Plant Brains Solve Problems

Without a physical brain or nervous system, plants know how to get about in place.

Shade sensor (PhysOrg): How do you find light without eyes? And without skin, how do you sense that someone’s shadow is getting in your light’s way? Plants solve these and other problems.  “Despite seeming passive, plants wage wars with each other to outgrow and absorb sunlight. If a plant is shaded by another, it becomes cut off from essential sunlight it needs to survive,” this article says.

To escape this deadly shade, plants have light sensors that can set off an internal alarm when threatened by the shade of other plants. Their sensors can detect depletion of red and blue light (wavelengths absorbed by vegetation) to distinguish between an aggressive nearby plant from a passing cloud.

Scientists at the Salk Institute have discovered a way by which plants assess the quality of shade to outgrow menacing neighbors, a finding that could be used to improve the productivity of crops. The new work, published Dec. 24, 2015 in Cell, shows how the depletion of blue light detected by molecular sensors in plants triggers accelerated growth to overcome a competing plant.

Their secret lies in light-sensitive organelles called cryptochromes. When activated, they turn on epigenetic controls to switch on genes for growth. “We found that cryptochromes contact these transcription factors on DNA, activating genes completely different than what other photoreceptors activate,” the Salk scientists said. It’s a short pathway so that the plant can respond quickly, but not too quickly.

Latex survival: The milky-white sap in dandelions is there for a reason. It repels bug larvae in the soil that might munch on the roots. “Dandelions are survival experts,” Science Daily says, pointing out two other amazing feats for the tender-looking little herb. It’s cosmopolitan and has muscle!

Dandelions (Taraxacum officinale agg.) are well-known plants of European and Asian origin that have spread around most of the temperate world. Children love their yellow flowers and even more the fluffy seed heads with their parachute-like seeds that can travel long distances by wind. Young plants grow with such force that they can penetrate even asphalt. Therefore dandelions have become a symbol for survival in modern cities.

Geological instrumentation: You’re a seedling in the soil. You have sensors telling you to move upward, but how do you know how far it is to get into the air? This could be crucial to survival. You have to conserve resources before sunlight can help your developing shoots to grow leaves. Seedlings have special equipment to measure the depth and mechanical pressure of the soil above them, report scientists in Current Biology. The instrumentation involves a protein, COP1, that responds to light to adjust the transcription factors for ethylene production, a chemical that mediates seedling emergence. Did you have any idea a little bean seedling you grew in science class has the equivalent of a PhD in mechanical engineering and organic chemistry? Here’s a taste of what happens as the little seedling grows through that heavy soil toward the light:

We show that COP1 directly targets the F box proteins EBF1 and EBF2 for ubiquitination and degradation, thus stabilizing EIN3. As seedlings grow toward the surface, the depth of soil overlay decreases, resulting in a gradual increase of light fluences. COP1 channels the light signals, while ethylene transduces the information on soil mechanical conditions, which cooperatively control EIN3 protein levels to promote seedling emergence from the soil. The COP1-EBF1/2-EIN3 module reveals a mechanism by which plants sense the depth to surface and uncovers a novel regulatory paradigm of an ubiquitin E3 ligase cascade.

Plants are so beautiful and smart, don’t you just want to hug them sometimes? Just don’t reach for the ragweed or poison oak. They’ll perceive you as a threat and call their defense agency. If a dandelion can punch through asphalt, imagine what it could do to you if it operated at high speed.