Downregulation of γECS gene affects antioxidant activity and free radical scavenging system during pod development and maturation in Lablab perpureus L

Abstract

Fruit development and maturation has been recognized as an oxidative phenomenon, which results in the generation of reactive oxygen species (ROSs). Plants cells contain several antioxidants which help to retained these ROS at low level by indulging them to enter in signalling pathways. The present work describes, the changes occurring in the components of enzymatic antioxidant defence systems during pod development and maturation in two hyacinth bean varieties viz. VRSEM-3 and VRSEM-8, which differ in their pod qualities. The experiment was conducted in randomized block design with three replications and pod samples were collected at the following day post anthesis (DPA) stages: immature (15 DPA), mature (25 DPA) and over mature (40 DPA). Activities of catalase (CAT) and ascorbate peroxidase (APX) reduced up to 1.5/2.0 folds, respectively, during the subsequent stages of pod maturation, indicating a higher accumulation of reactive oxygen species (ROSs) at the latter stages. Glutathione reductase (GR) and superoxide dismutase (SOD) activities decreased progressively during pod development in VRSEM-3 which continued towards the end of maturation as pods turn to the over-mature stage. The role of glutathione-mediated free-radical scavenging was also investigated at transcriptional level, as a plausible system for coping with oxidative stress. The transcript level of γECS (glutamylcysteine synthetase) gene remained relatively constant at the immature and mature stages, whereas it sharply decreased about 15–30 folds at the over-mature stage in both the varieties, which correlated well with the subsequent decrease in the levels of enzymatic antioxidants. Hence, the present study confirmed that the glutathione mediated free radical scavenging system was down-regulated at over-mature stage, conceivably in response to the growing oxidative stress resulting from the inflation of reactive oxygen species, increased solid content and concomitant with a decline in enzymatic and non-enzymatic antioxidants towards the end of maturation.