Kobae Yoshihiro, Mizutani Masahiro, Segami Shoji, Maeshima Masayoshi
Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan.
Biosci Biotechnol Biochem. 2006 Apr;70(4):980-7. doi: 10.1271/bbb.70.980.
Aquaporins mediate the movement of water across biomembranes. Arabidopsis thaliana contains 35 aquaporins that belong to four subfamilies (PIP, TIP, SIP, and NIP). We investigated their expression profiles immunochemically in suspension-cultured Arabidopsis thaliana cells during growth and in response to salt and osmotic stresses. Protein amounts of all aquaporins were much lower in cultured cells than in the plant tissues. This is consistent with the low water permeability of protoplasts from cultured cells. After treatment with NaCl, the protein amounts of PIP2;1, PIP2;2, and PIP2;3 in the cells increased several-fold, and those of TIP1;1 and TIP1;2, 15- and 3-fold respectively. PIP1 did not change under the stress. Cell death began after 19 d in culture, accompanied by marked accumulation of PIPs and TIPs and a gradual decrease in SIPs. Our results suggest the followings: (i) Accumulation of aquaporin isoforms was individually regulated at low levels in single cells. (ii) At least PIP2;2, PIP2;3, TIP1;1, and TIP1;2 are stress-responsive aquaporins in suspension cells. (iii) A sudden increment of several members of PIP2 and TIP1 subfamilies might be related to cell death.
水通道蛋白介导水跨生物膜的转运。拟南芥含有35种水通道蛋白，它们分属于四个亚家族（PIP、TIP、SIP和NIP）。我们采用免疫化学方法研究了它们在悬浮培养的拟南芥细胞生长过程中以及对盐胁迫和渗透胁迫的响应中的表达谱。所有水通道蛋白在培养细胞中的蛋白量都远低于植物组织中的蛋白量。这与培养细胞原生质体的低水渗透性一致。用NaCl处理后，细胞中PIP2;1、PIP2;2和PIP2;3的蛋白量增加了几倍，而TIP1;1和TIP1;2的蛋白量分别增加了15倍和3倍。PIP1在胁迫下没有变化。培养19天后细胞开始死亡，同时伴随着PIP和TIP的显著积累以及SIP的逐渐减少。我们的结果表明：（i）水通道蛋白亚型的积累在单细胞中受到低水平的单独调控。（ii）至少PIP2;2、PIP2;3、TIP1;1和TIP1;2是悬浮细胞中的胁迫响应性水通道蛋白。（iii）PIP2和TIP1亚家族几个成员的突然增加可能与细胞死亡有关。
