DIFFERENTIAL LEVELS OF CAROTENOIDS AND DECREASE OF ZEAXANTHIN CYCLE PERFORMANCE DURING LEAF DEVELOPMENT IN A GREEN AND AN AUREA VARIETY OF TOBACCO

The level of the individual leaf carotenoids and the performance of the high-light induced violaxanthin/zeaxanthin cycle were determined during the course of leaf development in two tobacco varieties (Nicotiana tabacum I,.: green form su/su and chlorophyll-deficient aurea mutant Su/su). Young and fully developed leaves of green tobacco possessed a regular chlorophyll and carotenoid composition as in other green plants, and a 5 times higher chlorophyll content per leaf area unit than the aurea form Su/su. On a chlorophyll basis the aurea mutant contained a relatively higher carotenoid content, particularly in younger leaves, and initially low amounts of chlorophyll b, which resulted in high values for the ratio chlorophylla/b of 9-10 (green tobacco 2.8), and relatively low values for the ratio chlorophyll/carotenoids (1.8 to 2.8) as compared to 4.5 to 5.5 in the green tobacco form. During leaf development the aurea mutant Su/su exhibited a much prolonged greening process. With increasing age and chlorophyll content the ratios of the photosynthetic pigments a/b; a/c and (a+b)/(x+c) eventually approached values which were fairly close to those of green tobacco. The level of violaxanthin and the capacity for light-induced zeaxanthin formation was much higher in aurea than in green tobacco, and decreased in both plants with increasing age. Despite the observation that the young developing leaves of both tobacco varieties were sensitive to a 10 min high light treatment, it appears that the higher capacity of the violaxanthin/zeaxanthin cycle performance, found in the young leaves and particularly in those of the aurea mutant, functions in the protection of the photosynthetic apparatus against excessive light intensities. The possible function of zeaxanthin is discussed even though the mechanism of photoprotection by zeaxanthin is still open.