Foliar spraying KH2PO4 promotes shoot development by inducing stomatal opening and sugar transport in tea leaves

Abstract

Tea plant is a perennial woody plant that is mostly harvested for its new shoots. Photoassimilates made from mature leaves are the material basis for the formation of yield and quality of new shoots. Potassium dihydrogen phosphate (KH2PO4) as a common foliar fertilizer has been widely used to improve crop yield and quality formation. However, the effect of KH2PO4 on photosynthesis, photoassimilates formation and transportation in tea plants and underlying molecular mechanism remain unclear. Therefore, in the present study, physiological, metabolomics, and transcriptomics analysis between tea plants spraying KH2PO4 and control were performed. The results showed that spraying KH2PO4 could significantly enhance the growth of new shoots. Further, spraying KH2PO4 could effectively increase the proportion of stomatal opening of mature leaves, and significantly increase net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs). The targeted metabolomics analysis of phloem exudates revealed a significant elevation of sorbitol, arabinitol, d-glucuronic acid, and d-arabinose in mature leaves spraying KH2PO4. Combined with the transcriptome sequencing results, it was found that spraying KH2PO4 significantly induced the up-regulation of genes controlling stomatal opening including HAK17, POT2, ALMT2, ALMT14, PYL4 and PYL2. And the expression levels of photosynthetic antenna proteins such as RA, LHCII type III CAB-13, Lhca3 and LHCI type III LHCA6 were also significantly up-regulated. At last, we found that two polyol transporters, PLT4 and PLT5 were up-regulated. The results revealed the molecular mechanism of KH2PO4 in regulating stomatal opening and the transportation of photoassimilates, laying a theoretical foundation for the application of KH2PO4 in tea plants.