Plant bolting is regulated and controlled by various internal and external factors. We aimed to provide an improved method for breeding to determine whether there is a synergism between hormones and to explore the regulatory effect of plant hormones on the bolting of leaf lettuce. Lettuce plants were sprayed with exogenous auxin and gibberellin separately or in combination. The specific bolting period was determined by the change in stem length and cytological observation. The dynamic changes in endogenous hormones and genes closely related to bolting were analyzed. Treatment with gibberellin alone and the combined application of auxin and gibberellin induced bolting on the fourth day, and treatment with auxin alone resulted in bolting on the eighth day. In the early bolting stage, the auxin contents in the stems of the treatment groups, especially the combined gibberellin and auxin group, were higher than those of the control group. After the application of exogenous auxin and gibberellin, we found that the expression of the ARF8 and GID1 genes was upregulated. Based on the results of our study, combined treatment with exogenous gibberellin and auxin was the best method to promote the bolting of leaf lettuce, and the ARF8 and GID1 genes are closely related to this process.

Background: Lettuce (Lactuca sativa L.), one of the most economically important leaf vegetables, exhibits early bolting under high-temperature conditions. Early bolting leads to loss of commodity value and edibility, leading to considerable loss and waste of resources. However, the initiation and molecular mechanism underlying early bolting induced by high temperature remain largely elusive. Results: In order to better understand this phenomenon, we defined the lettuce bolting starting period, and the high temperature (33 °C) and controlled temperature (20 °C) induced bolting starting phase of proteomics is analyzed, based on the iTRAQ-based proteomics, phenotypic measurement, and biological validation by RT-qPCR. Morphological and microscopic observation showed that the initiation of bolting occurred 8 days after high-temperature treatment. Fructose accumulated rapidly after high-temperature treatment. During initiation of bolting, of the 3305 identified proteins, a total of 93 proteins exhibited differential abundances, 38 of which were upregulated and 55 downregulated. Approximately 38% of the proteins were involved in metabolic pathways and were clustered mainly in energy metabolism and protein synthesis. Furthermore, some proteins involved in sugar synthesis were differentially expressed and were also associated with energy production. Conclusions: This report is the first to report on the metabolic changes involved in the initiation of bolting in lettuce. Our study suggested that energy metabolism and ribosomal proteins are pivotal components during initiation of bolting. This study could provide a potential regulatory mechanism for the initiation of early bolting by high temperature, which could have applications in the manipulation of lettuce for breeding.

Background Lettuce (Lactuca sativa L.), one of the most economically important leaf vegetables, exhibits early bolting under high-temperature conditions. Early bolting leads to loss of commodity value and edibility, leading to considerable loss and waste of resources. However, the initiation and molecular mechanism underlying early bolting induced by high temperature remains largely elusive. Results To better understand this phenomenon, the bolting initiation period of lettuce was defined, and a comparative proteomic analysis was conducted in the initiation period of bolting induced by a high temperature (33 °C) and a control temperature (20 °C) using iTRAQ-based proteomics, phenotypic measurement, and biological verification by RT-qPCR. Morphological and microscopic observation showed that the initiation of bolting occurred 8 days after high-temperature treatment. Fructose rapidly accumulated after high-temperature treatment. During bolting initiation, of the 3305 identified proteins, a total of 93 proteins exhibited differential abundances, 38 of which were up-regulated, and 55 were down-regulated. Approximately 38% of the proteins were involved in metabolic pathways and were mainly clustered in energy metabolism and protein synthesis. Furthermore, some proteins involved in sugar synthesis were differentially expressed, which were also associated with energy production. Conclusions This is the first report on the metabolic changes involved in bolting initiation in lettuce. Our study suggested that energy metabolism and ribosomal proteins are pivotal components during bolting initiation. This study could provide a potential regulatory mechanism for the initiation of early bolting by high temperature, which could have applications in the manipulation of lettuce for breeding.