Carotenoids in ripe green and in autumn senescing leaves of apple tree: II - Seasonal changes of free carotenoids and xanthophyll esters and relationship between their content and senescing stage

Carotenoids (two carotenes, five free xanthophylls and seven xanthophyll esters previously isolated and identified, Cardini 1982) were measured in apple leaves from the early spring to autumn senescence; a detailed quantitative investigation on different senescence stages was also carried out. The xanthophyll esters were determinated by extinction coefficients (E1 cm 1%) experimentally obtained in this laboratory. α-carotene shows a clear character of « summer carotene », moreover for its sudden decrease in late summer it could perhaps be considered a biological indicator of early autumn. Violaxanthin shows a unique seasonal behaviour: a minimum during the summer maturity, a very marked biosynthesis in spring and a very intense esterification in autumn. In spring and in the first summer, violaxanthin shows a slight negative correlation with zeaxanthin in relationship with the « violaxanthin cycle », and also a negative correlation with neoxanthin; these correlations and the possible role of violaxanthin as precursor of plant growth inhibitors, are discussed. β-carotene presents a curve pattern which follows the one of chlorophylls. Zeaxanthin shows its maximum in late autumn and it keeps its free form even in yellow leaves. Lutein is the major component (50-60% of total xanthophylls and 35-45% of total carotenoids); its free form shows its maximum in summer with an autumn increase in percentage; its esterification is marked but much less than violaxanthin. With age (plants 9 year old) in addition to the four major esters, three minor esters appear in detectable amounts (neoxanthin triester 5-7%, antheraxanthin monoester 3-4%, unknown monoester nearly 2-5% of total esters).