Good news! Could this be a game changer for e.g. agriculture?
"... researchers have discovered a previously unknown way plants regulate water that is so fundamental it may change plant biology textbooks – and open the door to breeding more drought-tolerant crops. ...
But a new study describes for the first time how water regulation also occurs under the leaf’s surface, at the membranes of photosynthesizing cells. The result was made possible thanks to AquaDust, a ... developed nanoscale sensor that measures water status inside leaves. ...
This study found that while the mesophyll cells remain saturated with water, the tiny intercellular spaces around them can become very dry. This difference in water status is created as the water moves across the mesophyll cells’ membranes, providing a second regulator of water flow along with stomata.
Having a window into how water moves inside the leaf made the finding possible.
“Our lab developed a tool to peer into the tiny airspaces in leaves to measure the dynamics of water stress at the cellular scale,” ... AquaDust, a soft, synthetic, water-absorbent gel that occupies intercellular spaces in the mesophyll area and swells and shrinks based on water availability in the leaves.
AquaDust also contains dyes that fluoresce depending on how close dye molecules are to each other. Fiber optics or fluorescence microscopy let the researchers shine a light and receive a spectral measurement that reveals the local water stress in the leaf. ..."
From the significance and abstract:
"Significance
This research provides experimental and theoretical evidence that stomates are not the sole regulators of transpiration in plants. We use a nanoreporter of water potential (AquaDust) to document significant nonstomatal control of transpiration, with significant gains in water-use efficiency and large local disequilibrium within leaf tissue under moderate drought stress.
With the methods and biophysical model introduced here, we quantitatively explain this nonstomatal control of water loss based on loss of conductance of plasma membranes in the leaf. These developments open paths to investigate this phenomenon and pursue its implications for the design of crops with high water-use efficiency and for our understanding of water stress responses across both agricultural and natural ecological contexts.
Abstract
The conventional assumption is that stomatal conductance () dominates the regulation of water and carbon dioxide fluxes between leaves and the atmosphere. Here, a nanoreporter of water status at the mesophyll cell surface and local xylem within intact maize leaves documents significant undersaturation of water vapor in the outside-xylem zone (OXZ) and a large loss of conductance of this zone () at moderate xylem water stress, without stomatal closure or turgor loss.
The ratio of the resistances serves as a predictive phenotype of undersaturation, nonstomatal regulation of transpiration, errors in standard gas exchange analysis, and an increase of intrinsic water use efficiency ().
Cell-scale access to water status reveals symplasmic-apoplasmic disequilibrium and informs a biophysical model that can explain experimental observations quantitatively based on localization of variable conductance to the plasma membrane. This work opens paths of inquiry into the molecular basis and functional consequences of nonstomatal regulation of transpiration."
Loss of conductance between mesophyll symplasm and intercellular air spaces explains nonstomatal control of transpiration (open access)
Fig. 1 Stomatal and nonstomatal control of transpiration.
Fig. 4 Model of leaf water transport in Outside-Xylem Zone with large loss of conductance in plasma membrane.
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