Temperature and Photoperiod Change the Flowering Process in Prunella vulgaris by Inducing Changes in Morphology, Endogenous Hormones, Carbon/Nitrogen Metabolites, and Gene Expression

The spicas of Prunella vulgaris are widely used in the medical, beverage, and ornamental fields. Temperature and photoperiod are the two main ecological factors that determine the transformation of many plants from vegetative growth to reproductive growth. To explore the response of P. vulgaris flowering to temperature and photoperiod induction, we adopted vernalization long-day, vernalization short-day, nonvernalization long-day, and nonvernalization short-day treatments. The results showed that the morphology (total number of leaves, number of branches, number of leaves per branch, and branch length) of the vernalization treatment groups was significantly different from that of other nonvernalization groups, and the photosynthetic pigments, net photosynthetic rate, water use efficiency, stomatal conductance, intercellular CO2 concentration, and transpiration rate increased in the vernalization treatment group. However, the gibberellin 3 (GA3), indole-3-acetic acid and zeatin riboside (ZR) contents were significantly increased under the short-day treatments groups, and the results were the same for the expression of endogenous hormone synthesis genes, except for abscisic acid (ABA). The flowering-related genes soc1, elf3, svp, ga20ox, and cry1 were highly expressed under the vernalization short-day. Therefore, the induction of vernalization is more conducive to the increase in the photosynthetic rate. Temperature and photoperiod synergistically induced the synthesis and accumulation of starch, sugar, amino acids, and protein and affected the content of endogenous hormones and the expression of genes involved in their synthesis. GA3 and ZR had thresholds for their regulation of the flowering process in P. vulgaris, and high concentrations of ABA promoted flowering. Temperature and photoperiod coordinate the expression of the flowering-related genes soc1, elf3, svp, ga20ox, and cry1, thereby affecting the flowering process in P. vulgaris.