Differences in hypericin synthesis between experimentally induced seedling shoot cultures of Hypericum hookerianum Wight & Arn

During seed germination trials of Hypericum hookerianum, seedlings of Lake View accession from Palni hills of Southern India segregated into green- (97.44 %) and red-pigmented (2.56 %) types. Seedlings cultured in Murashige and Skoog (1962) basal medium developed into fast growing green and slow growing red plant types in 6 weeks, the latter showing increased concentrations of total phenols, anthocyanins and flavonoids and 19-fold higher concentration of hypericin. Hypocotyls/cotyledons of red seedlings cultured using $2.325{\mu}M$ kinetin (KIN) produced hypericin-rich ($4.38{\pm}0.18$ mg/g DW), stunted (0.5-1.2 cm) shoots which ceased to grow in 8 weeks. Segments (4-6 mm) of these shoots sub-cultured in the dark for 4 weeks followed by 2-week light exposure and repeated subculture enabled mass multiplication of productive ($3.93{\pm}0.06$ mg hypericin/g DW) shoots. Green hypocotyls and cotyledons subjected to 4+2 weak dark-light treatment also produced $9.18{\pm}2.44$ and $4.25{\pm}0.96$ comparable hypericin-rich ($3.73{\pm}0.21$ mg/g DW) shoots. Red and green seedling explants cultured in basal medium in the dark produced $6.82{\pm}0.75$ cm etiolated shoots with reduced leaves which synthesized $2.27{\pm}0.15$ mg hypericin/g DW on illumination. Green cotyledons cultured in the dark using $2.45{\mu}M$ indole-3 butyric acid (IBA) formed calluses which on illumination formed $12.64{\pm}3.8$ productive ($3.86{\pm}0.31$ mg hypericin/g DW) 0.5- to 1.5-cmlong shoot clusters. Phenotypic segregation of seedlings, the ability of both red and green seedling explants to multiply in the dark and produce hypericin on illumination, and IBA-induced indirect shoots producing significant amounts of metabolite compared to wild plants ($0.35{\pm}0.09$ mg/g DW) and green shoot cultures ($0.91{\pm}0.03$ mg/g DW) are new to Hypericum.