Kaufmann M R
Department of Plant Sciences, University of California, Riverside, California 92502.
Plant Physiol. 1970 Jul;46(1):145-9. doi: 10.1104/pp.46.1.145.
Growing navel orange fruits (Citrus sinensis) 5.4 to 5.7 centimeters in diameter were used as a model system to determine the effects of transpiration and carbohydrate translocation on water and osmotic potentials in fruit tissues. Evidence supported the hypothesis that osmotic potential in the vesicles would be affected little by changes in transpiration or carbohydrate translocation because the vesicles are anatomically isolated from the transpiration stream and are at the end of the carbohydrate translocation pathway. In the mesocarp tissue, which contains a vascular network, osmotic potential decreased during the daytime when environmental conditions favored transpiration and increased at night. Exocarp water potential followed a similar pattern. Girdling of the stem above the fruits 5 days before sampling caused an increase of osmotic potential in the mesocarp but had no effect on exocarp water potential. Neither diurnal changes in transpiration nor girdling of the stem affected the osmotic potential of the vesicles.Osmotic potentials in all tissues of the fruit were in the range of -10 to -15 bars. Measurements of osmotic potential at 16 locations along a longitudinal plant through the fruit axis showed that osmotic potential increased from the stem to the stylar end, but it decreased from the pericarp tissues to the vesicles. As exocarp water potential decreased during a 20-day period after watering, osmotic potential decreased in the vesicles and exocarp. Turgor pressure, calculated as the difference between water and osmotic potentials, decreased with water potential in the vesicles but not in the exocarp. The lack of decrease of turgor pressure in the exocarp may result from a measurement error caused by pectins or from osmotic adjustment related to carbohydrate accumulation at low water potentials.
直径5.4至5.7厘米的生长中的脐橙果实（柑橘属）被用作模型系统，以确定蒸腾作用和碳水化合物转运对果实组织中水势和渗透势的影响。有证据支持这样的假设，即小泡中的渗透势受蒸腾作用或碳水化合物转运变化的影响很小，因为小泡在解剖学上与蒸腾流隔离，且处于碳水化合物转运途径的末端。在含有维管网络的中果皮组织中，当环境条件有利于蒸腾作用时，白天渗透势降低，夜间升高。外果皮水势遵循类似模式。在采样前5天对果实上方的茎进行环剥，导致中果皮渗透势增加，但对外果皮水势没有影响。蒸腾作用的昼夜变化和茎的环剥均未影响小泡的渗透势。果实所有组织中的渗透势在-10至-15巴的范围内。沿果实轴纵向穿过植株在16个位置测量渗透势表明，渗透势从茎向花柱端增加，但从果皮组织向小泡降低。在浇水后20天内，随着外果皮水势降低，小泡和外果皮中的渗透势也降低。以水势和渗透势之差计算的膨压，在小泡中随水势降低，但在外果皮中不降低。外果皮中膨压缺乏降低可能是由于果胶引起的测量误差，或与低水势下碳水化合物积累相关的渗透调节所致。
