University of Western Australia: Plants need light to live, but too much causes stress

New research from The University of Western Australia has revealed that too much sunshine can cause over seventy different “hidden” targets of damage to plant processes, causing “high light” stress as plants use up energy trying to repair the harm.

The findings, involving an international team of scientists from Australia and China and published today in PNAS, throws new light onto the effects of sunny climes on plant leaves.

Professor Harvey Millar, from UWA’s School of Molecular Science and Director at ARC Centre of Excellence in Plant Energy Biology, is an author of the study and said while solar radiation is important for plants as an energy source, it can also cause stress when too intense.

“Australia receives much more solar radiation than California or even the Mediterranean, which are often famed for their sunny summers,” Professor Millar said.

“Most research by plant scientists has focused on one event in photosynthesis, in which light is captured, and the damage to this process when there are too many photons of light intercepted.

“But in Western Australia, one of the sunniest parts of the world’s sunniest country, our research shows there’s not just one site of damage in plant photosynthesis, but over seventy different ‘hidden’ targets of damage right through different plant processes.

“Plants appear to continually replace all these broken systems, causing a major energy drain on a leaf in high light – damage that up until now hasn’t been recognised by scientists. We saw the stress on whole plants, but not the hidden reasons they were using their energy reserves. This won’t just be true for Australia, but anywhere the sun gets to a high irradiance level.”

Professor Millar, an internationally recognised plant biologist, said plants hide the damage (and what they have to do to overcome it) so well, that scientists had to develop a new technique at UWA, never before enacted in a plant system, to study it.

“The technique detected rapid protein replacement events inside plants that drain energy supply systems in response to a very sunny day,” Professor Millar said.

“It uses partial labelling with different carbon isotopes and detailed peptide mass spectrometry of hundreds of different enzymes across a day of high light conditions. Our analysis revealed for the first time that a light-induced replacement program exists, well beyond the regulation of photosystems, to replace many different enzymes in plants two or three times faster under high light stress.”

By pinpointing the reasons for the energy losses, Professor Millar said researchers can now consider genetic or engineering solutions to minimise the energy cost of high light to plant leaves.

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