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 propagatio n of Ranunculus asiaticus L. through axillary bud stimulation. In prelimina ry 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 the se agars on the In vitro performance of Ranunculus. On OX and MK gels, grow th was satisfactory, although the former had a more promotive effect on fre sh and dry weight production and on multiplication rate. Growth and develop ment of shoots were poor on RT; shoot clumps showed symptoms of hyperhydric ity, with shoots having large dark-green malformed leaves and very elongate d petioles. Epidermal strips of leaves from shoots grown on the different g els and collected at the end of the culture period revealed differences acc ording to the agar brand on which the plantlets were cultured. Severe struc tural deformations of stomata could be detected on RT-gown shoots. The anal yses of the sugar content of the gel at the end of the culture period demon strated that the explants grown on RT gels are strictly dependent on the ca rbohydrates in the medium. On OX and MK gels the heterotrophic metabolism w as lowered compared to RT-grown explants. The agar brand on which plantlets were grown also influenced water retention capacity and water content of t he shoots. Experiments with tritiated water were undertaken to better under stand the water fluxes inside the vessel and to investigate the difference in "pump function" exerted by shoots cultured on the three gels. Shoots gro wn 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 betw een gel properties and the growth of Ranunculus shoots, we conclude that th e different physiological responses on the three gels are a reflection of d ifferent water and nutrient availability in the different media.