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Water stress is one of the most important factors limiting the growth and productivity of crops. The implication of compatible osmolytes such as proline and polyamines in osmotic adjustment has been widely described in numerous plants species under stress conditions. In the present study, we investigated the response of five cherry tomato cultivars (Solanum lycopersicum L.) subjected to moderate water stress in order to shed light on the involvement of proline and polyamine metabolism in the mechanisms of tolerance to moderate water stress. Our results indicate that the most water stress-resistant cultivar (Zarina) had increased degradation of proline associated with increased polyamine synthesis, with a higher concentration of spermidine and spermine under stress conditions. In contrast, Josefina, the cultivar most sensitive to water stress, showed a proline accumulation associated with increased synthesis after being subjected to stress. In turn, in this cultivar, no rise in polyamine synthesis was detected. Therefore, all the data appear to indicate that polyamine metabolism is more involved in the tolerance response to moderate water stress.

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Roles of some nitrogenous compounds protectors in the resistance to zinc toxicity in Lactuca sativa cv. Phillipus and Brassica oleracea cv. Bronco Abstract 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 c-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.