Effects of low potassium stress on leaf photosynthesis and sucrose metabolism in sesame seedling stage

<bold>Objective</bold> To explore the response mechanisms of photosynthesis and leaf sucrose metabolism in sesame to low potassium（K）stress. <bold>Method</bold> The hydroponic experiment was conducted with the low-K sensitive cultivar Zhongzhi No.9（ZZ9）and low-K tolerant WZM6 selected as the materials.The leaf net photosynthetic rate（<italic>P</italic>_n），stomatal conductivity（<italic>G</italic>_s），and the activities of 1，5-ribulose diphosphate carboxylase（Rubisco），sucrose phosphate synthase（SPS），sucrose acid invertase（SAI），sucrose synthase（SuSy）as well as the content of soluble sugar，soluble protein，sucrose，starch of sesame seedlings were analyzed in response to low K and normal K conditions. <bold>Result</bold> Compared with the normal K treatment，the <italic>P</italic>_n，<italic>G</italic>_s，and activities of Rubisco，SPS，SuSy and soluble protein content of the ZZ9 cultivar significantly decreased by 22.0%，18.2%，40.0%，24.0%，7.9% and 25.5% respectively；while the contents of soluble sugar，sucrose，starch and SAI activity in leaves significantly increased by 110.0%，61.2%，38.1% and 8.1% respectively.The WZM6 cultivar showed smaller variations in leaf photosynthetic capacity and sucrose metabolism-related indicators under low K stress.Additionally，the absolute values of the stress coefficients of various physiological indicators of the low K-sensitive ZZ9 cultivar were higher than those of the low K-tolerant WZM6 cultivar，indicating that ZZ9 was more severely affected by low K stress. <bold>Conclusion</bold> Low K stress affects the growth and development of sesame seedlings by weakening photosynthesis，hindering the transport of photosynthetic products and interfering with the carbon metabolism pathway.The activities of sucrose metabolic enzymes，photosynthetic capacity and osmotic adjustment substances are more sensitive to K nutrition levels in ZZ9，while these indicators were minor changed by low-K stress in WZM6.