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 Post subject: Root of the Problem...
PostPosted: Fri May 31, 2013 11:10 pm 
Broken Crown Panelist
Broken Crown Panelist

Joined: Sun Oct 21, 2012 1:59 pm
Posts: 15
If you were to ask the average person, "What is the most important part of a plant", many would say "flowers" or "leaves", but I think I can argue that "roots" have to be considered the one of the most important and least understood parts of the plant.

So why is this important to our conversation about plants on other worlds? It appears that the ability of plants to anchor to a substrate and absorb water and minerals from the environment are two crucial hurdles that plants had to overcome in Earth's evolution.

The earliest plants were simple, small sticks that hugged the edges of water. This is mainly because land plants evolved from freshwater green algae, which were completely dependent on water for support and minerals absorption. As plants became to invade the land 500-450 million year ago, they need to gain a foot hold on the earth. They may have been able to absorb minerals from the shallow water environment, similar to how mosses absorb minerals today. But, as mutations proliferate and time passes, plants began to adapt to the land.

Image
Ordovician land plants from wikimedia.org

They need to find a way to anchor their body and absorb minerals from this Mars-like landscape. It appears that the fossil record shows us that fungi (once again) played a large role in this. Some of the earliest land plants have mycorrhizae associations, or fungi that serve as “roots” absorbing minerals for the plant in return for sugars from the photosynthesis. These plants may have simple root-like structures, called rhizoids, like modern mosses, and used the fungi to absorb minerals.

Image
Rhizoids of a living ancestral plants from commons.wikimedia.org

So why do plants need minerals and water anyway? Consider the minerals, such as nitrogen, phosphorous, potassium, magnesium, etc.; these are all used as building blocks for creating cell walls, chloroplasts, enzymes, and other metabolic pathways. Without these minerals, the plants begin to suffer from an inability to grow and develop normally. In simple terms, they start to show sign of mineral deficiency.

Water is crucial for photosynthesis for all plants. Many use water to create turgor pressure or support, and other save water for drought conditions, but almost all plants photosynthesize. They need water so they can split hydrogen from oxygen, called hydrolysis, so they begin the process of creating sugars. H2O is split with the plant keeping the hydrogen and releasing the oxygen. This is why plants “give off oxygen”… The plants then take in carbon dioxide, or CO2, and ultimately they combine the Hs with the Cs and Os, to get CHOs, or simple sugars. The water is the starting block for creating a solid form of energy for plants.

If we were to explore a landscape for photosynthetic life, which is devoid of liquid water, we would need to find sources of hydrogen, carbon and oxygen for these plants to complete the sugar making process. Maybe there is a photosynthetic organism in this strange world of Titan that can take in the abundant methane, or CH4, to start to create sugars. Maybe the limiting factor isn’t hydrogen, but oxygen in this landscape, which is needed to complete the CHO formula. We would need to find an organism that can hand the low light intensities and the freezing cold temperatures. All of these things would be hurdles for life to overcome, but maybe if intelligent life was around 600 million years ago on Earth, they would have thought the same thing.


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