Báo cáo khoa học: Variations in expression of episodic growth cultured shoots of oak (Quercus robur L.)

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Báo cáo khoa học: "Variations in expression of episodic growth cultured shoots of oak (Quercus robur L.)" in vitro-Variations in expression of episodic growth bycultured shoots of oak (Quercus robur L.)J.M. Favre B.Juncker Laboratoire de BP 239, 54506 Vandœuvre-Ies-NancyUniversit6 de Biologie des Ligneux, Nancy I,Cedex, FranceIntroduction Three main shoot growth patterns were obtained, depending upon the culture media.Under natural conditions, or controlled On media composed of a half-strengthconditions such as 25°C long days, shoots Murashige and Skoog (MS) (1962) solu-of Q. robur exhibit episodic growth. They tion with 1/4 NH or full-strength , 3 4 Ogrow by successive flushes that are Gresshof and Doy (GD) (1972) solution,composed of an elongation period, both supplerr!ented with activated char-12-14 d long, followed by a rest period, coal (AC), episodic growth was main-6-8 d long. tained. Several flushes developed (Fig. During the rest period, elongation stops, 1a). Shoot growth was more robust frombut leaf initiation is only reduced. Con- primary explants, than from subculturedsequently, one flush is composed of 2 explants. However, in both cases eachkinds of leaves: 1) leaves formed during flush expanded a number of leaves whichthe rest period of the previous flush called corresponded to the primordia content ofpreformed leaves; and 2) leaves formed the initial buds. All the leaves were thusduring the elongation period called new- preformed. The potential for subculture offormed leaves. these shoots was poor. The multiplication Usually the former represent about 60% rate was about 0.5 every 6 wk and cloningof the total number of leaves per flush, the failed rapidly.latter about 40%. These leaves differenti- On media composed of the sameate successively into scale leaves and mineral solutions but containing benzyl-photosynthetic leaves (Champagnat et adenine (BA), instead of AC, 2 differental., 1986). growth patterns occurred. a) In most cases, shoot elongation stopped after 1 mo in culture. A single flush was ob-Results tained with 2--3 times as many leaves as were contained in the initial buds. There- fore, each flush bore 50-60% new-formedUnder in vitro conditions, variation occurs leaves (Fig. 1 beD) Occasionally, a secondin the expression of the episodic growth. ’ episodic growth seemed to be abolished.flush developed from these subcultured These non-episodic shoots could be sub-explants (Fig. 1 . Shoots of this growth )b o cultured. During 2-3 consecutive subcul-pattern could be subcultured and cloned The tures, they continued to express non-epi-satisfactorily. multiplication rate was sodic growth. However, this was followed2-4 every 6 wk, upon the dependingclone. the 20 clones tested, the by a decline of the culture, apical necrosis Amongfrequency of this shoot growth pattern and failure to done. This evolution could was100% GD solution and 80% half- be stopped by transfer of cultures onto on on MS solution. media poor in total N and NH such asstrength , ...