Walker DJ, Black CR, Miller AJ
Biochemistry and Physiology Department, IACR-Rothamsted, Harpenden, Hertfordshire AL5 2JQ, United Kingdom (D.J.W., A.J.M.).
Plant Physiol. 1998 Nov;118(3):957-64. doi: 10.1104/pp.118.3.957.
In an earlier paper we showed that in fully developed barley (Hordeum vulgare L.) root epidermal cells a decrease in cytosolic K+ was associated with an acidification of the cytosol (D.J. Walker, R. A. Leigh, A.J. Miller [1996] Proc Natl Acad Sci USA 93: 10510-10514). To show that these changes in cytosolic ion concentrations contributed to the decreased growth of K+-starved roots, we first measured whether similar changes occurred in cells of the growing zone. Triple-barreled ion-selective microelectrodes were used to measure cytosolic K+ activity and pH in cells 0.5 to 1.0 mm from the root tip. In plants growing from 7 to 21 d after germination under K+-replete conditions, the mean values did not change significantly, with values ranging from 80 to 84 mM for K+ and 7.3 to 7.4 for pH. However, in K+-starved plants (external [K+], 2 &mgr;M), the mean cytosolic K+ activity and pH had declined to 44 mM and 7.0, respectively, after 14 d. For whole roots, sap osmolality was always lower in K+-starved than in K+-replete plants, whereas elongation rate and dry matter accumulation were significantly decreased after 14 and 16 d of K+ starvation. The rate of protein synthesis in root tips did not change for K+-replete plants but declined significantly with age in K+-starved plants. Butyrate treatment decreased cytosolic pH and diminished the rate of protein synthesis in K+-replete roots. Procaine treatment of K+-starved roots gave an alkalinization of the cytosol and increased protein synthesis rate. These results show that changes in both cytosolic pH and K+ can be significant factors in inhibiting protein synthesis and root growth during K+ deficiency.
在早期的一篇论文中，我们表明，在完全发育的大麦（Hordeum vulgare L.）根表皮细胞中，胞质K⁺的减少与胞质酸化有关（D.J.沃克、R.A.利、A.J.米勒[1996]《美国国家科学院院刊》93: 10510 - 10514）。为了证明胞质离子浓度的这些变化导致了缺钾根生长的减缓，我们首先测量了生长区细胞中是否发生了类似的变化。使用三管离子选择性微电极测量距根尖0.5至1.0毫米处细胞的胞质K⁺活性和pH值。在发芽后7至21天在钾充足条件下生长的植物中，平均值没有显著变化，K⁺的值在80至84 mM之间，pH值在7.3至7.4之间。然而，在缺钾植物（外部[K⁺]，2 μM）中，14天后胞质K⁺活性和pH的平均值分别降至44 mM和7.0。对于整根来说，缺钾植物的汁液渗透压总是低于钾充足的植物，而在缺钾14天和16天后，伸长率和干物质积累显著降低。钾充足植物根尖的蛋白质合成速率没有变化，但缺钾植物的蛋白质合成速率随年龄显著下降。丁酸盐处理降低了胞质pH值，并降低了钾充足根中的蛋白质合成速率。用普鲁卡因处理缺钾根会使胞质碱化并提高蛋白质合成速率。这些结果表明，在钾缺乏期间，胞质pH值和K⁺的变化都可能是抑制蛋白质合成和根生长的重要因素。
