Seed Development and Differentiation: A Role for Metabolic Regulation

Abstract

During seed growth, the filial organs, Vicia embryos and barley endosperm, differentiate into highly specialized storage tissues. Differentiation is evident on structural and morphological levels and is reflected by the spatial distribution of metabolites. In Vicia embryos, glucose is spatially correlated to mitotic activity whereas elongating and starch accumulating cells contain high levels of sucrose. Seed development is also regulated by phytohormones. In pea seeds, GA-deficiency stops seed growth before maturation. In Arabidopsis seeds, ABA regulates differentiation and inhibits cell division activity. The ABA pathway, in turn, is linked to sugar responses. In young Vicia embryos, invertases in maternal tissues control both concentration and composition of sugars. Embryonic and endospermal transfer cell formation represents an early differentiation step. Establishing an epidermis-localised sucrose uptake system renders the embryo independent from maternal control. cDNA array analysis in barley seeds revealed a massive transcriptional re-programming of gene expression during the transition stage, when gene clusters related to transport and energy metabolism are highly transcribed. Sucrose represents a signal for differentiation and up-regulates storage-associated gene expression. Sucrose signalling involves protein phosphorylation. Sucrose non-fermenting-1-related protein kinases are apparently induced in response to high cellular sucrose, and could act as mediators of sucrose-specific signals. Energy metabolism changes during seed development. In Vicia embryos metabolic responses upon hypoxia and low energy charge levels are characteristic for young undifferentiated stages when energy demand and respiration are high. During the transition stage, the embryo becomes adapted to low energy availability and metabolism becomes energetically more economic and tightly controlled. These adaptations are embedded in the embryo's differentiation program and coupled with photoheterotrophic metabolism. In Vicia cotyledons, ATP content increases in a development-dependent pattern and is associated with the greening process. The main role of seed photosynthesis is to increase internal O2 contents and to control biosynthetic fluxes by improving energy supply.

Vacuolar invertase regulates elongation of Arabidopsis thaliana roots as revealed by QTL and mutant analysis

“…Inv and Susy, the two types of enzymes capable of splitting sucrose in higher plants, have both been suggested to be involved in sink strength. However, they might play a role in different types of sinks being either consuming or accumulating sinks (1).…”

“…In terms of biomass, the most important components in assimilate partitioning and in total yield are carbohydrates. There is increasing evidence that a limited number of key enzymes, involved in primary (carbohydrate) metabolism, might be pivotal in this process (1).…”

Molecular cloning and biochemical characterization of three phosphoglycerate kinase isoforms from developing sunflower (Helianthus annuus L.) seeds

“…The sensitivity of (6His)HacPGK1 to pH below 7 would render the enzyme responsive to acidic conditions in the cytoplasm. Cytoplasmic acidosis has been shown to occur in conditions of hypoxia (Roberts et al, 1984;Drew, 1997;Gout et al, 2001), which is common in seed maternal and embryonic tissues (Rolletschek et al, 2002;Borisjuk et al, 2004;Borisjuk and Rolletschek, 2009). …”

Significance of Light, Sugar, and Amino Acid Supply for Diurnal Gene Regulation in Developing Barley Caryopses

“…to study diurnal changes in gene expression. This developmental stage, also referred to as the early maturation phase, is characterized by high Suc levels and a rapid accumulation of storage starch in filial tissues of the caryopsis (Borisjuk et al, 2004;Sabelli and Larkins, 2009). Caryopses from the mid region of the spike (Fig.…”