Gould Nick, Thorpe Michael R, Minchin Peter E H, Pritchard Jeremy, White Philip J
University of Waikato, Department of Biology, Hamilton, New Zealand. Corresponding author; email:
University of Waikato, Department of Biology, Hamilton, New Zealand. Current address: Brookhaven National Library Chemistry Department, Upton, NY 11973, USA.
Funct Plant Biol. 2004 May;31(4):391-397. doi: 10.1071/FP03231.
This work relates solute import to elongating root cells in barley to the water relations of the symplastic pathway under conditions of varied plant K status. K is a major constituent of phloem sieve element (SE) sap, and as an osmoticum, it is believed to have a role in maintaining SE hydrostatic pressure and thus sap flow from source to sink tissue. The hypothesis that the solute import to elongating root cells is linked to pressure driven flow from the sieve tube is examined.Plants were grown in solutions containing either 0.05 mM (low K) or 2.05 mM (high K) K concentration. Solute import to the root elongation zone was estimated from biomass accumulation over time accounting for respiration and root elongation rate. SE sap K concentration was measured using X-ray microanalyses and osmotic pressure by picolitre osmometry. SE hydrostatic pressure was measured directly with a pressure probe glued onto an excised aphid stylet. Elongating root cell hydrostatic pressure was measured using a cell pressure probe.The low-K plants had lower SE K concentration and SE hydrostatic pressure compared to the high-K plants, but the elongating root cell hydrostatic pressure was similar in both treatments, thus the pressure difference between the SE and elongating root cells was less in the low-K plants compared to the high-K plants.The solute import rate to elongating root cells was lower in the low K plants and the reduction could be accounted for as a pressure driven solute flux, with a reduction both in the pressure difference between root sieve elements and elongating cells, and in the sap concentration.
这项研究在不同植物钾素状况的条件下，将大麦伸长根细胞中的溶质吸收与共质体途径的水分关系联系起来。钾是韧皮部筛管分子（SE）汁液的主要成分，作为一种渗透剂，它被认为在维持SE静水压力以及由此产生的从源组织到库组织的汁液流动中发挥作用。本文检验了伸长根细胞的溶质吸收与筛管压力驱动流动相关的假说。
将植物种植在钾浓度为0.05 mM（低钾）或2.05 mM（高钾）的溶液中。根据考虑呼吸作用和根伸长速率的随时间生物量积累来估算根伸长区的溶质吸收。使用X射线微分析测量SE汁液中的钾浓度，并通过皮升渗透压测定法测量渗透压。用粘贴在切除的蚜虫口针上的压力探针直接测量SE静水压力。使用细胞压力探针测量伸长根细胞的静水压力。
与高钾植物相比，低钾植物的SE钾浓度和SE静水压力较低，但两种处理下伸长根细胞的静水压力相似，因此与高钾植物相比，低钾植物中SE与伸长根细胞之间的压力差较小。低钾植物中伸长根细胞的溶质吸收速率较低，这种降低可以解释为压力驱动的溶质通量，根筛管分子与伸长细胞之间的压力差以及汁液浓度均降低。
