Search

Tomato crop productivity under salinity can be improved by grafting cultivars onto salt-tolerant wild relatives, thus mediating the supply of root-derived ionic and hormonal factors that regulate leaf area and senescence. A tomato cultivar was grafted onto rootstocks from a population of recombinant inbred lines (RILs) derived from a Solanum lycopersicum × Solanum cheesmaniae cross and cultivated under moderate salinity (75 mm NaCl). Concentrations of Na+, K+ and several phytohormones [abscisic acid (ABA); the cytokinins (CKs) zeatin, Z; zeatin riboside, ZR; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC)] were analysed in leaf xylem sap in graft combinations of contrasting vigour. Scion leaf area correlated with photosystem II (PSII) efficiency ( Fv/ Fm) and determined fruit productivity. Xylem K+ (but not Na+), K+/Na+, the active CK Z, the ratio with its storage form Z/ZR and especially the ratio between CKs and ACC (Z/ACC and Z + ZR/ACC) were positively loaded into the first principal component (PC) determining both leaf growth and PSII efficiency. In contrast, the ratio ACC/ABA was negatively correlated with leaf biomass. Although the underlying physiological mechanisms by which rootstocks mediate leaf area or chlorophyll fluorescence (and thus influence tomato salt tolerance) seem complex, a putative potassium–CK interaction involved in regulating both processes merits further attention. [ABSTRACT FROM AUTHOR]

Leaf senescence is one of the most limiting factors to plant productivity under salinity. Both the accumulation of specific toxic ions (e.g. Na+) and changes in leaf hormone relations are involved in the regulation of this process. Tomato plants (Solanum lycopersicum L. cv Moneymaker) were cultivated for 3 weeks under high salinity (100 mM NaCl) and leaf senescence-related parameters were studied during leaf development in relation to Na+ and K+ contents and changes in abscisic acid (ABA), cytokinins, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and the auxin indole-3-acetic acid (IAA). Na+ accumulated to a similar extent in both leaves 4 and 5 (numbering from the base of the plant) and more quickly during the third week, while concurrently K+ contents sharply decreased. However, photosystem II efficiency, measured as the Fv/Fm ratio, decreased from the second week of salinization in leaf 4 but only at the end of the third week in the younger leaf 5. In the prematurely senescent leaf 4, ABA content increased linearly while IAA strongly decreased with salinization time. Although zeatin (Z) levels were scarcely affected by salinity, zeatin-riboside (ZR) and the total cytokinin content (Z+ZR) progressively decreased by 50% from the imposition of the stress. ACC was the only hormonal compound that increased in leaf tissue coincident with the onset of oxidative damage and the decline in chlorophyll fluorescence, and prior to massive Na+ accumulation. Indeed, (Z+ZR) and ACC contents and their ratio (Z+ZR/ACC) were the hormonal parameters best correlated with the onset and progression of leaf senescence. The influence of different hormonal changes on salt-induced leaf senescence is discussed. [ABSTRACT FROM PUBLISHER]