Reinvestigation of the Effects of Hormones and Sugars on Xylogenesis in Cultured Jerusalem Artichoke (Helianthus tuberoses) Tuber Slices, with Particular Emphasis on the Effects of Different Methods of Media Preparation and Tissue Analysis

Abstract

Summary This paper summarizes a reinvestigation of the effects of hormones and sugars on tracheary element differentiation in cultured tuber slices of Jerusalem artichoke ( Helianthus tuberoses ), with particular emphasis on differences in methodology which might account for conflicting results obtained by different laboratories as well as in our own laboratory. In this study we have obtained generally lower tracheary element percentages than previously reported, a consequence at least in part of different cell counting methods. The alkaline maceration previously used makes it difficult to count the many small cells present in cytokinin-containing media, a situation which leads to an artificially high tracheary percentage. Gibberellic acid, as previously reported from this laboratory, inhibits both cell proliferation and tracheary element differentiation. This contrasts with a number of reports from other laboratories where a generally stimulatory effect on differentiation was found. The different results presumably depend on different tuber varieties, media and culture conditions. However, we have found that the inhibitory effect of gibberellic acid is surprisingly independent of whether the hormone is autoclaved or filter-sterilized. It has been reported that autoclaving destroys the activity of the hormone. Abscisic acid increases cell number by fifty percent while drastically inhibiting tracheary element differentiation. The previously reported effect of a glucose-sucrose combination in inhibiting tracheary element differentiation was found to depend on autoclaving. In filter-sterilized media no inhibitory effect of this sugar combination was seen. Two known pyrolytic products of autoclaved sugar, 5-hydroxymethylaldehyde and levulinic acid, were tested and found not to be inhibitory to xylogenesis. Anatomy of the tissue correlates strongly with naphthaleneacetic acid (NAA) concentration, with discrete vascular nodules at low NAA levels and a more generalized distribution of tracheary elements at high NAA levels. Benzylaminopurine addition to a medium containing low NAA levels produces a tissue anatomy which resembles that of tuber slices grown on high NAA levels in the absence of exogeneous cytokinin.