How plants breathe - biomechanical modelling of guard cells

Abstract: Guard cells dynamically adjust their shape to regulate photosynthetic gas exchange, respiration rates and defend against pathogen entry. Guards are thus of key importance for drought and temperature tolerance and disease. Cell shape dynamics are determined by the interplay of cell wall material properties and turgor pressure. To investigate this relationship between turgor pressure, cell wall properties and cell shape, I will focus on kidney-shaped stomata and discuss a biomechanical model we recently developed of a guard cell pair. Treating the cell wall as a composite of the pectin-rich cell wall matrix embedded with cellulose microfibrils, I will show that strong, circumferentially-oriented fibres are critical for opening. We find that opening dynamics are dictated by the mechanical stress-response of the cell wall matrix, and as the turgor rises, the pectinaceous matrix stiffens. Furthermore, I will discuss how results from our models coupled with atomic force microscopy have challenged the text book model of guard cell mechanics and suggest a ‘pinning’ mechanism for maximising stomatal responses.