Since the discovery of topolins as naturally occurring aromatic cytokinins (CKs), they have emerged as genuine alternatives to the long serving CKs such as benzyladenine, zeatin and kinetin in plant tissue culture (PTC). Globally, the past 15 years has witnessed a surge in the use of topolins and their derivatives in research laboratories. Topolins, especially the meta-topolin and its derivatives have been employed for culture initiation, protocol optimization and for counteracting various in vitro induced physiological disorders in many species. Evidence from various studies indicate the rising popularity and advantages (although not universal for all species) of topolins compared to other CKs. In this review, we assess the use of topolins in PTC with emphasis on their metabolism, structure–activity relations and effect on morphogenesis in vitro. In addition, the review provides a detailed list of species that have been used to study the effect of topolins in comparison with other CKs, the growth parameters affected and recommended concentrations are also provided.

Topolins: A panacea to plant tissue culture challenges?

An important application of chemicals in plant biology is their use as plant growth regulators in in vitro plant tissue culture. In vitro propagation mainly relies on two classes of plant growth regulators: cytokinins and auxins. Together, they regulate cell proliferation and differentiation and are used to induce shoot or root organogenesis. Besides natural occurring cytokinins and auxins, many synthetic compounds are identified with similar action. These small molecules provide a diversified toolbox of plant growth regulators currently available for different applications in plant tissue culture. In this chapter, an overview of the different types of cytokinins and auxins is given, including their identification and mode of action. Special attention is given to new molecules identified via chemical screens. Finally, the application of the different types of cytokinins or auxins for specific processes required in plant tissue culture is discussed.

In Vitro Propagation

Protection for the Amino Group

Preparation, biological activity and endogenous occurrence of N6-benzyladenosines.

2.04 – Pyrroles and their Benzo Derivatives: Applications

Two derivatives of N6-isopentenyladenine, 3 and 4, bearing either a vinylic fluorine atom or a trifluoromethyl group, were easily synthesized from known fluorinated precursors. Both derivatives 3 and 4 were found to be more active, as cytokinins, than the parent compounds zeatin (1) and N6-isopentenyladenine (2). Keywords: Cytokinins; fluoro compounds; biological activity

Synthesis and Cytokinin Activity of Two Fluoro Derivatives of N6-Isopentenyladenine

The analogue of zeatin bearing a vinylic fluorine atom and its geometrical isomer were synthesized. The fluorine atom exerts a favorable influence on cytokinin activity in the fluoro analogue of cis-zeatin, but not in the fluoro analogue of zeatin itself. Another series of zeatin derivatives in which the methyl group was replaced by alkyl (ethyl, propyl, and isopropyl), phenyl, and benzyl groups were also obtained. The ethyl analogue was found to be more active than zeatin, while the others were inactive or slightly active. Keywords: Cytokinins; fluoro compounds; synthesis; biological activity

René Mornet

Papers

Synthesis and Cytokinin Activity of Two Fluoro Derivatives of N6-Isopentenyladenine

Synthesis and Cytokinin Activity of New Zeatin Derivatives

Synthesis of 6-(3-methylpyrrol-1-yl)-9-β-D-ribofuranosyl purine, a novel metabolite of zeatin riboside

The carbonochloridate cleavage of tertiary amines, a simple step in the preparation of di- and trisubstituted olefinic (allylic) synthons

The photosolvolysis of N-arylmethyladenines. Photoremovable N-arylmethyl protective groups for N-containing compounds.