The Distribution of Dry Matter in Bean Seedlings in Light and Darkness Conditions

Abstract

Plants express different stages of development to complete their life cycle, where in each phase have different demands on nutrition and the distribution of photosynthates among the structures. Thus, during growth, the plant accumulates and allocates different proportions of dry matter to their structures and root. In the seed is the embryo formed by the radicle and plumule, and cotyledons. They have stored nutrient reserves that proportion to the embryo that originate the root and plumule forms the stem and leaves of the seedling. The seeds can contain one cotyledon as monocotyledons such as maize, two in dicotyledonous plants such as beans and many cotyledons in gymnosperms. The seedling formed the hypocotyl located between the root and cotyledons and the epicotyl which includes the stem and plumule formed above the cotyledons. In a bean seedling formed are defined the root system which consists of the main root, adventitious roots, primary roots, secondary and tertiary roots and stem consists of the hypocotyl, cotyledons, epicotyl, simple leaves, first trifoliate leaf and second trifoliate leaf. Each structure complies with specific functions to maintain growth and seedling development. The roots absorb water and minerals and the vegetative part absorbs the solar radiation to produce the photosynthate that nourish the seedling. In the germination of the seed resumes growth by activating the metabolism of the embryo, which occurs when the seed absorbs water available around them and ends when specifically embryonic radicle elongates (Bidwell, 1990; Mayer and Poljakoff, 1989). From a practical standpoint, it is considered that germination is complete when the radicle has emerged from the shell and from this moment is considered the growth of the seedling. During germination different biochemical and morphological processes perform and it marks the beginning of the decline in reserves in the cotyledons and their exportation, which is accompanied by an increase in respiration (Bathellier et al., 2008). The first structure that appears in the seed is the radicle, which grows down, then hook plumule emerges as part of the hypocotyl and first structure that comes into contact with the light so soon chlorophyll actives and triggers photosynthesis. After the germination, growth begins, which leads to establish the seedling ranging from when the seedling emerges from the ground until it becomes autotrophic (Holman and Robbins, 1982). In light, the seedlings quickly initiate the synthesis of photosynthates and