Thermogenic Plants Research Articles

Heat-producing flowers

The flowers of some plants produce enough heat to raise their temperatures as much as 35°C above air temperature. Three species have been shown to regulate flower temperature within a narrow range by an unknown physiological mechanism that increases the rate of heat production as air temperature decreases. Thermogenic plants occur only in ancient families of seed plants, and have apparently evolved in association with beetle pollinators. Because many beetles require high body temperatures for activity, the warm environment inside thermoregulating flowers may be an energetic reward during their visits.

Identification of a soluble salicylic acid-binding protein that may function in signal transduction in the plant disease-resistance response.

It has recently been demonstrated that salicylic acid (SA) may serve as an endogenous signal molecule in the induction of systemic acquired resistance in tobacco and cucumber. In addition, SA is an endogenous regulator of heat and odor production in the inflorescence of some thermogenic plants. No information, however, is currently available concerning the mode(s) of action of SA in plant signal transduction. In a search for possible cellular factors that directly interact with SA, we have detected and partially characterized a SA-binding protein in tobacco leaves. The SA-binding activity is both SDS and proteinase sensitive and behaves as a soluble protein with an apparent mass of 650 kDa. The protein has an apparent Kd of 14 microM for SA, which is consistent with the range of physiological concentrations of SA observed for the induction of plant resistance responses. Furthermore, the ability of SA analogues to compete with SA for binding to this soluble protein is strictly correlated with their biological activity to induce the expression of genes associated with disease resistance. Biologically active analogues effectively inhibit SA binding while biologically inactive analogues do not. These results collectively indicate that this SA-binding protein may play a role in perceiving and transducing the SA signal to appropriate response elements, which ultimately activate one or more of the plant disease-resistance responses.

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

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.

Salicylic Acid: A Natural Inducer of Heat Production in Arum Lilies

For more than 50 years the identity of "calorigen," the agent that triggers pronounced heat production in the flowers and inflorescences of some thermogenic plants, remained obscure. Mass spectroscopic analysis of highly purified calorigen extracted from the male flowers of Sauromatum guttatum Schott (voodoo lily) revealed the presence of 2-hydroxybenzoic (salicylic) acid. Application of salicylic acid at 0.13 microgram per gram (fresh weight) to sections of the upper part of the plant's immature spadix, known as the appendix, led to temperature increases of as much as 12 Celsius degrees. These increases duplicated, in both magnitude and timing, the temperature increases produced by the crude calorigen extract. The sensitivity of appendix tissue to salicylic acid increases daily with the approach of anthesis and is controlled by the photoperiod. Thus, at least in some Arum lilies, salicylic acid functions as an endogenous regulator of heat production.