Assessment of dimethoate and malathion mediated toxicity on Solanum lycopersicum L

Nowadays organophosphate-based chemicals are most commonly used insecticides worldwide which are applicable to a wide range of crop plants. In this study, the effect of organophosphate insecticides, dimethoate (DM) and malathion (MT), was investigated on Solanum lycopersicum L. The seeds were germinated under in vivo conditions and after 1 month of germination, they were transferred to separate pots. Insecticides were applied in three different concentrations (X, 2X, and 4X) using a nozzle spray at 7-day intervals for 21 days where X was the recommended dose. After 21 days of treatment, the toxicological responses of plants were confirmed by evaluating the growth patterns, anatomical, photosynthetic pigments, expression of proteins, and antioxidant enzymes catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX). The study findings demonstrated that both DM and MT treatment resulted in adverse growth effects even at the initial recommended dose (X) of application. However, compared to MT, at 4X concentrations of DM, maximum decrease in plant height (43.43%), leaf length (43.16%), leaf width (41.09%), and total numbers of leaves per plant (50.57%) was observed. Plants subjected to higher doses of DM and MT showed a gradual reduction in chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids (67.25, 50.00, 62.03, and 41.04%, respectively, for DM and 61.75, 55.72, 59.87, and 41.04%, respectively, for MT). In addition, higher doses of these insecticides greatly disturbed micromorphology and protein contents. At high dose (4X) of treatment, the activities of CAT, GPX, and APX were found to increase by 14.01, 3.62, and 2.21 times the control value, respectively, for DM and 5.17, 2.53, and 1.46 times, respectively, for MT. Additionally, increased isoenzymes of CAT, GPX, and APX were demonstrated by nondenaturing PAGE and were also dependent on the concentrations of DM and MT. These results suggest that the isoforms of the antioxidant enzymes newly developed due to DM and MT excess may be used as biochemical markers for other crop plants grown under insecticide stress. This study provides insights into the biochemical mechanism associated with the toxicity caused to plants by the test insecticides.