Lehrstuhl Botanik I der Universität, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
Planta. 1984 Nov;161(6):562-8. doi: 10.1007/BF00407090.
Sucrose transport has been investigated in vacuoles isolated from barley mesophyll protoplasts. Rates of sucrose transfer across the tonoplast were even higher in vitro than in vivo indicating that the sucrose transport system had not suffered damage during isolation of the vacuoles. Sucrose transport is carrier-mediated as shown by substrate saturation of transport and sensitivity to a metabolic inhibitor and to competitive substrates. A number of sugars, in particular maltose and raffinose, decreased uptake of sucrose. Sorbitol was slowly taken up but had no effect on sucrose transport. The SH-reagent p-chloromercuribenzene sulfonate inhibited sucrose uptake completely. The apparent Km of the carrier for sucrose uptake was 21 mM. Transport was neither influenced by ATP and pyrophosphate, with or without Mg(2+) present, nor by protonophores and valinomycin (with K(+) present). Apparently uptake was not energy dependent. Efflux experiments with preloaded vacuoles indicated that sucrose unloading from the isolated vavuoles is mediated by the same carrier which catalyses uptake. The vacuole of mesophyll cells appears to represent an intermediary storage compartment. Uptake of photosynthetic products into the vacuole during the light apparently minimizes osmotic swelling of the small cytosolic compartment of vacuolated leaf cells when photosynthetic productivity exceeds the capacity of the phloem for translocation of sugars.
已研究了从小麦叶肉原生质体分离的液泡中的蔗糖转运。质膜上蔗糖的转移速率在体外比体内更高，这表明蔗糖转运系统在液泡分离过程中没有受到损伤。蔗糖转运是载体介导的，如转运的底物饱和和对代谢抑制剂以及竞争性底物的敏感性所示。一些糖，特别是麦芽糖和棉子糖，降低了蔗糖的摄取。山梨醇被缓慢摄取，但对蔗糖转运没有影响。SH 试剂对氯汞苯磺酸完全抑制了蔗糖的摄取。载体对蔗糖摄取的表观 Km 为 21mM。在存在或不存在 Mg(2+)的情况下，ATP 和焦磷酸盐均不影响转运，质子载体和缬氨霉素（存在 K(+)时）也不影响转运。显然，摄取不是能量依赖性的。用预加载的液泡进行的外排实验表明，从分离的液泡中卸载蔗糖是由催化摄取的相同载体介导的。质膜的液泡似乎代表了一个中间储存隔室。当光合作用生产力超过韧皮部转运糖的能力时，在光照期间将光合作用产物摄取到液泡中可明显最小化含有液泡的叶肉细胞中小胞质隔室的渗透肿胀。
