Sharp R E, Hsiao T C, Silk W K
Department of Land, Air and Water Resources, University of California, Davis, California 95616.
Plant Physiol. 1990 Aug;93(4):1337-46. doi: 10.1104/pp.93.4.1337.
Primary roots of maize (Zea mays L. cv WF9 x Mo17) seedlings growing in vermiculite at various water potentials exhibited substantial osmotic adjustment in the growing region. We have assessed quantitatively whether the osmotic adjustment was attributable to increased net solute deposition rates or to slower rates of water deposition associated with reduced volume expansion. Spatial distributions of total osmotica, soluble carbohydrates, potassium, and water were combined with published growth velocity distributions to calculate deposition rate profiles using the continuity equation. Low water potentials had no effect on the rate of total osmoticum deposition per unit length close to the apex, and caused decreased deposition rates in basal regions. However, rates of water deposition decreased more than osmoticum deposition. Consequently, osmoticum deposition rates per unit water volume were increased near the apex and osmotic potentials were lower throughout the growing region. Because the stressed roots were thinner, osmotic adjustment occurred without osmoticum accumulation per unit length. The effects of low water potential on hexose deposition were similar to those for total osmotica, and hexose made a major contribution to the osmotic adjustment in middle and basal regions. In contrast, potassium deposition decreased at low water potentials in close parallel with water deposition, and increases in potassium concentration were small. The results show that growth of the maize primary root at low water potentials involves a complex pattern of morphogenic and metabolic events. Although osmotic adjustment is largely the result of a greater inhibition of volume expansion and water deposition than solute deposition, the contrasting behavior of hexose and potassium deposition indicates that the adjustment is a highly regulated process.
在不同水势下于蛭石中生长的玉米（Zea mays L. cv WF9 x Mo17）幼苗的初生根，在生长区域表现出显著的渗透调节。我们已定量评估了这种渗透调节是归因于净溶质沉积速率的增加，还是归因于与体积膨胀减少相关的水沉积速率减慢。利用连续性方程，将总渗透物、可溶性碳水化合物、钾和水的空间分布与已发表的生长速度分布相结合，以计算沉积速率剖面。低水势对靠近根尖处单位长度的总渗透物沉积速率没有影响，但导致基部区域的沉积速率降低。然而，水的沉积速率比渗透物沉积速率下降得更多。因此，单位水体积的渗透物沉积速率在根尖附近增加，并且整个生长区域的渗透势更低。由于受胁迫的根更细，渗透调节发生时单位长度没有渗透物积累。低水势对己糖沉积的影响与对总渗透物的影响相似，并且己糖在中部和基部区域的渗透调节中起主要作用。相比之下，在低水势下钾的沉积与水的沉积密切平行下降，并且钾浓度的增加很小。结果表明，低水势下玉米初生根的生长涉及形态发生和代谢事件的复杂模式。虽然渗透调节在很大程度上是体积膨胀和水沉积比溶质沉积受到更大抑制的结果，但己糖和钾沉积的不同行为表明这种调节是一个高度调控的过程。
