Cation and anion balance in the xylem exudate of tobacco roots |
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Authors: | Arthur Wallace A M Abou-Zamzam E Motoyama |
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Institution: | (1) Soil Science and Agricultural Engineering, Riverside;(2) Present address: Agricultural Sciences, Univ. of Calif., 90024 Los Angeles, Calif. |
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Abstract: | Summary The sum of Na, K, Ca, Mg in the exudate of tobacco generally exceeded the sum of mineral anions. Insufficient organic acids
were present to account for the differences and bicarbonate appeared to be the other anion involved. Amino acids were present
in very low concentrations relative to mineral cations. When nitrate salts only were in the external solutions, the anions
were mostly, but not entirely, nitrate. When chloride salts only were in the external solutions, the cations far exceeded
the level of mineral anions in the exudate. It is postulated that nitrate is actively transported when nitrate salts are in
the external solution regardless of the cation, but when anions other than nitrate are in the external solution, the cations
are actively transported with the anions passively following. Nitrate transport was via a symplasm, but that of the other
anions seemed to be different. When bicarbonate is the only anion in the external solution and when present at relatively
high concentrations (5 × 10−3
M or higher), the volume of exudate is decreased. It appears that the organic acids which were synthesized as a result of the
bicarbonate absorption were not transferred to the xylem vessels. |
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Keywords: | |
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