Stimulatory role of smoke–water and karrikinolide on the photosynthetic pigment and phenolic contents of micropropagated ‘Williams’ bananas

At low concentrations, smoke–water (SW) and smoke-derived karrikinolide (KAR1) are compounds with potential cytokinin and auxin-like activity. Their roles on the growth, photosynthetic pigment and phenolic contents of micropropagated ‘Williams’ bananas were investigated in comparison with meta-topolin (mT). Explants were cultured on modified Murashige and Skoog basal media supplemented with either SW (1:125; 1:250; 1:500; 1:1,000; 1:2,000 dilutions) or KAR1 at four concentrations ranging from 4.8 × 10−22 to 3.3 × 10−12 M. After 42 days, growth parameters were measured while the photosynthetic pigments and phenolic contents were quantified using spectrophotometric methods. Chlorophyll a, b and total carotenoid contents were significantly enhanced by KAR1 (4.8 × 10−22 M) and SW (1:125 and 1:1,000 dilutions). The pigments in KAR1-treated plantlets were approximately two-fold to three-fold higher than those in the control and mT-treated plants, respectively. Total phenolic content was highest with KAR1 at 1.0 × 10−19 M in the leaves and 7.8 × 10−17 M in the roots. Furthermore, KAR1-treated plants at 1.0 × 10−19 M yielded the highest level of total phenolics (leaves) and proanthocyanidins (roots). At 1:500 dilutions, SW stimulated the highest total flavonoid content in the leaves across all the treatments. Combining mT with either SW (1:500) or KAR1 (4.8 × 10−22 M) significantly increased the quantity of secondary metabolites. However, the growth parameters and pigment contents were not improved. Based on the significant role of photosynthetic pigments and phenolic compounds on the defense and survival strategies of plants, current findings will have practical significance for important processes such as acclimatization and survival of micropropagated plants. These results are also demonstrating the potential of SW and KAR1 as an eliciting agent for secondary metabolite production.