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Nitrogen-use efficiency (NUE) is one of the determining factors in crop productivity. However, the accumulation and use of this nutrient can be affected by several elements, including the species or cultivar and the water supply. Currently, one agricultural priority is to improve NUE together with greater water-deficit tolerance of crops in Mediterranean environments in order to reduce the application of nitrogenous fertilizers and boost production. The aim of the present study was to evaluate the response of different tomato-plant genotypes in relation to NUE under water stress conditions and optimal nitrogen condition. The water deficit provoked a decline in the concentration and uptake of N in all the cultivars except in cv. Zarina, which improved its NUE under these conditions. In turn, it was this cultivar which underwent the strongest relative growth during water stress together with the greatest leaf relative-water content, which could be associated with improved NUE.
Tomato fruits are sensitive to storage at low temperatures after harvest. Under these conditions, the main mechanism induced in fruits is oxidative stress, which can translate as lipid peroxidation and in turn deteriorate fruit quality. The aim of the present work was to investigate whether the effect of a biofortification program with potassium (K) improves the postharvest storage of cherry tomato fruits at 4°C, through a better antioxidant response. Three K treatments were applied during the crop cycle of the plants: 5, 10, and 15 mM of KCl. The parameters in fruits on the day of harvest and after 21 days of postharvest cold storage at 4°C, such as activity of lipoxygenase, malondialdehyde, catalase, superoxide dismutase, and the enzymes involved in the AsA–GSH cycle as well as the forms of ascorbate (AsA) and glutathione (GSH), were analyzed. The tomato fruits harvested from plants treated with 15 mM of KCl after 21 days of postharvest at 4°C showed a lower degree of lipid peroxidation, an effective regeneration of AsA, and the highest pool of this compound in comparison with the other treatments. This response was because it presented the highest ascorbate peroxidase and monodehydroascorbate reductase activity. In addition, the treatments of 10 and 15 mM KCl presented the highest GSH pool, as well as a satisfactory regeneration of this tripeptide. All these results lead to the conclusion that the rate of 15 mM of KCl applied to this tomato variety (Solanum lycopersicum L. cv AsHiari grafted on cv. Maxifort rootstock) is adequate to mitigate the negative effects of postharvest chilling.
Zinc (Zn) pollution in the soil represents a major problem for crop production worldwide. In the present work, two horticultural plants exhibiting different tolerance to Zn, Lactuca sativa cv. Phillipus and Brassica oleracea cv. Bronco, were exposed to Zn to evaluate the contribution of compatible osmolytes such as proline (Pro), glycine betaine (GB) and γ-aminobutyric acid (GABA) in the mechanism(s) of tolerance to Zn stress. This study confirms the higher susceptibility of L. sativa to Zn stress: lettuce plants experienced a strong reduction in biomass, while the levels of Pro and GB increased. These results suggest that in L. sativa, the increase of Pro and GB does not represent a mechanism of resistance to toxicity, but it is likely a symptom of Zn stress. Conversely, in B. oleracea, a slight decrease in Pro levels, mainly catalysed by degradation through proline dehydrogenase, was observed; a similar behaviour affected GB levels. On the other hand, GABA synthesis was slightly, but significantly, increased. The presence of high levels of GABA in Zn-stressed B. oleracea would suggest that reactive oxygen species detoxification could be essential to improve the resistance to toxicity under metal stress conditions.
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