In celebration of July 4th, this typically green blog is going red, white and blue.
There are lots of connections between plants and the color red. Roses are red. Plants emit a faint red fluorescent glow, as I wrote about in my previous post. But it isn’t all about plants; there are other photosynthesizers, like algae. While green may dominate your perception of algae, there is an entire group of red algae, the Rhodophyta, that exist below the surface of marine environments. Like plants and green algae, they are eukaryotes, but they have many photosynthetic characteristics that are closer to the prokaryotic cyanobacteria. Most notably, they contain the phycobilisome antenna structures to funnel light into their photosynthetic machinery. Since the red algae live in the ocean below other photosynthetic organisms, they take advantage of the higher-energy blue light that penetrates deeper into the water. To do this, they make the phycoerythrin pigment which appears red. This may sound exotic, but you may be more familiar with red algae than you think. The agar and agarose used in microbiology labs is derived from species of red algae as well as the nori used to roll your sushi.
The ‘color’ white in plants is an interesting case. It means that no pigments are present, and all visible light is being reflected from the plant tissue. Very little, if any, light is being absorbed. Since their lives depend on converting sunlight into chemical energy, reflecting all of it away from themselves represents a risk by the plant. However, it is a calculated one that pays off. The white tissue of flowers depends on the other green parts of the plant to supply it with sugar and other energy molecules for biochemical support, but it creates a contrast from the rest of the plant. In this way, the plants have made it easier for pollinators to home in on flower tissue with its nectar and pollen. It creates the most basic win-win situation for plants and pollinators- no extra biochemical pathways required. Of course, some ‘plants’ take white too far and lose the ability to be photosynthetic as in the case of the ghost plant.
True blue can also be difficult to come by in the plant world. Because blue light resides on the high-energy side of the light spectrum, it is in the best interest of the plants to absorb that energy to drive photosynthesis. Indeed, the antenna pigments of photosynthetic organisms are very good at absorbing blue and red light. However, some plants can make a special class of anthocyanidin that reflect blue light. Pigments like delphinidin give larkspurs, violas and grapes their distinctive bluish hues. Alas, not all plants have the biochemical pathways to create blue flowers, but the demand for blue blooms in the horticultural sector doesn’t let nature get in its way. Plant scientists can use biotechnology to insert the genes necessary to produce the blue pigment. While true blue roses haven’t quite come to fruition, blue varieties of carnations and chrysanthemums have been engineered.
These examples show that the photosynthetic world can be patriotic as well. Colors, like red, can come from common places and overlooked depths, while white can be a beneficial sacrifice. Blue can be true or migrate in from exotic sources.
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