Reevaluation of the Effect of Calcium Ions on Auxin-induced Elongation

Abstract

The ability of high concentrations of calcium ions to inhibit cell elongation has long been recognized (1,13,20,21). This inhibitory effect has been rationalized (2,3,13,19) by assuming that calcium forms bridges between pectic carboxyl groups and that these bridges result in a mechanical stiffening of the wall which in turn prevents wall extension. The principal evidence for this theory consists of the demonstration by Tagawa and Bonner (19) that the ability of live Avena coleoptile sections to be deformed by an applied weight is reduced by pretreatment of the sections with CaC12. This bending technique, however, is not a reliable test of the wall's mechanical properties, as it is sensitive to changes in turgor, water permeability, and the activity of wall-loosening enzymes as well as to changes in the mechanical properties of the walls (7). The initial objective of this research, then, was to determine if calcium had a direct effect on the mechanical properties of cell walls, using a more definitive test, the Instron technique (5). Failing to find any significant effect of calcium on the mechanical properties of the walls, we then investigated four alternative mechanisms by which calcium might inhibit cell elongation: reduction in turgor pressure, reduction in auxin-induced H+ excretion, reduction in the capacity for the walls to undergo acid-induced wall loosening, and direct interference by calcium with the biochemical wall-loosening process. It will be shown that the growth-inhibitory effect of high calcium concentrations is most probably due to an inhibition by calcium of the biochemical wall-loosening process. MATERIALS AND METHODSThe plant material used in this study consisted of 10-or 14-mm sections cut from deleafed coleoptiles of Avena sativa, cv. Victory. Methods for growing the seedlings and harvesting the sections have been described (9). In some experiments the cuticle and epidermis were removed (peeled) from the sections with the aid of fine forceps (16). Elongation of live sections and acid-induced extension of frozen-thawed sections were measured by the procedure and apparatus of Rayle and Cleland (17). Since preliminary experiments confirmed earlier reports (13,19) that 0.02 M CaCl2 causes a maximal inhibition of cell elongation in nonpeeled sections and 0.002 M CaCl2 terminates growth in peeled sections (data not shown), these concentrations were used in all subsequent experiments unless otherwise noted.Hydrogen ion excretion2 experiments were carried out using groups of 10 peeled 14-mm segments. The sections were pretreated for 30 min in 1 mm K-phosphate buffer (pH 6.15

Phytochrome induces changes in the immunodetectable level of a wall peroxidase that precede growth changes in maize seedlings

“…3, the R and far-red light (FR) sources (source A) used were those described by Chen and Roux (11). Fluence rates of R were [8][9][10][11][12] jtmol/m2 sec; fluence rates for FR were 15-20 ,4mol/m2 sec.…”

“…3, the R and far-red light (FR) sources (source A) used were those described by Chen and Roux (11). Fluence rates of R were [8][9][10][11][12] jtmol/m2 sec; fluence rates for FR were 15-20 ,4mol/m2 sec.For the data in Fig. 3, R-irradiations were given in a 2-min pulse at 10-20 gmol/m2sec and measured by a quantum sensor (LI-185B; Li-cor, Lincoln, NE) by using a Schott KL1500 fiberoptic microscope illuminator (source B) filtered with a Schott RG610 filter.…”

Cell wall biosynthesis and the molecular mechanism of plant enlargement

“…Ca 2+ quenched part of the acceleration. Ca 2+ appeared to alter the biochemical wall-loosening in these structures (Cleland and Rayle 1977). Also like Chara, calcium chelators enhanced deformation of tomato (Lycopersicon esculentum Miller) epidermis when under tension, and Ca 2+ abolished the effect (Thompson 2005).…”

Calcium: A Central Regulator of Plant Growth and Development

“…Despite the attractiveness of the idea that cell wall Ca 21 achieves its effects through an interaction with pectates, it must be recognized that not all results can be easily accounted for by this explanation (Cleland and Rayle, 1977;Tepfer and Taylor, 1981). The failure to show a close correspondence between the ability of divalent cations to form a pectic gel with their ability to inhibit growth has led to a consideration of other ideas, for example, a direct affect of Ca 21 on cell wall modifying enzymes (Cleland and Rayle, 1977).…”

“…The failure to show a close correspondence between the ability of divalent cations to form a pectic gel with their ability to inhibit growth has led to a consideration of other ideas, for example, a direct affect of Ca 21 on cell wall modifying enzymes (Cleland and Rayle, 1977). It is important to keep in mind that within the complex framework of carbohydrates and proteins of the cell wall, there could be interactions between Ca 21 and molecules other than pectins that could contribute to cell wall structure and extensibility.…”