Biochemistry and Physiology Department, AFRC Institute of Arable Crops Research, Rothamsted Experimental Station, AL5 2JQ, Harpenden, Hertfordshire, UK.
Planta. 1992 Jul;187(4):554-7. doi: 10.1007/BF00199977.
Nitrate-selective microelectrodes were used to measure not only nitrate activity in the cytoplasm and vacuole of barley (Hordeum vulgare L.) root cells, but also the tonoplast electrical membrane potential. For epidermal cells, the mean cytoplasmic and vacuolar pNO3 (-log10 [NO3]) values were 2.3±0.04 (n=19) and 1.41±0.03 (n=35), respectively, while for cortical cells, the mean cytoplasmic and vacuolar nitrate values were 2.58±0.18 (n=4) and 1.17±0.06 (n=13), respectively. These results indicate that the accumulation of nitrate in the vacuole must be an active process. Proton-selective microelectrodes were used to measure the proton gradient across the tonoplast to assess the possibility that nitrate transport into the vacuole is mediated by an H(+)/NO 3 (-) antiport mechanism. For epidermal cells, the mean cytoplasmic and vacuolar pH values were 7.12±0.06 (n=10) and 4.93±0.11 (n=22), respectively, while for cortical cells, the mean cytoplasmic and vacuolar pH values were 7.24±0.07 (n=3) and 5.09±0.17 (n=7), respectively. Calculations of the energetics for this mechanism indicate that the observed gradient of nitrate across the tonoplast of both epidermal and cortical cells could be achieved by an H(+)/NO 3 (-) antiport with a 1∶1 stoichiometry.
硝酸盐选择性微电极不仅被用于测量大麦（Hordeum vulgare L.）根细胞细胞质和液泡中的硝酸盐活性，还用于测量液泡膜的电膜电位。对于表皮细胞，细胞质和液泡中 pNO3（-log10 [NO3]）的平均值分别为 2.3±0.04（n=19）和 1.41±0.03（n=35），而对于皮层细胞，细胞质和液泡中硝酸盐的平均值分别为 2.58±0.18（n=4）和 1.17±0.06（n=13）。这些结果表明，硝酸盐在液泡中的积累一定是一个主动的过程。质子选择性微电极被用于测量穿过液泡膜的质子梯度，以评估硝酸盐进入液泡是否是通过 H(+)/NO3(-)反向转运机制来介导的。对于表皮细胞，细胞质和液泡的 pH 值平均值分别为 7.12±0.06（n=10）和 4.93±0.11（n=22），而对于皮层细胞，细胞质和液泡的 pH 值平均值分别为 7.24±0.07（n=3）和 5.09±0.17（n=7）。根据该机制的能量计算，在表皮细胞和皮层细胞的液泡膜中观察到的硝酸盐梯度可以通过 H(+)/NO3(-)反向转运来实现，其化学计量比为 1∶1。
