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Chemically induced aneuploidy in higher plants.

Although there is extensive literature reporting aneuploidy in plants there has been little consideration of the mechanisms of induction of the observed changes in chromosome number and the role of environmental agents in its induction. This paper collates and analyses the literature on aneuploidy induction in plants with the aim of identifying the mechanisms involved. Many of the major events that occur during cellular segregation, such as respiration, spindle and phragmoplast functions and chromosome doubling, appear to be stressed by agricultural chemicals, drugs, natural and industrial products, leading to aneuploidy in both the mitotic and meiotic cells of approximately 60 plant species. Of the nearly 400 chemicals at present suspected to be aneugenic to plants, approximately 150 are agricultural chemicals, 60 are drugs, 60 are natural substances and 50-60 are industrial products. Nearly half of these agents were reported to affect spindle mechanisms in mitosis and meiosis. About 60 affected phragmoplast function in root meristems. Another 60 chemicals appear to modify chiasma frequencies. Nearly 40 chemicals appear to be clastogenic in such a way that could lead to aneuploidy by a secondary mechanism. About 45 plant species exhibit aneuploidy without any apparent cause or source of stress. This could arise from several metabolic and anthropogenic causes operating alone or together such as: (i) the nutritional status of the soil, (ii) irrigation by polluted water, (iii) the ageing of seeds, (iv) pathogenesis of plants, (v) cryptotoxins in plants, (vi) pesticide applications and (vii) pesticide residues. Environmental factors such as pH and temperature may further compound these stresses. Among the biota, plant systems alone seem to possess all the components to monitor every conceivable type of aneuploidy and respond to all kinds of stress in our environment. There are deficiencies in the work hitherto carried out which need to be rectified. Some aspects have to be reinvestigated with improved protocols. For a perspective understanding of the phenomenon of aneuploidy, so vital to human systems, it is imperative that we devise new approaches, some of which are outlined here.