Germination of Wheat: A Functional Proteomics Analysis of the Embryo

Abstract

Cereal Chem. 86(3):281-289Germination in the soft wheat (Triticum aestivum L.) cultivar Rosella was followed for three days after imbibition by proteomic analysis of the germ tissue. Two-dimensional electrophoresis was performed in triplicate for proteins extracted from embryos dissected from mature grain and from grains germinated for 1, 2, and 3 days. For this period, 63 proteins (in 86 spots) in the germ were identified as decreasing in abundance, 35 proteins (in 60 spots) as increasing in abundance, and 28 proteins (in 39 spots) as exhibiting no significant abundance change. Proteins with significant abundance changes are discussed in relation to physiology; these include proteases, amylases and amylase inhibitors, enzymes in lipid metabolism, proteins related to water stress, cell wall hydrolases, oxalate oxidase, and H + -ATPases. Functions associated with proteins synthesized during the germination period are inconsistent with the embryo of mature grain being fully primed for germination.Germination involves reanimation of the embryo from a state of quiescence in mature seed to a state of highly active metabolism. Germination is triggered by rehydration at a temperature within an acceptable range, and requires adequate rates of gas exchange. In grasses such as wheat, abundant stores of starch and protein are contained in the starchy endosperm, which loses its cellular structure as grains reach maturity, but is surrounded by a layer of intact aleurone cells. Breakdown of storage carbohydrates and proteins occurs during germination to provide nutrition for the rapidly growing embryo before autotrophy can begin.An extensive literature describes the storage proteins of the wheat endosperm, their variation between cultivars, and their influence on flour quality (see review in Singh et al [2005]). Many aspects of the biochemistry and control of storage protein (and starch) breakdown are well understood for wheat and other monocotyledonous cereals. In the earliest stage of germination, imbibition results in the synthesis of gibberellic acid (GA) by the embryo. This hormone acts to promote expression of genes for hydrolytic enzymes produced in the aleurone and scutellum. In the embryo, repair and synthesis of mitochondria and activation of respiration allows mobilization of the embryo's internal reserves of proteins, lipids, and carbohydrates.In this study, we focus on proteomic changes in the embryo that occur throughout the germination period, a relatively unexplored area. We aim to further our understanding of metabolic changes occurring during germination by correlating changes in protein abundance with physiological processes associated with germination and very early seedling development. Many questions concerning the role and status of proteins in the wheat embryo during germination remain unresolved. For example, to what extent is the embryo of the mature grain primed for germination? What types of proteins required for germination are synthesized during grain development or after imbibition? To what exten...

Integrated analysis of seed proteome and mRNA oxidation reveals distinct post‐transcriptional features regulating dormancy in wheat (Triticum aestivum L.)

“…Previous proteomic analyses of rice and wheat embryos and different tissues of barley seeds have shown that most storage proteins and proteases/enzyme inhibitors are mainly localized in the endosperm/aleurone tissues, whereas those involved in translation and protein folding such as eIF5A1 and PDIs, and cellular signalling such as 14‐3‐3s and CRT, in the embryos (Bønsager et al ., ; Kim et al ., ; Mak et al ., ). These results suggest the tissue specificity of the related proteins identified in this study, which involved whole seed samples.…”

Transcriptional programs regulating seed dormancy and its release by after‐ripening in common wheat (Triticum aestivum L.)

“…Moreover, a probeset annotated in wheat as α‐amylase/trypsin inhibitor (designated as CM1 because of its solubility in Chloroform: Methanol) showed a twofold higher expression in D than AR seeds (Table S1). As a decrease in the mRNA and protein levels of trypsin and α‐amylase inhibitors was observed during wheat seed germination (Mak et al. , 2009; Potokina et al.…”

“…, 2009). Moreover, the germination of non‐dormant seeds is associated with down‐regulation of trypsin and α‐amylase inhibitor proteins at both transcript and protein levels (Mak et al. , 2009; Potokina et al.…”

“…For example, genes coding for cell wall modifying enzymes such as glucan endo-1,3-b-glucosidases, xyloglucan endotransglycosylases and expansins exhibited up-regulation in the coleorhiza of AR relative to that of D seeds in barley (Barrero et al, 2009). Moreover, the germination of non-dormant seeds is associated with down-regulation of trypsin and a-amylase inhibitor proteins at both transcript and protein levels (Mak et al, 2009;Potokina et al, 2002). In contrary, D seeds are enriched with genes involved in abscisic acid (ABA) biosynthesis, gibberellin (GA) catabolism, stress response and genes with repressed translation capacity (Bassel et al, 2011;Cadman et al, 2006;Rajjou et al, 2004).…”

Zinc fortification as a tool for improving sprout hygienic and nutritional quality: a factorial design approach

“…Lipid and protein contents were higher in sprouted seeds soaked in zinc solution than in control seeds soaked in water. The evolution of these molecules during sprouting is mainly due to enzymatic mechanisms aiming to provide the embryo with nutrients . The increase in lipid and protein contents might be related to an effect of zinc on lipases and proteases: In fact, zinc plays a key role in structural and catalytic functions of numerous enzymes .…”