If a mature and viable seed does not germinate under favorable conditions, it is said to be dormant. Seed dormancy is called embryonic dormancy or internal resting phase and is caused by the endogenous properties of the embryo that prevent germination (Black M, Butler J, Hughes M. 1987). The resting phase should not be confused with the resting phase of the seminal coat, the external resting phase or persistence caused by the presence of a hard sperm cover or integument that prevents water and oxygen from reaching and activating the embryo. It is a physical barrier to germination, not a true form of dormancy (Quinliven, 1971; Quinliven and Nichol, 1971). Short photoperiods induce a resting phase and allow the formation of primordia needle. Primordia formation takes 8 to 10 weeks, followed by 6 weeks of cooling to 2°C. Bud hernia occurs immediately when the seedlings are then exposed to 16-hour photoperiods in the temperature range of 25 ° C / 20 ° C. The mode of free growth, a juvenile trait lost after about 5 years, stops in seedlings exposed to environmental stress (Logan and Pollard 1976, Logan 1977). [13] [14] Many insects go through periods of reduced metabolic activity called diapause. Diapause, which can occur at any stage of the life cycle – egg, nymph, larva, nymph or adult – is usually characterized by stunted growth in immature stages and cessation of sexual activity in adults. In some insects, it is a reaction to adverse environmental conditions; In others, such as some moths and butterflies, diapause is a necessary phase of the life cycle. The larval and pupal period of 17 years of the cicada are examples of diapause.
This form of dormancy period is especially common in insects that live in dry desert areas, where insects usually hide in the soil at appropriate depths or under available protective objects during dry, hot summers. Hibernation A time when a plant does not grow and waits for the necessary environmental conditions such as temperature, humidity, availability of nutrients, etc. A state of silent (but perhaps temporary) inaction; The volcano erupted after centuries of dormancy. Quiet and inactive rest. A state in which organisms are in adverse conditions and slow down their metabolic processes to a minimum in order to obtain resources until conditions are more favorable. Plants can do this when there is a lack of water, while animals, such as the garden dormitory, hibernate, which is also a form of dormancy. Two common things must happen before sperm with MPD can germinate: (1) the embryo must reach a critical size (in sperm) and (2) the embryo`s PD must be broken. The secret to germinating seeds with MPD is to discover which environmental conditions favor each event. In some species, embryo growth and rest are favored by the same environmental conditions, while in others they require different conditions. Depending on the species, the embryo growth and resting period may be (1) only warm (≥15°C) stratification (Baskin and Baskin, 1990d), (2) only cold (0–10°C) stratification (Baskin and Baskin, 1984b), (3) hot stratification followed by cold stratification (Baskin and Baskin, 1984a), (4) cold followed by hot stratification followed by cold stratification (Nikolaeva, 1977), or (5) cold followed by hot stratification (Walck et al., 1999).
In some species, embryonic PD is broken and growth then occurs (Baskin and Baskin, 1984a, 1985bBaskin and Baskin, 1984aBaskin and Baskin, 1985b), while in others, PD rupture and embryonic growth occur simultaneously (Baskin and Baskin, 1984b). Finally, PD rupture can occur in two parts, with embryonic growth (i.e., DM rupture) in the middle (Baskin and Baskin, 1989a). The nine levels of DPM and how they are broken in nature are discussed in Chapter 5. In March 2012, unusually warm temperatures in Michigan caused vegetation to emerge prematurely from dormancy, but were then destroyed by freezing weather in April. Laid in the fall and hatched the following spring, the eggshells are covered with a thick layer of wax to prevent them from drying out during their long resting period. In my field of studies, runners spend about half the year in hibernation. There are few environments where organisms are not exposed to some kind of stress. Some animals migrate long distances to avoid adverse situations. Others reduce environmental impacts by changing their behaviour and the habitats (immediate environment) they occupy. Arctic lemmings, for example, are able to avoid the harsh winter by limiting their winter life to activities under snow cover. Another mechanism used by some organisms to avoid stressful environmental conditions is the dormant state, in which an organism retains the amount of energy available and places few demands on its environment. Most of the main groups of animals, as well as plants, have representatives that can rest.
Rest periods vary in length and degree of metabolic reduction, ranging from slightly lower metabolism during the short-term periodic resting phase of deep sleep to more extreme reductions for longer periods. The resting phase has a hereditary component. This has been demonstrated for a large number of species, including many crops such as rice (Oryza sativa), soybeans (Glycine max) and barley (Hordeum vulgare), and weeds such as wild oats (Avena fatua). Classical genetic analysis has shown that between one and 10 often recessive genes are linked to the resting phase, depending on the species. However, mutational and molecular analyses now suggest that the number of genes directly or indirectly involved in the regulation of the resting phase is much higher. The degree of resting phase is also hereditary. For example, the rest period in 10 genetically pure lines of Avena fatua seeds ranges from 0% to almost 100%. In many species, the onset of the resting state is related to morphological or physiological characteristics. Examples are the colour and thickness of the seed layer, but also herbicide resistance. An example of the latter is the lower resting degree in atrazine resistant biotypes of Amaranthus spp. compared to sensitive biotypes. Hybridization studies with pure dormant and non-dormant lines of a species have shown that, depending on the species, seed dormancy can be controlled by the genotype of the maternal and paternal parents and the embryo or a combination of all three.
The volcano could now return to a period of rest after letting go of its anger. In plants, a distinction is made between the resting state and the resting state, which is of great importance from a physiological and practical point of view. Now it must be determined that pathogens retain their vital forces even over a longer period of time at rest.
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