2019 年 88 巻 4 号 p. 499-506
Plants produce a variety of crystals with different shapes and sizes. Based on their appearance, calcium oxalate crystals, especially raphides, have been suggested to play a key role in the defense mechanism against insect attack and microbial infections. Colocasia esculenta, a tropical plant primarily grown for its edible corms contains a large number of cells (idioblasts) with needle-like crystals of calcium oxalate (i.e., raphides). The concentration of raphides in the plant varies with the ploidy level, cultivar, organ, and micro environment. The objective of this study was to evaluate the physiological, organic and inorganic biochemical changes in the differentiated leaves of elephant ear (Colocasia esculenta var. aquatilis) and examine the rate of release of these compounds in water soluble forms. Regarding photosynthetic functions, the net photosynthetic rate (Pn) was positively related to light intensity, especially in fully expanded and old leaves. However, the Pn, transpiration rate (E), and stomatal conductance (gs) in young leaves were lower than those in fully expanded and older leaves, resulting in low levels of total soluble sugar content in both the petioles and leaf blades of young leaves. In contrast, oxalic acid and calcium in both petioles and leaf blades peaked at > 2.0 mg·g−1 FW and ~185 mg·g−1 FW, respectively. A large number of idioblasts (~5.5 idioblasts per observed microscopic field) were observed in young leaves. Oxalic acid and calcium ions extracted from the leaf tissues were rapidly dissolved in hot water (85°C) for 10–15 min, leading to a decline in the number of idioblasts. Based on these results, petioles and leaf organs of elephant ear may be eaten safely after boiling in hot water for 15 min to dissolve CaOx.
