Regulation of heat production in the inflorescences of an Arum lily by endogenous salicylic acid

Abstract

We have recently purified calorigen, the natural trigger for heat production in the inflorescences of Sauromatum guttatum Schott (voodoo lily), a thermogenic plant, and identified it as salicylic acid. Since then an analytical assay was developed that allows the quantitation of salicylic acid in plant tissues. This assay was used to demonstrate that on the day preceding the day of blooming the levels of salicylic acid in the thermogenic organs (appendix and lower spadix) of the voodoo lily increased almost 100-fold, reaching a level of 1 mug/g of fresh weight. The level of salicylic acid in the appendix started to rise in the afternoon and reached its maximum in the late evening, whereas the maximum accumulation of salicylic acid in the lower spadix occurred late at night. The increase in salicylic acid level in the appendix was followed the next morning by a spectacular metabolic burst that lasted for about 7 hr and at its peak increased the appendix temperature by over 12 degrees C. The second, 14-hr-long, thermogenic episode in the lower spadix started late at night and ended on the following morning, after maximum temperature increases of more than 10 degrees C. The concentration of salicylic acid in both thermogenic tissues promptly returned to basal, preblooming levels at the end of the thermogenic periods. The thermogenic response was under strong photoperiodic and developmental control, with salicylic acid eliciting much stronger thermogenic responses in light than in darkness. Similar surges in salicylic acid occurred in nonthermogenic male and female flowers, while the concentration of salicylic acid in the spathe remained consistently below 20 ng/g of fresh weight. Of 33 analogs of salicylic acid tested, only 2,6-dihydroxybenzoic acid and acetylsalicylic acid (aspirin) were thermogenic. The activity of 2,6-dihydroxybenzoic acid exceeded that of salicylic acid.