Arndt S K, Clifford S C, Wanek W, Jones H G, Popp M
Botany Department, The University of Western Australia, Nedlands, WA 6009, Australia.
Tree Physiol. 2001 Jul;21(11):705-15. doi: 10.1093/treephys/21.11.705.
The physiological basis of drought resistance in Ziziphus rotundifolia Lamk., which is an important, multipurpose fruit tree of the northwest Indian arid zone, was investigated in a greenhouse experiment. Three irrigation regimes were imposed over a 34-day period: an irrigation treatment, a gradual drought stress treatment (50% of water supplied in the irrigation treatment) and a rapid drought stress treatment (no irrigation). Changes in gas exchange, water relations, carbon isotope composition and solute concentrations of leaves, stems and roots were determined. The differential rate of stress development in the two drought treatments did not result in markedly different physiological responses, but merely affected the time at which they were expressed. The initial response to decreasing soil water content was reduced stomatal conductance, effectively maintaining predawn leaf water potential (Psi(leaf)), controlling water loss and increasing intrinsic water-use efficiency, while optimizing carbon gain during drought. Carbon isotope composition (delta13C) of leaf tissue sap provided a more sensitive indicator of changes in short-term water-use efficiency than delta13C of bulk leaf tissue. As drought developed, osmotic potential at full turgor decreased and total solute concentrations increased in leaves, indicating osmotic adjustment. Decreases in leaf starch concentrations and concomitant increases in hexose sugars and sucrose suggested a shift in carbon partitioning in favor of soluble carbohydrates. In severely drought-stressed leaves, high leaf nitrate reductase activities were paralleled by increases in proline concentration, suggesting an osmoprotective role for proline. As water deficit increased, carbon was remobilized from leaves and preferentially redistributed to stems and roots, and leaves were shed, resulting in reduced whole-plant transpiration and enforced dormancy. Thus, Z. rotundifolia showed a range of responses to different drought intensities indicating a high degree of plasticity in response to water deficits.
圆叶枣是印度西北部干旱地区一种重要的多用途果树，在温室试验中对其抗旱的生理基础进行了研究。在34天的时间里设置了三种灌溉方式：一种是灌溉处理，一种是逐渐干旱胁迫处理（灌溉处理供水量的50%），还有一种是快速干旱胁迫处理（不灌溉）。测定了叶片、茎和根的气体交换、水分关系、碳同位素组成以及溶质浓度的变化。两种干旱处理中胁迫发展的不同速率并未导致明显不同的生理反应，只是影响了这些反应出现的时间。对土壤含水量降低的初始反应是气孔导度降低，有效维持黎明前叶片水势（Ψ(leaf)），控制水分流失并提高内在水分利用效率，同时在干旱期间优化碳获取。叶片组织汁液的碳同位素组成（δ13C）比整片叶片组织的δ13C能更敏感地指示短期水分利用效率的变化。随着干旱加剧，叶片在完全膨压下的渗透势降低，总溶质浓度增加，表明存在渗透调节。叶片淀粉浓度降低，同时己糖和蔗糖增加，表明碳分配向可溶性碳水化合物倾斜。在严重干旱胁迫的叶片中，高叶片硝酸还原酶活性与脯氨酸浓度增加同时出现，表明脯氨酸具有渗透保护作用。随着水分亏缺增加，碳从叶片中重新分配并优先重新分配到茎和根中，叶片脱落，导致整株植物蒸腾作用降低并进入强制休眠状态。因此，圆叶枣对不同干旱强度表现出一系列反应，表明其对水分亏缺具有高度可塑性。
