Institute for Horticultural Production Systems, Leibniz-University Hannover, Hannover, Germany.
PLoS One. 2018 Nov 16;13(11):e0207626. doi: 10.1371/journal.pone.0207626. eCollection 2018.
Studies of fruit tree water relations often require data on water potentials of fruit. However, this is sometimes difficult because the fruit stalks are not sufficiently long for use in a pressure bomb. Also, because fruit xylem function is often lost during maturation. In the absence of significant turgor, the osmotic potential of the expressed juice is a useful proxy for a fruit's water potential. The osmotic potential of most fleshy fruit is determined largely by the concentration of soluble carbohydrates and this can be quantified by osmometry. Soluble solids may also be quantified by refractometry. Compared with osmometry, refractometry is markedly less expensive and also much faster. Hence, it is better suited to high-throughput analyses. The objective of this study was to establish relationships between the osmotic potentials of juices expressed from sweet cherries and sour cherries, grapes and plums as determined using a vapor pressure osmometer and their soluble solids concentrations as determined using a refractometer. The data reveal close relationships within all these species. Except for plums, the relationships between species were almost identical. This is due to similarity among cultivars and species in the relative abundances of the same set of major osmolytes-i.e. the carbohydrates glucose, fructose and sorbitol and the potassium salts of the organic acids malate or tartrate. For plums, the relationship between osmotic potential and soluble solids concentration was slightly displaced. Our findings indicate osmotic potentials may be reliably predicted from soluble solids concentrations determined by refractometry.
研究果树水分关系时，通常需要测定果实水势的数据。然而，由于果柄不够长，无法用于压力弹，有时这很难做到。此外，由于在成熟过程中果木质部的功能常常丧失，如果没有显著的膨压，渗出汁液的渗透势可作为果实水势的有用替代值。大多数肉质果实的渗透势主要取决于可溶性碳水化合物的浓度，可通过渗透压计进行定量。也可通过折光仪定量可溶性固形物。与渗透压计相比，折光仪的价格明显更低，速度也快得多。因此，它更适合高通量分析。本研究的目的是建立用蒸汽压渗透计测定甜樱桃和酸樱桃、葡萄和李果实渗出汁液的渗透势，以及用折光仪测定可溶性固形物浓度之间的关系。数据表明，在所有这些物种中都存在密切的关系。除李外，种间关系几乎相同。这是因为在相同的一组主要渗透物（即葡萄糖、果糖和山梨糖醇等碳水化合物以及苹果酸或酒石酸钾等有机酸的钾盐）的相对丰度方面，品种和物种之间存在相似性。对于李，渗透势与可溶性固形物浓度之间的关系略有偏移。我们的研究结果表明，可通过折光仪测定的可溶性固形物浓度可靠地预测渗透势。
