The Effect of Phosphate on the Activity and Sensitivity of Nutritropism toward Ammonium in Rice Roots.

Understanding how plants determine growth direction from environmental cues is important to reveal optimal strategies in plant survival. Nutritropism is the directional growth of plant roots towards nutrient sources. Our previous study showed that an NH 4 + gradient stimulates nutritropism in the lateral roots, but not in the main roots, of a rice cultivar. In the present study, we report nutritropism in the main roots of rice accessions among the World Rice Core Collection, including WRC 25. We investigated the effects of components in nutrient sources on nutritropism in WRC 25. Nutritropism in main roots was stimulated by NH 4 + and significantly enhanced by P i . We found that roots required more NH 4 + stimulation for nutritropic responses in the presence of higher P i , meaning that P i desensitized root nutritropism. These results indicate that P i acts as an activator and a desensitizer in nutritropism. Such a regulation of nutritropism would be important for plants to decide their optimum growth directions towards nutrient sources, gravity, moisture, or other stimuli.