The increased speed of stomata improved the plant’s water use efficiency without a penalty to CO2 uptake

Speedier stomata in optogenetically enhanced plants improve growth and conserve water

AAAS (2019)

In AAAS

https://eurekalert.org/pub_releases/2019-03/aaft-ssi032519.php

Abstract

By introducing an extra ion channel into the stomata of mustard plants, researchers have developed a new a way to speed up the stomatal response in their leaves.

The speedier stomata of the optogenetically enhanced plants improved their photosynthetic efficiency and water use – producing more than twice the amount of biomass expected in the fluctuating light typical of outdoor growing conditions.

Stomata are the tiny pores that cover the surface of a plant’s leaves, allowing for the uptake of CO2 for photosynthesis and for the transpiration of water, by opening and closing in response to environmental conditions. However, these dual roles are often conflicting.

While open stomata may allow a plant to assimilate large amounts of carbon for photosynthesis, this happens at the cost of increased water loss. What’s more, stomata respond slowly to changing conditions. In environments where natural light fluctuates – due to passing clouds, for example – stomata could stay open or closed for longer than they need to.

As a result, photosynthesis is generally not as efficient as it could be and too much water is lost from the plant. The ability to circumvent the carbon:water trade-off provides a promising avenue to improve crop productivity.

To address this challenge, Maria Papanatsiou and colleagues used the optogenetic tool BLINK1 (Blue Light-Induced K+ channel 1) to engineer an extra ion channel into the stomata of the mustard plant Arabidopsis.

According to Papanatsiou et al., the channel, which is triggered by exposure to blue light, causes the stomata to open or close more rapidly. According to the results, the increased speed improved the plant’s water use efficiency without a penalty to CO2 uptake.

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Stomata: Physiology

Stomata: Meaning, Types and Mechanism | Plant Physiology

Abhi I. R. (xxxx)

In

http://www.biologydiscussion.com/plant-physiology-2/water-loss/stomata-meaning-types-and-mechanism-plant-physiology/39657

In this article we will discuss about:- 1. Meaning of Stomata 2. Types of Stomata 3. Distribution 4. Daily Periodicity 5. Diffusive Capacity 6. Dynamic 7. Mechanism 8. Aspects of the Physiology of Stomatal Opening.

Contents:

  1. Meaning of Stomata
  2. Types of Stomata
  3. Distribution of Stomata
  4. Daily Periodicity of Stomatal Movements
  5. Diffusive Capacity of Stomata
  6. Dynamic of Stomata
  7. Mechanism of Stomatal
  8. Aspects of the Physiology of Stomatal Opening

Metabolism‐mediated mechanisms regulating stomatal movements

The sucrose‐to‐malate ratio correlates with the faster CO2 and light stomatal responses of angiosperms compared to ferns

Lima V. F., dos Anjos L., Medeiros D. B., Candido-Sobrinho S. A., Souza L. P., Gago J., Fernie A. R., Daloso D. M. (2019)

Valéria F. Lima, Letícia dos Anjos, David B. Medeiros, Silvio A. Cândido‐Sobrinho, Leonardo P. Souza, Jorge Gago, Alisdair R. Fernie, Danilo M. Daloso,

Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Ceará. Fortaleza‐CE, 60451‐970 Brasil

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In New Phytologist https://doi.org/10.1111/nph.15927

https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.15927?af=R

Abstract

Stomatal responses to environmental signals differ substantially between ferns and angiosperms. However, the mechanisms that lead to such responses remain unclear.

Here we investigated the extent by which leaf metabolism contributes to coordinate the differential stomatal behaviour among ferns and angiosperms.

Stomata from all species were responsive to light and CO2 transitions. However, fern stomatal responses were slower and minor in both absolute and relative terms. Angiosperms have higher stomatal density, but this is not correlated with speed of stomatal closure. The metabolic responses throughout the diel course and under different CO2 conditions differ substantially among ferns and angiosperms. Higher sucrose content and an increased sucrose‐to‐malate ratio during high CO2‐induced stomatal closure was observed in angiosperms compared to ferns. Furthermore, the speed of stomatal closure was positively and negatively correlated with sugars and organic acids, suggesting that the balance between sugar and organic acids aids to explain the faster stomatal responses of angiosperms.

Our results suggest that mesophyll‐derived metabolic signals, especially those associated to sucrose and malate, may be also important to modulate the differential stomatal behaviour between ferns and angiosperms, providing important new information that helps to understand the metabolism‐mediated mechanisms regulating stomatal movements across land plant evolution.

Optimization of photosynthesis and stomatal conductance during acclimation to heat and drought

Optimization of photosynthesis and stomatal conductance in the date palm Phoenix dactylifera during acclimation to heat and drought

by Kruse J., Adams M., Winkler B., Ghirardo A., Alfarraj S., Kreuzwieser J., Hedrich R., Schnitzler J.-P., Rennenberg H. (2019)

Jörg Kruse, Mark Adams, Barbro Winkler, Andrea Ghirardo, Saleh Alfarraj, Jürgen Kreuzwieser, Rainer Hedrich, Jörg‐Peter Schnitzler, Heinz Rennenberg,

Institute of Forest Sciences, Chair of Tree Physiology, University of Freiburg, Georges‐Köhler‐Allee 53/54, 79110 Freiburg, Germany

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In New Phytologist https://doi.org/10.1111/nph.15923

https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.15923?af=R

Abstract

We studied acclimation of leaf gas exchange to differing seasonal climate and soil water availability in slow‐ growing date palm seedlings (Phoenix dactylifera). We used an extended Arrhenius‐equation to describe instantaneous temperature responses of leaf net photosynthesis (A) and stomatal conductance (G), and derived physiological parameters suitable for characterization of acclimation (Topt, Aopt and Tequ).

Optimum temperature of A (Topt) ranged between 20 ‐33°C in winter and 28 ‐45°C in summer. Growth temperature (Tgrowth) explained ~50% of the variation in Topt, which additionally depended on leaf water status at the time‐ of‐ measurement. During water‐stress, light ‐ saturated rates of A at Topt (i.e, Aopt) were reduced to 30‐80% of control levels, albeit not limited by CO2‐ supply per se.

Equilibrium temperature (Tequ), around which A/G and substomatal [CO2] are constant, remained tightly coupled with Topt. Our results suggest that acclimatory shifts in Topt and Aopt reflect a balance between maximization of photosynthesis whilst minimizing the risk of metabolic perturbations caused by imbalances in cellular [CO2].

This novel perspective on acclimation of leaf gas exchange is compatible with optimization theory, and might help elucidating other acclimation and growth strategies in species adapted to differing climates.

A coupled photosynthesis-stomatal conductance model

Coupled photosynthesis-stomatal conductance model for leaves of C4 plants

by Collatz G. J., Ribas-Carbo M., Berry J. A. (1992)

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In Aust. J. Plant Physiol. 19: 519–538 – https://doi.org/10.1071/PP9920519

http://www.publish.csiro.au/fp/PP9920519

Abstract

Leaf based models of net photosynthesis (An) and stomatal conductance (g) are often components of whole plant, canopy and regional models of net primary productivity and surface energy balance. Since C4metabolism shows unique responses to environmental conditions and C4 species are important agriculturally and ecologically, a realistic and accurate leaf model specific to C4 plants is needed. In this paper we develop a simple model for predicting An and g from leaves of C4 plants that is easily parameterised and that predicts many of the important environmental responses.

We derive the leaf model from a simple biochemical-intercellular transport model of C4 photosynthesis that includes inorganic carbon fixation by PEP carboxylase, light dependent generation of PEP and RuBP, rubisco reaction kinetics, and the diffusion of inorganic carbon and O2 between the bundle sheath and mesophyll. We argue that under most conditions these processes can be described simply as three potentially limiting steps. The leaf photosynthesis model treats An as first order with respect to either light, CO2 or the amount of rubisco present and produces a continuous transition between limitations. The independent variables of the leaf photosynthesis model are leaf temperature (TI), intercellular CO2 levels and the absorbed quantum flux.

A simple linear model of g in terms of An and leaf surface CO2 level (ps) and relative humidity (hs) is combined with the photosynthesis model to give leaf photosynthesis as a function of absorbed quantum flux, T1 and ps and hs levels.

Gas exchange measurements from corn leaves exposed to varied light, CO2 and temperature levels are used to parameterise and test the models. Model parameters are determined by fitting the models to a set of 21 measurements. The behaviour of the models is compared with an independent set of 71 measurements, and the predictions are shown to be highly correlated with the data.

Under most conditions the leaf model can be parameterised simply by determining the level of rubisco in the leaves. The effects of light environment, nutritional status and water stress levels on An and g can be accounted for by appropriate adjustment of the capacity for rubisco to fix CO2. We estimate rubsico capacity from CO2 and light saturated photosynthesis although leaf nitrogen content or rubisco assays from leaf extracts could also be used for this purpose.

A Dynamic Hydro-Mechanical and Biochemical Model of Stomatal Conductance for C4 Photosynthesis

Figure 1. Modeling approach and framework. Blue boxes show input parameters/variables. Dashed boxes encapsulate the lightlimited and enzyme-limited models for C4 photosynthesis, and the purple box represents the hydromechanical stomatal model.
PPFD and CO2 concentration external to the leaf [Ca] are inputs to the photosynthesis models. Electron transport and ATP production rates (JATP) and [CO2] in M (CM) are fed into the light- and enzyme-limited models. The outputs from the photosynthesis
models are used to calculate chloroplastic ATP concentration, t. t is used in the stomatal model along with inputs for soil water
potential, CSoil, and evaporative demand, DS. The stomatal model also uses other set and fitted variables (e.g. pe, xb, and KPLANT
[see Table I]), along with t0, which relates to the chloroplastic ATP concentration in the dark and is calculated from gS in the dark
(gS0) and DS in the dark (DS0). In the model simulations, CM is calculated iteratively.

A Dynamic Hydro-Mechanical and Biochemical Model of Stomatal Conductance for C4 Photosynthesis

by Bellasio C., Quirk J., Buckley T. N., Beerling D. J. (2017)

Chandra Bellasio,a,b,2,3 Joe Quirk,a Thomas N. Buckley,c and David J. Beerlinga


a Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom
b Trees and Timber Institute, National Research Council of Italy, 50019 Florence, Italy
c Sydney Institute of Agriculture, University of Sydney, Narrabri, New South Wales 2390, Australia

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In Plant Physiol. 175(1): 104-119 – DOI: https://doi.org/10.1104/pp.17.00666

http://www.plantphysiol.org/content/175/1/104

http://www.plantphysiol.org/content/plantphysiol/175/1/104.full.pdf

Abstract

C4 plants are major grain (maize [Zea mays] and sorghum [Sorghum bicolor]), sugar (sugarcane [Saccharum officinarum]), and biofuel (Miscanthus spp.) producers and contribute ∼20% to global productivity.

Plants lose water through stomatal pores in order to acquire CO2(assimilation [A]) and control their carbon-for-water balance by regulating stomatal conductance (gS). The ability to mechanistically predict gS and A in response to atmospheric CO2, water availability, and time is critical for simulating stomatal control of plant-atmospheric carbon and water exchange under current, past, or future environmental conditions. Yet, dynamic mechanistic models for gS are lacking, especially for C4 photosynthesis.

We developed and coupled a hydromechanical model of stomatal behavior with a biochemical model of C4 photosynthesis, calibrated using gas-exchange measurements in maize, and extended the coupled model with time-explicit functions to predict dynamic responses.

We demonstrated the wider applicability of the model with three additional C4 grass species in which interspecific differences in stomatal behavior could be accounted for by fitting a single parameter. The model accurately predicted steady-state responses of gS to light, atmospheric CO2 and oxygen, soil drying, and evaporative demand as well as dynamic responses to light intensity. Further analyses suggest that the effect of variable leaf hydraulic conductance is negligible.

Based on the model, we derived a set of equations suitable for incorporation in land surface models. Our model illuminates the processes underpinning stomatal control in C4plants and suggests that the hydraulic benefits associated with fast stomatal responses of C4grasses may have supported the evolution of C4 photosynthesis.

The decline in stomatal and mesophyll conductance during drought

Leaf hydraulic vulnerability triggers the decline in stomatal and mesophyll conductance during
drought in rice (Oryza sativa)

by Wang X., Du T., Huang J., Peng S., Xiong D.2 (2018)

1 National Key Laboratory of Crop Genetic Improvement, MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, China.

2 Department of Plant Sciences, University of California, Davis, CA, USA.

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In J Exp Bot 69: 4033–4045 – doi: 10.1093/jxb/ery188. –

https://www.ncbi.nlm.nih.gov/pubmed/29788146

Abstract

Understanding the physiological responses of crops to drought is important for ensuring sustained crop productivity under climate change, which is expected to exacerbate the frequency and intensity of periods of drought.

Drought responses involve multiple traits, and the correlations between these traits are poorly understood.

Using a variety of techniques, we estimated the changes in gas exchange, leaf hydraulic conductance, and leaf turgor in rice (Oryza sativa) in response to both short- and long-term soil drought.

We performed a photosynthetic limitation analysis to quantify the contributions of each limiting factor to the resultant overall decrease in photosynthesis during drought. Biomass, leaf area, and leaf width significantly decreased during the 2-week drought treatment, but leaf mass per area and leaf vein density increased.

Light-saturated photosynthetic rate declined dramatically during soil drought, mainly due to the decrease in stomatal conductance (gs) and mesophyll conductance (gm).

Stomatal modeling suggested that the decline in leaf hydraulic conductance explained most of the decrease in stomatal closure during the drought treatment, and may also trigger the drought-related decrease of stomatal conductance and mesophyll conductance.

The results of this study provide insight into the regulation of carbon assimilation under drought conditions.