Physiological and biochemical responses of fruit exocarp of tomato (Lycopersicon esculentum Mill.) mutants to natural photo-oxidative conditions

Abstract

Photo-oxidative stress was imposed under natural solar radiation on exposed and shaded sections of detached fruit of immature green tomato (Lycopersicon esculentum Miller = Solanum lycopersicum L.) mutants (anthocyanin absent, beta-carotene, Delta, and high pigment-1) and their nearly isogenic parents ('Ailsa Craig' and 'Rutgers'). After 5 h exposure to high solar irradiance, either with or without ultraviolet (UV) radiation, surface colour changes, pigment composition, photosynthetic efficiency, antioxidant metabolites and enzyme activities, and selected flavonoids and antioxidant proteins in exocarp tissue were evaluated. The imposed photo-oxidative stress reproduced the symptoms observed on attached fruit. Both high temperature and solar irradiance caused fruit surface discoloration with faster degradation of chlorophyll (Chl) than carotenoids (Car), leading to an increase in the Car/Chl ratio. Surface bleaching was mostly caused by visible light, whereas elevated temperatures were mostly responsible for the inactivation of photosynthesis, measured as decreased F(v)/F(m). Ascorbate, glutathione, and total soluble protein concentrations decreased in the exocarp as the duration of exposure increased. Specific activities of superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), and catalase increased with exposure, suggesting that these proteins were conserved during the imposed stress. GR protein expression remained stable during the imposed stress, whereas, MDHAR protein expression increased. Quercetin and kaempferol concentrations increased rapidly upon exposure, but not to UV radiation, suggesting rapid photo-protection in response to visible light; however, naringenin synthesis was not induced. The apparent increased tolerance of hp-1 fruit is discussed.

Photosynthetic efficiency of apples under protected shade nets

“…Chlorophyll fluorescence has been a non-destructive tool widely used to evaluate abiotic and biotic stress in tissue containing chlorophyll, that is, leaves and fruit (Seo et al, 2008). Previous studies have demonstrated that the photochemical efficiency of photosystem II (Fv/Fm) decreases on the peel of apple and tomato fruit exposed to sun damage (Torres et al, 2006;Naschitz et al, 2015), which concurs with the results obtained in the present study (Figure 7). Information to date indicates that this as a consequence of chlorophyll loss in sun-exposed tissue and the malfunction of the photosystem II reaction center when the fruit peel displays damage (Naschitz et al, 2015).…”

“…On the other hand, a correlation between photo-inhibition and the decreased Fv/Fm relationship has been observed (Torres et al, 2006). We found that Fv/Fm significantly decreased with the number of hours fruit were exposed to the sun (picked from the tree) at full sun, which was mitigated by using netting (Figures 8 and 9).…”

Photo-Oxidative Stress during Leaf, Flower and Fruit Development

“…Three degrees of sunburn may occur: (1) photooxidative sunburn, in which fruits become photobleached by excessive levels of light (due to sudden changes in light conditions within the canopy); (2) sunburn browning, which is caused by changes in the light environment and enhanced temperatures and is associated with the severe degradation of chlorophylls and carotenoids; and (3) sunburn necrosis, which is associated with even higher temperatures that destroy tissues on the sun-exposed side of the fruit by causing a loss in cell integrity and cell leakage (Torres et al, 2006;Racsko and Schrader, 2012). Protection against sunburn includes developing sufficient leaf cover in the canopy to shade the fruit, activating the xanthophyll cycle-dependent excess energy dissipation system, and providing effective antioxidant protection through low-molecular-weight antioxidants, such as carotenoids, tocopherols, ascorbate, glutathione, and flavonoids, and by effectively using the ascorbateglutathione cycle and other enzymatic antioxidants (Torres et al, 2006;Chen et al, 2008;Zhang et al, 2015).…”

Not All Shrivels Are Created Equal—Morpho-Anatomical and Compositional Characteristics Differ among Different Shrivel Types That Develop during Ripening of Grape (<i>Vitis vinifera</i> L.) Berries

“…These changes in the physical structure of epicuticular wax will enhance water loss from berries as crystalline form of wax serves as a formidable barrier to water permeability than amorphous wax [64] accounting for the weight (volume) loss in sunburned berries. Moreover, sunburned berries had reduced color development similar to tomato fruit [65] indicating that sunburn inhibited color by degrading anthocyanin, which occurs when mRNA transcription of anthocyanins biosynthetic genes is inhibited [66]. By contrast, sunburn caused brown lesions in white grape varieties [23] attributable to cell death in the epidermal layers of the exocarp [67].…”