Seed Germination-The Biochemical and Molecular Mechanisms

Abstract

The chemical energy synthesized during photosynthesis as carbohydrates, lipids and proteins accumulates in seeds and provides a food source for animals. Seeds are also important genetic delivery systems essential for sustainable agriculture and environmental control. Genetic information in elite cultivars of crop species accumulated during breeding programs is distributed in the form of seeds. Ensuring successful germination and seedling establishment is a significant first step in agricultural production. The molecular and biochemical mechanisms of seed germination are not fully understood. Our knowledge of the interactions between the embryo, endosperm and testa has been advanced through tomato seed research, a model system for seed germination research. Recent discoveries using Arabidopsis thaliana have provided additional information about the molecular and genetic mechanisms of seed dormancy and germination. Genes expressed during seed development determine the size, shape and chemical properties of mature seeds and affect seed dormancy. In imbibed seeds, genes associated with hormone biosynthesis and degradation play critical roles in radicle emergence. The physical, chemical and physiological changes in the embryo, endosperm and testa, as well as the interactions between these tissues all contribute to successful germination. Recent literature on seed science research needs to be compiled to provide a clear picture for seed germination. Hypotheses to explain global mechanisms of seed germination are examined in this review.

Physiological, morphological and biochemical characteristics of the sexual propagation of Piper aduncum (Piperaceae)

“…In carrot seeds the embryo is immature and grows during the imbibition period before radicle protrusion. In the presence of ABA, the radicle emergence is blocked, but embryo growth is promoted, suggesting that the degree of embryo development is controlled by ABA (Nonogaki 2006). We suggest that permanence in the dark may have promoted the development of the embryo.…”

“…It is noteworthy that the differences between root protrusion and the seedlings formation were lower at 25 °C, indicating that this temperature We also observed the presence of tannins in drupes of P. aduncum. This compound has been associated with dormancy in Arabidopsis seeds (Nonogaki 2006), being speculated that its accumulation can improve the physical properties of the forehead, providing a mechanical strength that prevents radicle protrusion (Debeaujon & Koornneef 2000). It has also been considered as a factor of dormancy, the influence of the chemical properties of tannins, such as its antagonistic function to that of gibberellins (Debeaujon et al 2003).…”

“…Based on the results obtained in this study, it can be concluded that although root protrusion is favored at 30 °C, the number of seedlings formed after root protrusion is impaired. According to Nonogaki (2006), the seed metabolism differs considerably during the germination and postgermination processes, especially in terms of gene expression profiles and desiccation tolerance, and thus the radicle emergence can be viewed as an important parameter of the seed development. Thus, it is possible that besides the differences in the metabolic processes during the germination and post-germination phases, responses to environmental conditions might also be different.…”

“…Temperature alters the growth potential of the embryo, and also influences hormone levels. At high temperatures, termo-inhibition may occur due to induction of ABA synthesis and repression of GA (Toh et al 2008) and in addition the growth potential of the embryo is markedly reduced (Nonogaki 2006). On the other hand, endogenous levels of GA are increased at low temperatures (Penfield 2008, Yamaguchi 2008.…”

Truncation of LEAFY COTYLEDON1 Protein Is Required for Asexual Reproduction in Kalanchoë daigremontiana

“…Our results showed that GA 3 applications had no effect on transgenic leaf embryo developmental abnormalities. Although GA has been described to stimulate germination of dormant seeds in some species, there are many instances where GA alone is ineffective (Nonogaki, 2006), suggesting that GA is necessary but not sufficient for breaking the dormancy (Finkelstein et al, 2008).…”