Regeneration of Meristematic Activity Following Decapitation of the Root Tip of Vicia Faba L.

SUMMARY The numbers of primordia and secondary roots present in the terminal 5 mm of roots of Vicia faba were scored over the 6‐day period following the removal of 2, 10 or 20 mm of the root tip and compared with the corresponding numbers found in 5‐mm long segments of intact roots which were 2–7, 10–15 and 20–25 mm basal to the tip of the meristem at the start of the experiment (C2 segments). 144 h following decapitation the numbers of laterals emerging from the apical 5 mm of each batch of decapitated roots were greater than those in the corresponding C2 segments, the greater number in this part of the former roots reflecting the emergence of secondary roots through the cut surface at the stump apex in addition to those emerging laterally. The time course for complete secondary root formation in the apices of each batch of decapitated roots was no different from that in the intact controls. In contrast to the changes which took place at the root apex following the removal of 2 mm or more of tissue, the removal of the apical 0.5 mm of the root in addition to the cap resulted in regeneration of a meristem from the proliferating cells which remained behind at the time of decapitation. The latter type of regeneration was investigated by following the changes which took place in mitotic index, labelling index and the relative proportions of interphase nuclei with different amounts of DNA in the apical 2 mm of roots from which the apical 0.5 mm of the meristem had been removed over the 144 h period between decapitation and the resumption of normal root growth.