Developmental Biochemistry of Cottonseed Embryogenesis and Germination

Abstract

The synthesis of the principal cottonseed storage proteins during embryogenesis has been foUlowed by analyses of stained protein gels and of fluorographs of protein synthesized in vivo and from purified RNA in vitro in the wheat germ system. The kinetics of in vivo labeling as well as immunochemical cross-reactivity indicate that the 52-and 48-kiLodalton mature storage protein sets are derived from 70-and 67-kilodalton precursor protein sets that are abundant proteins in embryonic cotyledons and disappear in late embryogenesis. Identification of the initial translation products of the storage protein mRNA has not been clearly established although products of apparent molecular weights of 69,000 and 60,000 are the likely storage protein precursors.Storage protein synthesis falls off markedly in late embryogenesis simultaneously with the loss of a superabundant class of mRNAs (shown by cDNA:RNA reassociation) that are presumed to be those for the storage proteins. The synthesis of these proteins ceases abruptly when immature embryos are removed from the boll and allowed to germinate precociously or when this precocious germination is prevented by incubation in abscisic acid. Thus, abscisic acid is not implicated in the expression of the storage protein genes.A scheme involving co-translational processing into vesicles, glycosylation, and slow in situ cleavage to produce the mature storage proteins is proposed.We have attempted to follow during embryogenesis the synthesis of the principal storage proteins of cotton cotyledons which were identified and partially characterized in the preceding paper (8). The accumulation of these proteins (and their precursors) was followed by the 2D2 electrophoresis of proteins extracted at intervals during embryogenesis. To follow their synthesis, the incorporation of radioactive amino acids into them in intact cotyledons was assessed by the fluorography of 2D protein gels (in vivo synthesis) and estimates of the levels of their mRNAs were made by measuring the synthesis of their initial translation forms with mRNA isolated at stages in embryogenesis utilizing the wheat germ in vitro protein-synthesizing system.The measurements reported here were made with cotyledons taken from embryos that were 50 and 100 mg in wet weight and from cotyledons from the mature seed. with a solution containing the '4C-labeled algal hydrolysate (5 ,iCi ml-'), gramacidin D (10 Ag ml-') and, where indicated, AbA (5 EAM). After the incubation period, the embryos were thoroughly rinsed in distilled H20, axes removed and discarded, and the cotyledons extracted for protein as given above. In the pulse-chase experiment, the embryos were removed from the filter paper 187 www.plantphysiol.org on May 9, 2018 -Published by Downloaded from

Synthesis and processing of thionin precursors in developing endosperm from barley (Hordeum vulgare L.)

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“…LEA proteins were first described about 30 years ago in desiccation tolerant cotton seeds at maturation (Dure and Galau, 1981;Galau, 1986) and were thought to be unique to plants. LEA proteins were found to reduce the damage to seeds and seedlings by harsh environmental conditions such as drought, freezing, and osmotic stress (Bray, 1993;Espelund et al, 1992;Hundertmark and Hincha, 2008;Pammenter and Berjak, 1999;Shih et al, 2008).…”

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