Abstract
Soil salinization is an important agriculture-related environmental problem. Alkali stress and salt stress strongly influence the metabolic balance in plants. Salt and alkali stresses exert varied effects on old and young tissues, which display different adaptive strategies. In this study, we used cotton (Gossypium hirsutum L.) plants as experimental material to investigate whether alkali stress induces ionic and metabolism changes in old and young leaves of cotton plants exposed to alkali stress. Results showed that alkali stress exerted a considerably stronger growth inhibition on old leaves than on young leaves. Under alkali stress, young leaves can maintain low Na and high K contents and retain relatively stable tricarboxylic acid cycle, resulting in greater accumulation of photosynthetic metabolites. In terms of metabolic response, the young and old leaves clearly displayed different mechanisms of osmotic regulation. The amounts of inositol and mannose significantly increased in both old and young leaves of cotton exposed to alkali stress, and the extent of increase was higher in young leaves than in old leaves. In old leaves, synthesis of amino acids, such as GABA, valine, and serine, was dramatically enhanced, and this phenomenon is favorable for osmotic adjustment and membrane stability. Organs at different developmental stages possibly display different mechanisms of metabolic regulation under stress condition. Thus, we propose that future investigations on alkali stress should use more organs obtained at different developmental stages.
Highlights
Soil salinization is an important agriculture-related problem, which frequently co-exists with salt and alkali stresses (Wang et al, 2011)
Alkali stress increased the concentrations of chlorophylls a, b, a+b, and carotenoids in young leaves but it reduced their amounts in old leaves (Figure 1)
The young and old leaves of cotton exposed to 80 mM alkali stress for 6 days showed distinct differences in terms of growth; alkali stress exerted a stronger inhibitory effect on old leaves than on young leaves
Summary
Soil salinization is an important agriculture-related problem, which frequently co-exists with salt and alkali stresses (Wang et al, 2011). Understanding the distinct effects of alkali stress on old and young leaves is potentially important in elucidating the adaptation and tolerance of plants to alkali stress. In rice (Oryza sativa L.), alkali stress strongly affects the uptake and accumulation of some metabolites, such as nitrogen and proline; these changes in composition in response to physiological processes are possibly important in alkali tolerance in plants (Yang et al, 2008, 2009). Wang et al (2012b) showed that during adaptation of rice to alkali stress, young and old leaves have distinct mechanisms of ion balance and nitrogen metabolism regulation. We used cotton plants as experimental material to investigate whether alkali stress exerts different effects on ion balance and metabolism in old and young leaves of cotton
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