Abstract:Organic acids play an important role in fruit quality of plum, and malate transporters are involved in transtonoplast transportation and accumulation of organic acids in fruit. In order to reveal the organic acid composition and its correlation with malate transporter genes (PsALMT9 and PstDT) in plum fruit, this study used two plum cultivars (Prunus salicina ‘Huangguan’ and Prunus salicina ‘Black Amber’) as samples to determine the organic acid composition and content, single fruit weight, titratable acid (TA) and pH of fruits at different stages of fruit development, and using quantitative realtime PCR (PCR) to analyze the relative expression levels of PsALMT9 and PstDT. We also carried out the pearson correlation coefficient to determine the correlation of PsALMT9, PstDT and fruit acids. The results showed that: (1) malic acid is the main organic acid component at all developmental stages of ‘Huangguan’ and ‘Black Amber’ (proportion for 73.83%~92.10%), followed by tartaric acid (4.59%~14.26%), the contents of citric acid, oxalic acid, acetic acid and succinic acid are low (0.47%~7.21%), and the content of fumaric acid is trace. (2) The pearson correlation coefficient showed that malic acid was significantly positively correlated with TA, and significantly negatively correlated with pH; PsALMT9 was significantly positively correlated with tartaric acid, and significantly positively correlated with acetic acid and oxalic acid; PstDT was significantly positively correlated with citric acid and TA, but both PsALMT9 and PstDT were less correlated with malic acid. Our research indicated that ‘Huangguan’ and ‘Black Amber’ belong to malatetype fruits, and fruit acidity is mainly determined by malic acid. PsALMT9 may be involved in the transtonoplast transport of tartaric acid, acetic acid and oxalic acid simultaneously, and PstDT may be involved in the transtonoplast transport of citric acid, while the transtonoplast transport process of malate may be related to the synergistic regulation of varied membrane protein genes such as PsALMT9 and PstDT.