A minimally disruptive method for measuring water potential in planta using hydrogel nanoreporters

Abstract

Leaf water potential is a critical indicator of plant water status, integrating soil moisture status, plant physiology, and environmental conditions. There are few tools for measuring plant water status (water potential) in situ, presenting a critical barrier for developing appropriate phenotyping (measurement) methods for crop development and modeling efforts aimed at understanding water transport in plants. Here, we present the development of an in situ, minimally disruptive hydrogel nanoreporter (AquaDust) for measuring leaf water potential. The gel matrix responds to changes in water potential in its local environment by swelling; the distance between covalently linked dyes changes with the reconfiguration of the polymer, leading to changes in the emission spectrum via Förster Resonance Energy Transfer (FRET). Upon infiltration into leaves, the nanoparticles localize within the apoplastic space in the mesophyll; they do not enter the cytoplasm or the xylem. We characterize the physical basis for AquaDust’s response and demonstrate its function in intact maize (Zea mays L.) leaves as a reporter of leaf water potential. We use AquaDust to measure gradients of water potential along intact, actively transpiring leaves as a function of water status; the localized nature of the reporters allows us to define a hydraulic model that distinguishes resistances inside and outside the xylem. We also present field measurements with AquaDust through a full diurnal cycle to confirm the robustness of the technique and of our model. We conclude that AquaDust offers potential opportunities for high-throughput field measurements and spatially resolved studies of water relations within plant tissues.

Leaf Water Storage and Robustness to Intermittent Drought: A Spatially Explicit Capacitive Model for Leaf Hydraulics

“…The use of grass leaves as a model benefits from not only simpler stomata and venation arrangements than dicots, but also the clear presence of water-storage cells (capacitors). The spatially dependent xylem water potential profile, which decreases from base to tip in well-watered steady state (Figure 3) when capacitors are static, compares qualitatively well with earlier calculation results of wheat leaves by Altus et al [11] and most recent experimental measurements (using a novel method) and theoretical predictions of maize leaves by Jain et al [17]. By tuning the biolog- ically relevant parameters we choose, we can reproduce quantitatively matching results, though these previous works considered local resistances without explicit water storage.…”

“…Alternatively, a more direct stomatal dependence on VPD can also be established and implemented (Grossiord et al, 2020 ). Most recently, the sigmoidal behaviors of both xylem and stomatal conductances are applied in a spatially explicit study (Jain et al, 2021 ). The specific biophysical and biochemical mechanisms that control stomatal opening through water status, including the turgor pressure of guard cells and epidermal cells around stomata and the use of plant hormone abscisic acid, are broadly explored by existing literature (Buckley, 2005 ).…”

“…Indeed, the incorporation of xylem and stomatal conductances dependent on water potential is applied in several theoretical models, in which the stomatal dependence is also treated as sigmoidal or approximately piecewise linear functions [16]. Most recently, the sigmoidal behaviors of both xylem and stomatal conductances are applied in a spatially explicit study [17]. The specific biophysical and biochemical mechanisms that control stomatal opening through water status, including the turgor pressure of guard cells and epidermal cells around stomata and the use of plant hormone abscisic acid, are broadly explored by existing literature [18].…”

“…In Subsection II C we showed equivalence of the two equations in groups (17), (19) and (20). To make the…”

Can We Harness “Enviromics” to Accelerate Crop Improvement by Integrating Breeding and Agronomy?

“…Complexity, cost, and the timeliness of detailed measurements of the water status of environments and genotypic variation for plant responses to water deficits under field conditions have limited adoption and application of many discoveries and methods to the scale of breeding programs. Recently, new proximal and remote sensor technologies and data modelling capabilities have become available to enhance characterization of environments and measure plant responses under field conditions at higher throughput and at greater scales to enhance applications for crop improvement and yield prediction (Pauli et al, 2016;Guan et al, 2017;Araus et al, 2018;Messina et al, 2018;Van Eeuwijk et al, 2019;Cooper et al, 2020;Messina et al, 2020;Peng et al, 2020;Schwalbert et al, 2020;Costa-Neto et al, 2021;Jain et al, 2021;Jin et al, 2021;Potgieter et al, 2021;Smith et al, 2021;Yang et al, 2021).…”