Abstract
Plants experience changes in light intensity and quality due to variations in solar angle and shading from clouds and overlapping leaves. Stomatal opening to increasing irradiance is often an order of magnitude slower than photosynthetic responses, which can result in CO2 diffusional limitations on leaf photosynthesis, as well as unnecessary water loss when stomata continue to open after photosynthesis has reached saturation. Stomatal opening to light is driven by two distinct pathways; the ‘red’ or photosynthetic response that occurs at high fluence rates and saturates with photosynthesis, and is thought to be the main mechanism that coordinates stomatal behaviour with photosynthesis; and the guard cell-specific ‘blue’ light response that saturates at low fluence rates, and is often considered independent of photosynthesis, and important for early morning stomatal opening. Here we review the literature on these complicated signal transduction pathways and osmoregulatory processes in guard cells that are influenced by the light environment. We discuss the possibility of tuning the sensitivity and magnitude of stomatal response to blue light which potentially represents a novel target to develop ideotypes with the ‘ideal’ balance between carbon gain, evaporative cooling, and maintenance of hydraulic status that is crucial for maximizing crop performance and productivity.
Highlights
Stomatal opening to light is driven by two distinct pathways; the ‘red’ or photosynthetic response that occurs at high fluence rates and saturates with photosynthesis, and is thought to be the main mechanism that coordinates stomatal behaviour with photosynthesis; and the guard cell-specific ‘blue’ light response that saturates at low fluence rates, and is often considered independent of photosynthesis, and important for early morning stomatal opening
We focus on light-stimulated stomatal behaviour and on the red-(photosynthetic) and blue-light-driven responses, what is understood about the different signalling pathways involved, and guard cell (GC) metabolism that facilitates these responses.We further explore how a better understanding of stomatal response to irradiance, and the influence of the mesophyll on these responses, could provide novel targets for the development of plants with improved photosynthetic carbon gain and water use efficiency (WUE)
Significant progress has been made over the past few decades, understanding of stomatal responses to various environmental signals and substantial advances in GC metabolism and osmoregulatory pathways, many gaps remain regarding the integration and hierarchy of these diverse processes and the extent to which each contributes to stomatal function
Summary
Stomata control the flux of CO2 into the leaf and water lost through transpiration, and are crucial in maintaining plant water status, leaf temperature, and photosynthetic rates, depending on the current needs of the plant.The surface of most leaves is effectively impermeable to water and CO2; most of the CO2 fixed and water lost by plants must pass through stomatal pores (Cowan and Troughton, 1971; Caird et al, 2007; Jones, 2013), with stomata controlling the majority of gas exchange between the leaf and external environment, despite typically occupying only a small proportion (0.3–5%) of the leaf surface (Morison, 2003).The capacity of stomata to allow CO2 into or water out of the leaf is known as stomatal conductance (gs), with stomatal behaviour leading to alterations in stomatal aperture and diffusional fluxes.
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