Mechanisms on the increase of resistance to water transport which causes the acute wilting and death of organs in crop plants growing under sufficient siol moisture conditions.

即使农作物在充足的土壤水分条件下生长，但在剧烈蒸腾作用下有时会发生严重的急性枯萎和脱水。黄瓜植株对水分运输抗性的显著增加是导致黄瓜植株急性严重枯萎和水稻植株干燥白穗的主要原因。本研究旨在探讨抗旱性增加的机理1.(1)叶片萎缩性主要是由于茎底部水分输送能力的增强所致。与未枯萎植株相比，黄瓜枯萎植株下胚轴上的许多木质部维管束被酪藻所遮挡，这意味着黄瓜下胚轴上酪藻的形成是导致抗性增强的原因。部分去根降低叶片水势时，茎基端的阻力和木质部维管束中酪乳的形成显著增加。(2)白穗病的发病机理为：(1)在强蒸腾作用下，茎水势下降；(2)在某些临界低水势下，下胚轴木质部导管中形成的酪乳均为正反馈，导致叶片的急性严重萎萎和死亡。(1)白穗干化主要是由于茎对旗叶节向穗颈节的水分运输阻力显著增加所致。在高温、低湿和高风速条件下，茎阻力的增加可能是由于穗的蒸腾作用导致茎水势降低所致。(2)木质部导管中酪氨酸酶的形成可能是茎阻力显著增加的原因。

Even though crop plants are growing under sufficient soil moisture conditions, acute severe wilting and dehydration sometimes occur under intense transpiration. The remarkable increase in resistance to water transport is responsible for the acute severe wilting in cucumber plants and the desiccated white head in rice plants. This research was undertaken in order to investigate the mechanisms on the increase in the resistance.1.(1)The leaf wilting resulted mainly from the increase in resistance to water transport at the base of the stem. Many xylem vessels were occluded by tyloses significantly at the hypocotyl in the wilted cucumber plants compared to the non-wilted plants which means that formation of the tyloses is responsible for the increased resistance. When leaf water potential was decreased by partial excision of the root systems, the resistance at the base of the stem and the formation of tyloses in xylem vessels increased significantly. (2)The mechanism for the acute severe wilting was considered as follows : (i)stem water potential decreases under intense transpiration, (ii)tyloses form in xylem vessels of the hypocotyl at some critical low water potentials all occur as a positive feedback leading to the acute severe wilting and death of leaves.2.(1)The desiccated white head resulted maily from the remarkable increase in stem resistance to water transport from the flag leaf node to the neck node of panicle. The increase of the stem resistance might be induced by the reduction in stem water potential due to the increase of panicle transpiration under the conditions of high temperature, low humidity and high wind velocity. (2)Because the formation of tyloses in xylem vessels might be responsible for the remarkable increase of stem resistance.