But when researchers applied stress to the tip of a plant's roots a high concentration of sodium chloride salt it triggered a wave of red that traveled rapidly from the root to the top of the plant.
"We were kind of like, 'Why is it even working?' says Gilroy. "It was probably telling us we were looking in the wrong realm. It's like we could only hear the people shouting and we couldn't hear the talking."
The calcium wave, a flush of red on an otherwise green palette, traveled on a scale of milliseconds, traversing about eight plant cells per second too quick to be explained by simple diffusion of salt.
"It fit with a lot of our models," Gilroy says. "But the idea that it's a wave is one step beyond what our models would predict."
Within 10 minutes of applying a small amount of salt to the plants' roots, typical stress response genes were turned on in the plant.
Also turned on was the machinery to make more of a protein channel called two pore channel 1 (TPC1). Within one-to-two minutes, there was 10 times more of the building blocks needed to make the channel, which is thought to be involved in calcium signaling.
Gilroy and his team then looked at plants with a defect in TPC1. They had a much slower calcium wave about 25 times slower than plants with normal TPC1. When they studied plants expressing more of the TPC1 protein, the calcium wave moved 1.7 times faster.
Plants with more channels also grew larger and contained more chlorophyll than plants with normal or mutated TPC1 when grown in salt water.
The protein channel is present in all land plants, says Gilroy, and it's found throughout the plant. This is one of the many reasons it surprised the team to learn the calcium wave moves only through specific cells in the plant, like electrical signals moving through nerve cells in humans and other animals.<
|Contact: Simon Gilroy|
University of Wisconsin-Madison