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Experimental tests of the Münch–Horwitz theory of phloem transport: effects of loading rates *
Author(s) -
MAGNUSON C. E.,
GOESCHL J. D.,
FARES Y.
Publication year - 1986
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.1365-3040.1986.tb01572.x
Subject(s) - phloem , tracer , kinetics , chemistry , biophysics , mechanics , thermodynamics , botany , physics , biology , classical mechanics , nuclear physics
Extended square‐wave tracer kinetics using 11 CO 2 were used to measure the speed of transport and activity level (proportional to concentration) in the phloem at high and low loading rates in six species of plants. In all cases, increased loading rates resulted in increased concentration. In most cases speed also increased, however, in two cases speed was lower and tracer activity was much higher at the higher loading rate. All the responses are consistent with the Münch Horwitz theory of phloem transport, depending upon the equation used to represent the unloading mechanism as described in a previous paper (Goeschl & Magnuson, 1986). For example, the latter two cases are consistent with the assumption that the unloading rate was limited by a process with saturable kinetics (enzyme‐like).