No abstract

Changes in soluble sugars in cauliflower seeds were followed during 50 h of imbibition in relation to desiccation tolerance Sucrose and stachyose contents decreased, and glucose and fructose accumulated This occurred in radicles first and subsequently in hypocotyls and cotyledons Loss of desiccation tolerance in the various seed parts coincided with an increase in glucose and fructose and the complete loss of stachyose, but sucrose content, the major sugar, was still high Drying imbibed seeds over silica gel did not evoke resynthesis of stachyose, but did increase sucrose and decrease glucose and fructose contents Seeds primed in solutions of 30% polyethylene glycol for 10 days showed a loss of stachyose, while sucrose remained high and glucose and fructose contents were still very low Redrying of primed seeds did not change the sugar contents The primed seeds were still tolerant of desiccation We conclude that stachyose is not a prerequisite for desiccation tolerance, but that sucrose may be We suggest that glucose and fructose may be involved in desiccation damage

No abstract

Effect of abscisic acid and slow drying on soluble carbohydrate content in developing embryoids of carrot ( Daucus carota L.) and alfalfa ( Medicago sativa L.) (1994). Effect of abscisic acid and slow drying on soluble carbohydrate content in developing embryoids of carrot ( Daucus carota L.) and alfalfa ( Medicago sativa L.). AbstractIn the presence of abscisic acid (ABA), contents of glucose and fructose decreased in carrot embryoids, whereas umbelliferose increased during dehydration The acquisition of desiccation tolerance was tested by scoring germinated embryoids It did not keep pace with the changes in soluble carbohydrate contents during development, which suggests that in these somatic embryoids di-and oligosacchandes are not the determining factors for anhydrobiosis However, on slow dehydration, umbelliferose increased, while sucrose decreased and the monosacchandes declined completely These changes were positively correlated with increased desiccation tolerance A similar analysis of slowly dried, ABA-treated alfalfa embryoids showed that stachyose and sucrose increased and the monosacchandes declined with the acquisition of desiccation tolerance These data support the contention that carbohydrates are involved in anhydrobiosis

Abscisic acid-pretreated carrot (Daucus carota) somatic embryos survive dehydration upon slow drying, but fast drying leads to poor survival of the embryos. To determine whether the acquisition of desiccation tolerance is associated with changes in the physical stability of the cytoplasm, in situ Fourier transform infrared microspectroscopy was used. Although protein denaturation temperatures were similar in the embryos after slow or fast drying, the extent of the denaturation was greater after fast drying. Slowly dried embryos are in a glassy state at room temperature, and no clearly defined glassy matrix was observed in the rapidly dried embryos. At room temperature the average strength of hydrogen bonding was much weaker in the rapidly dried than in the slowly dried embryos. We interpreted the molecular packing to be "less tight" in the rapidly dried embryos. Whereas sucrose (Suc) is the major soluble carbohydrate after fast drying, upon slow drying the trisaccharide umbelliferose accumulates at the expense of Suc. The possibly protective role of umbelliferose was tested on protein and phospholipid model systems, using Suc as a reference. Both umbelliferose and Suc form a stable glass with drying: They depress the transition temperature of dry liposomal membranes equally well, they both prevent leakage from dry liposomes after rehydration, and they protect a polypeptide that is desiccation sensitive. The similar protection properties in model systems and the apparent interchangeability of both sugars in viable, dry somatic embryos suggest no special role of umbelliferose in the improved physical stability of the slowly dried embryos. Also, during slow drying LEA (late-embryogenesis abundant) transcripts are expressed. We suggest that LEA proteins embedded in the glassy matrix confer stability to these slowly dried embryos.Desiccation tolerance is the capacity of an organism or tissue to regain vital metabolism after almost complete dehydration. Seeds, pollens, resurrection plants, mosses and ferns, nematodes, tardigrades, yeasts, fungi spores, and bacteria have this capacity (for review, see Crowe et al., 1992Crowe et al., , 1997aVertucci and Farrant, 1995).Carrot (Daucus carota) somatic embryos can be rendered tolerant to severe desiccation by a proper combination of treatments (Tetteroo et al., 1994(Tetteroo et al., , 1995(Tetteroo et al., , 1996(Tetteroo et al., , 1998. Addition of ABA at the proper stage of development, a sufficient slow-drying time (at least 4 d), and a subtle rehydration are the main requirements for the acquisition of desiccation tolerance. Fast drying within a few hours leads to an almost complete loss of viability. These rapidly dried somatic embryos have a considerably greater leakage of K ϩ and soluble carbohydrates than slowly dried embryos. The excessive leakage of cytoplasmic components upon rehydration is associated with irreversible changes in the plasma membranes. Formation of irreversible protein aggregates and an increased T m have been detected in plasma membranes isolated...