Liquid-cultured primary roots of Yucca torreyi L. (Agavaceae), similar to its intact roots, develop uninterrupted files of calcium oxalate crystal idioblasts in their cortex, beginning just back of the terminal meristem. Each single file of idioblasts displays an 'ontogenetic' sequence acropetally. 14C-labeled glycolic acid, glyoxylic acid and ascorbic acid, potential precursors of oxalate were each added to different flasks, containing a sterile liquid root-growth medium and the isolated roots, and allowed to interact with the roots for 45 min. After thorough washing, the roots continued to grow for periods from 1.6-h to 24-h post incorporation. Autoradiography of root sections with the labeled ascorbic acid at the earlier incorporation times showed concentrations of silver grains over the idioblasts, and primarily over the vacuole crystal bundles and cytoplasmic plastids. The glyoxalic acid- and glycolic acid-labeled root sections showed a lesser amount of silver grains distributed over the entire sections, but not concentrated over the crystal idioblasts. These results strongly suggest that ascorbic acid is the primary precursor of oxalate in the crystal idioblasts of Yucca torreyi primary roots, and supports other recent biochemical data regarding oxalate synthesis in higher plants. The use of roots in liquid culture containing uninterrupted files of developing crystal idioblasts could serve as a model system for additional biochemical, physiological and molecular studies dealing with understanding the formation and functional significance of crystal idioblasts in higher plant organs.

Key words: ascorbic acid, autoradiography, crystals, culture, idioblasts, oxalate, roots, Yucca