Kenneth C. Eco and Beatriz S. Belonias
Calcium oxalate crystals are common constituents of plant tissues and are believed to play a role in protection against herbivory, calcium regulation and even heavy metal sequestration. In this study, calcium oxalate crystals in leaves of Colocasia esculenta were studied in order to elucidate the biomineralization process of these inorganic components in response to herbivory and different water regimes. Different crystal types occurring in the leaves of C. esculenta were identified, described and quantified in terms of density and distribution. Two general types of calcium oxalate crystals were found, namely: the raphides and druses. The raphides were of two types, the defensive and non- defensive, and both occurred as bundles of elongated crystals enclosed in specialized cells called idioblasts. Druses were spherical conglomerate crystals extensively distributed throughout the leaf. Although degree of herbivory did not significantly affect overall density of calcium oxalate crystals, there was a highly significant interaction effect between herbivory and crystal type. With increasing degree of herbivory from 10% to 30%, the density of druses and non-defensive raphides decreased significantly but that of the defensive type increased. Water availability had a highly significant effect on overall crystal density. Interaction effect between water regime and crystal type was also highly significant. Density of druses significantly increased under waterlogged than non-waterlogged conditions while those of the defensive and non-defensive raphides were unaffected.
Keywords: defensive raphides, non-defensive raphides druses, crystal density, idioblasts