Implication of potassium on the quality of cherry tomato fruits after postharvest during cold storage.

The influence of the potassium (K) content in tomato fruits over compounds or antioxidant characteristics during the postharvest period in cold storage is little known. The aim of this work was to determine whether the effect of a biofortification programme with K in KCl form can improve the postharvest storage of cherry tomato fruits at 4 °C. K treatments applied during the crop cycle of the plants: 5, 10 and 15 mM of KCl. Biomass parameters, levels of K, antioxidant capacity test, Vitamin C, carotenoids, phenolic compounds and free polyamines in tomato cherry fruits were measured. Our results show that the treatment with 15 mM KCl prevents weight and water loss during postharvest storage at 4 °C, increases K concentration, and bolsters the antioxidant capacity, since the concentration in lycopenes as well as flavonoids and derivatives rose, while the contents in Vitamin C together with hydroxycinnamic acids and derivatives remained stable.

Effects of climatic control on tomato yield and nutritional quality in Mediterranean screenhouse.

BACKGROUND: The quality of vegetables for fresh consumption is a complex issue. In this study the yield and quality of cherry tomato fruits were assessed under different environmental control conditions, namely in a screenhouse (S), in a screenhouse equipped with a fogging system (SF) and in a screenhouse with complements such as plastic sheeting to maintain the microclimate created by the fogging system (SFS), as well as under open field (OF) cultivation. Levels of vitamin C, carotenoids (lycopene, ß-carotene and lutein), phenolic compounds (flavonoids and phenolic acids), sugars (fructose, glucose and sucrose), organic acids (citric acid and malic acid) and flavour indices were measured. The aim of the study was to determine how different environmental control technologies could influence production and quality traits in tomato cherry fruits cultivated in a Mediterranean area. RESULTS: The results showed that the fogging system treatment's decline in maximum vapour pressure deficit (by 0.7 kPa compared with OF cultivation), increase in mean fruit weight (by about 4 g per fruit) and low radiation and temperature values may exert a positive effect on lycopene accumulation. CONCLUSION: For the production and nutritional parameters measured, it is postulated that the fogging system treatment offers a better balance between production and nutritional quality. This treatment proved to be best in terms of productivity, vitamin C and lycopene contents and antioxidant capacity.

Iodine effects on phenolic metabolism in lettuce plants under salt stress.

Iodine, applied as iodate in biofortification programs (at doses of ≤80 µM), has been confirmed to improve the foliar biomass, antioxidant response, and accumulation of phenol compounds in lettuce plants. The changes in phenolic compounds induced by the iodate application appear to have functional consequences in the response of salt-stressed plants. Thus, the aim of the present study was to determine whether the application of iodate can improve the response of severe salinity stress and whether the resistance can be attributed to the phenolic metabolism in lettuce ( Lactuca sativa cv. Philipus), a glycophyte cultivated for food and consumed year round. In this work, the application of iodate, especially at 20 and 40 µM, in lettuce plants under salinity stress (100 mM NaCl) exerted a significantly positive effect on biomass and induced higher activity in the enzymes shikimate dehydrogenase and phenylalanine ammonia-lyase as well as the lower MW phenol-degrading enzyme polyphenol oxidase. This increased hydroxycinnamic acids and derivatives in addition to total phenols, which appear to act as protective compounds against salinity. This study reveals that in agricultural areas affected by this type of stress, the application of iodate may be an effective strategy, as it not only improves lettuce plant growth but also supplements the human diet with phenolic compounds and the trace element iodine.

Response of carbon and nitrogen-rich metabolites to nitrogen deficiency in PSARK::IPT tobacco plants.

Wild type (WT) and transgenic tobacco plants expressing isopentenyltransferase (IPT), a gene coding the rate-limiting step in cytokinin (CKs) synthesis, were grown under limited nitrogen (N) conditions. Here, we analyse the possible effect of N deficiency on C-rich compounds such as phenolic compounds, as well as on N-rich compounds such as polyamines (PAs) and proline (Pro), examining the pathways involved in their synthesis and degradation. N deficiency was found to stimulate phenolic metabolism and increase these compounds both in P(SARK):IPT as well as in WT tobacco plants. This suggests that nitrate (NO(3)(-)) tissue concentration may act as a signal triggering phenolic compound accumulation in N deficiency plants. In addition, we found the maintenance of PAs in the WT plants would be correlated with the higher stress response to N deficiency. On the contrary, the reduction of free PAs and Pro found in the P(SARK)::IPT plants subjected to N deficiency would indicate the operation of an N-recycling mechanism that could stimulate a more efficient N utilization in P(SARK)::IPT plants.

Antioxidant response resides in the shoot in reciprocal grafts of drought-tolerant and drought-sensitive cultivars in tomato under water stress.

Recently grafted plants have been used to induce resistance to different abiotic stresses. In our work, grafted plants of tomato cultivars differing in water stress tolerance (Zarina and Josefina) were grown under moderate stress, to test the roles of roots and shoots in production of foliar biomass and antioxidant response. Stress indicators and activities of selected enzymes related to antioxidant response were determined. Our results showed that when shoots are of the drought tolerant genotype Zarina, the changes in antioxidant enzyme activities were large and consistent. However, when shoots are of the drought-sensitive genotype Josefina, the antioxidant enzyme activities were more limited and the oxidative stress was evident. These results reflect that the technique of grafting using Zarina as scion can be useful and effective for improving the antioxidant response in tomato under water stress.

Beneficial effects of exogenous iodine in lettuce plants subjected to salinity stress.

Salinity inhibits plant growth due to ionic and osmotic effects on metabolic processes and nutritional balance, leading to impaired physiological functions. Selenium (Se) and silicon (Si) can be partially alleviated by the effects wrought by NaCl on the plant metabolism. Iodine (I), applied as iodate (IO(3)(-)) in biofortification programmes, has been confirmed to improve the antioxidant response in lettuce plants. Thus, the aim of this study was to determine whether the application of IO(3)(-) can improve the response to severe salinity stress in lettuce (Lactuca sativa cv. Philipus). In this work, the application of IO(3)(-) (20-80 µM) in lettuce plants under salinity stress (100mM of NaCl) exerted a significantly positive effect on biomass and raised the levels of soluble sugars while lowering the Na(+) and Cl(-) concentrations as well as boosting the activity of antioxidant enzymes such as SOD, APX, DHAR and GR. Therefore, IO(3)(-) could be considered a possibly beneficial element to counteract the harmful effects of salinity stress.

Does iodine biofortification affect oxidative metabolism in lettuce plants?

Plants produce low levels of reactive oxygen species (ROS), which form part of basic cell chemical communication; however, different types of stress can lead to an overexpression of ROS that can damage macromolecules essential for plant growth and development. Iodine is vital to human health, and iodine biofortification programs help improve the human intake through plant consumption. This biofortification process has been shown to influence the antioxidant capacity of lettuce plants, suggesting that the oxidative metabolism of the plant may be affected. The results of this study demonstrate that the response to oxidative stress is variable and depends on the form of iodine applied. Application of iodide (I(-)) to lettuce plants produces a reduction in superoxide dismutase (SOD) activity and an increase in catalase (CAT) and L-galactono dehydrogenase enzyme activities and in the activity of antioxidant compounds such as ascorbate (AA) and glutathione. This did not prove a very effective approach since a dose of 80 µM produced a reduction in the biomass of the plants. For its part, application of iodate (IO (3) (-) ) produced an increase in the activities of SOD, ascorbate peroxidase, and CAT, the main enzymes involved in ROS detoxification; it also increased the concentration of AA and the regenerative activities of the Halliwell-Asada cycle. These data confirm the non-phytotoxicity of IO (3) (-) since there is no lipid peroxidation or biomass reduction. According to our results, the ability of IO (3) (-) to induce the antioxidant system indicates that application of this form of iodine may be an effective strategy to improve the response of plants to different types of stress.

Response of nitrogen metabolism in lettuce plants subjected to different doses and forms of selenium.

BACKGROUND: Currently, biofortification programmes are being carried out with selenium (Se), since it is an essential element for humans and its ingestion depends partly on a vegetable diet, this not being so for plants. In this sense, few studies have tested the effect that Se has on some of the main plant metabolisms, such as nitrogen (N) metabolism. Thus the aim of this study was to establish the effect of the application of different doses (5, 10, 20, 40, 60, 80 and 120 micromol L(-1)) and forms (selenate and selenite) of Se on the reduction of nitrate (NO3-) and subsequent assimilation of ammonium (NH4+). RESULTS: The results showed an increase in all enzyme activities analysed (nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamate synthase (GOGAT)), especially with application of the selenite form, in addition to a decline in foliar NO3- concentration. CONCLUSION: Se applied in both forms increased N metabolism, with selenite inducing this physiological process more strongly, since it prompted a stronger activation of NR, GS and GOGAT as well as a greater concentration of total reduced N.