LIGHT STRESS — TOO MUCH OF A GOOD THING BY CAROLINE WOOD
Light is the fundamental energy that drives plant growth and productivity, but outside the controlled conditions of our research laboratories, its intensity can fluctuate between extremes in a matter of seconds. This can present plants with the constant challenge of striking a delicate balance between maximising gains whilst keeping the delicate photosynthetic machinery safe from damage. Here, we take a look at fascinating new insights into the exquisite photoprotective mechanisms that help plants to stay safe from light stress.
GETTING THE GRADIENT RIGHT Intense spikes in luminescence—a sudden break in cloud cover, for instance—expose plants to potentially damaging amounts of excess light energy, capable of causing irreparable damage. Photoprotective mechanisms counteract this by dissipating excess light energy and downregulating photosynthesis during these events. Often, this involves adjusting the proton gradient across the thylakoid membrane that transiently stores the energy that powers photosynthesis. “Ongoing energy dissipation in shade periods, however, would decrease the efficiency of photosynthesis under natural, dynamically changing light conditions,” says Ute Armbruster, from the Max Planck Institute of Molecular Plant Physiology. “Consequently, plants rapidly turn off photoprotective mechanisms as soon as light intensity drops again. Our research has demonstrated that these switches in response to changes in light intensity are heavily accelerated by ion transporters in the thylakoid membrane.” An intriguing question was whether the activity of these photoprotective mechanisms varied depending on the environment of the plant during its early development. To investigate this, Ute and her colleagues grew Arabidopsis thaliana plants under a variety of different light regimes, with some that fluctuated according to regular or random patterns and non-fluctuating control regimes.1 Plants from these different light environments were then exposed to a sudden, ten-fold increase in light intensity. By measuring changes in chlorophyll fluorescence and absorptive processes related to photosynthesis, the team assessed the activity
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