The effect of environmental conditions on nutritional quality of cherry tomato fruits: evaluation of two experimental Mediterranean greenhouses.

BACKGROUND: The aim of this study was to examine how different environmental factors (temperature, solar radiation, and vapour-pressure deficit [VPD]) influenced nutritional quality and flavour of cherry tomato fruits (Solanum lycopersicum L. cv. Naomi) grown in two types of experimental Mediterranean greenhouses: parral (low technology) and multispan (high technology). RESULTS: Fruits were sampled three times during 3 years (2004, 2005 and 2006): at the beginning, middle and end of the fruit production period. Values for temperature, solar radiation, and VPD peaked in the third sampling in both greenhouses; values were higher in the parral-type greenhouse, triggering abiotic stress. This stress reduced the accumulation of lycopene and essential elements, augmenting the phytonutrient content and the antioxidant capacity of tomatoes. During the third sampling, sugars were increased while organic acid content diminished, producing tomatoes with a sweeter-milder flavour. The parral greenhouse produced tomatoes with higher phenolic compounds and ascorbic acid contents, together with a greater antioxidant capacity, without showing differences in flavour parameters. CONCLUSION: The higher phytonutrients content and antioxidant activity during the environmental stress, more pronounced in parral than multispan greenhouse, together with the sweeter-milder flavour, conferred a notable nutritional benefit, which considerably improved the nutritional and organoleptic quality of these tomatoes.

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.

Oxidative stress and antioxidants in tomato (Solanum lycopersicum) plants subjected to boron toxicity.

BACKGROUND AND AIMS: Boron (B) toxicity triggers the formation of reactive oxygen species in plant tissues. However, there is still a lack of knowledge as to how B toxicity affects the plant antioxidant defence system. It has been suggested that ascorbate could be important against B stress, although existing information is limited in this respect. The objective of this study was to analyse how ascorbate and some other components of the antioxidant network respond to B toxicity. METHODS: Two tomato (Solanum lycopersicum) cultivars ('Kosaco' and 'Josefina') were subjected to 0.05 (control), 0.5 and 2 mm B. The following were studied in leaves: dry weight; relative leaf growth rate; total and free B; H(2)O(2); malondialdehyde; ascorbate; glutathione; sugars; total non-enzymatic antioxidant activity, and the activity of superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, ascorbate oxidase and l-galactose dehydrogenase. KEY RESULTS: The B-toxicity treatments diminished growth and boosted the amount of B, malondialdehyde and H(2)O(2) in the leaves of the two cultivars, these trends being more pronounced in 'Josefina' than in 'Kosaco'. B toxicity increased ascorbate concentration in both cultivars and increased glutathione only in 'Kosaco'. Activities of antioxidant- and ascorbate-metabolizing enzymes were also induced. CONCLUSIONS: High B concentration in the culture medium provokes oxidative damage in tomato leaves and induces a general increase in antioxidant enzyme activity. In particular, B toxicity increased ascorbate pool size. It also increased the activity of l-galactose dehydrogenase, an enzyme involved in ascorbate biosynthesis, and the activity of enzymes of the Halliwell-Asada cycle. This work therefore provides a starting point towards a better understanding of the role of ascorbate in the plant response against B stress.