**2.3 Protein synthesis**

The synthesis and accumulation of storage proteins in seeds can vary due to genetic and environmental factors during seed filling. Synthesis of storage proteins occurs in specific tissues and depending on the stage of cell expansion during seed filling. During seed filling, endosperm, cotyledons, and embryo accumulate various proteins, including storage proteins, acid hydrolases, plant defense proteins and other reserve materials or metabolites. Vacuoles are the major storage organelles in seeds. Seed storage proteins undergo various modifications, including cleavage of signal peptides, glycosylation, folding, disulfide bond formation, and other proteolytic processes. These post-translational modifications are essential for seed protein functions (e.g., hydrolytic enzyme activity) and often have profound effects on seed protein accumulation in parenchymal storage cells (e.g., storage proteins). Proteins are transported simultaneously or shortly thereafter to the plastids, mitochondria, nucleus, and peroxisome/glyoxisome within plant cells by direct recognition through specific targeting signals. In contrast, transport to the vacuole and cell surface occurs through the endomembrane system with the endoplasmic reticulum, golgi complex, and transport vesicles. Proteins transported through the endomembrane system are synthesized on polyribosomes associated with the endoplasmic reticulum and first migrate into the lumen and enter the secretory system. In addition to seed storage proteins, other seed proteins are also transported via the secretory pathway during seed development, including those destined for the tonoplast (vacuolar membrane), plasma membrane, and cell wall matrix [45].
