Use of Psychotria punctata Callus in Study of Calcium Oxalate Crystal Idioblast Formation

Abstract

Summary Callus derived from Psycbotria punctata VATKE, grown on a modified Linsmaier and Skoog agar medium in the dark, produces calcium oxalate raphide crystal idioblasts. The callus was used to study factors involved in calcium oxalate crystal idioblast formation. The synthesis of oxalate in the callus was also explored. The number of crystal idioblasts formed per unit volume of callus varied directly with calcium concentration of the medium. Adding oxalate to the medium decreased the number of idioblasts probably because of calcium precipitation. During induced exogenous calcium deficiency, when calcium was absent, the callus lost crystals that had formed prior to the deficiency. L-ascorbic acid, an oxalate precursor in some plants, stimulated idioblast formation when added to the medium at low concentrations. At higher concentrations it inhibited idioblast formation. Lycorine, an inhibitor of L-ascorbic acid synthesis, had no substantial effect on idioblast formation. Allopurinol (4-hydroxypyrazolo [3,4-d] pyrimidine) and α-HPMS (2-pyridylhydroxymethanesulfonic acid), both inhibitors of enzyme-catalyzed reactions capable of converting glycolate or glyoxylate to oxalate, caused a large decrease in idioblast formation. Crystal idioblast formation and growth were inhibited as callus turned green in light. The results show that Psycbotria callus is useful in studying the factors controlling induction and development of crystal idioblasts. The availability of calcium and oxalate, and idioblast initiation are definitely related. Glycolate and/or glyoxylate are the probable precursors of oxalate in the callus, although metabolism of exogenously supplied L-ascorbic acid may also give rise to oxalate.