Temporal aspects of protophloem development in roots of Triticum aestivum L.

Abstract

Formation of protophloem cell-files, changes in cell length and the length of the division zone, number of mitotic cycles and duration of differentiation and nuclear degradation in roots of wheat ( Triticum aestivum L.) were studied. Protophloem cells are the narrowest and longest cells in the root. Their lengths at any site vary four-fold. Files of protophloem cells are formed at a distance of about 100 μm from the quiescent centre. Protophloem cells have time for only one or, rarely, two divisions. The inhibition of their transition to DNA synthesis occurs more distal than the inhibition of transition to division. Most cells start to differentiate from G 1. The duration of differentiation was determined by three methods. The average time from the exit of a cell from the mitotic cycle until nuclear degradation was found to be 15 hr and varied within the limits of the duration of one or two mitotic cycles. Nuclear degradation occurred most frequently in a single cell of a file at a distance of 430–590 μm from the root/cap junction. Nuclear degradation lasted 1.5–1.7 hr on average. The data obtained are discussed with special references to the problems of regulation of proliferation, differentiation and growth of root cells.