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

Abstract

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 NH4+ 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 NH4+ and significantly enhanced by Pi. We found that roots required more NH4+ stimulation for nutritropic responses in the presence of higher Pi, meaning that Pi desensitized root nutritropism. These results indicate that Pi 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.

Transcriptome Analysis of Rice Root Tips Reveals Auxin, Gibberellin and Ethylene Signaling Underlying Nutritropism

“…These inhibitors were added to the nutrient sources to limit the inhibitory effects specifically to the root tips. The effects of inhibitors on nutritropism were evaluated in changes of frequency of nutritropic coiled responses compared with the mock condition as previously described ( Yamazaki and Fujiwara 2022 ). Local exposure of root tips to phytohormone inhibitors did not cause obvious growth inhibition in roots ( Fig.…”

“…All procedures to prepare the nutrient sources are described in Yamazaki and Fujiwara 2022 . Stock solutions of 2 metre NH 4 Cl and NaH 2 PO 4 · 2H 2 O (Fujifilm Wako) were used as nutrient sources at a final concentration of 200 mM.…”

“…Recently, we discovered nutritropism in both lateral and main roots of rice ( Yamazaki et al. 2020 , Yamazaki and Fujiwara 2022 ). Rice roots exposed to an ammonium gradient generated around an ammonium source in agar medium showed nutritropism toward the source.…”

Non-destructive real-time monitoring of underground root development with distributed fiber optic sensing

“…This assumption was based on root gravitropism [41]. Although this applies to most existing cases, crop genetic engineering will likely target the genes responsible for root growth in the direction of optimizing the RSA for water and nutrient uptake [3]. Therefore, the assumption of gravitropism must be re-confirmed in these plants.…”

“…The root system architecture (RSA) has important implications for food security, climate action, and bio-inspired civil engineering technologies. For food security, the RSA determines crop resilience to environmental stress [1] and nutrient uptake efficiency [2,3]. With climate change, roots and root exudates are natural solutions for carbon sequestration [4].…”