【摘要】 用呼吸比重计及比重法、浮力法测量了水稻、高粱、玉米、豆类等作物水培苗及湿润培苗茎叶向根系运输的氧气的数量及根中空气间隙。结果证明这些幼苗茎叶向根系运输的氧气的量与其根中空气间隙的大小成正相关。用玻璃毛细管模拟根中空气间隙组成的通道实验表明:茎叶中氧气的下运主要是靠根基部与根尖之间的分压差,通过空气间隙以扩散方式进行的。沼生习性植物幼苗的氧气下运量及空气间隙均大于陆生习性的幼苗,水培苗大于湿润培苗。更多还原

【Abstract】 In the present investigation,seedlings of rice,pea,sorghum,and maize are raised both in water culture and moist culture.The former culture is to provide the roots with an oxygen deficient condition; while the latter,a direct access to air.The amount of oxygen transported downwards in the seedlings varies not only with the nature of plants but also with the way how they are raised: More oxygen is transported downwards in marsh plant (rice) than in land plants (pea,sorghum,maize) ; and,in case the same plant is concerned,more in water cultured seedlings than in moist cultured ones. Downward oxygen transport in the various seedlings is intimately correlated with the relative volume of the intercellular spaces in the root: the more the downward transport, the larger the air spaces in the cortex.The fractional volume of the intercellular spaces in a small plant segment can be conveniently estimated by determining the specific gravities of the fresh turgescent segment before and after it is filled with water by vaccum infiltration.The difference between the two consecutive measurements in specific gravity times 100 gives directly the percentage of the volume occupied by air spaces.When large root segments are used,the relative volume can also be determined by weighing before and after vaccum infiltration. To test whether oxygen diffusion in the intercellular spaces of roots could actually account for its downward transport,a model is built of capillary tubings with dimensions and oxygen pressure gradients similar to those found in roots.The amount of oxygen diffused in such a model is measured with a respiratory hydrometer (see Fig.1) and fits closely that measured in roots. By comparing the amount of oxygen transported downwards in a seedling with that consumed by its excised roots in air,it can be shown that,in case of rice,it could meet (and at times may even exceed) 100% of that consumed by roots in water cultured seedlings,but is less in moist cultured ones.In land plants (pea,sorghum,and maize), however,the downward oxygen supply is far below its requirement,being 80—100% in water cultured seedlings and 30—60% in moist cultured ones. The above results,together with those obtained in previous communications,support the view that adaptation of a plant to flooded condition is primarily achieved by its capacity of providing adequate intercellular spaces for downward oxygen diffusion.The capacity depends not only upon the phylogeny of the plant concerned but also upon its ontogenic development.更多还原