Dynamics of thermogenesis and structure of epidermal tissues in inflorescences of Arum maculatum

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Abstract
The temporal dynamics and spatial distribution of heat production by inflorescences of Arum maculatum L. were investigated by infra-red thermography. Two centres of (teat production, the appendix and the male flowers, and three thermogenic phases, two of the male flowers and one of the appendix, could be observed. On the first day of flowering, when the spathe was still firmly closed, the male flowers became thermogenic (= first thermogenic phase Of the in florescence) and reached surface temperatures of 4.1-8.0 °C above ambient temperature. Afterwards the spathe unfolded and the appendix started heating to temperatures of 5.0-14.0 °C above ambient temperature (second thermogenic phase of the inflorescence). On the second day of flowering the male flowers revealed a second temperature maximum of 0.5-601 °C above ambient temperature third thermogenic phase of the inflorescence) which was followed by the release of the pollen grains. When the male flowers started heating, a fruit-like and pleasant scent became evident and continued until the heat production in the male flowers stopped. Only during the heating phase of the appendix was this fruit-like scent overlaid by the dung-like odour typical of many aroid species. The surface of the spadix and the inner surface of the basal bulb (floral chamber) as investigated by scanning electron microscopy were characterized by smooth epidermal cells of papillate shape. These cells were rurgid before the onset of flowering and heat production and collapsed afterwards. Distinct intercellular spaces creating a lacunose epidermis ('Lückenepidermis') were observed between the papillate epidermal cells of the inner surface of the basal bulb (floral chamber). This coincided with a high density of stomata on its outer surface. It is suggested that, beside other pathways, these structures contribute to the maintenance of sufficient oxygen support of the captured insects and the thermngenic tissues inside the floral chamber.