Changes in carotenoid and ascorbic acid contents in fruits of different tomato genotypes related to the depletion of UV-B radiation.

The aim of the present study was to investigate if the depletion of UV-B radiation affected the most representative carotenoids as well as the ascorbic acid content in tomato fruits, harvested at both breaker and firm red stages. To do this, three tomato genotypes, DRW 5981, HP 1, and Esperanza, were grown inside a greenhouse either covered with polyethylene transparent to UV-B or depleted of UV-B by a special covering film. The antioxidant properties of the fruits were evaluated on the water-insoluble fractions according to the ABTS method. UV-B effect on antioxidant activity was negligible in DRW and HP 1 genotypes, whereas it was detrimental in Esperanza at both ripening stages. This genotype seems to have a negligible capability of accumulating carotenoids and a great susceptibility to detrimental effects of UV-B; conversely, the DRW genotype shows high carotenoid levels under sunlight conditions and a further promotion by UV-B. On the other hand, the HP 1 mutant displays an intermediate behavior and represents the only genotype favored by UV-B with respect to ascorbic acid accumulation.

Ozone-response mechanisms in tobacco: implications of polyamine metabolism.

• Polyamines have been suggested to counteract oxidative damage in plants. Here, we present a detailed analysis of polyamine accumulation and its relationship to photosynthetic parameters in two tobacco (Nicotiana tabacum) cultivars (ozone-sensitive Bel W3 and ozone-tolerant Bel B) after a single ozone pulse and after a 1-month exposure in the open air. • Free putrescine accumulated in undamaged tissue of both cultivars, whereas putrescine conjugated to soluble and cell-wall bound components accumulated predominantly in tissue undergoing cell death in Bel W3 plants. Accumulation was caused by a redirection of the conjugation pathway, as well as by a transient increase in arginine decarboxylase and ornithine decarboxylase specific activity. This increase seemed to be regulated at post-transcriptional level. • Measurements of chlorophyll content and fluorescence showed that, in addition to visible necrotic lesions, Bel W3 plants suffered considerable photosynthetic damage in other parts of the leaf. • Accumulation of conjugated putrescine is part of the ozone-induced programmed cell death response in Bel W3 plants. Ozone-induced synthesis of free putrescine is not correlated with ozone-resistance in Bel B plants, which are apparently impaired in signal transduction pathways that are necessary to control the cellular redox state. However, Bel B plants are able to perceive ozone stress and to induce a series of defense mechanisms without activating hypersensitive cell death.

Quenching analysis in poplar clones exposed to ozone.

Effects of ozone (O(3)) on photo-inhibition of photosynthesis were investigated in two poplar clones (Populus deltoides Bartr. ex Marsh. x maximowiczii A. Henry clone Eridano, O(3)-sensitive, and P. x euramericana (Dode) Guinier clone I-214, O(3)-resistant) by using pulse amplitude modulation chlorophyll fluorescence. After a 15-day exposure to O(3) at 60 nl l(-1) for 5 h day(-1), the effective photosynthetic quantum yield of photosystem II (PSII), as indicated by the ratio of variable to maximum chlorophyll fluorescence, significantly declined in both young and mature leaves of the two clones. Compared with control samples, mature leaves of both clones showed differences in fluorescence quenching and quantum yield of PSII when exposed to ozone fumigation. We conclude that photo-inhibition is caused by transformation of active reaction centers to photochemically inactive centers that dissipate excitation energy into heat, thus causing non-photochemical fluorescence quenching. The changes observed in chlorophyll a fluorescence of O(3)-treated young leaves in both clones are consistent with O(3) having a negligible effect on photosynthetic performance, but inducing a premature decrease in chlorophyll a concentration. A possible role of O(3) pollution on chlorophyll fluorescence yield is discussed.