Stages of germination
Furthermore, the latency of germination may require certain environmental stimuli such as light or low temperatures, or there is a weakening of the seed coats. Also contributes the climateof the place in which lies the crop . It is important to know and control the pests that may attack the future plant.
1. Embryo development .
2. Accumulation of food reserves . These are made in the green parts of the plant and are transported to the seed in development. In the seeds called endospérmicas, food reserves are deposited outside the embryo, forming the endosperm of the seed. In seeds endospérmicas calls, the food material is absorbed by the embryo and stored in special containers called cotyledons.
3. Maturation . During this phase, the seed is dried and separates the connection to the mother plant by cutting the water supply and forming a structural point of weakness which can be easily separated mature seed.
Most seeds enter a period of latency (metabolic inactivity) after complete maturation. During this period, the seed loses most of the moisture that had. It is this drying ( dehydration ) the main factor that ensures seed viability and ability to end inactivity, grow into new plants. This latency period varies from species to species, some seeds die quickly if they dry too, but there are many old seeds that have germinated after many hundreds of years.
To achieve germination the seeds needed primarily water and, depending on the variety of the plant in question, may require most attention in terms of temperature and light conditions are more specific. Each year, this cycle of reproduction invariably repeats itself. Only be altered if environmental conditions change. Thus, if a plant is changed wetland environment and climate, making it dry, the plant will adapt or die for not having the ability to adapt to new climatic conditions. Taking the minimum requirements, the plant will form seeds or spores . The wind or animals shall be responsible for bringing to fertile land, restarting the cycle of life, with the formation of a new plant.
The emergence of the root , which initiates the growth of the seedling, is triggered by turgor pressure. The initial growth requires the use of the reserve substances which had previously been stored in the endosperm or cotyledons. To do this, there must be a process of prior hydrolysis and mobilization to generate small molecules that can be used by the developing seedling. The hydrolysis ofproteins is catalyzed by a variety of endo peptidases and exopeptidases that release small peptides and amino acids . The mobilization of lipids involves three types of organelles: lipid bodies, theglyoxysomes and mitochondria , the enzymes in the metabolism of key lipids, which can be transformed into hexoses are the isocitrate lyase and malate synthase , whose levels increase markedly during germination.
The starch , the main carbohydrate reserve can be hydrolysed by the action of a- amylases and ß-amylases, or the starch phosphorylase , releasing monosaccharides , disaccharides andoligosaccharides . The mobilization of the reserves of phosphate is produced by the action of phytase . The embryo can exercise control of different enzymatic activities by the synthesis and release ofphytohormones .
The most typical example is the hormonal control of the hydrolysis of starch by activation of the a-amylases mediated gibberellins in seeds of cereal . Whilst gibberellins, and it appears that also theethylene , have a clear stimulatory effect on germination, abscisic acid , however, inhibit the germination processes involved.
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