Viability loss of neem (Azadirachta indica) seeds associated with membrane phase behaviour

Abstract

Storage of neem (Azadirachta indica) seeds is difficult because of their sensitivity to chilling stress at moisture contents (MC) > or =10% or imbibitional stress below 10% MC. The hypothesis was tested that an elevated gel-to-liquid crystalline phase transition temperature (Tm) of membranes is responsible for this storage behaviour. To this end a spin probe technique, Fourier transform infrared microspectroscopy, and electron microscopy were used. The in situ Tm of hydrated membranes was between 10 degrees C and 15 degrees C, coinciding with the critical minimum temperature for germination. During storage, viability of fresh embryos was lost within two weeks at 5 degrees C, but remained high at 25 degrees C. The loss of viability coincided with an increased leakage of K+ from the embryos upon imbibition and with an increased proportion of cells with injured plasma membranes. Freeze-fracture replicas of plasma membranes from chilled, hydrated axes showed lateral phase separation and signs of the inverted hexagonal phase. Dehydrated embryos were sensitive to soaking in water, particularly at low temperatures, but fresh embryos were not. After soaking dry embryos at 5 degrees C (4 h) plus 1 d of further incubation at 25 degrees C, the axis cells were structurally disorganized and did not become turgid. In contrast, cells had a healthy appearance and were turgid after soaking at 35 degrees C. Imbibitional stress was associated with the loss of plasma membrane integrity in a limited number of cells, which expanded during further incubation of the embryos at 25 degrees C. It is suggested that the injuries brought about by storage or imbibition at sub-optimal temperatures in tropical seeds whose membranes have a high intrinsic Tm (10-15 degrees C), are caused by gel phase formation.

Optimizing nursery and plantation methods to grow Cedrela odorata seedlings in tropical dry agroecosystems

“…However, an increasing number of tropical seeds hitherto classed as orthodox are being included in a third behavioral class, which is characterized by sensitivity to different combinations of water content and chilling during storage. These seeds may be damaged when stored at 10-15°C, particularly during the transition from a liquid crystalline to a gel phase which occurs in their membranes upon subsequent rehydration (Sacandé et al 2001). Our results confirmed that storage in paper bags under normal ambient conditions permits preserving the viability of C. odorata seeds for at least 6 months, which may be of particular interest to ensure a local supply of seeds given the unpredictable climatology of the dry tropics.…”

Triacylglycerol phase and ‘intermediate’ seed storage physiology: a study of Cuphea carthagenensis

“…1, 2; Crane et al 2003). The loss of viability of intermediate seeds during dry storage has been attributed to phase transitions or amphiphile partitioning within the aqueous portion of the seed (Sacande´et al 1998(Sacande´et al , 2000(Sacande´et al , 2001 ONSET TEMPERATURE (°C) in C. carthagenensis seeds as a function of the water content of the seeds. The onset temperature of the transition is reported and represents the average value (points) and standard deviation (error bars) for seeds stored at 5°C for 10-120 days (see representative scans in Fig.…”

Massive cellular disruption occurs during early imbibition of Cuphea seeds containing crystallized triacylglycerols

“…Crystallization and melting of storage lipids are completely reversible in dry seeds, as is evident from the routine storage of many crop species (so-called orthodox seeds) at liquid nitrogen temperatures (< ¡135°C; Stanwood and Bass 1981; Walters et al 2004). We have used principles developed from the imbibitional chilling injury literature (Crowe et al 1989;Hoekstra et al 2001;Sacandé et al 2001;Golovina and Hoekstra 2003) and from the freeze-desiccation damage literature (Crowe and Crowe 1992;Steponkus et al 1995) to hypothesize about the mechanisms of damage induced when seeds with crystallized triacylglycerols are imbibed (Crane et al 2003(Crane et al , 2006. These hypotheses may be explained by decompartmentalization within cells because of altered hydrophilic and hydrophobic interactions on the liposome membrane.…”