Studies on Pi homeostasis by artificial manipulation of intracellular Pi levels.

无机磷是植物生长所必需的分子之一。然而，在自然环境中，土壤中的磷水平极低。即使在PI缺乏的情况下，细胞质的PI水平也是通过改变跨膜的PI转运活性来保持恒定的，尽管液泡PI水平的变化与PI的供应有关。我们称之为植物中的PI动态平衡。然而，我们还没有信息，植物细胞如何检测PI供应的变化并控制细胞中的PI状态。到目前为止，与磷供应相关的细胞磷运输机制的研究大多是以生长的植物或增殖培养的细胞为实验材料进行的。在这种情况下，由于细胞的生理状态总是在变化，因此很难只分析PI的动态平衡机制。在本研究中，我们试图控制与细胞生长无关的PI情况。首先，我们测量了不同PI情况下大麦植株的PI分布，以了解通常的实验条件。然后，我们以分离的成熟的轮状细胞为材料。它们不会生长、分裂，当然也不会分化。使用这种细胞，我们首先发现，通过灌流将PI从液泡中移除并不能引起液泡膜PI转运活性的任何变化。此外，我们还发现，细胞膜的PI吸收活性也不受细胞质和液泡型PI池的影响。此外，我们还发现，悬浮培养的长春花细胞经酸处理后，PI代谢发生了变化。我们现在正在分析所有这些现象的关系。

Inorganic phosphate is one of the essential molecules for plant growth. In natural environment, however, Pi level in soil is extremely low. Even under Pi deficiency, it is well-known that the cytoplasmic Pi level was kept at constant by changing Pi transport activities across the membrane, although the vacuolar Pi level changed related to Pi supply. We call it is Pi homeostasis in plants. However, we have no information, yet how the plant cell detects changes in Pi supply and controls Pi status in the cell. Until now, most of works on the cellular Pi transport mechanisms related to Pi supply were carried out using growing plants or proliferating cultured cells as experimental materials. In these situation, since the cellular physiological status is always changing, it is difficult to analyze Pi homeostatic mechanisms only. In the present study, we tried to control Pi situation independent of cell growth.First we measured the Pi distribution of barley plants under different Pi situation in order to know the usual experimental conditions. Then we used an isolated and matured Chara internodal cells as material. They do not grow, divide and of course differentiate. Using such cells, we have found first that the removal of Pi from the vacuole by perfusion could not induce any changes in Pi transport activity of the tonoplast. Furthermore, we found that the Pi uptake activity of the plasma membrane also changes independent of both the cytoplasmic and the vacuolar Pi pools.Besides above, we found that the acid treatment of suspension cultured Catharanthus cells induced changes in the Pi metabolisms. We are now analyzing the relationship of all these phenomena.