水分胁迫及复水条件下外源Ca2+对玉米幼苗根系水力导度及生长的影响

利用10%PEG-6000模拟–0.2 MPa的水分胁迫，研究了外源Ca²⁺(在1/2 Hoagland营养液中添加10 mmol L^-1 CaCl₂)对水分胁迫7 d后及复水2 d，玉米幼苗整株根系水力导度(Lp_r)、根系生长及叶水势(ψ_w)的影响。结果表明，正常水分条件下，外源Ca²⁺处理降低了Lp_r，但对叶水势无影响；水分胁迫条件下，外源Ca²⁺显著提高了Lp_r、叶水势，减缓了水分胁迫对植物的伤害；复水1 d，两种钙水平下Lp均无明显恢复，但Ca²⁺处理的Lp_r显著高于对照，而叶水势无显著差异且均能恢复至正常供水时的水平；复水2 d，Ca²⁺处理的Lp_r即能恢复至正常供水时的水平，对照仅恢复为正常供水时的59.06%。进一步用HgCl₂检测表明，正常水分条件下外源Ca²⁺对水通道蛋白(AQP)活性没有影响；而水分胁迫下，外源Ca²⁺提高了AQP活性，对照AQP活性下降，说明水分胁迫时外源Ca²⁺促进了水分跨膜途径运输；复水2 d，外源Ca²⁺处理AQP活性恢复至正常供水时的水平，对照AQP活性未能恢复。另外，外源Ca²⁺处理减缓了水分胁迫对植物生长发育的抑制作用，促进了复水时侧根发育，增加根系吸水面积，为植株迅速恢复供水提供了形态学基础，增加了复水后的补偿效应。

Effect of Calcium on Maize Seedling Root Hydraulic Conductivity and Growth under Water Stress and Rehydration Conditions

The effects of extra calcium (additions of 10 mmol L^-1 CaCl₂ into half-strength Hoagland solution) on maize (Zea mays L.) seedling root hydraulic conductivity (Lp_r), morphology and leaf water potential (ψ_w) were investigated under water stress, which was simulated by 10% PEG-6000 with osmotic potential (ψ_{s) value of -0.2 MPa for seven days, and subsequent two days rehydration. Whole root hydraulic conductivity (Lpr) and leaf water potential (ψw) were determined by pressure chamber. After these treatments, it could be seen that water stress reduced Lpr, which was restored when calcium was added to the solution for growing the water-stressed plants. In addition, the Lpr recovered to the level of the control after re-watering at high Ca²⁺ level, but the recovery of Lpr was only 59.06% at regular Ca²⁺ level. HgCl2 (50 μmol L^-1) treatment caused a sharp decline in Lpr, which was almost restored by treatment with 5 mmol L^-1 β-mercaptoethanol. The reduction of Lpr by Hg²⁺ was 53.20% and 74.55% at regular and high calcium levels, respectively under water stress condition, and 62.1% under normal condition. The results suggest that Ca²⁺ increased the passage of water through the cell membrane of roots by increasing the activity of Hg-sensitive AQP under water stress. The percentage of reduction by Hg²⁺ was decreased to the control level two days after re-watering in CaCl2 treated plants. The leaf water potential was declined significantly under water stress, particularly at regular calcium level with respect to the decrease of Lpr. However, ψw recovered rapidly onw day after re-watering. Furthermore, water stress had a detrimental effect on the root growth. The addition of calcium, especially at low water potential, increased the root surface area and primary root diameter, and it promoted primary root enlongation and lateral root development. Compared with the controls, the growth of Ca treated plants was recovered gradually with the prolonging of rehydration. Therefore, these results indicated that the extra calcium, with respect to root growth and water uptake, mitigates the negative effect of water stress and enhances the compensatory effects of rehydration.}