Analysis Of The Physiological Mechanism Of Low Potassium Affecting Tomato Fruit Color Formation

Tomato（Solanum lycopersicum L.）has important economic and scientific value as an important vegetable crop and model crop for plant research.In tomato production,fruit color is an important factor affecting the commercial traits of tomato.Studies have shown that potassium has an important physiological function in the plant body and that uneven fruit coloration occurs during tomato cultivation when potassium supply is insufficient,affecting quality formation,but the detailed mechanism of action is not clear.In this experiment,five large pink tomatoes（JF16,JF18,JF19,L1,L2）and two purple tomato lines（LA1996,L9）,whose fruit color is easily affected by the environment,were grown in coconut coir substrates and treated with normal potassium(CK:4 mmol·L^-1)and low potassium(LK:0.5 mmol·L^-1)nutrient solutions.The physiological and biochemical analyses were conducted to further elucidate the mechanism of low potassium on tomato fruit color formation and to lay the foundation for the future elucidation of the molecular mechanism of potassium on tomato coloration.The main findings are as follows:1.Analysis of fruit color and plant potassium content of seven tomato lines at red ripening stage showed that pink-fruited tomato JF16 had dull and yellowish fruit color and purple-fruited tomato L9 had reduced purple fruit shoulder range and light red and bright fruit color under low potassium treatment.In addition,JF16 and L9 differed significantly from the control in plant growth and development,fruit morphology,fruit firmness,plant photosynthesis,potassium content of different parts of the plant（roots,stems,and leaves）and fruit,thus screening JF16 and L9 as tomato lines sensitive to low potassium in fruit color and color.2.The pigment content of JF16 and L9 fruits was further measured,and real-time fluorescence quantification of genes related to pigment synthesis was performed.It was clear that low potassium mainly inhibited the expression of genes related to carotenoid synthesis PSY and PDS in tomato JF16 fruits,resulting in a significant decrease in lycopene content during ripening of pink fruits;low potassium inhibited the expression of L9 anthocyanin synthesis genes PAL and ANS,resulting in a significant decrease in anthocyanin content at green and red ripening stages,thus affecting fruit coloration.3.Analysis of potassium content and potassium transport-related genes in JF16 and L9fruits showed that low potassium reduced fruit potassium content at all periods;JF16 KAT1,KLT1,LKT1 and AKT2/3 were significantly up-regulated at all periods under low potassium treatment,while only KAT1 and AKT2/3 were significantly up-regulated at all periods in L9.KAT1 and AKT2/3 genes were up-regulated in both lines of tomatoes This indicates that the potassium channel KAT1 and AKT2/3 genes are associated with tomato color formation.4.The content of carbon metabolism-related products and related enzyme activities of JF16 and L9 fruits were measured,and it was found that low potassium significantly reduced the activities of sucrose synthase,sucrose phosphate synthase,neutral convertase and acid convertase in carbon metabolism,resulting in a significant increase in starch content and a significant decrease in soluble sugar,glucose and fructose.5.The content of nitrogen metabolism-related products and related enzyme activities of JF16 and L9 fruits were measured,and it was found that low potassium significantly reduced nitrate reductase and glutamine synthetase activities during nitrogen metabolism,resulting in a significant increase in nitrate nitrogen content and a significant decrease in soluble protein and free amino acid content.