脱水和高氧压过程中单叶蔓荆叶片细胞膜透性分析

Permeability of Cells in Leaves of Vitex trifolia var. simplicifolia under Stresses of Dehydration and High Oxygen Pressure

【目的】分析植物细胞在组织脱水过程中电解质外渗量增加的原因以及细胞膜透性变化与细胞脱水胁迫和高氧压胁迫关系,并从非平衡态热力学角度对细胞脱水程度与细胞电解质外渗量增加的比例关系进行描述,以辨明细胞膜在组织脱水过程中对离子透性的变化是否与组织脱水胁迫的伤害有关。【方法】采用植物P-V曲线测定技术测定单叶蔓荆叶片的水分关系并收集不同压力区间的组织压出液,用原子吸收分光光度计测定压出溶液中的钠、钾离子含量,并据此分析细胞脱水过程中细胞膜透性的变化情况。【结果】在用压力室测定植物细胞水分关系的P-V曲线时,随着细胞失水程度和氧分压的增大,组织压出液中钠、钾离子的总量不断增加,但组织压出液中钠、钾离子的浓度随着压力升高反而下降,同时,组织压出液中钠、钾离子的总量与压力呈接近线性的正相关关系,表明细胞连续脱水和高氧分压没有导致细胞膜透性的增大。另外,组织压出液中离子累积量与压出液体积累积量的关系呈现出2个具有不同斜率的双相线性关系,首先是离子累积量快速上升的阶段,然后是离子累积量缓慢上升、累积速度大大下降的阶段。离子累积量快速上升的阶段可能表明细胞间隙溶液压出阶段,钠、钾离子含量较高;随后的压出液离子累积速度大幅下降阶段可能代表了细胞内溶液经过细胞膜超滤作用压出阶段,这一阶段压出液中钠、钾离子含量较低,说明细胞膜对钠、钾离子的透性很低,未受到脱水和高氧压胁迫的明显伤害而透性增大。【结论】在本试验的压力区间内,无论是细胞脱水程度的增大,还是压力室氧分压的大幅度升高(最高达大气氧分压的24倍),都没有引起细胞膜对钠、钾离子透性的增大。这些结果表明植物细胞膜的透性相当稳定。因此,在没有其他证据的条件下,仅仅通过组织相对电导率的增大做出脱水导致细胞膜透性增大的结论时应该更加谨慎。

Objective]Analysis was made based on the cause of increase in electrolyte leakage from plant cells during tissue dehydration,on the relationships between the changes in the permeability of cell membrane and high oxygen stress, as well as on the ratio of cell dehydration and cell electrolyte leakage in terms of the irreversible thermodynamics,in order to investigate if there would be any link between the permeability of cell membrane and the dehydration induced injury during tissue dehydration. [Method]The water relations of leaves in Vitex trifolia. var. simplicifolia Cham was measured according to the P-V curve with a pressure bomb,and the expressed cell sap between different pressure range was collected and analysed for potassium and sodium content with an atomic spectrophotometer,thus yielding the changes in cell permeability during cell dehydration.[Results]The results showed that along with the progression in cell dehydration and high oxygen stresses,the cumulative ion content in the expressed xylem sap increased steadily,but the rate of ion accumulation in the expressed xylem sap decreased with the increase in cell dehydration and high oxygen stresses. Similarly,the cumulative ion content in the expressed xylem sap also increased steadily against the pressure increase. This implies that the progression in cell dehydration and high oxygen stresses did not result in the increase in the permeability of the cell membrane to ions. The cumulative amount of sodium and potassium ions in the expressed xylem sap increased almost linearly with the increase in the pressure,meaning that the permeability of the cell membrane was not obvious altered by the high oxygen pressure. A biphasic linear curve with different slops was observed between the cumulative ion content and the cumulative volume of the expressed xylem sap. The first was a faster phase of ion content increase in the lower pressure region,followed by a slower phase of ion content increase in the higher pressure region. The former may have represented the xylem sap from the root with a higher ion concentration,and the latter may have represented the sap expressed from the leaf cells ultrafiltrated by the cell membrane with a lower ion concentration. [Conclusions]In the experimented pressure range,neither the progression of cell dehydration,nor the great increase in the partial pressure of oxygen （ as high as 25 times the partial pressure of oxygen in the atmosphere） ,resulted in the increase in the permeability of the cells to either sodium or potassium ions. The results showed that the permeability of the cell membrane was relatively stable. Therefore it is suggested that more caution must be taken in drawing the conclusions that dehydration results in the increase in the permeability of the cell membrane,when just the relative conductivity method was used without other evidences.