The long-term co-evolution of plants and herbivores has lead to intricate chemical relationship within the plant secondary metabolites. When the plants are attacked by herbivores, they trigger specific defensive signals to synthesize a series of defensive substances and releases volatiles，which act directly or indirectly against herbivores. Furthermore, plant defensive substances are mainly derived from secondary metabolites under different biosynthetic pathways. There is a considerable variability and diversity in quantity and quality of these substances synthesized by herbivore damaged plants. This variability and diversity are determined not only by developmental period, organ or part attacked, but also by the period time of attack. It is well known that the substrates of plant secondary metabolites and defensive enzymes are all derived from primary metabolism, such as polyphenol oxidase, peroxidase, lipoxygenase. The allocation of carbohydrates between plant growth and defence may lead to variations in secondary metabolites of different species. Recently, there are many reports about physiological response of rice under adverse stress, especially, some research works have indicated that brown plant hopper and white-back plant hopper elicits rice burst response, but physiological response of different rice cultivars under herbivore stress at different time interval still needs to elucidated.
In this present study, rice-brown plant hopper was used as a model system for the study of plant chemical defense at physiological level in relation to time course changes of soluble sugar and chlorophyll contents, photosynthesis and transpiration rates, stomatal conductance, intercellular carbon dioxide concentration and defense enzymes. The results shows that soluble sugar contents decreased significantly in different rice cultivars infected by herbivore with a corresponding decrease in photosynthesis rate and chlorophyll contents. Non significant changes were observed with respect to transpiration rate, stomatal conductance and intercellular carbon dioxide concentration. Polyphenol oxidase, peroxidase and lipoxidase in the rice plant were induced by herbivore attack. Such induction was found to have time constraint, and were not consistent with different rice cultivars.