Hawaiian Sugar Planters' Association, Aiea, Hawaii 96701.
Plant Physiol. 1988 Mar;86(3):873-9. doi: 10.1104/pp.86.3.873.
Solute concentration in the apoplast of growing sugarcane (Saccharum spp. hybrid) leaves was measured using one direct and several indirect methods. The osmotic potential of apoplast solution collected directly by centrifugation of noninfiltrated tissue segments ranged from -0.25 megapascal in mature tissue to -0.35 megapascal in tissue just outside the elongation zone. The presence of these solutes in the apoplast manifested itself as a tissue water potential equal to the apoplast osmotic potential. Since the tissue was not elongating, the measurements were not influenced by growth-induced water uptake and no significant tension was detected with the pressure chamber. Further evidence for a significant apoplast solute concentration was obtained from pressure exudation experiments and comparison of methods for estimating tissue apoplast water fraction. For elongating leaf tissue the centrifugation method could not be used to obtain direct measurements of apoplast solute concentration. However, several other observations suggested that the apoplast water potential of -0.35 to -0.45 megapascal in elongating tissue had a significant osmotic component and small, but significant tension component. Results of experiments in which exudate was collected from pressurized tissue segments of different ages suggested that a tissue age-dependent dynamic equilibrium existed between intra- and extracellular solutes.
采用直接法和间接法测量了生长中的甘蔗（甘蔗属杂种）叶片质外体中溶质的浓度。用离心法直接收集未渗透组织段的质外体溶液的渗透压，从成熟组织的-0.25 兆帕斯卡到伸长区外组织的-0.35 兆帕斯卡不等。这些溶质存在于质外体中，表现为与质外体渗透压相等的组织水势。由于组织没有伸长，测量不受生长诱导的水分吸收的影响，用压力室也没有检测到明显的张力。从压力渗出实验和比较估计组织质外水分数的方法中得到了质外体中存在显著溶质浓度的进一步证据。对于伸长的叶片组织，不能用离心法直接测量质外体溶质浓度。然而，其他一些观察结果表明，伸长组织的质外体水势为-0.35 至-0.45 兆帕斯卡，具有显著的渗透成分和较小但显著的张力成分。从不同年龄的加压组织段收集渗出物的实验结果表明，细胞内和细胞外溶质之间存在与组织年龄相关的动态平衡。
