Cytological effects of organophosphorus insecticides on Allium cepa root meristems.

Abstract

The use of organophosphorus insectiscides in current agricultural practices is steadily in creasing. The efficacy of these insecticides in the better exploitation of plant species of eco nomic importance is well known. However, the potentialities of these pesticides as mutagenic and/or carcinogenic agents to the non-target organisms, as has been demonstrated by several workers (Wuu and Grant 1966, Epstein and Legator 1971, Fishbein 1972, are worthy of ex tended studies and in greater depth. In this context four insecticides, viz. Dichlorvos , Mono crotophos (non-systemic), Phosalone and Oxydementonmethyl (systemic) are selected to assess their cytological effects on Allium cepa root meristems. Material and methodsRoot meristems raised from common onion (Allium cepa L., 2n=16) were used as assay system. Four insecticides tested in this study are Dichlorvos (0,0-dimethyl, 2, 2-dichlorovinyl phosphate), Monocrotophos (dimethyl phosphate of 3-hydroxy-N-methyl-cis-crotanamide) (non-systemic), Phosalone (0,0-diethyl S-(2-oxo-6-chloro-2H-benzoxyazolinyl-3) methyl phos phorodithioate) and Oxydemetonmethyl (0, 0-dimethyl S-(2-(ethyl suophinyl) ethyl) phosphoro thioate) (systemic). Prior to the initiation of the experiment treatment solutions were prepared by dissolving the test compounds (by volume) in 1-2 drops of acetone and subsequently diluting in distilled water. The range of test concentrations selected was below the cytotoxic threshold of each chemical (by LD 50 method) to the test system. Root meristems of 2-3cm length were exposed to the test solutions of different concentra tions for one hour followed by recovery periods of 0, 4, 12, 24 and 48hrs in Hoagland's nutrient solution adjusted to pH 7. Water controls were maintained simultaneously in order to com pare the spontaneous aberrations. After the exposure and recovery regimen the root tips were excised, fixed in 3:1 ethanol-acetic acid and stained by the Feulgen method (Darlington and La Cour 1976). For metaphase studies, both the treated and untreated material were pre treated with 0.05% colchicine for 21/2hrs, washed and fixed at the end of recovery schedule. For each variable 5-6 root tip squashes were made and a minimum of 600 cells at anaphase/ metaphase were counted in order to assess the clastogenic and turbagenic (Bragger 1979) manifestations. ObservationsThe effects of the different treatments with the four insecticides on the mitotic divisions in the root meristems of Allium cepa are given in Tables 1-5. As can be seen the Mitotic Index decreased with increasing concentrations in all the treatments.However, in case of Oxyde metonmethyl this trend was different at 200ppm concentration (see Table 5).

Cytogenetic Effects of Wastes of Copper Mine on Root Tip Cells of Allium cepa L.

“…As could be seen from Table 1, the mitotic index (MI) decrease with increasing concentration. Similar results were obtained after treating A. cepa root cells with insecticides, herbicides, pesticides and chemical mutagens (Rao et al, 1987;El-Khodary et al, 1989;Jain and Sarbhoy, 1987;Shanker et al, 1987). A drop of mitotic index indicates that copper wastes interferes in the normal sequences of mitosis.…”