A research group from the National Agriculture and Food Research Organization (NARO), National Institutes for Quantum Science and Technology (QST), University of Tsukuba, the University of Tokyo and RIKEN, has revealed that Vigna riukiuensis, a closely related species of azuki bean, accumulates in its leaves special starch, which traps and sequesters sodium, making it harmless. This newly elucidated mechanism of salt tolerance is different from known mechanisms, such as the suppression of sodium influx into the leaves, and hence it is expected to be applied to the development of salt-tolerant crops in the future.
In many plants, sodium allocation to the leaves inhibits photosynthesis and causes severe leaf damage. There is a demand for the development of salt-tolerant crops that can be cultivated in salt water with high sodium concentration as the available freshwater resources are declining worldwide. Hence it is essential to elucidate the mechanisms of salt-tolerance.
In the past, NARO and QST have revealed that several species of salt-tolerant plants related to azuki bean have acquired unique salt-tolerance mechanisms.
NARO Press Release - https://www.naro.go.jp/english/laboratory/ngrc/press/salttolerance/index.html.
Among them, V. riukiuensis has a unique property of accumulating sodium in its leaves, contrasting from many other salt-tolerant plants that suppress sodium allocation to the leaves. The research group from NARO, QST, University of Tsukuba, the University of Tokyo, and RIKEN has investigated its mechanism of salt tolerance.
A series of experiments and analyses have revealed that V. riukiuensis accumulates starch granules that are able to trap sodium and suppress the adverse effects of sodium, such as the inhibition of photosynthesis. The research group has also tested a close relative V. riukiuensis that also accumulates lots of starch granules and revealed the sodium-trapping ability is specific feature of V. riukiuensis.
The next step will be identification of genes related to the formation of the special starch granules in V. riukiuensis. By combining the special salt-tolerance mechanism of this species with other salt-tolerance mechanisms, it is expected to be applied to the development of crops that are more resistant to salt damage in response to the global depletion of freshwater resources.
Budget:Japan Science and Technology Agency PRESTO "Creation of essential technologies to utilize carbon dioxide as a resource through the enhancement of plant productivity and the exploitation of plant products" JPMJPR11B6
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research "Sodium dynamics and transcriptome of salt tolerant species in the genus Vigna" 18H02182
Moonshot R&D Program for Agriculture, Forestry and Fisheries by Cabinet Office, Government of Japan "Achieving zero food risk by improving crop robustness through cyber-physical systems" (JPJ009237)
Starch-dependent sodium allocation in the leaves of Vigna riukiuensis. Noda Y, Hirose A, Wakazaki M, Sato M, Toyooka K, Kawachi N, Tanoi K, Furukawa J and Naito K. Journal of Plant Research DOI: https://doi.org/10.1007/s10265-023-01470-8