Influence of agar on in vitro cultures:: II.: Biological performance of Ranunculus on media solidified with three different agar brands

The type of gelling agent can influence to a large extent clonal propagation of Ranunculus asiaticus L. through axillary bud stimulation. In preliminary experiments we identified three agar brands (Oxoid = OX, Merck = MK, and Roth = RT) which affect the availability of water and minerals to tissues in different ways. Ln the present study we investigate the influence of these agars on the In vitro performance of Ranunculus. On OX and MK gels, growth was satisfactory, although the former had a more promotive effect on fresh and dry weight production and on multiplication rate. Growth and development of shoots were poor on RT; shoot clumps showed symptoms of hyperhydricity, with shoots having large dark-green malformed leaves and very elongated petioles. Epidermal strips of leaves from shoots grown on the different gels and collected at the end of the culture period revealed differences according to the agar brand on which the plantlets were cultured. Severe structural deformations of stomata could be detected on RT-gown shoots. The analyses of the sugar content of the gel at the end of the culture period demonstrated that the explants grown on RT gels are strictly dependent on the carbohydrates in the medium. On OX and MK gels the heterotrophic metabolism was lowered compared to RT-grown explants. The agar brand on which plantlets were grown also influenced water retention capacity and water content of the shoots. Experiments with tritiated water were undertaken to better understand the water fluxes inside the vessel and to investigate the difference in "pump function" exerted by shoots cultured on the three gels. Shoots grown on OX media showed the best "pump function," which would account for the better results obtained on this gel. On the basis of the relationship between gel properties and the growth of Ranunculus shoots, we conclude that the different physiological responses on the three gels are a reflection of different water and nutrient availability in the different media.