NUCLEAR CONDITIONS IN NORMAL STEM TISSUE OF VICIA FABA

Abstract

Previous cytological studies of plant tumors have been carried out on unsuitable material, and on the assumption that the normal tissues in which tumors are induced are exclusively diploid. The present study investigates the condition in normal stem cortex and pith of Vicia faba, in which tumors can be regularly induced through inoculation with pure cultures of Agrobacterium rubi. Mitoses were induced by treatment with indole-3-acetic acid, and it was found that a very considerable degree of polyploidy exists in both tissues. In the pith the percentage of polyploid mitoses increases with some regularity from the nodal to the mid-internodal region, where it may be as high as 50% of the total. In the cortex, the difference in this regard is less striking, but still exists. Both tetraploid and octoploid cells were found, the latter being less than 10% of the total. In both cases, there was usually close association of homologues in both pro- and metaphase, but in the cortex a considerable number of nuclei did not show this association. The pairing is at times accompanied by chiasma formation. These findings must be taken into account in studying the relation of polyploidy to tumor development.