No abstract

Exogenous phytohormones has become a common strategy to study plant stress and defense, which triggering complex and diverse cross-actions between endogenous phytohormones, which significantly regulate plant growth and defense. In this study, Methyl Jasmonate (MeJA) promoted the most obvious growth phenotype among four different exogenous phytohormones, especially promoted the growth of roots obviously. Subsequently, principal component analysis between physicochemical indexes and MeJA treatment suggested that MeJA promoted the growth of R. Roxburghii. MeJA could increase the contents of JA-Ile, IAA and triterpenoids. qPCR results showed that key genes in the JA signal transduction pathway up-regulated trends. And tryptophan synthesis genes, ANTHRANILATE AYNTHASE α1/β1 (ASA1/ASB1), IAA receptor protein gene TIR1, as well as the IAA polar transport protein gene PIN2 were all up-regulated by MeJA treatment. While, seven key genes of triterpene synthesis pathway performed a similar up-regulated trends. The results of the chord diagram analysis indicated there might be possible mutual regulation relationship among exogenous MeJA, endogenous JA-Ile, IAA and triterpenoids. The correlation analysis among triterpenoids, IAA and JA-Ile suggested that exogenous MeJA could promote the growth of Rosa Roxburghii through regulating the JA signal tranduction pathway, synthesis and transport of IAA. At the meanwhile, MeJA promoted the synthesis of triterpenoids which could not only regulate the root growth, but also make Rosa Roxburghii a certain defense ability. Finally, we speculate that exogenous MeJA pushed endogenous JA-Ile and IAA involved in regulated the metabolism of triterpenoids, they together regulated the positive growth of plants.