An assessment of intermediate storage behaviour in Neem ( Azadirachta indica A. Juss) seeds

Abstract

Mature seeds of neem (Azadirachta indica A. Juss.), shed at 42.2% water content (wc), fresh weight basis exhibited 100% germination up to 15 days after harvest, and deteriorated on natural desiccation below 10.9% wc at ambient conditions. The seeds showed complete loss of viability after 20 weeks (5.9%wc) in storage. Seeds dried rapidly over silica gel to 7.1%wc could not only be cryopreserved but also showed high survival after one year of storage in liquid nitrogen. Our results suggest that neem seeds are desiccation-tolerant to this water content, but once further dehydrated, exhibit desiccation-sensitivity. An effort to understand the mechanism of desiccation-sensitivity below this water content revealed that loss of viability was closely associated with the over-accumulation of ROS and lipid peroxidation products (LPP) both in the embryonic axes and cotyledons. The antioxidant enzymes showed a differential expression in the embryonic axes of the desiccating seeds. Activities of catalase, ascorbate peroxidase and guaiacol peroxidase exhibited substantially higher levels in the 100% viable seeds dehydrated up to LSWC. Their activities declined sharply in the embryonic axis of seeds dried below LSWC. On the contrary a high level of superoxide dismutase was discernible in highly desiccated and low viability seeds aswell. Impairment of catalase and peroxidase activity probably led to high accumulation of ROS. Significant role of drying in loss of viability and vigour and role of ROS and antioxidant enzymes is discussed to explain the intermediate storage physiology of these seeds.