Transport and distribution of benzyladenine in Actinidia deliciosa explants cultured in liquid and solid media

The effect of the culture medium on the transport and distribution of N6-benzyladenine along the microshoots of kiwifruit cultured on solid and liquid media in the presence of 8-〚14C〛-BA was studied. Three complementary approaches were used: quantification of the radioactivity present in the different portions in which the explants were divided; distribution of BA and its metabolites in apoplast and symplast; and autoradiography. In both media, there was a gradual decrease of BA content from the basal to the apical segment, but this decrease was more uniform in explants from liquid media than from solid media, where a higher accumulation in the first two (more basal) segments was observed. Apoplast/symplast distribution of BA showed that BA and its metabolites were localized both in the symplast and in the apoplast. However, the major radioactive fraction was associated with the symplast, where the explants cultured in liquid medium had most of the BA active forms (BA and BAR). In the explants cultured in solid medium, the proportion of active and inactive (BA9G, BA3G and BA7G) forms was similar. The autoradiography of buds development showed a major concentration of radioactivity in those grown in liquid medium. Radioactivity distribution showed a similar pattern in the explants from both media, nevertheless the density of labelling was higher in meristematic than in differentiated zones. In conclusion, the explants from liquid medium have a higher BA content, its inactivation is slower, its distribution is more effective, and its presence in the meristematic tissue is also greater than in the solid medium. Therefore, it seems that BA might be responsible for different developmental patterns observed in explants grown in both media types.