Rood Stewart B., Zanewich Karen, Stefura Corey, Mahoney John M.
Department Biological Sciences, University of Lethbridge, Alberta T1K 3M4, Canada.
Tree Physiol. 2000 Jun;20(12):831-836. doi: 10.1093/treephys/20.12.831.
Cottonwoods occur in riparian areas where water table depth generally varies with the elevation of the adjacent river. Plant adaptation to the riparian zone requires the coordination of root elongation to maintain contact with the water table during the summer decline. We investigated the effects of rate of water decline on growth allocation and concentrations of endogenous gibberellins (GAs) in black cottonwood (Populus trichocarpa Torr. & A. Gray ex Hook.) saplings. Rhizopods were used to achieve water decline rates of 0, 2 and 4 cm day(-1). Root elongation approximately doubled in response to the 2 cm day(-1) treatment, whereas leaf area was reduced. A water decline rate of 4 cm day(-1) led to water stress, as evidenced by reduced growth, increased leaf diffusive resistance, decreased water potential, and leaf senescence and abscission. Endogenous GAs were extracted, purified and analyzed by gas chromatography-selected ion monitoring with internal [(2)H(2)]GA standards. Across the sampled plant organs, GAs were generally highest in shoot tips and sequentially lower in basal stems, root tips, leaves and upper roots; GAs were thus abundant in rapidly growing tissues. Of the GAs measured, GA(1) tended to predominate, followed sequentially by GA(3), GA(8), GA(19), GA(20), GA(29) and GA(4). There was little relationship between GA concentration and growth allocation across the water table decline treatments, although GA(8) was consistently reduced in plants experiencing water table decline. Because GA(8) is the final gibberellin in the metabolic sequence, it might be useful for assessing historic patterns of GAs and growth rate. This study demonstrated changes in growth allocation in response to water table decline, but provided little evidence that endogenous GAs play a primary role in the regulation of root elongation in response to water table decline.
三角叶杨生长在河岸地区，那里地下水位深度通常随邻近河流的海拔高度而变化。植物适应河岸带需要协调根系伸长，以便在夏季水位下降期间与地下水位保持接触。我们研究了水位下降速率对黑三角叶杨（Populus trichocarpa Torr. & A. Gray ex Hook.）幼树生长分配和内源赤霉素（GAs）浓度的影响。使用根箱来实现0、2和4厘米/天的水位下降速率。响应2厘米/天的处理，根系伸长几乎翻倍，而叶面积减小。4厘米/天的水位下降速率导致水分胁迫，表现为生长减缓、叶片扩散阻力增加、水势降低以及叶片衰老和脱落。内源GAs经提取、纯化后，采用气相色谱 - 选择离子监测结合内标物[(2)H(2)]GA进行分析。在采样的植物器官中，GAs通常在茎尖中含量最高，依次在基部茎、根尖、叶片和上部根中较低；因此，GAs在快速生长的组织中含量丰富。在所测定的GAs中，GA(1)往往占主导地位，其次依次是GA(3)、GA(8)、GA(19)、GA(20)、GA(29)和GA(4)。尽管在经历水位下降的植株中GA(8)持续降低，但在不同水位下降处理中，GA浓度与生长分配之间几乎没有关系。由于GA(8)是代谢序列中的最终赤霉素，它可能有助于评估GAs的历史模式和生长速率。这项研究表明了生长分配随水位下降的变化，但几乎没有证据表明内源GAs在响应水位下降调节根系伸长中起主要作用。
