Effects of agar brand and concentration on the tissue culture medium

In tissue-cultured Cynara scolymus L. (globe artichoke) vitrification (hyperhydric transformation) can only be overcome by increasing the concentration of agar. However, with increasing concentrations of Difco Bacto agar (8–15 g/I) the availability of labelled kinetin is decreased. There is some evidence for postulating that cytokinins under inductive conditions of low agar concentration or high matrix potential are evocators of vitrification.
Both the brand and concentration of agar also affect the chemical and physical characteristics of a culture medium.
Impurities introduced with the agar are responsible for significant differences in the concentration of an element in comparable media with different levels of agar, and are easily detected by conductance.
Penetrometer measurements also show large ranges in solidity of media with increasing concentrations, not only within the type of agar, but also for the same concentration within different brands.