I’ve been reading on plant water sensing to get some better background for projects we’re starting in the lab this summer. I came across the photo below in a paper describing the identification of a gene involved in sensing water gradients, called miz1, short for MIZU-KUSSEI1, the words for “water” and “tropism” in Japanese.
The photo shows an elegant experiment the researchers designed to pick out mutants in water sensing. They allowed the roots to grow in a Petri dish along a block of agar (seen in the upper left part of each panel) and into an opening. Normally, an open space in a closed Petri dish would have very high humidity, but they added a solution that soaks up water vapor, so the air was very dry.
The two photos across the top (D1 and D2) show the response of a wild-type root when it grows into the dry chamber — it immediately turns back toward the agar surface, where the water is. The two photos across the bottom (E1 and E2) show the mutant failing to curve back toward the agar. They found this mutant like a needle in a haystack, by looking at 20,000 mutant lines for ones like this, that fail to respond to the water vapor gradient.
The researchers have gone on to study this gene in great detail, and have made a number of exciting discoveries about how plants sense water.
Citation: Kobayashi, A., A. Takahashi, Y. Kakimoto, Y. Miyazawa, N. Fujii, A. Higashitani, and H. Takahashi. 2007. A gene essential for hydrotropism in roots. Proceedings of the National Academy of Sciences of the United States of America 104: 4724–4729.