Wednesday, August 26, 2015

Mighty Titan!

Currently the web is abuzz about the once a decade blooming of the so-called corpse flower, Amorphophallus titanum (Titan arum). Not only is it rare, the corpse flower only blooms once every 7 - 10 years, it is HUGE! While it looks like one giant flower, it is actually a group of flowers on the large stem. In botany, we call this an inflorescence. And Titan arum has the largest unbranched inflorescence known on this planet measuring, on average, 6 feet tall, with the record over 11 feet, and can be well over 100 pounds.

Credit: US Botanic Garden, Public Domain
The corpse flower moniker has stuck with these giants as they emit a foul stench that smells of rotting flesh. What's a gorgeous flower like that doing smelling so pungent?

The answer, looking for hot dates with carrion-eating insects, of course! The stinky chemicals wafting off the inflorescence attract these insects with the promise of a rotting flesh buffet. Both male and female flowers are found on the inflorescence stem of Titan arum. On the first night that the large spath (the funnel looking piece) is open, the female flowers bloom and will hopefully be pollinated by the insects attracted to the stench. On the second night, the male flowers bloom where the attracted insects pick up pollen. The fact that the female and male flowers open on back to back nights cuts down the potential for self pollination.

In addition to the foul stench, this particular flower is also capable of raising its internal temperature above that of room temperature! This warming up is another attractant for the pollinators, as the heat increases when the flowers are blooming and insects are cold blooded. But how is this heat generated?

To answer this question, lets delve a little into some biochemistry. As I've said before, plants are the world's best biochemist and this is certainly one of their cooler processes. For heat-producing plants, this temperature increase is due to the action of a single enzyme: alternative oxidase.

Alternative oxidase is found in the mitochondria, where cellular energy is produced. During normal cellular respiration (the process by which energy is created), electrons pass through several different enzyme complexes inside the mitochondrial membrane, creating a proton gradient which then drives ATP (energy) generation. When thermogenessis is required, alternative oxidase interrupts this process, absorbing electrons and releases heat. During flowering, almost all of the electron energy that enters the mitochondria is passed through alternative oxidase into heat. The triggering of the alternative oxidase pathway is thought to occur via 2 ways, which may be exclusive or occur simultaneously. 1) the alternative oxidase present in the cell is activated by the breakage of a disulfide bridge within the enzyme and/or 2) the amount of alternative oxidase present in the cells increases. Either way, a plant that can control when it warms up is very impressive.

There is a lot of attention on the corpse flower right now as many of these giants have been in bloom recently. Today, I know they are waiting anxiously at Chicago Botanic Garden ("Spike"), Binghamton University, and Virginia Tech for ones to bloom. Last week, "Stinky" bloomed at Denver Botanic Garden who actually sent some pollen to Chicago to pollinate "Spike"! Earlier this year, the Royal Botanic Garden of Edenburgh's Titan bloomed with its own Twitter account: @TitanArumRBGE. The size, rarity, and biochemical prowess of the flower results in a well deserved, standing room only reception. If one is blooming near you, get out to see, and smell, this impressive plant.

References (with video of Sir David Attenbrough!)

Korotkova, N., & Barthlott, W., 2009. On the thermogenesis of the Titan arum (Amorphophallus titanum). Plant Signaling & Behavior, 4(11), 1096–1098.

Wagner AM1, Krab K, Wagner MJ, Moore AL., 2008. Regulation of thermogenesis in flowering Araceae: the role of the alternative oxidase. Biochim Biophys Acta:993-1000.