Forstbotanisches Institut der Universität Göttingen, Göttingen, Germany.
Planta. 1971 Sep;100(3):208-21. doi: 10.1007/BF00387037.
Sieve-tube exudate which appears on cut surfaces of stems of Cucurbita maxima as distinct droplets has been depicted in electron micrographs of longitudinal sections of the phloem. The exudate, which was produced from mature sieve tubes only, contained filaments of P-protein, but no mitochondria or vesicles of endoplasmic reticulum. The water-soluble part of the exudate contained at least 12 proteins, as shown by disc-electrophoresis. Enzymic activity was found for peroxidases, acid phosphatases, and aldolases. Color tests and assays for other enzymes, including ATPase, fructokinase, several dehydrogenases, and UDP-glucose: D-fructose-2-glucosyl transferase, gave negative results. With repeated cutting of a stem, the protein content of the exudate increased, while the amount of exudate decreased.
在南瓜茎的纵切片的电子显微镜照片中，可以看到明显的液滴状筛管渗出物。这种渗出物仅由成熟的筛管产生，其中包含 P 蛋白丝，但没有线粒体或内质网小泡。渗出物的水溶性部分至少含有 12 种蛋白质，这一点通过圆盘电泳得到了证明。过氧化物酶、酸性磷酸酶和醛缩酶的酶活性也被发现。颜色测试和其他酶的测定，包括 ATP 酶、果糖激酶、几种脱氢酶和 UDP-葡萄糖：D-果糖-2-葡萄糖基转移酶，均得到阴性结果。随着对茎的反复切割，渗出物的蛋白质含量增加，而渗出物的量减少。
