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Low‐temperature pretreatment of the root system of Brassica rapa L. plants: effects on the xylem sap exudation and on the nitrate absorption rate
Author(s) -
BIGOT J.,
BOUCAUD J.
Publication year - 1994
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1994.tb00164.x
Subject(s) - xylem , exudate , shoot , transpiration , nitrate , brassica , chemistry , botany , brassica rapa , horticulture , biology , photosynthesis , organic chemistry
Brassica rapa plants were exposed for a 52 h period (as pretreatment) to a differential temperature (DT) between roots (5°C) and shoots (20°C), while control plants were maintained with both shoot and roots at 20°C (warm grown = WG). Measured at 20°C, volume flow of xylem exudate from roots of DT plants was enhanced compared with that from WG plants, while transpiration flows were similar in pretreated and control plants. Both transpiration and exudation flows were dependent upon shoot/root ratio. Differences in the volume flow of exudate were principally related to increases in root hydraulic conductance. Anion fluxes (notably nitrate) into xylem exudate of DT plants were significantly greater than those into exudate of WG plants. This enhancement of nitrate flow from the pretreated roots was associated with a two‐fold increase in nitrate uptake rate. The relationship of the cold‐induced change in nitrate uptake capacity with shoot/root ratio is discussed in terms of control of nitrate absorption by shoot sink strength.