Plant pores give up their secrets EU-funded research is set to trigger a rethink of the way plants release water vapour into the atmosphere in a process called transpiration. The study, published in the Proceedings of the National Academy of Sciences, has implications for fields as diverse as weather forecasti... EU-funded research is set to trigger a rethink of the way plants release water vapour into the atmosphere in a process called transpiration. The study, published in the Proceedings of the National Academy of Sciences, has implications for fields as diverse as weather forecasting, climate change, agriculture and hydrology. EU support for the work came from the LIFT ('Laser-induced fluorescence transient: a remote sensing approach to scale and quantify photosynthetic light use efficiency in ecosystems') project, a 3-year Marie Curie Outgoing International Fellowship which received EUR 250,000 from the Sixth Framework Programme (FP6). Plants' leaves are dotted with tiny, lip-shaped pores called stomata, through which plants release water vapour to the atmosphere. This process cools and humidifies the atmosphere over the vegetation, affects the climate and influences precipitation. In addition, the carbon dioxide (CO2) that plants use for photosynthesis is drawn into the leaf via the stomata. Crucially, plants are able to alter the size of their stomata to regulate the rate of CO2 uptake and water-vapour release. Stomata therefore have a major impact on plant productivity, climate change and the water cycle. However, pinning down the mechanisms controlling stomata size has proven difficult. As a result, the descriptions of stomatal response used in computer models of climate change are rather weak. 'Scientists have been studying stomata for at least 300 years,' commented Joseph Berry of the Carnegie Institution in the US. 'It's amazing that we have not had good grasp about the regulatory mechanisms that control how much stomata open or close in response to a constantly changing environment.' Part of the problem lies in the fact that the control of transpiration takes place over a large range of scales, from atmospheric turbulence right down to channels in the membranes of the cells that form the stomatal pore. The issue is further complicated by the fact that it is studied by two separate disciplines that have traditionally taken very different approaches to the problem. Meteorologists have taken a top-down approach, investigating the amount of energy needed to support the evaporation of water, for example. Meanwhile, plant physiologists have tended to focus on the sensory systems and movements controlling the stomatal opening. Until now, scientists believed that the guard cells around the stomata adjusted the pore size in response to light and other environmental cues. However, this research, by scientists in Germany and the US, reveals that the energy absorbed by pigments and water deep inside the leaf actually drives the rate of water loss by stomata. The team's experiments demonstrate that the leaf epidermis is very sensitive to the difference between the transpiration rate and the rate of water vapour production inside the leaf. 'This means that the current model for what drives stomata to change their size has to change,' noted Marie Curie Fellow Roland Pieruschka of the Carnegie Institution (currently at the Research Center Jülich in Germany). 'For a long time researchers have thought that heat from the sun, which is absorbed by pigments, moves from cell to cell until it gets to the cavities beneath the stomata where evaporation has been thought to take place. This probably happens to some degree, but the results presented here are more consistent with our hypothesis that much of this heat is transferred through air spaces inside the leaf that are saturated with water vapour.' Countries Germany, United States
