Effects of exogenous nitric oxide and cytokinin on the growth and photosynthesis of wheat seedlings under water deficit

Using sodium nitroprusside (SNP) and 6-benzyl aminopurine (6-BA) as exogenous nitric oxide (NO) donor and a synthetic cytokinin, respectively, the study tried to characterize the roles and interaction of NO and cytokinin in the responses of wheat (Triticum aestivum L.) growth and photosynthesis to water deficit. The parameters such as biomass, roots growth, water status, membrane stability (MS), photosynthetic pigments and light response curves (LRCs) were measured in the study. SNP or 6-BA increased root elongation and leaf MS, however, 6-BA was a more potential regulator for stressed wheat. In addition, when both SNP and 6-BA were simultaneously added, their combined effects on the above indexes were more prominent than that of singly added SNP or 6-BA. In the chloroplasts of stressed wheat, SNP plus 6-BA increased the Chl a and Chl b contents and PSII functional activities described in LRCs-the opening (qP) and absorbed energy conversion (F-v'/F-m') of PSII reaction centers, but failed to influence the carotenoid (Car) content. In the meantime, exogenous NO could regulate the LRCs although it exerted weaker influence on photosynthetic pigment level. However, NO inhibitor (hemoglobin, Hb) also arrested the promotion of 6-BA to the growth and development of the leaves and roots. Considering these results as a whole, NO could act as second messenger in cytokinin regulating growth and photosynthetic responses of wheat seedlings to water deficit.