Abstract:

Pyrus bretschneideri‘Dangshan Suli’was used as the experiment material,sprayed with distilled water,200 mg·L^-1 PP₃₃₃ and 400 mg·L^-1 GA₃ at full bloom stage;the calyx-persistence fruit and calyx-shedding fruit were respectively collected at the young fruit differentiation stage;the single fruit weight,chlorophyll,sorbitol,sucrose,glucose and fructose content were measured and the expression of genes related to photosynthesis,sorbitol and sucrose metabolism was analyzed by quantitative real-time PCR（qRT-PCR）. Besides,the enzyme activities of S6PDH,NAD⁺-SDH,NADP⁺-SDH,SPS and SUS were determined. The results showed that the contents of sorbitol and sucrose in calyx-persistence fruit were significantly higher than those in calyx-shedding fruit of all treatments. In terms of the autologous photosynthesis,the significantly increase sorbitol and sucrose content in all calyx-persistence fruit could be supported by the obvious higher relative expression of PSII protein subunits psbD and Rubisco activase genes in calyx-persistence fruit than those in calyx-shedding fruit. From the perspective of sorbitol synthesis pathway,the prominent higher sorbitol content in calyx-persistence fruit was related to the higher expression of S6PDH1 and the outstanding higher activity of sorbitol-6-phosphate dehydrogenase. From the perspective of ‘source-sink’transport,it was related to the distinct higher expression of sorbitol transporter genes SOT3/4/8/14/15/2/25/29/30/31/34 in calyx-persistence fruit than that in calyx-shedding fruit. Likewise,the apparent increased sucrose content in calyx-persistence fruit was related to the significant higher expression of sucrose phosphate synthase genes SPS1 and SPS8,sucrose synthase genes SUS1/3/12/13/15/17,and their clear higher enzyme activities from the perspective of sucrose synthesis pathway. When it comes to the perspective of sucrose transport pathway,it was related to distinct higher expression of the sucrose transport genes SUT1/2/3and the tonoplast monosaccharide transporter TMT2/3/4in calyx-persistence fruit. This experiment preliminary clarified that the morphogenesis of calyx-persistence fruit and calyx-shedding fruit is determined by the relative sorbitol and sucrose metabolism activities.

Key words: pear, calyx-persistence fruit, calyx-shedding fruit, photosynthesis, sorbitol, sucrose