Is oxidative stress involved in the loss of neem (Azadirachta indica) seedviability?

Neem (Azadirachta indica) is a valuable multipurpose tree of tropical arid and semi-arid regions. The use of its seeds is hindered by their short stor age longevity. The possible causes of rapid loss of viability were investig ated on different seed lots during exposure to 32% and 75% RH at 20 degrees C. Within 6 months the seeds almost lost germinability at 75% RH, whereas a t 32% RH viability decreased only slightly. On rehydration, the axis cells from nongerminable seeds had lost turgor, whereas those from viable seeds w ere turgescent as visualized by low temperature scanning electron microscop y images of fractured axes. Glutathione oxidation status was used to estima te oxidative stress during storage. Oxidative stress was much higher at 75% RH storage than at 32% RH, mainly caused by the rapid loss of reduced glut athione at 75% RH. Oligosaccharides and phospholipids decreased, and free f atty acids increased during storage at the high RH but remained at a consta nt level at the low RH. However, the degree of fatty acid unsaturation betw een viable and nonviable seed lots was similar. During the (slow) dehydrati on of fresh seeds, total glutathione, oligosaccharides and phospholipids ac cumulated, particularly in the initially more hydrated seeds. We interpret this accumulation as a post-maturation process associated with acquisition of the capability for long-term survival in the dry state. The mass ratio o f oligosaccharides to sucrose was 0.19 on average in dehydrated neem seeds. The data suggest that the storage behaviour of neem seeds has features tha t characterize it as orthodox.