The influence of the inhibition of root respiration on the photosynthetic activity in rice plant.

Abstract

Japonica typc cv. Kinmaze and Indica type cv. IR8 were grown on water culture. Seasonal changes in photosynthesis and root respiration of the both cultivars were measured by assimilation chamber method and Warburg manometric method, respectively. At the time of maximum tillering, the roots were submerged in a solution on nine different of enzyme inhibitors at three concentrations (10-2, 10-3, 10-4M) and in a reductive solution of -300mV, prepared by addition of soluble starch in water culture solution in order to inhibit root respiration. Photosynthetic rate was measured prior to treatment as well as for a period during treatment. Cultivarietal differences grown under the same nutrient condition revealed that IR8 had high quantity of roots, much more leaf area per plant and lower activity in photosynthetic rate per leaf area throughout its whole growing stages (Figs. 1, 2). The roots of cv. Kinmaze showed higher per-cent in nitrogen and carbohydrate (starch + total sugar) compared with cv. IR8. Further it also showed higher rate of root respiration than that that of IR8 at ripenning period (Tables 1, 2). The degree of inhibition of root respiration by treatments of enzyme inhibitors, reductive solution and 70°C hot water almost coincided with the degree of decline in photosynthesis of the treated plant (Fig. 5). The influence of As2O3, NaN3 and DNP in 10-2M on the drop in root respiration was remarkable (Table 5). Submerging of root in the reductive solution resulted in a sharp decline in photosynthetic rate at the time of maximum tillers, however significant influence at mid-period of ripenning was not recognized in the same treatment. Degree of inhibition of root respiration by the reductive solution was different according to the stage of growth and root age, i.e., aged roots showed lower rate in respiration and a slight drop compared with vigorous roots at ripenning period (Fig. 6). Transmittance of β-ray through the leaf blade suggested that rapid decline of the photosynthesis by the root submerged in the inhibitor solution was caused by leaf water deficit due to decrease of root activity for water absorption (Fig. 7).