HOT, Stinking Plants AND Thermogenesis

Plants bypass Electron Transport Chain for thermogenesis and attract insects (dung beetle) for pollination.


What is a Skunk Cabbage?

As you can understand by the name that these cabbages emit a stinking odour which is pollinating mechanism for them to attract dung beetles which are mostly found laying eggs on rotting flesh and waste material. By emitting the foul stench they attract the dung beetle to lays eggs on them and in the process bring about their pollination.

     The skunk cabbage belong to the family of Araceae. These plants have tiny flowers, densely on an erect structure, the spadix, surrounded by a modified leaf, the spathe. The spadix emits odours of rotten flesh or dung. Before pollination the spadix heats up to as much as 20 to 40°C above the ambient temperature. This thermogenesis helps to evaporate the odorant molecules for better dispersal and because dung is usually warm due to hyperactive microbial metabolism on them. These skunk cabbages flower in late winter when snow still covers the ground, the heat generated help them to melt the surrounding snow.

How does skunk cabbage heat it’s spadix?

The mitochondria of plants, fungi and unicellular-eukaryotes have an Electron Transport Chain same as that of animals except that they have a cyanide resistant ubiquinol-oxidase transfers electron to oxygen bypassing the two proton translocating  steps of complex III and complex IV. So energy conserved in production of ATP is released as heat. Also plants have an alternative NADH-dehydrogenase insensitive to complex I inhibitor rotenone, that transfers electron from NADH directly to ubiquinone bypassing Complex I and it’s associated proton pumping. Also plant mitochondria have yet another NADH dehydrogenase, on the external face of inner membrane that transfers electron that transfers electron from NADPH on NADH to ubiquinone again bypassing Complex I. Thus when electrons enter the alternative respiratory pathway through the rotenone-insensitive NADH dehydrogenase, the external NADH dehydrogenase (Complex II), and pass to O2 via the cyanide-resistant alternative oxidase, energy is not conserved as ATP but lost as heat. A skunk cabbage can use the heat to melt snow, produce a foul stench, or attract beetles or flies.

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