Salicylic acid regulates sugar metabolism that confers tolerance to salinity stress in cucumber seedlings

Salicylic acid (SA) plays a critical role in plant development and defense responses to biotic and abiotic stresses. Sugars can act as osmotic adjustors or nutrient and metabolic signals in the activation of plant defense responses. To uncover the effects of SA on sugar metabolism, we assayed the altered components and levels of sugars in cucumber seedlings treated with SA. After SA treatment, the levels of glucose, fructose, raffinose and stachyose were increased in both leaves and roots. In contrast, sucrose and starch responded differently in leaves and root, decreasing in leaves but accumulating in roots. These changes could be due to the effects of SA on the activities of metabolism-related enzymes. In leaves, SA promoted the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS) and amylases, while the SA-treated root showed a reduced amylase activity and an unchanged activity in SPS. The changes in various sugar contents resulted in the accumulation of soluble sugars in SA-treated cucumber seedlings, especially non-reducing sugars in roots. These increased sugars could function as osmotic regulators and facilitate water uptake and retention in plant cells, thereby conferring seedlings an enhanced tolerance to salinity stresses caused by NaCl treatment. Taken together, our findings provide an important insight into the effects of SA on sugar metabolism, and a protective mechanism for SA against water deficiency is discussed.     

The inheritance of two novel subgynoecious genes in cucumber (Cucumis sativus L.)

Cucumber (Cucumis sativus L.), which is a vegetable crop, has served as the model system for sex expression in flowering plants, and the inheritance of sex expression in cucumber is well documented. However, the genetics of subgynoecism expression in cucumber had rarely been described. In this study, we investigated the inheritance of subgynoecious traits in cucumber plants with the inbred cucumber lines of subgynoecious (C. sativus L. var sativus cv 97-17 and S-2-98) as the materials. Genetic analysis had showed the two subgynoecious inbred lines were controlled by one pair of recessive gene and one pair of incompletely dominant gene, which were designated presently as mod-F2 and Mod-F1, respectively. Furthermore, the mod-F2 and Mod-F1 loci, which enhance the intensity of femaleness, also inherited independently with F and M genes.     

Fertilization regulates soil enzymatic activity and fertility dynamics in a cucumber field

Different fertilizers may affect soil enzymatic activity and soil fertility dynamics. These effects were investigated in a field experiment with cucumber (Cucumis sativus L.) and the relationship with yield and soil nutrient availability was assessed. Soil enzymatic activity, measured as phosphatase, catalase, invertase and urease activities, decreased in the early growth stages of cucumber, but increased in the late ones, when plant were supplied with partially decomposed horse manure. Chemical N fertilizer inhibited soil enzymatic activity but P and K fertilizers enhanced it. Activity of different soil enzymes was positively correlated with soil NH₄⁺–N and available P concentration, but negatively correlated with leaf N and P concentration. Cucumber yield was also positively correlated with the soil enzymatic activity. Our results demonstrate that soil enzymatic activity acted as a useful indicator of soil fertility dynamics.