Boron deficiency energizes cyanide uptake and assimilation through activating plasma membrane H+-ATPase in rice plants

Abstract

The effect of boron (B) deficiency on mediating the contribution of H⁺-ATPase in the uptake and assimilation of exogenous cyanide (CN^-) is investigated. Under CN^- treatments, rice seedlings with B-deficient (-B) conditions exhibited significantly higher CN^- uptake and assimilation rates than B-supplemented (+B) seedlings, whereas NH₄⁺ uptake and assimilation rates were slightly higher in -B rice seedlings than in +B. In this connection, the expression pattern of genes encoding β-CAS, ST, and H⁺-ATPase was assessed to unravel their role in the current scenario. The abundances of three β-CAS isogenes (OsCYS-D1, OsCYS-D2, and OsCYS-C1) in rice tissues are upregulated from both "CN^--B" and "CN^-+B" treatments, however, only OsCYS-C1 in roots from the "CN^--B" treatments was significantly upregulated than "CN^-+B" treatments. Expression patterns of ST-related genes (OsStr9, OsStr22, and OsStr23) are tissue specific, in which significantly higher upregulation of ST-related genes was observed in shoots from "CN^--B" treatments than "CN^-+B" treatments. Expression pattern of 7 selected H⁺-ATPase isogenes, OsA1, OSA2, OsA3, OsA4, OsA7, OsA8, and OsA9 are quite tissue specific between "CN^-+B" and "CN^--B" treatments. Among these, OsA4 and OsA7 genes were highly activated in the uptake and assimilation of exogenous CN^- in -B nutrient solution. These results indicated that B deficiency disturbs the pattern of N cycles in CN^--treated rice seedlings, where activation of ST during CN^- assimilation decreases the flux of the innate pool of NH₄⁺ produced from CN^- assimilation by the β-CAS pathway in plants. Collectively, the B deficiency increased the uptake and assimilation of exogenous CN^- through activating H⁺-ATPase.

Keywords: CN(−) assimilation; H(+)-ATPase; Rice; Sulfurtransferase; β-cyanoalanine synthase.