Researchers at New York’s Boyce Thompson Institute for Plant Research have taken a first step in understanding how plants respond to stress, with the eventual goal of creating crops that are more tolerant to drought and light stress, without losing productivity.
When plants absorb sunlight with their chlorophyll pigments to perform photosynthesis, they first take electrons from water and pass them along a chain of different proteins. But a stressful situation, such as a drought, too much light or low temperatures can disrupt the chain, leaving the plant pigments holding the electrons and absorbed light energy — almost like a molecular game of hot potato.
Those energized pigments become “photosensitizers” and can shed the absorbed light energy or allow electrons to be passed onto oxygen molecules in the cell, creating special forms of oxygen called reactive oxygen species. Also called ROS, these oxygen molecules are unstable, and can attack vital structures within the cell.
But cells even have their own natural metabolites and proteins that act as antioxidants to regulate ROS concentrations in the cell, and researchers were suspicious of the blanket idea that all ROS simply cause damage and have no other function in the plant. To figure out exactly what ROS were doing inside the cell, they had to find a way to trigger the creation of just one type at a time, while the plant was still alive and growing.
To surmount this challenge, researchers used a special mutant plant. They grew a small, fast-growing plant commonly used for genetic experiments called Arabidopsis thaliana, which had a mutation in a gene called FLU. When FLU functions properly, it tells the plant to stop making a compound called protochlorophyllide when it’s dark out. Protochlorophyllide that is bound to a certain enzyme transforms into chlorophyll when it absorbs the sun’s energy.
But without FLU to regulate this process, the mutant’s cells keep pumping out protochlorophyllide all night long. When the light comes back on in the greenhouse, the excess free protochlorophyllide acts as a photosensitizer and releases a burst of a type of ROS called singlet oxygen and the whole plant bleaches and dies in minutes.
Of course, a scientist can’t study a mutant plant variety if it dies each morning, so researchers grew these mutants in constant light so that the protochlorophyllide doesn’t build up and kill the plant.
The findings show that singlet oxygen doesn’t deserve its bad reputation for wrecking cells and killing the plant. It’s simply the messenger that tells the plant that something bad happened, so it should close up shop and wait for better times. By slowing its growth and losing a few leaves, the plant might survive the rough patch and resume growing later on.
For more information, visit http://bti.cornell.edu/news/of-spray-paint-and-plant-stress/
