A new model of stomatal function

Plants need to draw water up from the soil to the shoots. They do this by losing water vapour via small, controllable pores on the leaf surface, termed stomata. Open stomata allow plants to pull water throughout the plant and, at the same time, they allow carbon dioxide into the leaf where it is used for photosynthesis, the process by which all our food is made.

However, if stomata were always open this would lead to catastrophic water loss, wilting, and eventual death of the plant. Therefore, plants continually adjust their stomata, making sure that they are open enough to allow the plant to grow when conditions are good, but closed when there is the danger of losing too much water.

Due to their critical role in plants, how stomata work has been a topic of extensive research for over 150-years. Most of this work has focussed on the two cells (guard cells) between which the stomatal pore is formed, leading to the widely accepted paradigm that these cells swell and deflate via the gain or loss of water, and that this change of guard cell size and shape is the primary mechanism by which stomatal pores open and close.

Our recent research, using 3-dimensional imaging, has revealed that cells neighbouring the guard cells also undergo very large changes in size and shape in response to triggers known to close stomata. In addition, our imaging experiments have shown that the guard cells themselves undergo a much more complicated change in shape than has generally been described.

Taken together, our new results suggest that the classical text-book descriptions do not fully capture the mechanism by which changes of cell size and shape lead to stomatal opening and closing. In particular, our new findings suggest that a combination of guard cell and neighbouring epidermal cell responses is required for a full and efficient mechanism for stomatal pore opening and closure.

As well as providing a new insight into a classical and fundamental aspect of plant biology, these data may open new paths to optimising or improving stomatal performance, leading to new approaches to reducing crop water requirements and improving drought tolerance, major challenges for agriculture in a changing global environment.

To test our ideas, we will use a combination of advanced imaging and computational modelling techniques, combined with an array of genetic resources. For example, we will expand our present investigations where we have looked at two known triggers of stomatal closure to see whether the guard cell/neighbouring cell response that we have observed reflects a general aspect of stomatal function.

We will then use a variety of approaches to alter either neighbouring cell viability or responsiveness to stomatal opening/closure triggers, testing the idea that neighbouring cell function is required for full stomatal function. These same approaches will also be used to alter the guard cell shape response that we have observed, testing the idea that this specific shape change is intimately connected with the mechanism of stomatal pore opening and closure.

Throughout the project we will create computational models of the stomatal systems that we are investigating. These models, which will be informed by our experimental results, will provide a strong theoretical underpinning to the project, helping us both to interpret our experiments, and allowing us to design further experiments to test our ideas on the mechanism by which both guard cells and their neighbouring cells work together in the opening and closure of stomata.

The improved understanding of stomatal mechanics gained through this research could, in the future, aid the production of more resilient crops that are better suited to growth under climate change.