Keith A. Mott

Utah State University

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David Peak

Utah State University

Thomas N. Buckley

University of California, Davis

Ian E. Woodrow

University of Melbourne

Joseph C. Shope

Utah State University

Joseph A. Berry

Carnegie Institution for Science

Jon Y. Takemoto

Utah State University

Susanna M. Messinger

Yale University

Zoë G. Cardon

Marine Biological Laboratory

Richard G. Jensen

University of Arizona

David F. Parkhurst

Indiana University Bloomington

Cooperative Institutions

Utah State University

Sapienza University of Rome

University of Naples Federico II

University of Arizona

Stanford University

National Research Council

University of Connecticut

University of Utah

Australian National University

University of Rome Tor Vergata

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A new, vapour‐phase mechanism for stomatal responses to humidity and temperature

Plant Cell & Environment (2010)

David Peak Keith A. Mott

A new mechanism for stomatal responses to humidity and temperature is proposed. Unlike previously-proposed mechanisms, which rely on liquid water transport to create water potential gradients within the leaf, the new mechanism assumes that water transport to the guard cells is primarily through the vapour phase. Under steady-state conditions, guard cells are assumed to be in near-equilibrium with the water vapour in the air near the bottom of the stomatal pore. As the water potential of this air varies with changing air humidity and leaf temperature, the resultant changes in guard cell water potential produce stomatal movements. A simple, closed-form, mathematical model based on this idea is derived. The new model is parameterized for a previously published set of data and is shown to fit the data as well as or better than existing models. The model contains mathematical elements that are consistent with previously-proposed mechanistic models based on liquid flow as well as empirical models based on relative humidity. As such, it provides a mechanistic explanation for the realm of validity for each of these approaches.

Water Transport

10.1111/j.1365-3040.2010.02234.x

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Citations (131)

Effects of pH on Activity and Activation of Ribulose 1,5-Bisphosphate Carboxylase at Air Level CO₂

PLANT PHYSIOLOGY (1986)

Keith A. Mott Joseph A. Berry

The effects of pH on catalysis and activation characteristics of spinach ribulose 1,5-bisphosphate (RuBP) carboxylase were examined at air level of CO(2). Catalysis at limiting CO(2) was independent of pH over the range of pH 8.2 to 8.8 However, the kinetics of activation and the apparent equilibrium between the activated and inactivated forms of the enzyme were strongly dependent upon the pH and the presence or absence of the substrate RuBP. When incubated at air level of CO(2) at pH 8.2 in the absence of RuBP, the enzyme activation state was approximately 75% of that achieved with saturating CO(2) at that pH. The extent of activation increased with pH reaching 100% at pH values of 8.6 or higher. Adding RuBP to the activation medium after equilibrium activation state had been established decreased the apparent equilibrium activation level at pH values below 8.6. This effect was reversed at pH values above 8.6. Activation of inactive enzyme by CO(2) and Mg(2+) was inhibited dramatically at pH values below 8.6 and less so at pH values above 8.6. Studies showed that binding of RuBP to the inactive form of the enzyme was pH dependent with tighter binding occurring at lower pH values. It is suggested that the tight binding of RuBP to the inactive enzyme tends to decrease the equilibrium concentration of the activated form at pH values less than 8.6. These studies indicate that stromal pH could have a strong effect on the activation state of this enzyme in vivo, and possible feedback interactions which might adjust the apparent V(max) to match the rate of RuBP regeneration are discussed.

Enzyme Kinetics

10.1104/pp.82.1.77

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Citations (54)

Limitation of Photosynthesis by RuBP Regeneration Rate

Springer eBooks (1986)

Keith A. Mott Richard G. Jensen Joseph A. Berry

Carboxylation

C4 Photosynthesis

Ribulose

10.1007/978-94-009-4384-1_2

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Citations (4)

Light-Dependent Changes in Ribulose Bisphosphate Carboxylase Activase Activity in Leaves

PLANT PHYSIOLOGY (1992)

Yun Lan Ian E. Woodrow Keith A. Mott

An assay for the activity of ribulose bisphosphate carboxylase (Rubisco) activase in crude leaf extracts was developed. The assay is based on a spectrophotometric assay of Rubisco, and activase activity (in nanomoles activated Rubisco per minute per milligram chlorophyll) was calculated from the rate of increase in Rubisco activity over time. Activase activity measurements were made using samples from spinach (Spinacia oleracea) leaves undergoing (a) steady-state photosynthesis at various photon flux density (PFD) values and (b) nonsteady-state photosynthesis following an increase from darkness to a high PFD. Analysis of these samples showed that steady-state Rubisco activase activity was relatively low in darkness, increased with PFD, and saturated below 300 micromoles per square meter per second. Rubisco activity (measured spectrophotometrically) was also found to be low in darkness and to increase with PFD, but it saturated at much higher PFD values (approximately 1000 micromoles per square meter per second) along with the rate of photosynthesis. Following an increase in PFD from darkness to 650 micromoles per square meter per second, activase activity increased more or less linearly over a period of 5 to 6 minutes, after which it was constant. Rubisco activity, however, increased more slowly. The light-dependence of Rubisco activase is consistent with previous gas-exchange data showing two interdependent processes in the activation of Rubisco following an increase in PFD.

Spinacia

Ribulose 1,5-bisphosphate

Darkness

Ribulose

10.1104/pp.99.1.304

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Citations (40)

Evidence that Ribulose 1,5-Bisphosphate (RuBP) Binds to Inactive Sites of RuBP Carboxylase in Vivo and an Estimate of the Rate Constant for Dissociation

PLANT PHYSIOLOGY (1989)

Zoë G. Cardon Keith A. Mott

The binding of ribulose 1,5-bisphosphate (RuBP) to inactive (noncarbamylated) sites of the enzyme RuBP carboxylase in vivo was investigated in Spinacia oleracea and Helianthus annuus. The concentrations of RuBP and inactive sites were determined in leaf tissue as a function of time after a change to darkness. RuBP concentrations fell rapidly after the change to darkness and were approximately equal to the concentration of inactive sites after 60 s. Variations in the concentration of inactive sites, which were induced by differences in the light intensity before the light-dark transition, correlated with the concentration of RuBP between 60 and 120 s after the change to darkness. These data are discussed as evidence that RuBP binds to inactive sites of RuBP carboxylase in vivo. After the concentration of RuBP fell below that of inactive sites (at times longer than 60 s of darkness), the decline in RuBP was logarithmic with time. This would be expected if the dissociation of RuBP from inactive sites controlled the decline in RuBP concentration. These data were used to estimate the rate constant for dissociation of RuBP from inactive sites in vivo.

Darkness

Spinacia

Ribulose 1,5-bisphosphate

Dissociation constant

Photorespiration

Helianthus

10.1104/pp.89.4.1253

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Citations (34)

Changes in photon flux can induce stomatal patchiness

Plant Cell & Environment (1996)

J. Eckstein Wolfram Beyschlag Keith A. Mott Ronald J. Ryel

ABSTRACT Images of chlorophyll fluorescence were used to detect the occurrence of stomatal patchiness in leaves from eight species under variable photon flux conditions. Pronounced stomatal patchiness was induced within 5–10 min after PFD was changed from intermediate (∼450 μmol quanta m −2 s −1 ) to low (∼150 μmol quanta m −2 s −1 ) levels. This effect was completely reversible by returning PFD to intermediate levels. The pattern of heterogeneous fluorescence for each leaf was usually similar during repeated applications of medium and low PFD. In three species, stomatal patchiness could only be induced in slightly water‐stressed plants. Leaves of more severely water‐stressed Xanthium strumarium plants in low air humidity exhibited oscillations in fluorescence that corresponded with oscillatory changes in leaf diffusion conductance for water vapour. Stomatal patchiness was also induced by illuminating dark‐adapted leaves with low PFD (below 200–300 μmol quanta m −2 s −1 ). Infiltration of leaves with distilled water showed that heterogeneous chlorophyll fluorescence was caused by changes in stomatal apertures.

Stomatal Conductance

Photon flux

10.1111/j.1365-3040.1996.tb00213.x

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Citations (63)

Carbon balance in relation to drying in four epiphytic mosses growing in different vertical ranges

Canadian Journal of Botany (1979)

Peter Tobiessen Nancy G. Slack Keith A. Mott

The response of photosynthesis and respiration to drying was measured in four species of epiphytic mosses, Ulota crispa (Hedw.) Brid., Neckera pennata Hedw., Anomodon rugellii (C. Mull.) Keissl., and Plagiomnium cuspidatum (Hedw.) T. Kop., from habitats along a desiccation gradient. There was little difference among the mosses in these responses. The relationship of water content to water potential did differ among the mosses, with Plagiomnium, the facultative epiphyte, showing a typical response of more mesic species and the other three showing a more xeric response, i.e., water potential does not begin to fall steeply until a lower water content is reached in Ulota, Neckera, and Anomodon. Both photosynthesis and respiration in all four moss species were quite sensitive to moderate water stress.

Epiphyte

Facultative

10.1139/b79-249

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Citations (25)

Photosynthesis Research (1997)

Jerriann Ernstsen Ian E. Woodrow Keith A. Mott

Plant Physiology

10.1023/a:1005847500471

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Citations (23)

Effect of Root Cooling on Photosynthesis of Artemisia tridentata Seedlings under Different Light Levels

Botanica Acta (1993)

Hormoz BassiriRad M. M. Caldwell Keith A. Mott

Abstract Root chilling has been shown to inhibit shoot photosynthesis yet the mechanism for such an action is not clearly understood. A study was designed to elucidate the mechanism by which root cooling may affect net photosynthesis. Roots of Artemisia tridentata seedlings were cooled from 20°C to 5°C while their shoot temperature remained at 20°C. This was conducted at two light levels (700 and 1300 μmol m −2 s −1 ). The time course of shoot net photosynthesis (A), stomatal conductance to water vapor (g s ), intercellular CO 2 concentration (C i ) and root respiration (R s ) were determined on a whole‐plant basis. Root cooling caused a 25% reduction in A at high PPFD, which was preceded by more than 50% reduction of g s and about 10% reduction in C i . A versus C i curves for single branches showed no difference between cold and warm soil temperatures, although stomatal conductance was lower for the lower soil temperature. This suggests that a stomatal limitation may have been involved in the inhibition of A. Furthermore, a concomitant decrease of as much as 23% in leaf relative water content (RWC) indicated that root cooling affected stomatal closure due to decreased water supply to the foliage. At lower PPFD, root cooling did not cause a decrease in A of the whole plant despite a moderate drop in g s , C i and RWC. Cold soil also led to a substantial and rapid reduction in root respiration rate (R s ) regardless of the light level.

Stomatal Conductance

Respiration rate

10.1111/j.1438-8677.1993.tb00744.x

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Citations (11)

Leaf hydraulic conductivity and stomatal responses to humidity in amphistomatous leaves

Plant Cell & Environment (2007)

Keith A. Mott

ABSTRACT The response of stomata to changes in humidity for a single surface of an amphistomatous leaf was investigated in Xanthium strumarium and Vicia faba using gas exchange and direct observation of stomatal apertures. The stomatal response to humidity for a given surface was found to be the same whether or not the humidity for the opposite surface was changed concurrently. Stomata on the surface for which humidity was constant showed no response to changes in humidity for the opposite surface. Despite large changes in epidermal turgor on the surface for which humidity was changed, there was no change in epidermal turgor for the surface with constant humidity. Measurements of transpiration and epidermal turgor as functions of the mole fraction gradient of water between leaf and air were used to calculate a value for leaf hydraulic resistance. The results suggest that in these species, the mechanism for the stomatal response to humidity resides in the epidermis or the mesophyll very close to the epidermis, and that most of the hydraulic resistance of the leaf occurs between the xylem and the evaporating sites.

Turgor pressure

Epidermis (zoology)

10.1111/j.1365-3040.2007.01720.x

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Citations (64)