Physiological Research Laboratory, Scripps Institution of Oceanography, University of California, La Jolla, California 92037.
Plant Physiol. 1968 Jul;43(7):1042-8. doi: 10.1104/pp.43.7.1042.
A direct method is described for measuring the pressure in secondary phloem sieve tubes of oak trees. One end of a 26-gauge stainless steel tube was shaped such that when it penetrated the outer bark and transected a few sieve elements, it was stopped by the xylem so that small openings in the end allowed phloem sap to enter the tube. The other end of the stainless tube (phloem needle) was joined to a long glass capillary sealed at its other end to form a manometer for measuring phloem sap pressure. A method for measuring the average osmotic and turgor pressures in cells of leaves is also described. Phloem turgor pressures varied greatly in a series of phloem punctures around the trunk at 1.5 and at 6.3 meters. The variation in turgor pressure was always greater than the variation in osmotic pressure. In a series of turgor pressures arranged in descending order, the values in a sequence for the upper level was usually a little (0-3 atm) larger than the values for the lower level. These results may suggest that translocation of assimilate is favored by a small turgor pressure gradient, but they do more to emphasize the complications in measuring gradients in an elastic low resistance distribution system composed of contiguous longitudinal conduits. The results also imply that the sieve tubes are inflated with assimilate fluid under high pressure which can readily move longitudinally and with less pressure drop than would be necessary if the sieve tubes were rigid.
一种直接测量橡树次生韧皮部筛管内压力的方法。将 26 号不锈钢管的一端加工成这样的形状：当它穿透外树皮并横切几个筛管时，会被木质部挡住，从而使管子末端的小孔允许韧皮部汁液进入。不锈钢管的另一端（韧皮针）与长玻璃毛细管相连，玻璃毛细管的另一端密封，形成测量韧皮部汁液压力的压力计。还描述了一种测量叶片细胞平均渗透和膨压的方法。在树干 1.5 米和 6.3 米处的一系列韧皮部穿刺中，韧皮部膨压变化很大。膨压的变化总是大于渗透压的变化。在一系列按降序排列的膨压值中，上一级序列的值通常比下一级序列的值大一点（0-3 大气压）。这些结果可能表明，同化物的转运有利于较小的膨压差，但它们更强调了在由连续的纵向导管组成的弹性低阻力分布系统中测量梯度的复杂性。结果还表明，筛管中充满了高压的同化物流体，它可以很容易地纵向移动，并且压力下降比如果筛管是刚性的话要小。
