Effects of Meta-topolin on the Growth, Physiological and Biochemical Parameters in Plant Tissue Culture

Abstract

Cytokinins (CKs) are essential plant growth regulators that control virtually all physiological activities in plant tissue culture (PTC). CKs are adenine derivatives carrying either an isoprene derivative or an aromatic side chain at the N6 terminus. Aromatic CKs have greater in vivo stability than isoprenoid CKs due to their resistance against cytokinin oxidase/dehydrogenase (CKX). Although N6-benzyladenine (BA) is the most commonly used aromatic cytokinin in PTC due to its effectiveness and low cost, hydroxylated derivatives, especially those that are hydroxylated in the meta-position, are emerging as viable alternatives. Meta-topolin (mT, 6-(3-hydroxybenzylamino)purine) is the most promising example in the place of BA due to its ability to obviate some of the drawbacks of BA use during the micropropagation of some medicinal and ornamental plant species and also improve shoot proliferation. New findings have been revealed in studies aimed at increasing the morphogenetic activities of this new cytokinin. A series of substituted topolin derivatives in the N9 position was synthesized to increase the cytokinin biological activity without greater cytotoxicity. Tetrahydropyran-2-yl (THP)-substituted CKs have positive effects on rooting and the photosynthetic apparatus in micropropagated plants. Positive reports on important tissue culture parameters such as increasing shoot growth rate, alleviating physiological defects, better acclimatization and rooting and secondary metabolite production have made the topolins, especially meta-topolins and derivatives, popular among plant tissue culture experts. The aim of this chapter is to assess the influence of meta-topolin (mT) on the growth, senescence process and photosynthesis, antioxidants, secondary metabolite production and in vitro propagation.