused, respectively, 43% and 26% increases in the total phospholipid contents of the leaves. After treatment with choline chloride, the phosphatidylcholine content was higher than the content of phosphatidylethanolamine; the reverse was true after treatment with ethanolamine. The chlorophyll concentration increased less than the phospholipid concentration, resulting in a decreased chlorophyll/phospholipid ratio of treated leaves. During chilling in the light, degradation of phosphatidylcholine, ethanolamine and phosphatidyl glycerol occurred. Phosphatidyl glycerol was less sensitive than phosphatidylcholine and ethanolamine. The degradation was equally inhibited by pretreatment with either amino alcohol. Possible connections between the phospholipid content of leaf membranes and the inhibition of chilling-induced photooxidative leaf damage are discussed.
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