Effects of APETALA2 on embryo, endosperm, and seed coat development determine seed size in Arabidopsis

Arabidopsis APETALA2 (AP2) controls seed mass maternally, with ap2 mutants producing larger seeds than wild type. Here, we show that AP2 influences development of the three major seed compartments: embryo, endosperm, and seed coat. AP2 appears to have a significant effect on endosperm development. ap2 mutant seeds undergo an extended period of rapid endosperm growth early in development relative to wild type. This early expanded growth period in ap2 seeds is associated with delayed endosperm cellularization and overgrowth of the endosperm central vacuole. The subsequent period of moderate endosperm growth is also extended in ap2 seeds largely due to persistent cell divisions at the endosperm periphery. The effect of AP2 on endosperm development is mediated by different mechanisms than parent-of-origin effects on seed size observed in interploidy crosses. Seed coat development is affected; integument cells of ap2 mutants are more elongated than wild type. We conclude that endosperm overgrowth and/or integument cell elongation create a larger postfertilization embryo sac into which the ap2 embryo can grow. Morphological development of the embryo is initially delayed in ap2 compared with wild-type seeds, but ap2 embryos become larger than wild type after the bent-cotyledon stage of development. ap2 embryos are able to fill the enlarged postfertilization embryo sac, because they undergo extended periods of cell proliferation and seed filling. We discuss potential mechanisms by which maternally acting AP2 influences development of the zygotic embryo and endosperm to repress seed size

Castor Bean Metabolomics: Current Knowledge and Perspectives Toward Understanding of Plant Plasticity Under Stress Condition

Metabolomics provides vital information for the understanding of biological processes and has been vastly applied in plant studies. Several metabolite-profiling studies have correlated physiological events, such as germination or seedling establishment, with metabolic and molecular changes under different environmental conditions. Castor bean displays high plasticity during initial vegetative growth, which is reflected in the metabolome of the seeds and seedlings. In general, several metabolite-profiling techniques are required to obtain a complete response in terms of metabolism plasticity of the studied biological system. Carbohydrates, amino acids, and organic acids have been measured in castor bean seeds and seedlings by nuclear magnetic resonance, gas chromatography coupled to a quadrupole time of flight mass spectrometry (GC-TOF-MS), as well as by high-performance liquid chromatography (HPLC). Fatty acids and some secondary metabolites have been quantified in castor bean seeds and seedlings by gas chromatography coupled to a triple-axis detector (GC-MS). In this chapter, we initially discuss how metabolomics studies suggested a possible role of gamma-aminobutyric acid (GABA) accumulation during early imbibitions and seedling establishment. Later, we consider a specific metabolic signature of castor bean: a shift in carbon–nitrogen metabolism as its main biochemical response to high temperatures. This metabolic shift is usually associated with adjusted growth, and it is likely involved in maintaining cellular homeostasis under heat stress. The castor bean metabolome has been vastly investigated, especially with regard to its ability to respond to external stimuli. These results might help us understand the molecular requirements for vigorous castor bean seed germination and seedling growth under different environmental conditions

Storage Reserve Accumulation in Arabidopsis: Metabolic and Developmental Control of Seed Filling

In the life cycle of higher plants, seed development is a key process connecting two distinct sporophytic generations. Seed development can be divided into embryo morphogenesis and seed maturation. An essential metabolic function of maturing seeds is the deposition of storage compounds that are mobilised to fuel post-germinative seedling growth. Given the importance of seeds for food and animal feed and considering the tremendous interest in using seed storage products as sustainable industrial feedstocks to replace diminishing fossil reserves, understanding the metabolic and developmental control of seed filling constitutes a major focus of plant research. Arabidopsis thaliana is an oilseed species closely related to the agronomically important Brassica oilseed crops. The main storage compounds accumulated in seeds of A. thaliana consist of oil stored as triacylglycerols (TAGs) and seed storage proteins (SSPs). Extensive tools developed for the molecular dissection of A. thaliana development and metabolism together with analytical and cytological procedures adapted for very small seeds have led to a good description of the biochemical pathways producing storage compounds. In recent years, studies using these tools have shed new light on the intricate regulatory network controlling the seed maturation process. This network involves sugar and hormone signalling together with a set of developmentally regulated transcription factors. Although much remains to be elucidated, the framework of the regulatory system controlling seed filling is coming into focus