Microtubules and Sieve Plate Development in Differentiating Protophloem Sieve Elements ofTriticum aestivumL.

Abstract

Sieve plates of root protophloem of wheat differentiate from the end walls of very young sieve elements. Sieve pore development from single plasmodesmata is associated with small quantities of callose Cortical microtubules overlie the lateral walls of differentiating sieve elements in abundance, but they are entirely absent from the end walls which differentiate into sieve plates Microtubule populations of the lateral walls only extend up to the corners between the lateral and end walls. The microtubule features (abundance, distribution, orientation) were also investigated in some deviating patterns of sieve element arrangement Some cells of the companion cell files differentiate into sieve elements instead of companion cells A portion of the lateral wall between a normal and a deviating sieve element becomes a sieve plate. Like the normal end-wall sieve plates, these wall parts, which normally would be overlain by numerous microtubules, are not accompanied by any microtubules