Anatomical study of in vitro obtained fasciated shoots from Betula pendula Roth.

The effect of Simola nutrient medium in combination with different zeatin levels (0, 2, 5 and 10 mg 1(-1)) on adventitious bud formation from leaf callus was tested. The fasciated shoots were formed only when 5 mg 1(-1) and 10 mg 1(-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.