The suppression of meiosis and the origin of diplochromosomes

Abstract

The effects of abnormal temperatures on the meiotic divisions in various plants have been investigated by Sax (1937), Straub (1938), Matsuura (1937) and others. The effects which they have described arise in two ways: (1) by prevention of the pachytene pairing and subsequent chiasma formation in the chromosomes, and (2) by inhibition of the action of the spindle. In the first case we have a development very similar to that described in numerous hybrids, which can be adequately understood in terms of the irregular behaviour of univalents. They may, for instance, give rise to restitution nuclei at the end of the first division, and divide equationally at the second to give diploid pollen grains (Sax on Rhoeo 1936, and Tradescantia 1937). The suppression of the spindle gives rise to similar effects in the pollen grains. Separation of the bivalents and wall formation are affected so that diploid and tetraploid grains are formed as well as many unbalanced types. The present paper gives an account of a new type of derangement produced by high temperatures. In addition to the upset of developmental processes external to the chromosomes, as in the above cases, the internal development of the chromosomes is affected, so that a nucleus at early diplotene changes directly into a pollen-grain resting nucleus.