Sodium and Potassium Absorption by Bean Stem Tissue

Abstract

Abstract. The effect of various periods of pretreatment in CaSO4 solutions (aging) on the absorption of Na and K by bean stem slices was investigated. Freshly sliced tissue absorbed Na over the entire range of concentrations studied (0.02-50 mM). Potassium absorption by fresh tissue was nil at concentrations below 0.5 mM but at higher concentrations was similar to that of Na. When tissue was aged 'by aerating slices for 20 hr in 0.5 mm CaSO4, K absorption was substantia,l over the entire range (0.01-50 mM), with evidence of a dual mechanism of absorption, whereas Na absorption was nil at concentrations below 0.2 mm. The formation of K-absorbing capacity with aging, and the loss of Na-absorbing capacity at low concentrations, were temperature-dependent and did not result from significant changes in rates of efflux of either ion. The absorption of Na by fresh tissue and K by aged tissue was sensitive to antimetabolites, with K uptake the more sensitive. Benzyladenine, an analog of kinetin, suppressed the formation of K-absorbing capability in aged tissue but did not prevent the 4loss of Naabsorbing oapacity. Possible mechanisms for this alteration in ion-specificity of transport mechanisms are discussed.

Induction and Development of Increased Ion Absorption in Corn Root Tissue

“…The apparent Km values do not change significantly with washing. This result is like that of Liittge and Laties (15) for corn roots, but is unlike that obtained with some other vegetative tissues (7,8,20,24,25). In corn roots the enhancement of accumulation rate must lie not with the formation of different and more efficient transport agents (or carriers), but rather with a greater quantity or a greater turnover of existing agents.…”

“…Hence, the development of increased absorption rates does not involve any detectable change in dependence on respiratory metabolism. (8,18,19,24,26). The greatest inhibition, however, was secured with the antiauxin, 2,4, 6-T. We checked the auxin properties of the 2,4,6-T in cucumber radicle growth inhibition: at 10 /.M the 2,4, 6-T gave 11% inhibition while the same concentration of 2,4-D gave 64% inhibition.…”

“…Rains (24) showed that washing bean segments induced a high affinity potassium-absorbing mechanism; concurrently sodium absorption rates declined. The induction was temperature dependent and sensitive to metabolic inhibitors and could not be explained by changes in efflux rates of either K+ or Na+.…”

Sodium Absorption by Intact Sugar Beet Plants

“…Such an observation would seem to be easily explained by assuming that the second mechanism (operating at Na concentration higher than 1 meq/liter) is not active in Na absorption during early stages of growth (3). The characteristics of ion absorption can change considerably under artificial conditions, i.e., aging (10,15). Rains (15) reported that in freshly sliced bean stem tissue, mechanisms 1 and 2 operate for Na absorption; when the tissue is aged, Na transport is mediated only by mechanism 2. The inability of the second mechanism to absorb Na during the early period of growth could be due to the lack of Na transport to the shoots until the plants are beyond the 10-leaf stage.…”

“…The characteristics of ion absorption can change considerably under artificial conditions, i.e., aging (10,15). Rains (15) reported that in freshly sliced bean stem tissue, mechanisms 1 and 2 operate for Na absorption; when the tissue is aged, Na transport is mediated only by mechanism 2. The inability of the second mechanism to absorb Na during the early period of growth could be due to the lack of Na transport to the shoots until the plants are beyond the 10-leaf stage. It was reported that in the long distance transport ions behave differently depending on their concentration, i.e., system 1 or system 2 ranges (9).…”