Abstract
The quantitative and qualitative changes of proteins, free amino acids, and sugar fractions in the leaf blade of rice plants infested with the brown planthopper, Nilaparvata lugens (STÅL), were examined. The amount of protein in the leaf blades showed a steady decrease in proportion with increased disease severity. Its concentrations in the chlorotic and browned leaf blades decreased by about 33% and 73% respectively when compared with healthy leaf blades.On the contrary, a remarkable accumulation of free amino acids was found in the chlorotic leaf blades, where the total free amino acid contents increased by about 4.1 times compared to that of the healthy leaf blades, and considerable amouts of arginine and amides such as asparagine and glutamine appeared. The browned leaf blades still contained about 1.8 times more free amino acids than the healthy ones. There was no definite difference in the total sugar concentrations between the healthy and chlorotic leaf blades, but the amounts of reducing sugars such as glucose and fructose which were very few in the former increased markedly in the latter. In the browned leaf blades, almost all sugars disappeared. It is reasonable to assume that the decrease in the protein level and the accumulation of free amino acids and amides in the infested leaf blades were due to disturbanses in protein metabolism as a result of the draining of free amino acids and a hormone-like substance to regulate protein synthesis in the leaf blade by the sucking of the brown planthopper.
