Nitrogen recycling in the brown planthopper, Nilaparvata lugens: Involvement of yeast-like endosymbionts in uric acid metabolism

Planthopper harbour yeast-like symbionts in the mycetocyte. A possible role that the symbionts may play for the host insect is nitrogen recycling, i.e. conversion of nitrogenous waste products of the insect into compounds of nutritional value. To examine this possibility, we determined the uric acid content in the honeydew and the whole tissues of control and symbiont-depleted brown planthoppers, Nilaparvata lugens. The symbiont-depleted insects were obtained by exposing newly hatched nymphs to 35 degrees C for three days. In the honeydew, uric acid was not detected regardless of the presence or absence of symbionts, Nevertheless, a considerable amount of uric acid was found in the insect tissues, and the content was markedly higher in heat-treated insects than in controls. We also determined the uricase activity in the insect whole tissues and in the isolated symbionts. While in control insects uricase was detectable, there was no uricase activity in heat-treated insects. Isolated symbionts had uricase activity 15 times higher than in the whole tissues of control insects. These results suggested that uric acid synthesized by the insect is stored in insect tissues rather than excreted, and that uric acid is recycled in the planthopper with the aid of its endosymbionts.