Fisher D B
Department of Botany, Washington State University, Pullman, Washington 99164-4238.
Plant Physiol. 1990 Oct;94(2):455-62. doi: 10.1104/pp.94.2.455.
An indicator-dilution technique for the measurement of flow rates, commonly used by animal physiologists for circulation measurements, was adapted to the measurement of phloem translocation rates in the wheat (Triticum aestivum L.) peduncle. The approach is based on the observation that, during the transport of a given amount of solute, its mean concentration will be inversely proportional to flow rate. For phloem transport in the wheat peduncle, the necessary measurements are (a) the time course of tracer kinetics in the peduncle phloem, (b) the volume of sieve tubes and companion cells in the monitored segment of the peduncle, and (c) the amount of tracer transported past that point. The method was evaluated by in situ monitoring of (32)PO(4) transport in pulse-labeling experiments. Specific activities (i.e.(32)P concentrations) of phloem exudate were in good agreement with those calculated from in situ count rates and measured phloem areas. Mass transport rates, calculated from volume flow rates and phloem exudate dry matter content, also agreed well with expected mass transport rates based on measurements of grain growth rate and net CO(2) exchange by the ear. The indicator-dilution technique appears to offer good precision and accuracy for short-term measurements of phloem transport rates in the wheast peduncle and should be useful for other systems as well. In contrast to velocities based on time-delay measurements, it is more precise, more accurate, and produces an estimate of mean, rather than maximum, velocity. Also, since only a single detector is required, it can be applied to very short transport paths.
一种用于测量流速的指示剂稀释技术，动物生理学家常用于循环测量，现已适用于测量小麦（Triticum aestivum L.）穗轴中的韧皮部运输速率。该方法基于这样的观察结果：在给定数量溶质的运输过程中，其平均浓度将与流速成反比。对于小麦穗轴中的韧皮部运输，必要的测量包括：（a）穗轴韧皮部中示踪剂动力学的时间进程；（b）穗轴监测段筛管和伴胞的体积；（c）通过该点运输的示踪剂数量。通过在脉冲标记实验中对（32）PO（4）运输进行原位监测来评估该方法。韧皮部渗出液的比活度（即（32）P浓度）与根据原位计数率和测量的韧皮部面积计算得出的结果高度一致。根据体积流速和韧皮部渗出液干物质含量计算得出的质量运输速率，也与基于籽粒生长速率和穗部净CO（2）交换测量得出的预期质量运输速率高度一致。指示剂稀释技术似乎为短期测量小麦穗轴中的韧皮部运输速率提供了良好的精度和准确性，并且对其他系统也应有用。与基于时间延迟测量的速度相比，它更精确、更准确，并且产生的是平均速度而非最大速度的估计值。此外，由于只需要一个探测器，它可以应用于非常短的运输路径。
