24-Epibrassinolide and 2,6-Dichlorobenzonitrile Promoted Celery Petioles and Hypocotyl Elongation by Altering Cellulose Accumulation and Cell Length

BRs (brassinosteroids), an endogenous hormone in plants, regulate cellulose accumulation, cell elongation and plant growth. Propiconazole (PCZ) is an effective inhibitor of BR biosynthesis. DCB (2,6-Dichlorobenzonitrile) can inhibit the synthesis of cellulose and affects the chemical composition of cell walls. Celery is one important leafy vegetable of the Apiaceae family with rich dietary fiber (including cellulose). The petioles length, leaf blades number and cellulose content determine the yield and quality of celery. The family members of <i>AgCESAs</i> are related to cellulose biosynthesis in higher plants. To investigate the effects of BRs, PCZ and DCB on the growth of celery, celery cv. ‘Jinnan Shiqin’ plants were treated with 24-epibrassinolide (24-EBL, most active form of BRs), PCZ and DCB, respectively. The results showed that exogenous application of BRs up-regulated the expression of <i>AgCESAs</i> genes and accumulated more cellulose in celery. The length of petioles and number of leaf blades in celery plants applied with exogenous BRs (1.24 × 10⁻⁶ mol/L 24-EBL) were increased 2.16 and 1.37 times of that in the control. The addition of PCZ inhibited the effects of exogenous BRs application. The lengths of hypocotyl and hypocotyl cells of celery plants treated with BRs were longer than that of the control. Under DCB treatments, the expression levels of <i>AgCESAs</i> genes in celery petioles and leaf blades were down-regulated compared with the control, and the celery plants showed decreased cellulose content, shorter petiole length and fewer leaf blades. The length of hypocotyl and hypocotyl cells of celery treated with DCB were shorter than that of the control. This study provided a reference for the functions of BRs and DCB on the growth and development of celery.