Morphological Changes and Function of Calcium Oxalate Crystals in Eddo Roots in Hydroponic Solution Containing Calcium at Various Concentrations

Abstract

Morphological changes and function of calcium oxalate crystals in eddo roots in hydroponic solution containing calcium at various concentrations were investigated. Bundles of needle-shaped crystals in crystal idioblasts were tubularly arranged in the peripheral part of cortex in the apical zone of primary roots. Under scanning electron microscopy and optical microscopy, crystals in the idioblasts of roots cultured in 1 mM calcium nitrate solution were larger than those in 0 mM calcium solution but smaller than those in the solutions containing either 15 mM calcium nitrate or 15 mM calcium chloride. The number and area of crystal bundles in the sections of the apical zone in 1 mM calcium nitrate solution were significantly larger than those in 0 mM calcium solution and smaller than those in the solutions containing 15 mM calcium. The calcium mapping image obtained by energy dispersive X-ray spectrometry showed that the amount of calcium in crystal idioblasts was increased with increasing calcium concentration in the solutions. However, the weight percentage of calcium per cortex parenchyma cell in root apical zone did not vary significantly with the concentration of calcium in the solutions. In the root zone apart from the root apex having no crystals, the weight percentage of calcium per cortex parenchyma cell in the solutions containing 15 mM calcium was significantly higher than that in either 0 mM calcium or 1 mM calcium nitrate solution. These results suggested that the crystals in the tubular arrangement participated in the regulation of calcium levels in the apical zone of primary roots.