Osmond C B, Laties G G
Department of Botanical Sciences and Molecular Biology Institute, University of California, Los Angeles, California 90024.
Plant Physiol. 1969 Jan;44(1):7-14. doi: 10.1104/pp.44.1.7.
Malate in beet discs treated in different salt solutions was labeled by a 30 min pulse of (14)CO(2), and subsequent changes in specific activity were followed for several hr. In treatments which resulted in net acid synthesis in response to excess cation absorption, malate specific activity fell slowly after removal of (14)CO(2). In solutions where no net acid synthesis occurred, and from which cation and anion were absorbed equally, malate specific activity fell rapidly when (14)CO(2) was removed. The foregoing suggests that the net synthesis of organic acids in response to excess cation absorption leads to the removal of organic anions from cytoplasmic metabolic pools as counter-ions in salt transport to the vacuole.The latter hypothesis was further examined by direct measurement of the distribution of labeled malate between cytoplasm and vacuole using the wash-exchange method of compartmental analysis, previously described for inorganic ions. The method satisfied the criterion of exchange specificity necessary for this purpose. Much higher retention of label in the cytoplasm was observed in KCl solutions (no net synthesis) than in K(2)SO(4) solutions (net synthesis) after 3 hr (14)CO(2) fixation and subsequent wash-exchange. The observed distribution is consistent with the rapid removal of organic anions to the vacuole during net acid synthesis. The significance of organic acid transport in relation to metabolism is discussed.
用（14）CO₂ 脉冲处理30分钟，标记不同盐溶液处理的甜菜圆片中的苹果酸，随后跟踪几个小时内比活度的变化。在因过量阳离子吸收而导致净酸合成的处理中，去除（14）CO₂ 后苹果酸比活度缓慢下降。在没有净酸合成且阳离子和阴离子吸收量相等的溶液中，去除（14）CO₂ 时苹果酸比活度迅速下降。上述情况表明，因过量阳离子吸收而导致的有机酸净合成会使细胞质代谢库中的有机阴离子作为盐转运到液泡中的抗衡离子而被去除。通过使用先前针对无机离子描述的区室分析的洗涤交换方法，直接测量标记苹果酸在细胞质和液泡之间的分布，进一步检验了后一种假设。该方法满足了为此目的所需的交换特异性标准。在3小时（14）CO₂ 固定及随后的洗涤交换后，在KCl溶液（无净合成）中观察到的细胞质中标记保留率远高于在K₂SO₄ 溶液（净合成）中的保留率。观察到的分布与净酸合成过程中有机阴离子迅速转运到液泡一致。讨论了有机酸转运与代谢相关的意义。
