Friday, June 26, 2009

Misplaced Macroalga

When that twister dropped Dorothy off in Oz she still had her house - and it afforded her protection from the withering elements of new places and faces. Not so for this luscious kelp. This is no Oz, it's a beach - and that is no good home for a seaweed.

The kelp's choice in settlement substrate cannot be faulted - it's a fair sized cobble by any measure. But the surf in the Gulf of Maine can be fierce and apparently even such a weighty foundation can be lifted and tumbled over the substrate and up onto Wells Beach.

Our discovery is a brown macroalgae, a type of heterokont (the nature of which is tied to its chloroplast - which we will explore anon). It is a large multicellular organism with a distinct undulating blade, a smooth stipe, and branching hold-fast. Specifically, this is Saccharina latissima, commonly called the Sugar Kelp, and historically (until 2006) known as Laminaria saccharina.

Sweet as a Peanut?

Sadly, I learned too late that this doomed macroalga that caught my fancy could have found an alternate demise in my digestive tract. It seems that this Sugar Kelp is a delicate treat that has long been appreciated for its stores of the sugar mannitol: "In the 19th Century L. saccharina was sold in the streets of Edinburgh, as a snack", which was "said to have a taste reminiscent of peanuts."

* ID of the kelp species in my photos is tentative *
***and insufficient to confirm edibility!
* do not eat any kelp based on the information in this blog!*

Consumption of kelp has been implicated in arsenic and heavy metal poisoning. The alginic acids of brown algae contain carboxylic acid groups that bind to bivalent metal ions and result in elevated concentrations of heavy metals in algal biomass (including plutonium). Because of the higher elevations of heavy metals these effects are likely to be more significant in densely populated coastal areas.

Chloroplasts with Baggage

The diet of a macroalga, just as of the elm, is carbon dioxide. In every cell is a chloroplast that photosynthesizes using the energy of light to split water and generate ATP and NADPH (the molecules that cells use to store energy).

But wait - a curiosity - the chloroplast, it has 4 membranes! The chloroplasts of green algae and land plants have only 2 membranes... There is a family history, a glimpse into the distance past, to be had in this observation.

Start your consideration with this interesting fact: every cell must have a membrane to keep its insides in and its outsides out. And yet, the chloroplasts inside the cells of the brown algae have 4 membranes around their insides!

Next, consider that many cells in the world (within the Bacteria & Archaea) have only one membrane for themselves and no other compartments within them that are bounded by discrete membranes.

What would happen if cell #1 were to swallow cell #2 by simply indenting its own membrane (imagine the equivalent of pushing your thumb into a balloon), taking cell #2 into that little dent, and then sealing the dent on the other side with its own membrane? The result is one cell inside another - but now wrapped in an additional cloak of membrane. The swallowed cell, cell #2, now has two membranes around it.

And so we are but half way to four...

Imagine then, that a third cell, cell #3, is to repeat the process, but with cell #2 now playing the part of the swallowed.

Counting in from the outside there are now 4 intracellular membranes to be accounted for (contained within the cell membrane of cell #3), these are:

1 - the cloaking membrane derived from cell #3, that was used to wrap around cell #2
2 -the cellular membrane of cell #2
3 - the cloaking membrane derived from cell #2 and used to wrap around cell #1
4 - the cell membrane of cell #1

This is the story of millions of years of evolution, competition, and survival. Endosymbiosis (endo: within, sym: together, biosis: life) theory explains the difference between major divisions of life and their divergence. There are lineages derived from primary, secondary, and even tertiary endosymbiosis events.

Even our own cells contain organelles derived from an endosymbiosis event that occurred in ancient evolutionary history. Your mitochondria, those organelles that you must get from your mother's egg (very rarely from your father's sperm), are derived from proteobacteria and they still have their own chromosomes and DNA sequences that group them closer to modern day proteobacteria than anything else.

So, as if carried by a twister from a foreign world and an ancient past, this big brown leathery kelp has washed up from the sea to remind me that there are powerful forces at work in the world around me. Forces that thrust a creature and a cobble from their moist home in the sea to a dry death under a hot sun. And forces that blend the lives and deaths of creatures great and small, to create ever new winning combinations.

Some Links

Clues to identification came from a invasive species card with information about some native Gulf of Maine kelps.

On the historical uses, both culinary and military, of Laminaria saccharina

More kelp in the blogosphere at Jessica's Nature Blog on WordPress

Some Papers

(Bryan 1979 PTRSL) Bioaccumulation of Marine Pollutants

(Schwartz 2002 NEJM) Paternal inheritance of mitochondrial DNA

(Seki 1998 Journal of Colloid and Interface Science) Biosorption of Heavy Metal Ions to Brown Algae,Macrocystis pyrifera, Kjellmaniella crassiforia,andUndaria pinnatifida

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