The mechanism for the determination of soluble sugar content of fruits

光合产物从源器官到库器官的转运涉及通过流经韧皮部的水流递送糖。已经发现，进入果实的超过90%的水通过韧皮部输送，而只有一小部分水通过木质部输送。这一发现表明，果实的固形物含量，这应该是高度相关的糖运输到水果中的水运输的比例，将由韧皮部汁液的糖浓度决定。在这项研究中，我们试图发展一种方法来确定在番茄韧皮部汁液的糖浓度。该方法基于EDTA溶液中钙螯合抑制胼胝质形成。切下花梗，将切下的末端在含有细胞膜不可渗透的荧光探针HPTS的EDTA溶液中孵育。采用HPTS稀释率计算渗出液体积。韧皮部分泌物的体积以热环剥法减少的分泌物量来确定，用这种方法可以收集到0-50μL的韧皮部汁液，并可以测定韧皮部汁液中的蔗糖浓度。然而，根据植物条件，收集有时不成功。相反，我们可以成功地收集木质部汁液，并可以测定其钙浓度。由于钙主要通过木质部运输，因此可以估计通过木质部的总运输量，然后水流过韧皮部和糖。韧皮部汁液的浓度可以相应地确定。在实验中，番茄植株具有不同的源/库比，韧皮部汁液的蔗糖浓度表现出高度的相关性，果实的固体含量。结果表明，韧皮部在水分向果实的运输中有很大的贡献。

The translocation of photosynthates from source to sink organs involves the delivery of sugars by water flow through the phloem. It has been found that more than 90% of water that enter fruits is delivered through the phloem, while only a small portion of water is through the xylem. This finding suggests that solid content of fruits, which should highly correlates to a ratio of sugar transport to water transport into fruits, would be determined by the sugar concentration of the phloem sap.In this study, we attempted to develop a method to determine the sugar concentration of the phloem sap in tomato. This method is based on the inhibition of callose formation by Ca chelation in EDTA solution. The pedicel was excised and the cut end was incubated in EDTA solution containing cell membrane impermeable fluorescent probe, HPTS. The volume of the exudates was calculated by using the dilution rate of HPTS. The volume of the phloem exudate was determined as the exudation reduction by heat girdling on the pedicel.By this method, we could collect 0-50μL of phloem sap, and sucrose concentration of phloem sap could be determined. However, the collection was sometimes unsuccessful depending on plant conditions. In contrast, we could successfully collect xylem sap and could determine its calcium concentration. Since calcium is mainly transported through the xylem, total transport of water through the xylem could be estimated, and then water flow through the phloem and the sugar. concentration of the phloem sap could be determined accordingly. In experiments where tomato plants with different source/sink ratios were used, the sucrose concentration of the phloem sap showed a high correlation to the solid content of the fruits. The results indicated a high contribution of the phloem in total water transport into fruits.