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summary This report combines chemical, electron microscopic and ecological studies on the volatiles liberated by the Sauromatum guttatum appendix on D‐Day, the day of inflorescence‐opening and heat‐production. More than 100 compounds from at least nine different chemical classes (monoterpenes, sesquiterpenes, fatty acids, ketones, alcohols, aldehydes, indole, and phenolic and sulphur compounds) are liberated during the thermogenic activity. The volatiles were identified using gas chromatography‐mass spectrometry. Electron microscopy provides additional evidence that the endoplasmic reticulum (ER) interacts with the plasma membrane, creating novel routes of excretion of the volatiles to the exterior of the cell. It seems that the fusion event creates channels from the interior to the exterior of the cell. Furthermore, a multitubular body, conceivably originating in the ER, seems to fuse with the plasma membrane and to appear only on D‐day. This multitubular body is closely associated with lipid bodies during heat‐production and might be involved in the oxidation of lipids to volatile products. The foul odour produced by the appendix attracts at least 30 species of insects.

The infrared radiation emitted from the surface of inflorescences of 12 aroid species was monitored with an infrared camera, capable of 0.1°C resolution, and the data were converted to temperature values by means of temperature reference standards. Images representing surface temperatures were obtained forAmorphophallus bulbifer Blume,A. campanulatus Blume,A. forbesii Engl. et Gehrm.,A. rivieri Dur.,Philodendron selloum Koch,Monstera deliciosa Liebm.,Dracunculus vulgaris Schott,Arum italicum Mill.,A. dioscoridis Sibth.,A. creticum Boiss et Heldr.,Caladium sp., andRemusatia vivipara Schott. These images were different among species with respect to temperature, duration of detectable heat development, and organ type (male and female flowers, spathe and appendix) found to be thermogenic. All these species, however, exhibited three common characteristics: 1) production of heat by the male flowers; 2) pollen-shedding immediately after heat production had ceased; and 3) when male flowers were some distance away from female flowers along the spadix, heat was not detected in female flowers. Heat emission was associated with the alternative, cyanide-insensitive pathway that was fully operative.

The pattem of surface temperatures of the inflorescence of Sauromatum guttatum was investigated by using an infrared camera. The male flowers are weakly thermogenic on the first day of inflorescence opening (D-day) as well as on the next day (D + 1), reaching 0.5 to 1°C above ambient temperature. The appendix (the upper sterile part of the inflorescence) is highly thermogenic on D-day, reaching 320C, and is faintly thermogenic on D + 1, reaching 1°C above ambient temperature. The lower part of the spadix, close to the female flowers, is also thermogenic on D-day and D + 1, reaching a temperature similar to that of the appendix only on D + 1. Salicylic acid does not induce heat production in the lower part of the spadix, as it does in the appendix. Respiration of tissue slices obtained from the appendix shows that the capacity for cyanide-insensitive respiration is present in young and mature appendices. This altemative respiratory pathway is not, however, utilized in young appendix tissue, but is engaged during the maturation of that tissue. MATERIALS AND METHODS Plant MaterialSauromatum guttatum inflorescences were grown in a growth chamber under 15-h light/9-h dark periods with a photon flux density of 150 ,umol m-2. s-' at 19°C. The developmental stage of S. guttatum was determined retroactively with respect to D-day, the day of inflorescence opening.Thermal Image-Processing System A thermographic system previously described was used to obtain surface temperatures of the inflorescence (6). Fifty to 100 images were recorded during the thermogenic response, and images were analyzed only for periods during a change in heat-production pattern. More than 10 inflorescences were examined.c. 1)The inflorescence ofSauromatum guttatum is a widely used material for the study of heat production in plants. Salicylic acid was recently identified as 'calorigen', the plant hormone that induces heat-production in the inflorescence-appendix of S. guttatum (4). The alternative (cyanide-insensitive) oxidase that is required for plant thermogenicity has been purified from appendix mitochondria (2). The production of two of the proteins associated with the alternative oxidase activity is regulated by salicylic acid in vivo (3).Although much is now known about the alternative oxidase and the levels of salicylic acid in various parts of the Sauromatum inflorescence, a detailed description of heat production by that inflorescence has not yet been reported. We now present an analysis of heat production during anthesis by using infrared thermography. We also sought to determine whether salicylic acid can trigger heat production in thermogenic parts other than the appendix (the male flowers and the lower part of the spadix).