Impact of some phytohormones, metabolic inhibitor and agrochemicals on senescing paddy leaves and its relevance to productivity

Abstract

The influence of hormones viz. Indole acetic acid (IAA), Gibberellic acid (GA3), Cytokinins viz. Benzyladenine (BA), Benzimidazole (BZI), biocides viz. 2,4-Dichlorophenoxy acetic acid (2,4-D), Diathane M-45, Dimecron and metabolic inhibitors viz. Cycloheximide (CHI) and Actinomycin-D (Act-D) on senescence in detached paddy (Oryza sativa L.) leaves was studied under dark and illuminated conditions. Cytokinins were found to be more effective senescence retardants in light than in dark while auxins were effective in light. Biocides proved to be milder senescence retardants. Effective concentration, a concentration away from the ineffective and toxic range, chosen from IAA, GA3, BA, BZI, 2,4-D, Diathane M-45 and Dimecron were 25,100, 5, 100, 25, 1500 and 0.50 ppm respectively. Application of Act-D (inhibitor of mRNA synthesis) with in 15 min after detachment and cycloheximide (inhibitor of cytoplasmic protein synthesis) from the start of the incubation resulted in suppression of peroxidase activity both under light and dark. Catalase activity exhibited an inverse relation with peroxidase activity under both the experimental conditions. It is recommended that attempts must be made in a more sophisticated way to study the changes in activities of different enzymes suspected to be linked with leaf senescence at a deeper level using all modern techniques available so that the exact nature of enzymes, the isoenzymes pattern and their relation with yield can be understood. Such studies may also help in future in manipulating the projects for the improvement of this economically important cereal crop.