Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
Plant Physiol. 1968 Aug;43(8):1169-84. doi: 10.1104/pp.43.8.1169.
rate = cell extensibility x turgor. All growth rate responses can in principle be resolved into changes in the 2 latter variables. Extensibility will relate primarily to the yielding properties of the cell wall, turgor primarily to solute uptake or production. Use of this simple relationship in vivo requires that at least 2 of the 3 variables be measured in a growing cell. Extensibility is not amenable to direct measurement. Data on rate and turgor for single Nitella cells can, however, be continuously gathered to permit calculation of extensibility (rate/turgor). Rate is accurately obtained from measurements on time-lapse film. Turgor is estimated in the same cell, to within 0.1 atm or less, by measurement of the ability of the cell to compress gas trapped in the closed end of a capillary the open end of which is in the cell vacuole. The method is independent of osmotic equilibrium. It operates continuously for several days, over a several fold increase in cell length, and has response time of less than one minute. Rapid changes in turgor brought on by changes in tonicity of the medium, show that extensibility, as defined above, is not constant but has a value of zero unless the cell has about 80% of normal turgor. Because elastic changes are small, extensibility relates to growth. Over long periods of treatment in a variety of osmotica the threshold value for extensibility and growth is seen to fall to lower values to permit resumption of growth at reduced turgor. A brief period of rapid growth (5x normal) follows the return to normal turgor. All variables then become normal and the cycle can be repeated. The cell remains essentially at osmotic equilibrium, even while growing at 5x the normal rate. The method has potential for detailed in vivo analyses of "wall softening."
速率=细胞延伸性×膨压。所有生长速率的响应都可以原则上归结为后两个变量的变化。延伸性主要与细胞壁的屈服特性有关，而膨压主要与溶质的摄取或产生有关。在活体中使用这个简单的关系至少需要在生长的细胞中测量其中的 2 个变量。延伸性不适于直接测量。然而，可以连续收集单个 Nitella 细胞的速率和膨压数据，从而允许计算延伸性（速率/膨压）。速率可以通过对延时电影的测量准确获得。在同一个细胞中，可以通过测量细胞压缩被困在毛细管封闭端的气体的能力来估计膨压，而毛细管的开口端位于细胞液泡中。该方法不依赖于渗透平衡。它可以连续运行数天，在细胞长度增加几倍的情况下，响应时间不到一分钟。介质渗透压的变化引起的膨压的快速变化表明，如上所述，延伸性不是恒定的，除非细胞具有正常膨压的 80%左右，否则其值为零。由于弹性变化很小，因此延伸性与生长有关。在各种渗透物中长时间处理后，会发现延伸性和生长的阈值值下降到较低的值，从而允许在降低的膨压下恢复生长。在恢复到正常膨压后，会出现一个短暂的快速生长（正常生长的 5 倍）时期。所有变量都恢复正常，并且可以重复该周期。即使以正常生长速度的 5 倍生长，细胞仍基本处于渗透平衡状态。该方法具有对“细胞壁软化”进行详细体内分析的潜力。
