Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55108.
Plant Physiol. 1987 Jun;84(2):467-71. doi: 10.1104/pp.84.2.467.
Short-term transport studies were conducted using excised whole Zea mays kernels incubated in buffered solutions containing radiolabeled sugars. Following incubation, endosperms were removed and rates of net (14)C-sugar uptake were determined. Endogenous sugar gradients of the kernel were estimated by measuring sugar concentrations in cell sap collected from the pedicel and endosperm. A sugar concentration gradient from the pedicel to the endosperm was found. Uptake rates of (14)C-labeled glucose, fructose, and sucrose were linear over the concentration range of 2 to 200 millimolar. At sugar concentrations greater than 50 millimolar, hexose uptake exceeded sucrose uptake. Metabolic inhibitor studies using carbonylcyanide-m-chlorophenylhydrazone, sodium cyanide, and dinitrophenol and estimates of Q(10) suggest that the transport of sugars into the developing maize endosperm is a passive process. Sucrose was hydrolyzed to glucose and fructose during uptake and in the endosperm was either reconverted to sucrose or incorporated into insoluble matter. These data suggest that the conversion of sucrose to glucose and fructose may play a role in sugar absorption by endosperm. Our data do not indicate that sugars are absorbed actively. Sugar uptake by the endosperm may be regulated by the capacity for sugar utilization (i.e. starch synthesis).
采用放射性标记糖的缓冲溶液孵育离体整玉米籽粒进行短期转运研究。孵育后，去除胚乳并测定净（14）C-糖摄取率。通过测量从花梗和胚乳收集的细胞液中糖的浓度来估计内核的内源性糖梯度。发现了从花梗到胚乳的糖浓度梯度。（14）C 标记葡萄糖、果糖和蔗糖的摄取率在 2 至 200 毫摩尔的浓度范围内呈线性。在糖浓度大于 50 毫摩尔时，己糖摄取量超过蔗糖摄取量。使用羰基氰化物 m-氯代苯腙、氰化钠和二硝基苯酚进行的代谢抑制剂研究以及 Q(10)的估算表明，糖进入发育中的玉米胚乳的转运是一个被动过程。蔗糖在摄取过程中水解为葡萄糖和果糖，然后在胚乳中要么重新转化为蔗糖，要么掺入不溶性物质。这些数据表明，蔗糖转化为葡萄糖和果糖可能在胚乳吸收糖中起作用。我们的数据表明，糖不是主动吸收的。胚乳对糖的摄取可能受糖利用能力（即淀粉合成）的调节。
