Explants from 3 clones of this variety were cultured in the same agar induced medium(MS + 2,4-D 0.05mg/l + 6-BA 0.5mg/l). Five kinds of calli were obtained from each clone: yellow semi-transparant (YS), green semi-transparant (GS), yellow friable (YF), green hard (GH) and white hard (WH). After transplanting them to the same agar medium (MS without 2,4-D and 6-BA), their somatic embryogenetic potentials were much different: YS > GS > YF > GH > WH.
Histological microphotographs showed that YS callus consists of epidermis and 46 layers of smaller regular cells in the outer part, and consists of rather bigger parenchyma like cells in the inner part. GS is similar to the above, but young chloroplast appeared in the outer layer smaller cells; YF is a loosen cells mass, with very small and uniform cell size, without epidermis and chloroplast; GH and WH have the appearance of matured tissue, with stomata initiated in the epidermis, with vascular bundles and heteromorphic cells initiated in the inner part of the calli. However GH presented many chloroplasts whereas WH had none at all.
Average contents of IAA and ABA measured in calli listed above by HPLC: YS has highest IAA (9.38ng/g) and lowest ABA (1.12ng/g); WH has lowest IAA (1.04ng/g) and highest ABA (7.50ng/g); IAA/ABA contents (ng/g) of GS,YF and GH are 6.70/1.34, 8.42/2.44 and 2.04/4.95 respectively.
The results may be concluded as follows: (1) Histologocally rather young cells are easier to differentiate than the matured cell. (2) Somatic embryogenetic potential increases as the endogenous IAA gets higher and ABA gets lower. (3) Cell structure and endogenous hormones balance of YF seem in a good condition, but its differentiation and embryogenetic potential are limited; this shows that more work in ultrastructure and other hormones is needed.
Key words: callus, structure, hormone, somatic embryogenesis.