Abstract
Cereal grain germination provides the basis for crop production and requires a tissue-specific interplay between the embryo and endosperm during heterotrophic germination involving signalling, protein secretion, and nutrient uptake until autotrophic growth is possible. High salt concentrations in soil are one of the most severe constraints limiting the germination of crop plants, affecting the metabolism and redox status within the tissues of germinating seed. However, little is known about the effect of salt on seed storage protein mobilization, the endomembrane system, and protein trafficking within and between these tissues. Here, we used mass spectrometry analyses to investigate the protein dynamics of the embryo and endosperm of barley (Hordeum vulgare, L.) at five different early points during germination (0, 12, 24, 48, and 72 h after imbibition) in germinated grains subjected to salt stress. The expression of proteins in the embryo as well as in the endosperm was temporally regulated. Seed storage proteins (SSPs), peptidases, and starch-digesting enzymes were affected by salt. Additionally, microscopic analyses revealed an altered assembly of actin bundles and morphology of protein storage vacuoles (PSVs) in the aleurone layer. Our results suggest that besides the salt-induced protein expression, intracellular trafficking and actin cytoskeleton assembly are responsible for germination delay under salt stress conditions.
Highlights
IntroductionThe cereal germination process starts with the uptake of water by the quiescent dry grain (imbibition), triggering the degradation of food reserves [2,3]
Since seed germination is the most crucial phase for plant growth and development and subsequently influences crop yield and quality, germination studies of crop plants are an important aspect of plant biology [1].The cereal germination process starts with the uptake of water by the quiescent dry grain, triggering the degradation of food reserves [2,3]
As temperature has an effect on the germination rate, growth rate, and total protein content during barley germination [24], we tried to use a suitable temperature representative of central Europe for barley early germination processes
Summary
The cereal germination process starts with the uptake of water by the quiescent dry grain (imbibition), triggering the degradation of food reserves [2,3]. Three phases are characterized within this process [4]: Phase I, the early phase, where the imbibition of the dry grain takes place, and an early plateau phase of the water uptake is reached. Cereal grains contain distinct layers, each with different spatiotemporal physiological roles and molecular mechanisms [5,6]: the endosperm, the major seed storage tissue; the dry coat on the outside, which includes the pericarp/fruit coat; the seed coat, which encloses the embryo; and the scutellum in the embryo, which stores high amounts of lipids and proteins. During cereal grain germination, stored lipids, carbohydrates, and proteins are mobilized to the embryo. For the activation of this mobilization process, gibberellic acids (GA3 ) accumulated in the embryo are transported to the aleurone layer of the endosperm, a living tissue surrounding the dead starchy endosperm
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