Starch-dependent sodium accumulation in the leaves of Vigna riukiuensis.

Abstract

This research provides insight into a unique salt tolerance mechanism of Vigna riukiuensis. V. riukiuensis is one of the great genetic resources of salt tolerance. We have previously reported that V. riukiuensis accumulates a higher amount of sodium in the leaves, whereas V. nakashimae, a close relative of V. riukiuensis, suppresses sodium allocation to the leaves. We first suspected that V. riukiuensis would have developed vacuoles for sodium sequestration, but there were no differences compared to a salt-sensitive accession. However, many starch granules were observed in the chloroplasts of V. riukiuensis. In addition, forced degradation of leaf starch by shading treatment resulted in no radio-Na (22Na) accumulation in the leaves. We performed SEM-EDX to locate Na in leaf sections and detected Na in chloroplasts of V. riukiuensis, especially around the starch granules but not in the middle of those. Our results could provide the second evidence of Na-trapping system by starch granules, following the case of common reed that accumulates starch granule at the shoot base for binding Na.

Unique Salt-Tolerance-Related QTLs, Evolved in Vigna riukiuensis (Na+ Includer) and V. nakashimae (Na+ Excluder), Shed Light on the Development of Super-Salt-Tolerant Azuki Bean (V. angularis) Cultivars

“…The QTLs detected in population A might be related to genes involved in the formation of Na + -binding starch granules in the chloroplasts of the leaf cells, which could be part of the mechanism for salt tolerance in "Tojinbaka". Interestingly, Noda et al reported that "Ukushima" also contained starch granules in the chloroplasts [42]. However, they could not observe the co-localization of 22 Na + with starch granules in the chloroplasts of "Ukushima".…”

“…However, Noda et al reported that there was no difference in the development and features of vacuoles between salt-sensitive V. angularis cv. "Erimoshouzu" and "Tojinbaka" after 3 days of 100 mM salt (NaCl) treatment with 5 kBq 22 Na + [42]. The only difference they could find between "Erimoshouzu" and "Tojinbaka" was that "Tojinbanka" contained well-developed starch granules in the chloroplast, whereas "Erimoshouzu" did not.…”

“…In addition, 22 Na + was co-localized around starch granules developed in chloroplasts in the leaves of "Tojinbaka" and was not detected in other parts in the leaf cell. Therefore, they speculated that "Tojinbaka" has a Na + trapping system using Na + -binding starch granules, which may be related to salt tolerance [42]. Common reed (Phragmites australis), a well-known salt-tolerant plant, also produced a large number of Na + -binding starch granules at the shoot base when salt stressed, and it was proposed as a novel salt tolerance mechanism not reported before [43].…”

“…This phenomenon suggests that the "Tojinbaka" allele of qDtW1-1/qPWL1-1 might be involved in the detoxification of Na + in the leaves. It is possible that these QTLs were involved in the Na + trapping system using starch granules [42]. In population C, the "Tojinbaka" allele of qNa8-1 had no significant effect on DtW and PWL but an increased Na + concentration in leaves (Table 3, Figure 3).…”

2024 Awards in the Journal of Plant Research

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w information to describe the new species has received high praise.In Noda et al (2023), the distinctive salt tolerance mechanisms of Vigna riukiuensis are reported. Vigna riukiuensis accumulates a high amount of sodium in the leaves, whereas the close relative Vigna nakashimae suppresses sodium allocation to the leaves as was shown previously using radio-Na imaging.

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