Flower Morphology and Development In Artemisia Annua, a Medicinal Plant Used as a Treatment against Malaria

Artemisia annua produces a wide spectrum of bioactive phytochemicals that possess pharmacological properties including antimalarial, antitumor, anti-inflammatory, and anthelmintic activities.  The main active ingredient, artemisinin, is extremely effective against multi-drug resistant Plasmodium falciparum, and is recommended by the World Health Organization to be used, in combination with a second drug, in artemisinin-based combination therapies (ACTs).  Breeding to develop high-artemisinin producing Artemisia annua cultivars would provide a means to meet the worldwide demand of artemisinin and its derivatives. However, the fundamental processes of flower development, stigma receptivity, self-incompatibility, and seed development are poorly understood, and severely impairs breeding programs. Consequently morphological and histological evaluations of flower development in Artemisia, were made to define the developmental timing of flower types within inflorescences, and to evaluate stigma receptivity and pollen-stigma interactions. Plants were given short-day treatments to induce flowering, and floral development was evaluated using light and scanning electron microscopy.  Flowers are born in a capitulum, with pistillate ray flowers and centrally located bisexual disc flowers. Pistillate flowers have elongated, bifurcated stigmas which are extended prior to the opening of the disc flowers. In bisexual flowers, the appearance of a pollen presenter and pollen release precedes the emergence of two sigma lobes that expand and become reflexed.  The stigmatic surfaces of both types of flower have unicellular papillae and appear to be of the dry type lacking a copious exudate.  Pollen-stigma interactions and the effects of flower age and pollen source will be described.