Source-sink physiological changes and metabolic adjustments triggered by water deficit in two Solanum lycopersicum L. genotypes

Drought stress limits the growth and yield of crops, affecting source-sink relationships. A dynamic signalling network, in which hormones, reactive oxygen species and sugars are mainly involved, is activated by plants to cope with water shortage. Tolerant plants have developed efficient adaptive mechanisms to establish new cell metabolism homeostasis avoiding and/or reducing permanent impairments triggered by drought. The Southern Italy tomato landrace Ciettaicale and the wellknown tomato cultivar Moneymaker were compared evaluating their biometrical and metabolic responses to 20 days-water deficits under controlled growth chamber conditions. We evaluated in vivo chlorophyll a fluorescence, gas exchanges and leaf water potential, together with the analyses of non-structural carbohydrates in source and sink organs and with the hormonal and antioxidative responses. Leaf gas exchange measurements revealed higher water use efficiency (WUE) in Ciettaicale comparing to Moneymaker thanks to more efficient CO2 assimilation capacity. Under drought Moneymaker showed lower starch content and, in parallel, higher sucrose level than Ciettaicale, both in leaves and roots. Moreover, elevated levels of hydrogen peroxide, lipid peroxidation and abscisic acid were recorded in Moneymaker leaf and root tissues. Changes in the antioxidant pool, including enzymes and compounds like ascorbate peroxidase, ascorbate and phenols, and compatible osmolites, such as proline, played a key role to counteract redox and osmotic pressure in both genotypes. Overall, while Moneymaker showed a survival strategy leading to the accumulation of metabolites to maintain more negative leaf water potential but at same time effecting the source-sink balance, Ciettaicale increased WUE and maintained carbon translocation from source to sink supporting the investment in root metabolism and growth to avoid drought-related osmotic pressure.