A NAD(P) reductase like protein is the salicylic acid receptor in the appendix of the Sauromatum guttatum inflorescence

Thermoregulation in the appendix of the Sauromatum guttatum (Schott) inflorescence

BACKGROUND

Three phenolic compounds are capable of activating the process that simultaneously leads to temperature rise and odor-production in the Sauromatum appendix. These compounds are salicylic acid, aspirin, and 2,6 dihydroxybenzoic acid. The objectives of the present study were to examine the effect of various concentrations of the these inducers on the temperature rise and to study the effect of mitochondrial inhibitors (KCN and SHAM) and an uncoupler (DNP) on the temperature rise.

RESULTS

In sections of the Sauromatum appendix two successive temperature rate maxima were detected in the presence of the three inducers. Two temperature maxima were also detected in appendices of intact inflorescences. The temperature profiles demonstrated a considerable variability within sections of one appendix in both magnitude and time of reaching a peak. When the Sauromatum temperature decreased it returned either to the same temperature baseline or to a slightly different baseline. The temperature rise was blocked by KCN (20 mM) and SHAM (40 mM) alone or when added together. DNP, an uncoupler, at 2.5 mM also blocked the rise in temperature. The thermogenic inducers also triggered a temperature rise in Arum appendix.

CONCLUSIONS

The presence of two rate maxima may indicate different heat-generating sources. The blockage of the temperature rise in the presence of KCN or SHAM implies that the activity of the cyanide-resistant and -sensitive pathways is required for generating heat. The variability in temperature profiles maybe related to changes in cellular control factors. This study provides the basis for investigating thermoregulation in plants.

Human ortholog of a plant salicylic acid receptor found in SK-N-SH cell line

Our previous studies have described the purification and characterization of a novel plant NAD(P)-reductase like protein (RL) from the thermogenic appendix of the Sauromatum guttatum inflorescence. RL is mainly located in cytoplasm of thermogenic plants and it can act like a bistable switch. It adopts a compact conformation during heat-production and a more expanded conformation when heat is not generated. Addition of salicylic acid, a natural thermogenic inducer, at picomolar concentration to a solution of purified RL induced a discontinuous volume phase transition in which the volume of RL in the oligomeric form expanded and shrunk repeatedly every 4-5 min. In the present study using ESI-MS analysis we have demonstrated the existence of RL in the human SK-N-SH cell line and in mouse brain tissue. The molecular mass of human RL is in the same range as of its plant counterpart, 34,140 ± 34 Da. The charge state distribution of the human RL is identical to its plant counterpart from the Sauromatum appendix during heat-production. Human RL was present in the compact state when it was purified from the SK-N-SH cell line When these cells were treated with salicylic acid (10 μM) a shift to a much more compact conformation was observed. It seems that the potential of RL to respond to salicylic acid was conserved. These results may reveal the existence of a thermoregulation system that is evolutionarily conserved and is operating by conformational changes. This discovery may also represent an opportunity for a better understanding of some of the diverse functions of salicylic acid and aspirin in plants and humans.