Active oxygen species metabolism in neem (Azadirachta indica) seeds exposed to natural ageing and controlled deterioration

Success of ex situ storage of germplasm for trade and conservation essentially depends upon the precision of the protocol employed for the assessment of germination potential. Active oxygen species and antioxidative enzymes during natural ageing (NA) and controlled deterioration (CD) was monitored during the loss of seed vigour and germination potential in neem seeds showing intermediate seed storage behaviour. Higher levels of SOD, CAT and APX were strongly and positively associated with germination and vigour. The loss of CAT and APX activity estimated quantitatively and number of isoenzymes were closely accompanied with the simultaneous increase in the amounts of H2O2 and OH-radical. The decline in germination and vigour was negatively related with the levels of H2O2 and OH-radical and enhanced electrolyte leakage. The amounts of OH-radical were positively correlated with the decline in DNA content and DNA damage. The levels of SOD isoenzymes initially increased as the germination index of seeds declined from 5250 to 762 and 882 under NA and CD conditions, respectively. Increasing activity of SOD in the ageing seeds were associated with the accumulation of H2O2. The role of antioxidative enzymes in maintaining signalling and damaging amounts of AOS as well as revelations of different pathways of ageing during NA and CD in the ageing neem seeds were discussed.