A study of water relations in neem (Azadirachta indica) seed that is characterized by complex storage behaviour

Neem (Azadirachta indica) seed is reputed to have limited tolerance to desi ccation, to be sensitive to chilling and imbibitional stress, and to displa y intermediate storage behaviour. To understand this behaviour the properti es of water in seed tissues were studied. Water sorption isotherms showed t hat at similar relative humidity (RH), the water content was consistently h igher in axes than in cotyledons, mainly due to the elevated lipid content (51%) in the cotyledons. Using differential scanning calorimetry, melting t ransitions of water were observed at water contents higher than 0.14g H2O g (-1) DW in the cotyledons and 0.23 g H2O g(-1) DW in the axes. Beside melti ng transitions of lipid, as verified by infrared spectroscopy, changes in h eat capacity were observed which shifted with water content, indicative of glass-to-liquid transitions. State diagrams are given on the basis of the w ater content of seed tissues, and also on the basis of the RH at 20 degrees C, Longevity was considerably improved, and the sensitivity to chilling/su bzero temperatures was reduced when axis and cotyledons were dehydrated to moisture contents less than or equal to of approximately 0.05 g H2O g(-1) D W, However, longevity during storage at very low water contents was limited . A possible mechanism for the loss of sensitivity to chilling/subzero temp eratures at low water contents is discussed. the results suggest that dry n eem seeds in the glassy state have great potential for extended storability , also at subzero temperatures.