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STUDIES ON THE LEAF OF AMARANTHUS RETROFLEXUS (AMARANTHACEAE): QUANTITATIVE ASPECTS, AND SOLUTE CONCENTRATION IN THE PHLOEM
Author(s) -
Fisher David G.,
Evert Ray F.
Publication year - 1982
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1982.tb13386.x
Subject(s) - phloem , sieve tube element , sieve (category theory) , biology , botany , lamina , anatomy , biophysics , mathematics , combinatorics
The vascular system of the leaf of Amaranthus retroflexus L. was examined quantitatively, and plasmolytic studies were carried out on it to determine the solute concentration in cells of the phloem at various locations in the leaf. The proportion of phloem occupied by sieve tubes varies considerably with vein size and leaf size. Collectively, the cross‐sectional area of sieve tubes of all tributaries at their points of entry into either a secondary or midvein far exceeds the total cross‐sectional area of sieve tubes at the bases of those major veins. In addition, the total volume of sieve tubes in the “catchment area” of a secondary vein is much greater than total sieve‐tube volume of the secondary vein itself. The plasmolytic studies revealed the presence of positive concentration gradients in the sieve tubes of the lamina from the minor veins and tips of the secondaries to the bases of the secondaries and from the tip to the base of the midvein. The C 50 (the estimated mannitol concentration plasmolyzing, on the average, 50% of the sieve‐tube members) was 1.5 m for minor veins and tips of secondary veins and 1.1 m for the bases of secondaries; 1.3 m for the tip of the midvein and 0.6‐0.7 m for the midvein in the basal third of the lamina.