G Dermendjiev, M Schnurer, J Weiszmann, S Wilfinger, E Ott, C Gebert, W Weckwerth, Verena Ibl
International journal of molecular sciences 22 (17), 9642
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.
Model for the effect of salt on the cytoskeleton, protein trafficking, and protein mobilization during barley germination. The expression of proteins was most different between H2O and EC30 at 48 HAI and 72 HAI in the embryo and endosperm, respectively. We hypothesize that on the one hand, ABA is induced in the embryo by EC30, which inhibits the expression of α-amylase, α-glucosidase, peptidases, mannosidase, and defence-related proteins. On the other hand, the expression of GA3-responsive proteins seemed to be negatively affected by the salt treatment. Subsequently, starch and SSPs are less hydrolysed and digested, leading to less mobilization of amino acids and sugars to the embryo. The actin cytoskeleton is altered in the aleurone, and vacuolization is inhibited by salt stress, putatively affecting the vesicular trafficking in the secretory pathway. Arrow up/down: high/low substance level, T-line: inhibition/reduction. Created with BioRender.com.