Requirement of both ZTL and OST1 in the regulation of guard cell turgor and suggestion of a direct link between the circadian clock and OST1 activity.

Figure 1. General model of ion fluxes during stomatal opening and closure. Stomatal opening is induced via activation of plasma membrane H+ -ATPase. The protein provides H+ extrusion outside of guard cell which leads to decreased membrane potential (-110 mV) and hyperpolarization. The consequent activation of inward-rectifying K+ channels provides K+ influx. As one of the counter anions, Cl- enters guard cell by symport with H+ , whereas malate is produced in the cytosol. The electrochemical proton gradient across vacuolar membrane is provided by V-Type ATPases which transfers H+ inside the vacuole lumen. Anion channels transport Cl inside the vacuole along the vacuolar electrical potential (-40 mV). A malate carrier maintains cytoplasmic levels of malate decreased. An H+ -driven antiporter takes up K+ against the vacuolar membrane potential. During stomatal closure, K+ efflux through outward rectifying channels causes vacuolar membrane depolarization (0 mV) which is accompanied by Clextrusion through an anion channel. Consequent activation of plasma membrane anion channels provides anion efflux from cytoplasm and depolarization of plasma membrane (-50 mV). Due to membrane potential change, K+ outward-rectifying channels are activated and release K+ .

 

New Insights into the Regulation of Stomatal Movements by Red Light, Carbon Dioxide and Circadian Rhythms

by Matrosova A. (2015)

Anastasia Matrosova, Faculty of Forest Sciences Department of Forest Genetics and Plant Physiology, Umeå, Sweden

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in Doctoral Thesis Swedish University of Agricultural Sciences Umeå 2015 –

https://pub.epsilon.slu.se/12812/1/matrosova_a_151113.pd

Screen Shot 2018-02-18 at 20.03.12
Figure 3. An overview of signaling pathways involved in red and blue light-induced stomatal opening. (a) Epidermal pavement cell, (b) guard cell and (c) mesophyll cell. Red light induces photosynthesis and decreases the [CO2] within the leaf, thereby deactivating anion channels in guard cells. Blue light is perceived by phototropins and activates H+ -ATPase. Both red and blue light cause hyperpolarization of the guard cell with consequent K + uptake, turgor increases and stomatal opening. When more CO2 is taken up, an activation of guard cell anion channels will lead to stomatal closing, thus providing a negative feedback mechanism. Figure adapted from Roelfsema and Hedrich, 2005.
Abstract

Stomata are small adjustable pores formed by pairs of guard cells that enable gas exchange between leaves and the atmosphere, thus directly affecting water loss and CO2 uptake in plants. The current work focuses on the regulation of stomatal movements by red light, carbon dioxide and the circadian system and attempts to uncover molecular mechanisms that control guard cell function. The signaling pathway that underlays stomatal opening in response to red light is yet to be fully elucidated. Here, the HIGH LEAF TEMPERATURE 1 (HT1) protein kinase, known as a negative regulator of high CO2 stomatal closure, is shown to be a key component of stomatal signaling in response to red light (Paper I). It was demonstrated that HT1 is epistatic to the positive regulator of ABA- and high CO2- induced stomatal closure OPEN STOMATA1 (OST1) protein kinase both in red lightand CO2-induced signal transduction in guard cells (Paper I). A photosynthesis-induced drop in intercellular CO2 as well as processes originating in the photosynthetic electron transport chain (PETC) have been proposed to signal the guard cell response to red light. Investigation of the effect of PETC inhibitors on stomatal conductance in Arabidopsis thaliana ecotypes Col-0 and Ely-1a has suggested the redox state of plastoquinone (PQ) pool to be involved in the regulation of stomatal movements (Paper II). The full mechanisms that link the regulation of stomatal movements to the circadian clock are yet unknown. The blue light receptor, F-box protein and key element of the circadian clock ZEITLUPE (ZTL) was here shown to physically interact with OST1 protein kinase (Paper III). Furthermore, Arabidopsis thaliana mutant plants and Populus transgenic lines that lack the activity of ZTL or OST1 demonstrated similar phenotypes, affected in stomatal movement control (Paper III). The work supports a requirement of both ZTL and OST1 in the regulation of guard cell turgor and suggests a direct link between the circadian clock and OST1 activity.

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Dust affects net photosynthetic rate by covering and plugging stomata, and by increasing leaf temperature.

 

 

The Effects of Dust by Covering and Plugging Stomata and by Increasing Leaf Temperature on Photosynthetic Rate of Plant Leaves

by Hirano T., Kiyota M., Aiga I. (1990-1991)

Takashi HIRANO, Makoto KIYOTA, Ichiro AIGA,

College of Agriculture, University of Osaka Prefecture

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in Journal of Agricultural Meteorology 46(4): 215-222 – https://doi.org/10.2480/agrmet.46.215 –

https://www.jstage.jst.go.jp/article/agrmet1943/46/4/46_4_215/_article

Abstract

 

The physical effects of dust on gaseous exchange through stomata were investigated by measuring stomatal conductance of dusted and clean leaves. The effects of dust by increasing leaf temperature on net photosynthetic rate and transpiration rate were investigated.
Four classes of dust (JIS Z 8901: three classes of Kanto-loam powder and carbon-black), which were different in particle size and were chemically inert to plants, were made to adhere to upper surface of leaves of cucumber plants. In order to except the shading effect of dust, stomatal conductance, net photosynthetic rate and transpiration rate were measured under the condition of fairly high light intensity.
The stomatal conductance of upper surface of dusted leaves whose stomata had been open in exposure of dust to leaves decreased in light peoriod and increased in dark peoriod. As particle size of dust became smaller, the changes of stomatal conductance increased both in light peoriod and dark peoriod. There was no change of stomatal conductance of leaves which had been exposed to dust when stomata had been closed. It seemed that dust caused these changes of stomatal conductance by covering and plugging stomata.
Temperature of leaves covered with carbon-black were higher than clean leaves by 1.7-3.7°C in 15-40°C of air temperature. The net photosynthetic rates of leaves which had been exposed to carbon-black when stomata had been closed were higher than the rates of clean leaves below 25°C of air temperature, and were lower above 30°C. The transpiration rates of the same dusted leaves were higher than the rates of clean leaves by 0.4-0.6g·dm-2·hr-1 in 15-40°C of air temperature.
The results suggest that dust affects net photosynthetic rate by covering and plugging stomata, and by increasing leaf temperature.

The mechanisms and adaptive implications of the observed communication of stress cues

 

 

Rumor Has It…: Relay Communication of Stress Cues in Plants

by Falik O., Mordoch Y., Quansah L., Fait A., Novoplansky A. ( 2011)

Mitrani Department of Desert Ecology, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel

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in PLOS One November 2, 2011 – https://doi.org/10.1371/journal.pone.0023625

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023625

Abstract

Recent evidence demonstrates that plants are able not only to perceive and adaptively respond to external information but also to anticipate forthcoming hazards and stresses. Here, we tested the hypothesis that unstressed plants are able to respond to stress cues emitted from their abiotically-stressed neighbors and in turn induce stress responses in additional unstressed plants located further away from the stressed plants. Pisum sativum plants were subjected to drought while neighboring rows of five unstressed plants on both sides, with which they could exchange different cue combinations. On one side, the stressed plant and its unstressed neighbors did not share their rooting volumes (UNSHARED) and thus were limited to shoot communication. On its other side, the stressed plant shared one of its rooting volumes with its nearest unstressed neighbor and all plants shared their rooting volumes with their immediate neighbors (SHARED), allowing both root and shoot communication. Fifteen minutes following drought induction, significant stomatal closure was observed in both the stressed plants and their nearest unstressed SHARED neighbors, and within one hour, all SHARED neighbors closed their stomata. Stomatal closure was not observed in the UNSHARED neighbors. The results demonstrate that unstressed plants are able to perceive and respond to stress cues emitted by the roots of their drought-stressed neighbors and, via ‘relay cuing’, elicit stress responses in further unstressed plants. Further work is underway to study the underlying mechanisms of this new mode of plant communication and its possible adaptive implications for the anticipation of forthcoming abiotic stresses by plants.

Stomata measurements and plant performance

Stomatal aperture was used as a highly sensitive phenotypic expression of plant response to osmotic stress [27]. Stomatal aperture was estimated by measuring the average width of stomata immediately before the external induction (0 min; water treatment only), and 15 and 60 minutes following the external induction (in both water and mannitol treatments).

Stomatal aperture was estimated from epidermal impressions following Sachs et al. 1993 [28]: the lower surfaces of 1–2 fully-unfurled 20–30 mm2 leaflets of each sampled plant were copied using a fresh mixture of Vinyl Polysiloxane dental impression material (Elite HD+, Badia Polesine, Rovigo, Italy). Following hardening, the resulted imprints were further copied with clear nail polish, which resulted in transparent preparations suitable for microscopic examination. Because the preparation of the imprints was disruptive, each plant set (depicted in Fig. 1) was only measured once, i.e. separate replication sets were sampled at different times and water and mannitol treatments.

Stomata measurements were carried out using AxioVision software (Carl Zeiss MicroImaging, Thornwood, NY, USA) on digital images of the nail-polish preparations. Average stomatal width was calculated from the data of at least 10 stomata per plant, selected haphazardly from 2–5 0.02 mm2 areas in the centre of each microscopic preparation. Accordingly, each data point (Fig. 2) represents the average width of at least 60 stomata nested within six replication sets (N = 6) per treatment per time interval.

 

 

How do plants breathe ?

by Morris R., Woolfenden H. (2018)

Richard Morris , Hugh Woolfenden,

in JIC 17 January 2018 –

This article originally appeared on TheScienceBreaker.com

https://www.jic.ac.uk/news-and-events/blog-copy/2018/01/how-do-plants-breathe/

Whether or not you like your sprouts, plants will likely form a major component of your diet: cereals, bread, potatoes, pasta, rice, chips, etc. all come from plants.

Rice, maize and wheat alone make up 60% of the world’s food intake.

Not only are plants essential for food security, they make most of your clothes, such as cotton and linen products.

So, plants play an indispensable role in our lives. More than that, without photosynthesis we wouldn’t even have oxygen to breathe.

Plants and algae perform photosynthesis, which converts atmospheric carbon dioxide and water to sugar using the energy from the sun. This process produces oxygen as a by-product and this by-product of green life is thought to have given rise to the current atmospheric oxygen levels of around 20 %. Simplified, we breathe in oxygen and carbon dioxide out, and plants do the opposite.

We breathe in and out through our mouths but how do plants breathe?

Plants also have mouths. The green parts of land plants are covered with tiny units called stomata, which is Greek for mouths.

Stomata are formed by two cells, called guard cells, each a mirror image of the other, which together form a ring shape like a doughnut (those with a hole).

Unlike doughnuts, stomata are exquisitely regulated and dynamic.

Method for simultaneously measurement of leaf hydraulic conductance (Kleaf) and stomatal conductance (gs) for transpiring excised leaves.

 

 

Measurement of Leaf Hydraulic Conductance and Stomatal Conductance and Their Responses to Irradiance and Dehydration Using the Evaporative Flux Method (EFM)

Sack L., Scoffoni C. (2012)

University of California, Los Angeles

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in J. Vis. Exp. (70), e4179, doi:10.3791/4179 (2012).

https://www.jove.com/video/4179/measurement-leaf-hydraulic-conductance-stomatal-conductance-their

SUMMARY

We describe a relatively rapid (30 min) and realistic method for simultaneously measurement of leaf hydraulic conductance (Kleaf) and stomatal conductance (gs) for transpiring excised leaves. The method can be modified to measure the light and dehydration responses of Kleaf and gs.

ABSTRACT

Water is a key resource, and the plant water transport system sets limits on maximum growth and drought tolerance. When plants open their stomata to achieve a high stomatal conductance (gs) to capture CO2 for photosynthesis, water is lost by transpiration1,2. Water evaporating from the airspaces is replaced from cell walls, in turn drawing water from the xylem of leaf veins, in turn drawing from xylem in the stems and roots. As water is pulled through the system, it experiences hydraulic resistance, creating tension throughout the system and a low leaf water potential (Ψleaf). The leaf itself is a critical bottleneck in the whole plant system, accounting for on average 30% of the plant hydraulic resistance3. Leaf hydraulic conductance (Kleaf = 1/ leaf hydraulic resistance) is the ratio of the water flow rate to the water potential gradient across the leaf, and summarizes the behavior of a complex system: water moves through the petiole and through several orders of veins, exits into the bundle sheath and passes through or around mesophyll cells before evaporating into the airspace and being transpired from the stomata. Kleaf is of strong interest as an important physiological trait to compare species, quantifying the effectiveness of the leaf structure and physiology for water transport, and a key variable to investigate for its relationship to variation in structure (e.g., in leaf venation architecture) and its impacts on photosynthetic gas exchange. Further, Kleaf responds strongly to the internal and external leaf environment3Kleaf can increase dramatically with irradiance apparently due to changes in the expression and activation of aquaporins, the proteins involved in water transport through membranes4, and Kleaf declines strongly during drought, due to cavitation and/or collapse of xylem conduits, and/or loss of permeability in the extra-xylem tissues due to mesophyll and bundle sheath cell shrinkage or aquaporin deactivation5-10. Because Kleaf can constrain gs and photosynthetic rate across species in well watered conditions and during drought, and thus limit whole-plant performance they may possibly determine species distributions especially as droughts increase in frequency and severity11-14.

We present a simple method for simultaneous determination of Kleaf and gson excised leaves. A transpiring leaf is connected by its petiole to tubing running to a water source on a balance. The loss of water from the balance is recorded to calculate the flow rate through the leaf. When steady state transpiration (E, mmol • m-2 • s-1) is reached, gs is determined by dividing by vapor pressure deficit, and Kleaf by dividing by the water potential driving force determined using a pressure chamber (Kleaf= E /- Δψleaf, MPa)15.

This method can be used to assess Kleaf responses to different irradiances and the vulnerability of Kleaf to dehydration14,16,17.

Stimulating Story of Stomata

Takeaway: Evolutionary wonders, stomata are vital to plant health. Knowing how they work and what they do for the plant is important knowledge for every kind of grower.

 

How Plants Breathe: The Stimulating Story of Stomata

by McKee S. (2018)

in Maximum Yield February 8, 2018 –

https://www.maximumyield.com/how-plants-breathe-the-stimulating-story-of-stomata/2/3827

Take a second and just breathe. Think about how you are bringing air full of oxygen into your lungs through your mouth. Now, take a drink of water and think of how that water travels through your mouth down toward your stomach. You don’t have to think about the air and water going to the right place unless something goes wrong and it slides down the wrong tube.

You may not consider the fact that plants have a mouth, but they do. Plants have many tiny openings called stomata, which is the Greek word for mouth. These microscopic openings are found on the surface of your plants and they play a significant role in your plants’ survival.

Stomata Basics

When you think about how plants draw in the essential things they need to live, you probably focus on the roots and how they bring in water and nutrients from the soil. The roots are a critical system, but there’s another way that plants bring in the essentials and that’s through their stomata. Stomata are found on the leaves of the plant in the highest concentration, but they’re also located along the stem and other parts that are above the soil. Having a large number of stomata around the entire plant assists in improving the potential of survival for plants.

The functional coordination between stomata and hydraulic traits

 

 

Plants resistance to drought depends on timely stomatal closure

by Martin-StPaul N.Delzon S.Cochard H. (2017)

Nicolas Martin-StPaul, Sylvain Delzon, Hervé Cochard,

=======

in Ecol Lett, 20: 1437–1447. doi:10.1111/ele.12851 –

http://onlinelibrary.wiley.com/doi/10.1111/ele.12851/abstract

Abstract

Stomata play a significant role in the Earth’s water and carbon cycles, by regulating gaseous exchanges between the plant and the atmosphere. Under drought conditions, stomatal control of transpiration has long been thought to be closely coordinated with the decrease in hydraulic capacity (hydraulic failure due to xylem embolism).

We tested this hypothesis by coupling a meta-analysis of functional traits related to the stomatal response to drought and embolism resistance with simulations from a soil–plant hydraulic model.

We report here a previously unreported phenomenon: the existence of an absolute limit by which stomata closure must occur to avoid rapid death in drought conditions. The water potential causing stomatal closure and the xylem pressure at the onset of embolism formation were equal for only a small number of species, and the difference between these two traits (i.e. safety margins) increased continuously with increasing embolism resistance.

Our findings demonstrate the need to revise current views about the functional coordination between stomata and hydraulic traits and provide a mechanistic framework for modeling plant mortality under drought conditions.