481 Anatomical Study of In Vitro Obtained Fasciated Shoots from Betula pendula Roth. I. Iliev 1 , A. Rubos 2 , A. Scaltsoyiannes 3 , C. Nellas 2 and P. Kitin 4 1 Department of Dendrology, University of Forestry, Sofia 1756, Bulgaria 2 Tehnological Education Institute, 54101 Thessaloniki, Greece 3 School of Forestry, Aristotle University, 54124 Thessaloniki, Greece 4 Department of Forest Science, Hokkaido University, Sapporo 060-8589, Japan Keywords: Fasciation, silver birch, stem anatomy, zeatin Abstract The effect of Simola nutrient medium in combination with different zeatin levels (0, 2, 5 and 10 mg l -1 ) on adventitious bud formation from leaf callus was tested. The fasciated shoots were formed only when 5 mg l -1 and 10 mg l -1 zeatin were used in the medium and reached 3.4% and 4.2%, respectively. These results showed that under in vitro conditions the zeatin concentration was the main factor for the expression of this phenotype trait. The anatomical study showed that the tissues were ordered correctly and subordinate to the same structural peculiarities as in normal shoots. The most striking difference between normal and fasciated stems is in the shape of the vascular cylinder and the pattern of development of the vascular tissues. The appearance of fasciation under in vitro conditions may be the result of suppression of a gene under the influence of zeatin. Zeatin could relieve this suppression by either inhibiting the formation of a repressor or facilitating the synthesis of a faulty repressor. INTRODUCTION Fasciation was one of the seven characteristics that Gregor Mendel chose when illustrated the concept of dominant and recessive traits in his cross breeding of peas. Fasciations are described in many trees, shrubs and flowers (Mertens and Burdick, 1954; Karagiozova and Meshineva, 1977; Srivastava and Glock, 1987; Tang and Knap, 1998). In recent years further evidences for inheritable trait of fasciations were accumulated. Isolated genes CLAVATA1 (Leyser and Furner, 1992) and CLAVATA3 (Fletcher et al., 1999) were associated with fasciated stems in Arabidopsis. Research with the bacteria Rhodococcus fascians (Crespi et al., 1992) revealed the transfer of a gene from the bacteria into the host cell which causes fasciations. Once the bacterial gene is transferred into the host plant, the tendency toward fasciation can be transferred to other plants through cuttings and grafts from the gene-infected plant. There are different theories about in vivo and in vitro fasciations origination and this phenomenon is still not clearly understood. The aim of the present work was to study the anatomical peculiarities of in vitro obtained fasciated and normal shoots in Betula pendula. MATERIAL AND METHODS Plant Material Adventitious bud formation and shoot proliferation were induced on leaf callus cultivated on Simola (1985) medium (S) containing different levels of zeatin (0, 2, 5 and 10 mg l -1 ), 30 mg l -1 adenine, 20 g l -1 sucrose and 6 g l -1 agar. All media were prepared in 3 replications and each of them contained 16 callus segments. All media were adjusted to 5.6 before autoclaving at 1.2 atm and temperature 115-120°C for 30 min. The cultures were grown in a growth room at temperature 22±2°C at a 16/8h light/dark regime from cool white fluorescent lights at intensity of 40 µmol m -2 s -1 . The influence of the zeatin levels on the fasciated shoot formation was verified statistically by SPSS program. Proc. 1 st IS on Accl. & Estab. Micropop. Plants Eds. A.S. Economou & P.E. Read Acta Hort. 616, ISHS 2003