Biology subjects

Rockwell, F. E.

Publications and source records attributed to Rockwell, F. E..

6 recordsLinked to original sources

bioRxiv2026

The origin of mechanical advantage in angiosperms

O_LIMechanical interaction between guard cells and epidermal pavement cells enables large stomatal apertures and high productivity in angiosperms. We do not know when this response evolved, but over the last 169 years we have found that mechanical advantage has been tested in at least 230 species from 85 families. To date no data on this trait exists among angiosperms outside magnoliids, monocots and eudicots. C_LIO_LITo resolve the evolutionary origins of this critical stomatal response we tested for mechanical advantage across 14 additional species including the earliest diverging lineages of angiosperms. C_LIO_LIWe find that mechanical advantage, while variable in magnitude, is present in all angiosperm species that have been measured, including Amborella trichopoda sister to all angiosperms. C_LIO_LIThis response likely evolved once in flowering plants, in the common ancestor of this clade, remaining widespread across angiosperms today. We hypothesize that angiosperms could not have realized the full potential of physiological innovations in water transport without the evolution of this key trait that increased operational stomatal aperture. C_LI

plant biology↗

bioRxiv2025

Emergence of a maximum soil flux under drought governs stomatal responsiveness to vapor pressure deficit over sub-daily and daily timescales

Drought and heat waves have synergistic effects on mortality as plants experience both supply and demand-side water stress. Which of these stresses ultimately controls stomatal conductance (gs) and whether patterns of regulation represent biological strategies or are imposed on the plant are addressed by way of a mechanistic hydraulic null model. O_LIDynamic losses of soil hydraulic conductivity are modeled in a soil domain fed by a maximum water flux from a deep-water source. A root-uptake plane extracts water from the soil in a two-node (root and leaf) plant model, with gs a function of leaf water potential. C_LIO_LIMulti-day simulations reproduce previously published experimental observations of anisohydric to isohydric transitions, driven by the balance of soil supply and atmospheric demand. Feedforward control of transpiration E emerges from steep declines in soil hydraulic diffusivity that confine diurnal variation in moisture gradients and water discharge/recharge cycles to a shallow region at the root plane that thins with increased demand. C_LIO_LIEmpirical models of VPD sensitivity are compared to the full model to provide mechanistic insight into empirical parameters. Apparent responses of gs to VPD are shown to emerge from plant, soil and atmospheric feedbacks that are both time and scale dependent. C_LI

plant biology↗

bioRxiv2025

Secreting salt glands constrain cuticle fracture to enhance desalination efficiency

Plants responding to excessive soil salinity by discharging brine onto their leaf surface risk dehydration through the osmotic continuity between the living tissue and the surface brine, which further enriches with evaporation. Cuticle cracks have long been identified as essential for salt to reach the leaf surface but provide the potentially desiccating continuity between the brine and the gland interior. Using the secreting salt gland of Nolana mollis as a model system, we integrate mathematical modeling, imaging, and physiological measurements to examine the mechanical and biochemical processes required for efficient desalination. We find that the subcuticular space between the concentrated surface brine and the more dilute secreting cell eases the energetic limits of active desalination by reducing the concentration gradient of salt across the cell membrane. We show that crack size plays a critical role in balancing the osmotic and pressure gradients required for salt removal without runaway foliar desiccation.

plant biology↗

bioRxiv2025

Loss of plasma membrane conductance in outside-xylem zone explains non-stomatal control of transpiration

The conventional assumption is that stomatal conductance (gs) 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 (goxz) at moderate xylem water stress (no turgor loss). The ratio of the resistances (1/goxz)/(1/gs) serves as a predictive phenotype of undersaturation, non-stomatal regulation of transpiration, errors in standard gas exchange analysis, and an increase of intrinsic water use efficiency (iWUE). 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 new paths of inquiry into the molecular basis and functional consequences of non-stomatal regulation of transpiration.

plant biology↗

bioRxiv2024

Ohmic analogies and metaphorical circuits: Vascular partitioning of leaf air spaces and stomatal patchiness can create apparent undersaturation and gradient inversion.

RationaleAnalyses of leaf gas exchange rely on an Ohmic analogy that arrays single stomatal, internal air space, and mesophyll conductances in series. Such models underlie inferences of mesophyll conductance and the relative humidity of leaf airspaces, reported to fall as low as 80%. An unresolved question is whether such Ohmic models are biased with respect to real leaves, whose internal air spaces are chambered at various scales by vasculature. DescriptionTo test whether undersaturation could emerge from modeling artifacts, we compared Ohmic model estimates with true parameter values for a chambered leaf with varying distributions and magnitudes of leaf surface conductance ("patchiness"). Key ResultsDistributions of surface conductance can create large biases in gas exchange calculations. Both apparent unsaturation and internal CO2 gradient inversion can be produced by the evolution of particular distributions of stomatal apertures consistent with a decrease in surface conductance, as might occur under increasing vapor pressure deficit. Main conclusionIn gas exchange experiments, the behaviors of derived quantities defined by simple Ohmic models are highly sensitive to the true partitioning of flux and stomatal apertures across leaf surfaces. We need new methods to disentangle model artifacts from real biological responses.

plant biology↗

bioRxiv2023

Localized measurements of water potential reveal large loss of conductance in living tissues of maize leaves

The water status of the living tissue in leaves between the xylem and stomata (outside xylem zone - OXZ) play a critical role for plant function and global mass and energy balance but has remained largely inaccessible. We resolve the local water relations of OXZ tissue using a nanogel reporter of water potential ({psi}), AquaDust, that enables an in-situ, non-destructive measurement of both{psi} of xylem and highly localized{psi} at the terminus of transpiration in the OXZ. Working in maize, these localized measurements reveal gradients in the OXZ that are several fold larger than those based on conventional methods, and values of{psi} in the mesophyll apoplast well below the macroscopic turgor loss potential. We find a strong loss of hydraulic conductance in both the bundle sheath and the mesophyll with decreasing xylem potential but not with evaporative demand. Our measurements suggest an active role played by the OXZ in regulating the transpiration path and our methods provide novel means to study this phenomenon.

physiology↗