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

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in vitro- Variations in expression of episodic growth by cultured shoots of oak (Quercus robur L.) J.M. Favre B.Juncker Laboratoire de BP 239, 54506 Vand&oelig;uvre-Ies-Nancy Universit6 de Biologie des Ligneux, Nancy I, Cedex, France Introduction Three main shoot growth patterns were obtained, depending upon the culture media. Under natural conditions, or controlled On media composed of a half-strength conditions 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 O grow 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 from but leaf initiation is only reduced. Con- primary explants, than from subcultured sequently, one flush is composed of 2 explants. However, in both cases each kinds of leaves: 1) leaves formed during flush expanded a number of leaves which the rest period of the previous flush called corresponded to the primordia content of preformed leaves; and 2) leaves formed the initial buds. All the leaves were thus during the elongation period called new- preformed. The potential for subculture of formed leaves. these shoots was poor. The multiplication Usually the former represent about 60% rate was about 0.5 every 6 wk and cloning of the total number of leaves per flush, the failed rapidly. latter about 40%. These leaves differenti- On media composed of the same ate successively into scale leaves and mineral solutions but containing benzyl- photosynthetic leaves (Champagnat et adenine (BA), instead of AC, 2 different al., 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-formed Under in vitro conditions, variation occurs leaves (Fig. 1 beD) Occasionally, a second in 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 followed 2-4 every 6 wk, upon the depending clone. the 20 clones tested, the by a decline of the culture, apical necrosis Among frequency of this shoot growth pattern and failure to done. This evolution could was 100% GD solution and 80% half- be stopped by transfer of cultures onto on on MS solution. media poor in total N and NH such as strength , 4 MS with a diluted concentration of On media composed of half-strength NH or Knop’s solution. Reversion to 3 NO 4 MS with BA, a third shoot growth pattern growth pattern 2 could be obtained and occurred in about 20% of the clones. potential for micropropagation recovered. Shoots elongated continuously. After 2 mo in culture, elongation decreased, probably due to starvation. Within this growth pe- Discussion and Conclusion riod, no more scale leaves were formed. However, shoots had 5-7 times as many photosynthetic leaves as the primordia These results point out the importance of content of the initial buds (Fig. 1 c). There- 2 components of the culture medium in fore, 80-90% of the leaves were new- controlling the shoot growth pattern and formed leaves. Finally, in these shoots, the potential for in vitro propagation.
possible to reverse non-episodic shoots to The first component is BA episodic ones by transfer onto a medium with low nitrogen and ammonium concen- Without BA, growth was episodic. How- trations, the nitrogen composition of the ever, leaf initiation was restricted to the medium must also play a role in the rest period of the buds. Shoot elongation control of the growth pattern under in vitro and leaf initiation followed each other. conditions. Therefore, this kind of episodic growth dif- In summary, the growth pattern of oak in fered from that obtained under natural vitro appeared to be mainly controlled by conditions. When BA was added, leaf ini- the cytokinins and nitrogen composition of tiation increased and occurred simultane- the culture medium. ously with elongation. Depending upon the clone, this resulted in a shoot growth pat- tern that was similar to what happens References under natural conditions, or in non-episo- dic growth. Therefore, BA is one of the main factors controlling the shoot growth Champagnat P., Payan E., Champagnat M., Barnola P., Lavarenne S. & Bertholon C. (1986) pattern of oak in vitro. La croissance rythmique de jeunes chenes p6doncul6s cultives en conditions contr6l6es et uniformes. Nat. M Colt. International sur onspeA The second component is nitrogen or, I Arbre, Montpellier Sept 1985. 303-337 precisely, the NH concentration 4 more Gresshoff P.M. &. Doy C.H. (1972) Development and differentiation of haploid Lycopersicon esculentum (tomato). Planta 107, 161-170 We have that non-episodic growth seen Murashige T. &. Skoog F. (1962) A revised half-strength MS solu- occurred only on medium for rapid growth and bioassays with the medium with the highest tion, i.e., on tobacco tissue cultures. Physiol. Plant. 15, 473- concentrations. Since it N and 4 NH 497 was

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