低钾营养条件下水稻源叶碳同化物输出的障碍

An Impediment to Export of Assimilates in Mature Leaf of Rice Stressed by Low Potassium Nutrition

通过黑暗或连续光照处理，使水培水稻体内可溶性糖及ＡＴＰ造成梯度，再用１４ＣＯ２饲喂，促使低钾和正常钾营养下，稻叶碳同化物的输出均与蔗糖含量呈两相动力学曲线，但低钾下启动相Ⅱ所需的蔗糖含量上升，Ｖｍａｘ值明显降低；低钾下稻叶叶肉细胞、筛管、伴胞的质膜ＡＴＰａｓｅ分布较少．叶脉韧皮部发育不良。表明低钾营养下同化物输出的障碍与韧皮部装入有关，并非叶内蔗糖和能量不足。

The export of assimilates frommature leaves in rice cultured in solution was studied by feeding 14 CO2 to aleaf after prolonged dark and. light Period resulting in various grades of sugarcontent in the leaves. The resultsshowed that the curves of carbon assimilate export rate against sucrosecontent were of a type which had twophases, each with Menten--Michaeliskinetics, for both low and normalPOtassium conditions, but the minimum sucrose eontent for phase Ⅱ export kinetics to start rose from 20 μmolg--1 FW for normal plant to 25 μmolg -1 FW for plant with low potassiumnutrition, while K. and Imax were lowered from 45 μmol g-1 FW and 152pmol g-1 FW h-1in plant with normalPOtassium nutrition to 42. 5 μ molg-1FW and 121 μmol g-1 FW h-1 in plantgrown under low potassium nutrition,respectively. Under microscope, it wasseen that ATPase distribution and aetivity in plasmalemma of sieve elements, companion cells and mesophyllcells were lower under low potassiumnutrition than under normal one. Inaddition, condueting tissues, especiallyphloem, in the leaf treated with lowpotassium was not fully developed. Itis concluded that a significant impediment to export of carbon assimilatesfrom mature rice leaf results from animpediment to phloem leading of sucrose, not from a deficiency of sugaror ATP in the leaf with low potassiumnutrition.