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پاییز  95  برشما عزیزان  تبریک و تهنیت باد



بهاره سازی و ارتباطش با دوران رکود VERNALIZATION AND RELATIONS DORMANCY
ارسال شده توسط سیدمهدی شمس تاریخ ارسال : یکشنبه ۱۳۸۸/٢/۱۳

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MECHANISMS OF VERNALIZATION

 

VERNALIZATION AND ITS RELATIONS TO DORMANCY!

From embryogenesis to flowering, a plant grows through successive stages. The identification ofthese stages is useful in further analyzing every mechanism in their ontogeny. The "stadial theory" however, is exacting; it holds that the same stages occur in all plants and that they are fundamentally irreversible. For further information refer to Lysenko who proposed the theory (155 to 159) and to commentators on the theory (279). If these stages are believed to be ontogenetic natures or properties defined according to an a priori postulate and unaltered by experiment, they are to be considered as expressing a faith that does not fall within the scope of scientific experimental analysis. If we hold to mere facts that can be repeated in experiments we speak another language. We indeed recognize stages in plant development, but these are neither universal nor irreversible. For example, we cannot say that the vernalization process, or "thermo stage, " is universally imposed merely as a temperature­controlled period of development. Bidens radiatus reacts to photoperiods as soon as its cotyledons turn green, without any previous thermo stage (37); also, the "photostage" is not always necessary for flowering. Flowering primordia exist in mature peanut seeds before any light treatment of the seedling. When a thermostage is

 

required, it may be experimentally reversible in certain cases, as we have seen for experimental successions of devernalization and revemalization. What is the obligate requirement for new vernalizing chilling ifnot the need for a new thermo stage, the former having been fully eliminated? Bud regeneration returns the plant to most of its juvenile stages. In experiments with proliferating flowers (44) the partly differentiated floral apex is reversibly returned to a vegetative apex of a shoot which again will have to go through all the previous stages before flowering. As far as the words are concerned, we prefer to consider purely empirical stages as observed for each species in our experiments and their reversible or irreversible sequence, and to analyze the various regulating mechanisms, whether independent or correlated, that control the sequence ofthe development

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