Hormonal changes during salinity-induced leaf senescence in tomato (Solanum lycopersicum L.)

Abstract

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.

Arabidopsis AHP2, AHP3, and AHP5 histidine phosphotransfer proteins function as redundant negative regulators of drought stress response

“…2B). Because the endogenous CK levels are known to decrease under stress conditions (8,23) as an adaptive mechanism to tolerate adverse environments (8, 9), we hypothesize that during stress, plants activate a yet-unknown mechanism to reduce endogenous CK levels. This in turn leads to a repression of CK signaling, at least by down-regulation of the AHP2, AHP3, and AHP5 genes (Fig.…”

Roles of enzymes in anti-oxidative response system on three species of chenopodiaceous halophytes under NaCl-stress condition

“…Malondialdehyde (MDA) content in leaves was measured as 2-thiobarbituric acid-reactive substances (TBARs) following the method of Ghanem et al (2008). We used only leaf samples, because excessive NaCl impairs electron transport in chloroplasts (Asada 1999).…”

“…More than 23% of irrigated lands have been salinized (Tanji 1990) and its adverse effect is increasing (Ghanem et al 2008). Excessive sodium chloride (NaCl), a major salt in these lands, causes many types of stress symptoms in plants, such as potassium (K) deficiency (Dodd et al 2010;Fraile-Escanciano et al 2010) and osmotic stress (Yang et al 2008).…”

Plant Responses to Salt Stress: Adaptive Mechanisms

“…An indirect effect related to an initial abscisic acid (ABA) accumulation and a decrease in indol-3-acetic acid (IAA) and cytokinin (CK) contents certainly favours the progression of senescence in salinized leaves. However, the ethylene precursor ACC is the major hormonal signal that is temporally correlated with the onset of the oxidative damage, decreases in chlorophyll fluorescence and massive Na + accumulation [63,64].…”