It is becoming increasingly evident that the formation of arbuscular mycorrhiza (AM) enhances secondary metabolite production in shoots. Despite mounting evidence, relatively little is known about the underlying mechanisms. This study suggests that increase in artemisinin concentration in Artemisia annua colonized by Rhizophagus intraradices is due to altered trichome density as well as transcriptional patterns that are mediated via enhanced jasmonic acid (JA) levels. Mycorrhizal (M) plants had higher JA levels in leaf tissue that may be due to induction of an allene oxidase synthase gene (AOS), encoding one of the key enzymes for JA production. Non-mycorrhizal (NM) plants were exogenously supplied with a range of methyl jasmonic acid concentrations. When leaves of NM and M plants with similar levels of endogenous JA were compared, these matched closely in terms of shoot trichome density, artemisinin concentration, and transcript profile of artemisinin biosynthesis genes. Mycorrhization increased artemisinin levels by increasing glandular trichome density and transcriptional activation of artemisinin biosynthesis genes. Transcriptional analysis of some rate-limiting enzymes of mevalonate and methyl erythritol phosphate (MEP) pathways revealed that AM increases isoprenoids by induction of the MEP pathway. A decline in artemisinin concentration in shoots of NM and M plants treated with ibuprofen (an inhibitor of JA biosynthesis) further confirmed the implication of JA in the mechanism of artemisinin production.

Artemisia annua L. is an aromatic-antibacterial herb that destroys malarial parasites, lowers fevers and checks bleeding, and of which the secondary compound of interest is artemisinin. Enhanced production of the artemisinin content in the whole plant is highly desirable. Keeping in mind, the importance of this valuable antimalarial plant, field experiments were conducted to investigate the effects of triacontanol alone and in combination with gibberellic acid on growth attributes, photosynthesis, enzymatic activities, essential oil and artemisinin content and yield of Artemisia. The results indicate that combination of triacontanol and gibberellic acid (1.5 mg l(1 '75 mg l (1 ) significantly increased activities of nitrate reductase and carbonic anhydrase by 25.9% and 21.5%, and net photosynthetic rate, stomatal conductance and internal CO 2 by 25.4%, 14.1% and 15.4% higher, respectively, when compared to unsprayed plants. This combined treatment also significantly enhanced artemisinin content and yield (29% and 61% higher values).

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