Development of a simple method for measuring resistance to water transport in crop plants.

即使作物在土壤水分充足的条件下生长，在晴天的下午，气孔导度和光合速率也会下降，而且，由于缺水，有时会发生严重的叶片枯萎和叶片死亡。植物对水分输送的抵抗力增加是植物水分亏缺的主要原因。为了研究水分亏缺的原因和培育抗旱植物，需要估计植物各部分对水分输送的抗性。本研究的目的是建立一种简单的方法来测定作物的抗性，特别是根和茎的抗性被认为是可变的。为了估算茎段阻力，(1)在茎段切割端施加低静水压力(P),(2)测量茎段另一端的渗出速率(E),(3)通过式(1)计算茎段内的输水阻力（Rs）。在严重萎蔫的黄瓜植株和白穗干枯的水稻植株上，穗基部的抗性显著增加，穗基部的抗性明显增加，这与其他可靠的测定结果一致。结果表明，该方法可用于估算茎秆的抗性。r=P /E (1), r=Pr/Er (2)为了估算根阻力，(1)测量茎基部的渗出速率（Er）和根压（Pr），通过式(2)计算根到茎基部的阻力。这种抗性可以被认为是活性水分吸收中的根抗性。在强蒸腾条件下，主动吸水的根系阻力远大于被动吸水。然而，我们认为主动吸水阻力与被动吸水阻力之间存在着密切的相关性，即主动吸水阻力越大，被动吸水阻力越大。结果表明，在强蒸腾条件下，根系被动吸水阻力可通过测定主动吸水阻力进行比较。少

Even though crop plants are growing under sufficient soil moisture conditions, stomatal conductance and photosynthetic rate decrease in the afternoon on a clear day and, moreover, severe leaf wilting and leaf death sometimes occur due to water deficits. Increase of resistance to water transport in plants is responsible for the plant water deficits. It is required to estimate resistance to water transport in various parts of a plant for investigating the cause of the water deficits and for breeding drought-resistant plants. This investigation was to develop a simple method for measuring the resistance in crop plants especially in roots and stem of which resistance is thought to be variable.1. For estimating stem resistance, (1) low hydrostatic pressure (P) was applied on the cut end of a stem segment, (2) exudation rate (E) from the other cut end of the segment was measured and (3) resistance to water transport in the segment (Rs) was calculated by Eq(1). Resistance of the base of a ste … More m and of the panicle base increased markedly in the severely wilted cucumber plant and in the rice plant with desiccated white head, respectively, which agrees with the results obtained from other reliable measurements. It was concluded that this method can be employed for estimating stem resistance.Rs=P/E (1), Rr=Pr/Er (2)2. For estimating root resistance, (1) exudation rate (Er) and root pressure (Pr) were measured at the base of a stem and the resistance from roots to the base of a stem was calculated by Eq. (2). This resistance can be thought to be root resistance in active water uptake. Root resistance in active water uptake was far larger than that in passive water uptake under intense transpiration. However, it was supposed that there is a close correlation between the resistance in active and passive water uptake, that is, the higher the resistance in active water uptake, the higher, the resistance in passive water uptake. It was concluded from these results that root resistance in passive water uptake under intense transpiration could be compared by measuring the resistance in active water uptake. Less