A new mechanism for stomatal responses to humidity and temperature

 

 

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

by Peak D., Mott K. A. (2011)

David Peak, Keith A. Mott,

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in Plant Cell Environ 34162178 – DOI: 10.1111/j.1365-3040.2010.02234.x

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2010.02234.x/abstract

Abstract

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.

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Stomatal responses to humidity in isolated epidermes

Photo credit : Google

Tradescantia pallida

Stomatal responses to humidity in isolated epidermes

by Shope J. C., Peak D., Mott K. A. (2008)

JOSEPH C. SHOPE, DAVID PEAK, KEITH A. MOTT,

Biology Department, Utah State University, Logan, UT 84322-5305, USA.

in Plant, Cell and Environment 31: 1290-1298 – DOI: 10.1111/j.1365-3040.2008.01844.x – 

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2008.01844.x/full

ABSTRACT

The ability of guard cells to hydrate and dehydrate from the surrounding air was investigated using isolated epidermes of Tradescantia pallida and Vicia faba. Stomata were found to respond to the water vapour pressure on the outside and inside of the epidermis, but the response was more sensitive to the inside vapour pressure, and occurred in the presence or absence of living, turgid epidermal cells.

Experiments using helium–oxygen air showed that guard cells hydrated and dehydrated entirely from water vapour, suggesting that there was no significant transfer of water from the epidermal tissue to the guard cells.

The stomatal aperture achieved at any given vapour pressure was shown to be consistent with water potential equilibrium between the guard cells and the air near the bottom of the stomatal pore, and water vapour exchange through the external cuticle appeared to be unimportant for the responses.

Although stomatal responses to humidity in isolated epidermes are the result of water potential equilibrium between the guard cells and the air near the bottom of the stomatal pore, stomatal responses to humidity in leaves are unlikely to be the result of a similar equilibrium.

Stomatal heterogeneity in responses to humidity and temperature

 

Stomatal heterogeneity in responses to humidity and temperature: Testing a mechanistic model

Sweet K. J., Peak D., Mott K. A. (2017)

Kathryn J. Sweet, David Peak, Keith A. Mott

in Plant, Cell & Environment – DOI: 10.1111/pce.13051

Abstract

The role of stomatal heterogeneity in the response of stomatal conductance (gs) to the mole fraction difference in water vapor between the inside of the leaf and the ambient air (Δw) was determined using thermography and gas exchange for three species.

The value of Δw for the leaf was varied in two different ways: first by varying air humidity while holding leaf temperature constant and second by varying leaf temperature while holding air humidity constant.

Stomatal heterogeneity was explored by examining the response of gs in small areas of the leaf (as determined by thermography) and comparing them to each other and to the average value of gs (as determined by gas exchange).

These analyses show that despite substantial heterogeneity in gs values, the response of gs to Δw was qualitatively similar in all areas of the leaf, and all responses of gs to Δw were well predicted by a recently-proposed, vapor-phase mechanism for stomatal responses to temperature and humidity.

Remarkably, the two model parameters, Θ and Z that depend on leaf anatomy were constant for a given species, and only the maximum conductance varied in different regions of the leaf.

How Stomata Communicate

 

Leafy Social Network: USU Scientists Study How Stomata Communicate

by Peak D., Mott K. A.(2011)

102230587b
David Peak, Utah State University, USA
Keith cropped
Keith A. Mott, Biology Department , Utah State University, Logan, Utah

in Utah State Today – University News (Nov.23, 2011) –

http://www.usu.edu/ust/index.cfm?article=50552 

To survive, leafy plants need to take in as much carbon dioxide as possible through pores in their leaves without losing water. Known as stomata, these pores somehow work together, processing and exchanging the information necessary to open and close at opportune times to achieve constant, optimal balance.

An amazing and puzzling aspect of this process is that plants have no central processing unit, says Utah State University physicist David Peak.

“What we’re observing is a very primitive form of intelligence,” Peak says. “But how these stomata communicate, in what amounts to a sophisticated social network, remains a mystery.”

Peak and colleague Keith Mott, a professor of plant physiology at USU, have studied the function of stomata in intact leaves, with an emphasis on information processing, for nearly a decade. The team challenged a recent study on stomatal responses to radiant energy in a paper published in the Nov. 21, 2011 issue of Proceedings of the National Academy of Sciences.

“Colleagues in the science community made a potentially revolutionary proposal that stomata respond to total absorbed radiant energy rather than to visible radiation alone,” Mott says. “If true, this would have represented a major departure from currently accepted models of plant physiology. But our findings revealed an error in the proposal.”

Read the full article : USU

Stomatal responses to humidity

 

Testing a vapour-phase model of stomatal responses to humidity.

by Mott K. A., Peak D. (2013)

Keith cropped
Keith A. Mott, Biology Department , Utah State University, Logan, Utah
peak
David Peak, Physics Department , Utah State University, Logan, Utah

in Plant, Cell & Environment 36, 936944. – DOI: 10.1111/pce.12026 – 

Wiley Online LibraryCAS – 

http://onlinelibrary.wiley.com/doi/10.1111/pce.12026/full

ABSTRACT

This study tests two predictions from a recently proposed model for stomatal responses to humidity and temperature. The model is based on water potential equilibrium between the guard cells and the air at the bottom of the stomatal pore and contains three independent variables: gs0, Z and Θ.

gs0 is the value of stomatal conductance that would occur at saturating humidity and will vary among leaves and with CO2 and light. The value of Z is determined primarily by the resistance to heat transfer from the epidermis to the evaporating site and the value of Θ is determined primarily by the resistance to water vapour diffusion from the evaporating site to the guard cells.

This leads to the two predictions that were tested. Firstly, the values of Z and Θ should be constant for leaves of a given species grown under given conditions, although gs0should vary among leaves and with light and CO2. And secondly, the ratio of Z to Θ should be higher in leaves having their stomata in crypts because the distance for heat transfer is greater than that for water vapour diffusion.

Data from three species, Nerium oleander, Pastinaca sativum and Xanthium strumarium support these two predictions.

A new mechanism for stomatal responses to humidity and temperature

PCE_2234_f2
Schematic representation of water flow in the vapour phase model. Solid lines indicate liquid water flow; dashed lines indicate water vapour flow. Water evapourates at site i and diffuses with flux E through the stomatal pore (p) into the surrounding air (a). The diffusive flow draws liquid water from source S with flux E. In steady state, liquid water in the epidermis is in equilibrium with liquid water in the mesophyll and in the xylem at site M. Liquid water in the guard cells (g) is in equilibrium with vapour in the pore at site p. – http://onlinelibrary.wiley.com/store/10.1111/j.1365-3040.2010.02234.x/asset/image_n/PCE_2234_f2.gif?v=1&t=ishmcwrh&s=66432ef54ee408809a4e2bc68116964ca0dc0e50

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

by Peak D., Mott K. A.,  (2010)

David Peak, Keith A. Mott

Utah State University, Logan, Utah, USA

in Plant, Cell and Environment 34: 162–178. – DOI: 10.1111/j.1365-3040.2010.02234.x – 

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2010.02234.x/full

ABSTRACT

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.

Mechanisms for the stomatal response to humidity and temperature

PCE_2129_f5
Stomatal conductance or aperture in darkness as a function of Tl at a constant Δw. [CO2] = 100 µmol mol−1 and [O2] = 21 mmol mol−1. Data were taken for both increasing and decreasing Tl and corrected for temporal drift as described in the text. Solid and open circles represent a mean of six experiments (three with increasing Tl, and three with decreasing Tl), and data were normalized to the value at Tl = 30 °C. Error bars show one standard deviation on either side of the mean, and the regression lines for Δw = 17 mmol mol−1 and for Δw ≈ 0 mmol mol−1 are significantly different (P < 0.001). Open squares show individual aperture measurements from two separate experiments. – http://onlinelibrary.wiley.com/store/10.1111/j.1365-3040.2010.02129.x/asset/image_n/PCE_2129_f5.gif?v=1&t=ishmkfde&s=1121f7f84d8300fecaeab11510108b9da7472951

Stomatal responses to humidity and temperature in darkness

by Mott K. A., Peak D. (2010)

Keith A. Mott, David Peak

Utah State University, Logan, Utah 85433-4415, USA

in Plant, Cell and Environment 33: 1084-1090. – DOI: 10.1111/j.1365-3040.2010.02129.x

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2010.02129.x/full

ABSTRACT

Stomatal responses to leaf temperature (Tl) and to the mole fractions of water vapour in the ambient air (wa) and the leaf intercellular air spaces (wi) were determined in darkness to remove the potential effects of changes in photosynthesis and intercellular CO2concentration.

Both the steady-state and kinetic responses of stomatal conductance (gs) to wain darkness were found to be indistinguishable from those in the light. gs showed a steep response to the difference (Δw) between wa and wi when wa was varied. The response was much less steep when wi was varied.

Although stomatal apertures responded steeply to Tlwhen Δw was held constant at 17 mmol mol−1, the response was much less steep when Δwwas held constant at about zero. Similar results were obtained in the light for Δw = 15 mmol mol−1 and Δw ≈ 0 mmol mol−1.

These results are discussed in the context of mechanisms for the stomatal response to humidity.