Abstract:

Using the method of nutritional solution culture,effect of aluminum stress on seven-month Longan (Dimocarpus longan) seedlings was studied. The results showed that aluminum stress disturbed the nitrogen metabolism. Aluminum stress enhanced the activity of protease and reduced content of total soluble protein,heat_stable protein,and heat-unstable protein. The activity of protease in leaves and roots increased 33.76%～217.30%,70.45%～167.86% respectively. Soluble protein,heat-stable protein,and heat-unstable protein decreased 16.54%～58.53%,18.29%～64.56%,9.09%～32.87% in leaves and 17.84%～34.61%,21.47%～41.59%,12.85%～24.99% in roots respectively. There was significantly negative correlation between the soluble protein and the activity of protease. Under aluminum stress,the total nitrogen,protein nitrogen,NH⁺₄-N,and the activity of nitrate reductase(NR) in leaves decreased,and the non-protein nitrogen increased. NO^--₃-N increased when the aluminum concentration was lower than 0.185 mmol·L ^-1 ,and it decreased when the aluminum concentration was higher than 0.185 mmol·L^-1 with increasing the concentration. Aluminum stress reduced the increment of total hydrolytic amino in root and the reduction in leaves. The range of increment was 0.59%～11.74%,and the range of reduction was 0.90%～27.55%.The content of RNA and DNA in leaves decreased 13.10%～61.47%,12.61%～41.00%,and the activity of Rnase and Dnase increased 35.62%～63.47%,35.57%～183.27% respectively by the aluminum stress. The RNA and DNA negatively correlated with Rnase and Dnase respectively. The primary causation of the decrease in the protein and nucleic acid of Longan seedlings: the increase of the protease activity induced the proteolysis,with the increment of the Rnase and Dnase activity,the catabolism of DNA and RNA were accelerated; and with the reduction of the DNA and RNA content,the velocity of protein synthesis was reduced; the adversity stress induced the increase of AOS,and the acceleration of membrane-lipid peroxidation,and the restraint of protein and nucleic acid synthesis.

Key words: Longan(Dimocarpus longan), aluminum stress, nitrogen metabolism