Rethinking Guard Cell Metabolism

Abstract

ORCID IDs: 0000-0001-9686-1216 (D.S.); 0000-0002-4073-7221 (T.L.).Stomata control gaseous fluxes between the internal leaf air spaces and the external atmosphere and, therefore, play a pivotal role in regulating CO 2 uptake for photosynthesis as well as water loss through transpiration. Guard cells, which flank the stomata, undergo adjustments in volume, resulting in changes in pore aperture. Stomatal opening is mediated by the complex regulation of ion transport and solute biosynthesis. Ion transport is exceptionally well understood, whereas our knowledge of guard cell metabolism remains limited, despite several decades of research. In this review, we evaluate the current literature on metabolism in guard cells, particularly the roles of starch, sucrose, and malate. We explore the possible origins of sucrose, including guard cell photosynthesis, and discuss new evidence that points to multiple processes and plasticity in guard cell metabolism that enable these cells to function effectively to maintain optimal stomatal aperture. We also discuss the new tools, techniques, and approaches available for further exploring and potentially manipulating guard cell metabolism to improve plant water use and productivity.

Prompt chlorophyll fluorescence as a tool for crop phenotyping: an example of barley landraces exposed to various abiotic stress factors

“…The response may be due to the plants capability to survive for short time without S, due to minimising the need of S for the necessary processes. The deficiency of K was observed to influence significantly the transient fluorescence curve for both the landraces as K + is needed to balance the electrical charge at the site of ATP production (Santelia and Lawson 2016). When plants are deficient in K, the rate of photosynthesis and the rate of ATP production are reduced, and all processes based on ATP are slowed down, therefore we observed a significant decrease in the transient curve and its parameters after 7 DOT.…”

Transitory Starch Metabolism in Guard Cells: Unique Features for a Unique Function

“…After falling to near zero in the first hour after dawn, starch levels then begin to rise again, with net accumulation continuing past dusk into the early hours of the night (Horrer et al, 2016). Guard cell chloroplasts contain Rubisco and seem capable of net CO 2 assimilation (Lawson et al, 2002(Lawson et al, , 2003, so some of the carbon for starch synthesis in the light may come from guard cell photosynthesis but is likely to be supplemented by import of sugars from the apoplast or from sugars stored in the guard cells during the previous light phase (Daloso et al, 2016;Santelia and Lawson, 2016).…”

Stomatal Biology of CAM Plants

“…In this way, guard cell photosynthesis in CAM plants could assist in the maintenance of negligible diurnal stomatal conductance during the light period. Santelia and Lawson (2016), citing earlier work carried out by Pantoja and Smith (2002), recently highlighted the absence of the correlation between malate currents across the guard cell tonoplast and cytosolic calcium concentrations across CAM species that would be expected if they shared a uniform regulatory mechanism. This apparent diversity in stomatal physiology could have important consequences for our understanding of the evolution of complex syndromes like CAM.…”