Effect of Water Stress on Vegetative Growth, Relative Water Content and Nitrogen Metabolism of Citrange and Trifoliate Orange Seedling

摘要

In south China, rainfall is unequally distributed in different seasons, therefore, water deficit is one of the serious environmental stresses that affect citrus growth, fruit production and quality. Citrus is one of the most popular evergreen fruit tree crops in China. Citrange and trifoliate orange are the widely used rootstocks, and also are the potential sources of stress-tolerant stocks for citrus. The objective of this study was to quantify the effects of water-deficit stress on leaf and shoot relative water content (RWC) , and leaf concentrations of arginine, praline, poly amines, and related metabolites in citrange and trifoliate orange compared with non-water-deficit treated citrange and trifoliate orange seedlings. Replicate pots, each containing one young seedling in 2 L of soil were subjected to water deficit by withholding water or were maintained under well watered (control) conditions. Water stress reduced both total and shoot dry matter (DW) , but increased root DW and the root/shoot ratio compared to the control. Plant height and stem diameter were reduced by 23.2% and 33. 1% , respectively. In both citrange and trifoliate, the relative water content of leaves and shoots was significantly influenced by soil water content. Compared with well-watered plants, the relative water content of leaves and shoots of treated plants was low, and the variation trend was that the less the soil water content was, the lower the relative water content of leaves and shoots was. Water stress decreased protein concentration in leaves of citrange and trifoliate, under well water condition, leaves protein content of citrange and trifoliate was 17 mg/g fresh weight and 16.9 mg/g fresh weight, however, when soil water was withheld to 20% water content, leaf protein contents of citrange and trifoliate were 7. 3 mg/g fresh weight, decreased 56. 8% , and 7. 5 mg/g fresh weight, decreased 55. 5% , respectively. Water stress increased leaf concentration of NH3-NH4+, arginine and proline. Under well-watered condition, NH3-NH4+ , arginine and proline concentrations of young, fully expanded leaves of citrange and trifoliate were the lowest, and they were the highest in the 20% water content treatment. Compared with control plants, concentrations of NH3-NH4+ in both citrange and trifoliate leaves at 20% water content treatment increased 151.3% and 145.7%; free arginine concentration increased 77.8% and 77.3%; and concentration of proline increased 171.7% and 182.9%.