An integral feature of cereal seed

An integral feature of cereal seed growth (development and germination) is the programed cell death of its individual tissues. Maternal tissues, such as the nucellus and pericarp, undergo progressive degeneration via PCD during the early stages of seed development. This process allows mobilization of cellular contents to nourish new tissues, such as the embryo and the endosperm (Domínguez and Cejudo, 2014). Next, during seed maturation, the endosperm undergoes PCD but the contents of its Aprepitant australia are not mobilized until germination. Therefore, the only tissues that are alive when seed development is completed are those of the embryonic axis, scutellum and aleurone layer. During seed germination, the scutellum and aleurone layer are responsible for the production of the hydrolytic enzymes that allow mobilization of the storage materials of the starchy endosperm, which serve to support early seedling growth. After this process is completed, cells in the scutellum and aleurone layer undergo PCD and their contents are used to support the growth of the germinated embryo (Domínguez and Cejudo, 2014, Young and Gallie, 2000) (Fig. 1B).
The role of cysteine proteases in development and germination of cereal seeds Plant proteolysis is a complex process that involves many metabolic networks, different subcellular compartments, and various types of peptidases, mainly cysteine, serine, aspartic and metallo-proteases (Van der Hoorn, 2008). Among the proteases encoded by plants, approximately 140 are cysteine proteases that belong to 15 families distributed in five clans, as classified in the MEROPS peptidase database (Rawlings et al., 2012). Many research findings indicate that cysteine proteases may be the most abundant group of proteases responsible for degradation and mobilization of storage proteins (Grudkowska and Zagdańska, 2004, Martínez et al., 2009). Additionally, precursors of reserve proteins are processed into mature proteins via limited proteolysis in the storage tissue of developing seeds. Moreover, during seed growth, with the participation of cysteine proteases, all of the seed tissues undergo progressive degradation via PCD (Fig. 1B). The transcriptome analysis of barley seeds in two tissue fractions: starchy endosperm/aleurone and embryo/scutellum, during maturation, desiccation and germination, revealed the large group of GA-responsive genes (Sreenivasulu et al., 2008). These transcripts have been divided into two groups. Nearly all genes from the first group were synthesized and stored during seed maturation and used during germination, whereas the transcripts of the second group were newly synthesized during germination (Sreenivasulu et al., 2008). Among genes of both groups there are cysteine proteases from the papain family. Finnie et al. (2011) in the study of intracellular and secreted proteomes of barley aleurone layer also identified three intracellular and nine extracellular proteases from the papain family.