Esterase isozyme degradation and ROS-mediated protein oxidation as indicators of ageing induced seed deterioration in onion (Allium cepa L.)

Abstract

Saturated NaCl salt-induced accelerated ageing is a critical marker test for assessing the physiological viability and vigour of small-seeded, high–value crops with poor storability, such as onions. This study aimed to fill existing knowledge gaps in the biochemical changes associated with onion seed ageing and their impact on germination. The current investigation was conducted in Punjab Agricultural University, Ludhiana, Punjab, India. Seeds were aged in plastic chambers under controlled conditions (42 ± 2°C and 75 ± 1% RH) for 0, 12, 24, 48, 72, 144 and 288 hours. A 72-hour ageing treatment reduced germination to 50%, effectively producing low-vigour seeds, while 288-hours ageing resulted in complete loss of viability. Seed deterioration was primarily driven by increased malondialdehyde accumulation and moisture content along with loss of membrane integrity. Decline in germination and an increase in abnormal seedlings were linked to reduced activities of key viability enzymes—dehydrogenase and α-amylase—impairing reserve mobilization. Electrophoretic analysis demonstrated substantial degradation of esterase bands (Rf 0.39 and 0.45) and low molecular weight proteins (25–29 kDa) during prolonged ageing of onion seeds. Simultaneously, spectrophotometric and zymographic analysis revealed reduced activities of chief enzymatic antioxidants such as catalase and peroxidase in conjunction with elevated levels of malondialdehyde and advanced oxidation protein products following prolonged ageing, indicating a diminished capacity of aged seeds to neutralize reactive oxygen species due to inadequate antioxidant capacity. The findings of study suggest that esterase isozyme profiling may serve as a potential biochemical marker for assessing seed viability and vigour.