Reversion - varigation gone

Look at this weirdo shrub.  This happens sometimes.  A perfectly nice green columnar top shooting up from a yellow, spreading, variegated base.  Strange stuff like variegations and weeping forms are found from time to time growing on regular plants and these 'sports', mutant shoots, are kept by grafting them to regular root bases.  But every now and then portions of these 'sports' revert to the more normal type.  TPP has a variegated agave, and after it flowered, the main shoot began to die and in the process it produced side shoots that continue the growth of the plant.  But in this case half the side shoots were totally green probably because the population of cells in a particular meristem did not have chlorophyll free cells that make the variegation.  If they contain cells of both normal and cholorphyll free types, the shoots are called chimeras, part one thing, part another (see link below).  If TPP has left them alone, his agave would have been a regular green plant for the future.  Here, the reversion produced a green shoot without the yellowish pigmentation, or rather with it, but the yellow being masked by regular chloroplasts.  A quick nip with the clippers would have left this a spreading yellowish evergreen (yellow?) shrub.  But no one noticed, or they did but didn't clip the green shoot, now the more vigorous green shoot with the regular columnar growth pattern has taken over.  Sometimes people inadvertently prune away variegated portions of their ornamental plants, and they wonder what happened.  If the shoot becomes completely white, devoid of pigmentation, it will grow only as a "parasite" on the rest of the plant. These are best known for redwoods.

Really green animals

Generally organisms are green for one of two reasons: they use chlorophyll for photosynthesis, what the Phactor calls "really green", or they have a green-pigmented camouflage, which produces a pretty clear dichotomy between plants and animals. Down deep in the animal clade where you begin to get close to the never never land of unicellular organisms where distinctions like plant and animal do not work, you find some exceptions: green hydra, green clams, green sea slugs, green corals, and all of these harbor symbiotic algae in their bodies, but not in their cells. So of course once you get used to making such pronoucements, an exception pops up and forces you to go find the bloody thing in your book manuscript and add a dinged dang endnote! Algae are known to live within amphibian eggs in the "gell" surrounding the embryo, which might be considered intracellular, but maybe the Phactor misremembers something about amphibian eggs. The algal cells take up nitrogenous waste and get a nice wet habitat. But now the algal cells have been found inside a salamander embryo itself, the first truly cholophyll green vertebrate, although still lacking vertebrae at that stage of development. Does the embryo gain some benefit from the algal symbiont in addition to the removal of nitrogenous wastes? Does the algae share its photosyntetic products with the salamander? Maybe this will get those darned vertebrate physiologists to learn something about photosynthesis.

Celebrate the green!

What better day to celebrate the green than St. Patrick's day. And what green is more important than chlorophyll?

Chlorophyll is only found in two places those being green bacteria and chloroplasts, and as it turns out those are one and the same. Diverse evidences indicate that chloroplasts had their origin as a cyanobacterium (blue-green algae) that became a cellular slave rather than lunch. This particular symbiosis has been rather successful, in fact that bacterium that became a chloroplast is one of the most successful organisms in all of life history. And this success has had its impact on life.

The particular type of photosynthesis found only in cyanobacteria and chloroplasts liberates oxygen as a by-product because if obtains hydrogen from water. One of the more remarkable insights of biology is that all of the free oxygen in our atmosphere, the oxygen that makes aerobic respiration possible, the oxygen we think of as a life-giving gas, accumulated as a by-product of photosynthesis. And of course oxygen was toxic because life was anaerobic.

That much oxygen doesn't accumulate overnight, and diverse evidence suggests that oxygen-liberating photosynthesis has been around for 3.2 to 3.5 billion years.

So let's hear if for the green of chlorophyll and the most successful organism of all time, a cyanobacterial cellular symbiont! I'll drink to that.