Differential effects of linolenic acid and methyl jasmonate on the degradation of chlorophylls and carotenoids of senescing barley leaves

This study compares the effects of linolenic acid and methyl jasmonate, applied to isolated thylakoids and sections of senescent barley leaves, on photosynthetic pigment degradation. With regard to total chlorophylls, linolenic acid has little effect on leaf sections, whereas its effect on thylakoids is strong and rapid. Methyl jasmonate, on the other hand, has a great effect on sections and a very weak effect on thylakoids. Whereas in methyl jasmonate-treated sections chlorophyll a is degraded more quickly than chlorophyll b throughout the 3 days of treatment, in linolenic acid-incubated thylakoids the same only occurs during the first 12 hours. With regard to total carotenoid degradation, methyl jasmonate has no effect on sections whereas linolenic acid strongly stimulates such degradation in thylakoids. The general scavenger of free radicals, n-propyl-gallate, only inhibits chlorophyll and carotenoid degradation by linolenic acid in thylakoids. Chlorophyll retention in relation to effector concentration shows different kinetics for linolenic acid and methyl jasmonate. The results suggest different mechanisms for the action of linolenic acid and methyl jasmonate on photosynthetic pigments. Although the action of linolenic acid can be rather complex, one possibility is that it acts principally through free radicals during the last stages of senescence or stress, while it could act most as precursor of methyl jasmonate during the earlier stages.