A set of proteins that accumulates late in embryogenesis (Lea proteins) has been hypothesized to have a role in protecting the mature seed against desiccation damage. A possible correlation between their presence and the desiccation tolerant state in soybean seeds (Glycine max L. Chippewa) was tested. Proteins that showed the same temporal pattern of expression as that reported for Lea proteins were identified in the axes of soybean. They were distinct from the known storage proteins and were resistant to heat coagulation. The level of these "maturation" proteins was closely correlated with desiccation tolerance both in the naturally developing and in the germinating seed: increasing at 44 days after flowering, when desiccation tolerance was achieved, and decreasing after 18 hours of imbibition, when desiccation tolerance was lost. During imbibition, 100 micromolar abscisic acid or Polyethylene glycol-6000 (-0.6 megapascals) delayed disappearance of the maturation proteins, loss of desiccation tolerance, and germination. During maturation, desiccation tolerance was prematurely induced when excised seeds were dried slowly but not when seeds were held for an equivalent time at high relative humidity. In contrast, maturation proteins were induced under both conditions. We conclude that maturation proteins may contribute to desiccation tolerance of soybean seeds, though they may not be sufficient to induce tolerance by themselves.Like sugars, specific proteins are known to accumulate during late seed maturation (4,12,15), and some of these same proteins accumulate during drought stress of vegetative tissue (5,19). A role for this class of "late embryogenesis accumulating" (Lea) (9) or "maturation" (25) proteins in protecting against desiccation-induced damage has been proposed (2, 9) but correlations between protein level and desiccation tolerance have been reported only in developing barley seeds (3).The aim of this work is to test the correlation between levels of proteins that show this temporal pattern of expression (herein referred to as maturation proteins) and the desiccation tolerant state in soybeans (Glycine max [L.] Chippewa). Seeds gain and lose the ability to tolerate desiccation at identifiable points during maturation (3, 7) and germination (16). We have examined an array of proteins in soybean characterized by stability to heat coagulation, a characteristic of hydrophilic, ABA-responsive proteins (14, 23). We report here that the occurrence of certain of these proteins is correlated with desiccation tolerance in naturally maturing and germinating tissue. The levels of these maturation proteins can be experimentally manipulated by ABA or osmotic stress during imbibition as well as by premature drying during development. Their presence in all desiccation tolerant soybean tissue is consistent with a possible role in conferring tolerance. MATERIALS AND METHODSWe are interested in the mechanisms that confer to seeds the ability to survive extreme desiccation. Accumulation of certain sugars, a char...
The consistent correlation between desiccation tolerance in orthodox seed tissue and an accumulation of certain “late embryogenesis abundant” (LEA) proteins suggests that these proteins reduce desiccation‐induced cellular damage. The aim of the present work was to test this hypothesis. Exogenous abscisic acid (ABA) was used to elevate the level of heal‐soluble LEA‐like proteins in axes from immature (30 days after flowering: mid‐development) seeds of soybean (Glycine max [L.] Merrill cv. Chippewa 64). As the LEA‐like proteins accumulated in response to ABA, the leakage of all elements after desiccation and subsequent rehydration markedly declined. Both LEA‐like protein accumulation and the decline in desiccation‐induced electrolyte leakage were apparently dependent on the presence of ABA. Both effects of ABA were inhibited by cycloheximide. Light microscopy revealed a marked effect of the ABA on cellular integrity following desiccation. Osmotic stress also caused a decrease in desiccation‐induced electrolyte leakage and stimulated the accumulation of LEA‐like proteins. Our data are consistent with the hypothesis that the LEA‐like proteins contribute to the increase in desiccation tolerance in response to ABA, and are consistent with a general protective role for these proteins in desiccation tolerance.
The present work examines the requirement for RGD-binding sites, such as those in the plasma membrane protein integrin during somatic embryogenesis in carrot (Daucus carota L. cv. Scarlet nantes). It is possible to assay for this requirement by competitively inhibiting binding of the site to the natural RGD-containing ligand by adding an excess of synthetic RGDS. We found that treatment of carrot callus cultures with RGDS (2.7 mM) inhibited the development of a normal shoot pole in carrot somatic embryos. The structures that formed contained separate zones of highly cytoplasmic and vacuolate cells and no evidence of embryonic organization, although occasionally a root-like structure was observed. If the aspartic acid residue in the peptide was replaced by a chemically similar amino acid (glutamic acid), the resultant somatic embryos were indistinguishable from those developing in untreated cultures. These effects are similar to those reported in animal systems where the protein receptor involved has been identified as integrin. Our results are thus consistent with the conclusion that a binding site for a motif similar to the integrin-binding site in a variety of animal extracellular matrix proteins exists in plants and appears to be important in somatic embryo development in carrot.
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