Circulation Patterns for Phosphorus, Sulfur and Calcium in the Bean Plant.

Abstract

Perhaps the earliest suggestion that soluble materials may make a circuit within a plant was made by Hartig (16). He concluded that materials assimilated in the leaves moved downward in the bark and were stored in the parenchyma and rays. In the spring these materials were brought into solution, passed into the trachea and ascended with the moving current of water. Atkins (1) expressed essentially the same views, and later the data of 'Mason and Maskell (20) indicated that such a circuit might be made without an intervening storage period. The latter investigators suggested that nitrogen, phosphorus, potassium, and other minerals ascended the stem primarily in the xylem, and any excess not currently used in the leaves was re-exported downward in the phloem. The ratios of N, P, and K to the carbohydrate moving downward in the phloem appeared to be in excess of that required for growth of the roots, so it was suggested that the excess was liberated into the xylem sap to re-ascend the stem. Biddulph (2) showed the rapidity of movement of phosphorus in the phloem of the bean plant and the possibility of a more or less continual circulation of this element throughout the plant. Helder (17) has confirmed the circulation of phosphorus in barley and bean plants. A free circulation of phosphorus is to be expected on the basis of its mobility in the phloem and its rapid metabolic turnover in many cellular reactions which serve to maintain a supply of inorganic phosphate in the cellular fluids.Prior to the work of Thomas et al (28) sulfur was considered to be relatively immobile in plants (Wood (29)), but the demonstration by Thomas et al of movement from the leaves on one stem of a multistemmed alfalfa plant downward to the crown and then upward in another stem, left little doubt of its mobility. Biddulph et al (5) showed sulfur to be freely mobile in the phloem of the bean plant, moving at rates comparable to other mobile substances. It is suspected that the earlier views of immobility may stem from the rapidity with which sulfur may be metabolically incorporated into newly formed protein, leaving little free to re-circulate. The present investigation is intended to test this concept.Calcium has been considered immobile in the phloem since the early investigations of the withdrawal of minerals from leaves prior to their abscission in the autumn (22). Bledsoe et al (9) recently provided a very direct demonstration of the immobility of calcium in the phloem of the peanut plant, and subse-

Estimation of Potassium Recirculation in Tomato Plants by Comparison of the Rates of Potassium and Calcium Accumulation in the Tops with Their Fluxes in the Xylem Stream

“…In the roots malate is decarboxylated to pyruvate and a negative charge is excreted from the plant as HCO3 in exchange for the uptake of a further N03-ion. This is consistent with the general observation that intact plants supplied with N03N almost always take up an excess of anions over cations (6,14,15 (3,5,10). Once Ca is translocated to the tops via the xylem pathway it is not redirected.…”

Effect of Water Movement on Ion Movement into the Xylem of Tomato Roots

“…Ca, however, is known to be less mobile in plant roots than P (3,19), and at the higlher pressures, Ca movement may have been less responsive to permeability changes than wvas Pimovement. Wlhether the increased rate of ion movement under pressure is the result of mass flow, increased diffusion, or increased active transport is not known. However, a more general explanation for the over-all increase in rate of salt movement can be suggested.…”

Effect of Phosphorus and Zinc Levels in The Substrate on 65Zn Distribution in Subterranean Clover and Flax

“…It has been shown by different workers, including Biddulph et al (1958) and Norton and Wittwer (1963), that phosphorus shows preferential movement into areas of high metabolic activity including the young leaves, stem apex, and root tips. These are the same general areas in which the highest concentrations of 66Zn were found in flax and subterranean clover, particularly when zinc was in deficient supply, and during the early development of zinc-deficiency symptoms.…”