Assessment of the role of meta-topolins on in vitro produced phenolics and acclimatization competence of micropropagated 'Williams' banana

The effects of five topolins (meta-Topolin, mT; meta-Topolin riboside, mTR; meta-Methoxy topolin, MemT; meta-Methoxy topolin riboside, MemTR and meta-Methoxy topolin 9-tetrahydropyran-2-yl, MemTTHP) on the phenolic content and subsequent acclimatization potential of micropropagated 'Williams' bananas were compared to benzyladenine (BA). Sterile shoot-tip explants were cultured on modified Murashige and Skoog (MS) media containing 10, 20 or 30 mu M of the above aromatic cytokinins (CKs) for 42 days. Phenolic contents were quantified spectrophotometrically. Growth parameters and photosynthetic pigments of the greenhouse-acclimatized plants were determined after 5 months. Total phenolic levels were highest in 10 mu M mT-treated plantlets within the aerial parts and 30 mu M MemTTHP for the underground parts. In the underground parts, 10 mu M mT resulted in the production of the highest amount of proanthocyanidins which was approximately five-fold higher than in the control plants. Furthermore, 10 mu M MemTTHP-treated plantlets had significantly higher total flavonoids (30.1 +/- A 0.24 mg CE/g DW) within the aerial parts. Plantlets regenerated using MemT, MemTR and MemTTHP had significantly longer roots and better shoot/root ratios compared to the control and BA-treated plants. In terms of root fresh weight, it was significantly higher in MemT-treated plantlets than in the control and BA treatments. Chlorophyll a/b ratio was significantly improved with the use of MemT, mTR and mT compared to control. Current findings indicate the potential of topolins in stimulating the accumulation of phenolic compounds in micropropagated plantlets. In view of the importance of plant secondary metabolites, their substantial accumulation probably enhanced the acclimatization and subsequent ex vitro survival of the micropropagated plantlets. Topolins, particularly, the new derivative MemTTHP could be an alternative CK for the micropropagation of plant species based on their stimulatory effect on ex vitro rooting that inevitably enhances acclimatization competence. Furthermore, topolins are demonstrated as potential elicitors in micropropagation.