Evidence for the Role of Salicylic Acid in Thermoregulation in Sporophylls of Male Cones of Six Cycad Species

The objective of this research was to provide a framework for the study of induction of thermogenesis by aspirin, salicylic acid, and 2,6-dihydroxybenzoic acid in detached sporophylls from male cones of six cycad species. The thermogenic species were: Zamia elegantissima Schutzman, Vovides & R. S. Adams; Z. furfuracea L.f.; Z. pseudomonticola L.D.Gómez ex D.W.Stev. & Sabato; Z. skinneri Warsz; Encephalartos hildebrandtii A. Braun & C. D. Bouché; and Cycas siamensis Miq. Temperature of single sporophylls was measured for 48 h using thermocouples in the absence and presence of inducers. Sporophylls treated with salicylic acid generated asymmetric temperature waves and square and sinusoidal temperature waves. Also a jump in temperature at a rate of ~ 1 ºC/h was detected in sporophylls treated with salicylic acid. A drop in temperature preceded the temperature jump to a new and higher steady-state level and it stayed unchanged. These unexpected thermal activities suggest cellular controls of mitochondrial thermoregulation.