Calcium and Plant Growth

Abstract

Summary Calcium as a plant nutrient is characterized by its relatively high content in the plant coupled with a requirement not much higher than that of a micro nutrient element and an exceedingly uneven occurrence in soils. The difficulties in defining its actions are accentuated by a weak biochemical activity. In ecological conditions the secondary consequences of variations in calcium content may be more striking than the direct ones. Electron‐microscopical studies have revealed that calcium is required for formation and maintenance of lamellary systems in cell organellae, a fact which might suffice to explain its indispensability for meristematic growth. Calcium is required for cell elongation in both shoots and roots; the common experience that it inhibits shoot elongation is certainly due to calcium additions far above actual requirement. It must be assumed for a rational interpretation of cell elongation that the fundamental mechanism is the same in shoots and roots. The one action which can be ascribed with certainty to calcium is a stabilizing of the cell wall with an increase in rigidity, an effect which, with over‐optimal supply, may lead to growth inhibitions. The function is, however, necessary for the normal organization of cell walls. Calcium has, on the contrary, no significant effect on the synthesis of cell wall compounds but appears to act on their proper incorporation into the cell wall. The growth‐active calcium may be bound not only to pectins but also to proteins and nucleoproteids in or in close contact with the cell wall. The supposition that calcium interacts directly with auxin in the cell wall has not been verified and does not seem very probable. There are reasons to believe that the points of action of calcium and auxin in the cell wall differ, auxin inducing growth by wall loosening and calcium establishing new wall parts. For submerged organs it may be necessary to consider an indirect effect of calcium on growth by its regulation of cytoplasmic permeability and thus affecting the exudation of growth‐active compounds. The ecological problem is to characterize calcifuges (acid soil plants) from calcicoles (base soil or calcareous soil plants). Growth inhibitions on acid soils depend upon poisoning by A13+ and Mn2+. Opinions differ as to what extent this can be antagonized by calcium. Lime‐induced chlorosis in calcifuges depends upon iron deficiency or iron inactivation in the plant. No acceptable explanation is given, but it might be related to an interaction of calcium carbonate, phosphorus, and iron. A hypothesis that it is linked to formation of organic acids is not tenable in the given form. Plants react to the calcium ions in the concentrations found in soils. Calcifuges have a low calcium‐optimum for growth and show growth inhibition at high concentrations. Calcicoles have a high optimum for growth. Calcifuges are resistant to aluminium poisoning. Attempts made to explain the differences in calcium uptake and generally in salt uptake are tentative only, and relevant data are l...

Stimulation of Root Elongation and Curvature by Calcium

“…Ca2+-stimulated curvature of pretreated roots was 33.2 ± 1.8°in 4 h, whereas roots without pretreatment showed no curvature. The curvature of light-exposed roots was 46.2 ± 1.9° (Table IV).…”

“…Despite strong arguments that Ca" mediates inhibition of root growth (6,7,10,11), there is no consensus as to how, where, or when the cation has its effect (4,10,15). The proposed inhibitory action of Ca> has been emphasized particularly in studies of root gravitropism (7,(10)(11)(12).…”

Pectic Polysaccharide Breakdown of Cell Walls in Cucumber Roots Grown with Calcium Starvation

“…DISCUSSION Inasmuch as a high concentration of CaC12 has been observed to inhibit the breakdown of pectic polysaccharides in hypocotyl segments during in vitro incubation, Ca2" is known to be an inhibitor of cell wall loosening during growth process (14,18). One explanation for this inhibition was based on the production of a mechanical stiffening of cell walls, particularly pectic polysaccharide structure (5,23). Recently, another suggestion has been made (7) that Ca2' does not stiffen cell walls directly, and the inhibition of growth by Ca2+ is probably due to an inhibition of the biochemical wall loosening process such as an enzymic degradation.…”

“…Plant growth depends on the change in mechanical structure of cell walls, a process which could involve alterations in amount and/or structure of pectic polysaccharides serving structural elements of cell walls. For many years, the suggestion has been made (5,23) that the presence of Ca2l in the pectic polysaccharide matrix could be important in the strength of the cell wall structure (the Ca2l-bridge hypothesis) and for the inhibition ofthe breakdown of pectic polysaccharides during growth. In recent studies, Rees and co-workers (9,17,19) presented evidence that the cooperative binding of Ca2" in polygalacturonan in the pectic polysaccharide matrix was through 'egg-box' complexes with the polysaccharide chains.…”

Produtividade de amendoim em função da calagem e do método de secagem

“…O Ca é um dos fatores que influencia o crescimento dessas estruturas, já que interfere na divisão e no alongamento celular (Burström, 1968). Como esse elemento é absorvido pelas raízes e movimenta-se seguindo o fluxo transpiratório , a absorção foi favorecida pela maior superfície evaporante (maior área foliar) no tratamento com calcário (Tabela 2).…”