The effects of exogenous Ca2+ on endogenous polyamine levels and drought-resistant traits of spring wheat grown under arid conditions

This study investigates the effects of exogenous Ca2+ on physiological and phenotypic characteristics of spring wheat (Triticum aestivum L.) in an arid region of China. These traits, which are closely linked to drought tolerance in plants, include alteration in endogenous levels of polyamines (PAs), root-to-stem ratios and relative water content (RWC). Exogenous Ca2+ was applied to the seeds by soaking in a 0.5% CaCl2 solution before sowing and also by spraying the leaves with the same solution. It was determined that the foliar RWC increased at all stages of development following the Ca2+ application. The levels of endogenous PAs in the leaves were altered: the putrescine (Put) content decreased whereas the spermidine (Spd) and spermine (Spm) content increased. The ratio of Put to PAs titers was reduced. At the same time, phenological events of wheat were also changed in response to the application of Ca2+. In particular, reproductive maturity was significantly delayed. Moreover, the application of Ca2+ increased both the root-to-shoot ratios of wheat at the early stages of growth and the final grain yield. The results obtained from this study show that the exogenous Ca2+ could not only enhance the tolerance of spring wheat to drought but also delay its senescence. Finally, the role of Ca2+ in the signal regulation of endogenous PA metabolism is discussed. We suggest that exogenous Ca2+ may have a role in modifying endogenous PAs levels under drought stress leading to increased drought tolerance.