INVOLVEMENT OF PHOTOSYNTHETIC PIGMENTS IN TOTAL BEAN LEAF LIPID EXTRACT SENSITIVITY TO PHOTOPEROXIDATION

Total lipid leaf extracts from bean (Phaseolus vulgaris L. cv Carioqui nha) plants well watered or subjected to two different levels of droug ht (mild and severe) were submitted to peroxidation in an ill vitro ap paratus. In the three cases, they were more resistant to peroxidation than pure alpha-linolenic acid. When a mixture of chlorophyll a + b beta-carotene was added to linolenic acid, a significant delay in the formation of conjugated polyenic compounds was observed. Thus, we assu me that photosynthetic pigments play a protection role for Lipids in t he peroxidation apparatus. On the other hands, conjugated diene and tr iene pattern formations were higher for mildly and severe-droughted th an for well-watered total leaf lipid extracts. The comparison of HPLC analysis of leaf pigments and spectrometric evolution of total leaf li pid extracts during in vitro peroxidation showed that under drought an d under peroxidation: chorophylls decreased, the decrease being greate r for chlorophyll a than for chlorophyll b, and the amount of beta-car otene was significantly reduced. Under drought, a rearrangement of the xanthophyll distribution occurred with the appearance of antheraxanti n and zeaxanthin at the expense of violaxanthin. However chlorophyll f luorescence measurements showed that drought had little influence on P SII and PSI activity. This indicates that in vivo, leaf membranes are relatively stable and, due to the intactness of the ultrastructures, t he lipids are less prone to peroxidation attacks than in the ill vitro apparatus.