Radin J W, Parker L L, Sell C R
Science and Education Administration, Western Cotton Research Laboratory, United States Department of Agriculture, Phoenix, Arizona 85040.
Plant Physiol. 1978 Oct;62(4):550-3. doi: 10.1104/pp.62.4.550.
The level of endogenous sugars was inversely related to nitrate availability in young cotton (Gossypium hirsutum L.) plants, with high nitrate causing a greater decline in sugar content of roots than of shoots. High nitrate (low sugar) plants also displayed relatively more shoot growth and less root growth than low nitrate (high sugar) plants. These data are consistent with the theory that roots are poor competitors for sugar, and that sugar supply is a major factor limiting root growth in vivo.The effects of endogenous sugar level on root growth and on nitrate reductase activity in the root were different. When root sugar level was experimentally controlled by varying nitrate concentration in the nutrient solution, root growth was less sensitive than nitrate reductase activity to sugar deficiency. Also, in sterile root tips cultured on media containing a wide range of sucrose concentrations, growth rate was considerably less sensitive to endogenous sugar deficiency than was nitrate assimilation rate. Similarly, in plants which were detopped or girdled, nitrate reductase activity in the roots declined more rapidly than did root sugars, especially glucose and fructose. These results suggest that when sugar is deficient, cotton roots preferentially use it for growth at the expense of nitrate reduction.
在棉花（陆地棉）幼苗中，内源糖水平与硝酸盐有效性呈负相关，高硝酸盐条件下根系糖含量的下降幅度大于地上部。与低硝酸盐（高糖）植株相比，高硝酸盐（低糖）植株地上部生长相对较多，根系生长相对较少。这些数据与以下理论一致：根系对糖的竞争力较弱，糖供应是体内限制根系生长的主要因素。内源糖水平对根系生长和根系硝酸还原酶活性的影响有所不同。当通过改变营养液中的硝酸盐浓度来实验性地控制根系糖水平时，根系生长对糖缺乏的敏感性低于硝酸还原酶活性。此外，在含有不同蔗糖浓度的培养基上培养的无菌根尖中，生长速率对内源糖缺乏的敏感性远低于硝酸盐同化速率。同样，在去顶或环剥处理的植株中，根系硝酸还原酶活性的下降比根系糖（尤其是葡萄糖和果糖）更快。这些结果表明，当糖缺乏时，棉花根系优先利用糖进行生长，而以减少硝酸盐还原为代价。
