Impact of light and sucrose supplementation on cellular differentiation, metabolic shift and modulation of gene expression in hairy roots of Daucus carota
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Green hairy root cultures of Daucus carota were subjected to gradually lowered sucrose concentrations to understand the modulation of secondary metabolism upon carbon-starved conditions. An apparent negative correlation with the sucrose concentrations in the media was observed with chloroplast development, as confirmed by both histological studies and relevant biochemical assays. Expansion of relative vascular area and well-developed multi-layered endodermis were evidenced in green hairy roots with low sucrose concentrations as compared to normal hairy roots cultivated with 2% sucrose under dark condition. Thus, anatomical modulation was evident in photo-oxidatively stressed green hairy roots because of their maintenance under continuous illumination. This was demonstrated further by the expression analysis of glutathione peroxidase and NADPH reductase genes which showed upregulation in green hairy roots maintained in ½ MS media containing 0.5% sucrose as compared to normal hairy roots. The amount of phenolic marker compound p-hydroxybenzoic acid was reduced to half, while enhanced levels of emitted terpenoid volatiles were noticed in these carbon-starved green hairy roots. Analysis of primary metabolites in green hairy roots showed increased levels of amino acids and sugar alcohols accumulation. Further, analysis revealed the elevated accumulation of organic acids which have significant bearing towards redirection of primary metabolites leading to the formation of enhanced terpenoid volatiles in green hairy roots. Thus, our study revealed the impact of light and sucrose supplementation towards cellular differentiation and redirection of secondary metabolism in hairy roots of D. carota.
KeywordsDaucus carota Green hairy roots Volatile terpenoid p-Hydroxybenzoic acid Sucrose Organic acids
Variable long chain fatty acids
Cinnamoyl Co-A reductase
Large subunit of RuBisCo
Phenylalanine ammonia lyase
Light harvesting complex b
1-Deoxy-d-xylulose 5-phosphate reductoisomerase
Oxidative pentose phosphate pathway
This work was supported from a research grant [38(1201)/08/EMR-II to A. Mitra] obtained from the Council of Scientific and Industrial Research (CSIR), India. S Mukherjee was a recipient of Joint M. Tech -PhD fellowship from the institute. N N Kutty was a recipient of individual doctoral fellowship from CSIR, India.
SM and AM conceived and designed research. SM conducted experiments. SM and NK did HPLC and GC–MS analysis. SM and PB did molecular biology experiments. SM, NK, PB and AM analyzed data. SM and AM wrote the final manuscript. All authors read and approved the manuscript.
Compliance with ethical standards
Conflict of interest
Authors declared no competing interest.
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