The science of the stomata of plants: a continuously growing list of references, abstracts and illustrations, helping researchers to data on publications.
Embora haja autoconsistência entre as estimativas paleobiológicas e geoquímicas de CO2, deve-se reconhecer que a resposta não linear é uma limitação da abordagem estomática para estimar os altos níveis de CO2 paleo.
Aunque existe autoconsistencia entre las estimaciones paleobiológicas y geoquímicas de CO2, se debe reconocer que la respuesta no lineal es una limitación del enfoque estomático para estimar los altos niveles de CO2 paleo.
The inverse relationship between atmospheric CO2 and the stomatal index (proportion of epidermal cells that are stomata) of vascular land plant leaves has led to the use of fossil plant cuticles for determining ancient levels of CO2. In contemporary plants the stomatal index repeatedly shows a lower sensitivity atmospheric CO2 levels above 340 ppm in the short term. These observations demonstrate that the phenotypic response is nonlinear and may place constraints on estimating higher-than-present palaeo-CO2 levels in this way. We review a range of evidence to investigate the nature of this nonlinearity. Our new data, from fossil Ginkgo cuticles, suggest that the genotypic response of fossil Ginkgo closely tracks the phenotypic response seen in CO2 enrichment experiments. Reconstructed atmospheric CO2 values from fossil Ginkgo cuticles compare well with the stomatal ratio method of obtaining a quantitative CO2 signal from extinct fossil plants, and independent geochemical modelling studies of the long-term carbon cycle. Although there is self-consistency between palaeobiological and geochemical CO2 estimates, it should be recognized that the nonlinear response is a limitation of the stomatal approach to estimating high palaeo-CO2 levels.
Developments in plant physiology since the 1980s have led to the realization that fossil plants archive both the isotopic composition of atmospheric CO2 and its concentration, both critical integrators of carbon cycle processes through geologic time. These two carbon cycle signals can be read by analyzing the stable carbon isotope composition (δ13C) of fossilized terrestrial organic matter and by determining the stomatal characters of well-preserved fossil leaves, respectively.
We critically evaluate the use of fossil plants in this way at abrupt climatic boundaries associated with mass extinctions and during times of extreme global warmth. Particular emphasis is placed on evaluating the potential to extract a quantitative estimate of the δ13C of atmospheric CO2 because of the key role it plays in understanding the carbon cycle. We critically discuss the use of stomatal index and stomatal ratios for reconstructing atmospheric CO2 levels, especially the need for adequate replication, and present a newly derived CO2 record for the Mesozoic that supports levels calculated from geochemical modeling of the long-term carbon cycle. Several suggestions for future research using stable carbon isotope analyses of fossil terrestrial organic matter and stomatal measurements are highlighted.
Assessing the potential for the stomatal characters of extant and fossil Ginkgo leaves to signal atmospheric CO2 change
by Chen L. C., Li C. S., Chaloner W. G., Beerling D. J., Sun Q. G., Collinson M. E., Mitchell P. L. (2001)
Laboratory of Systematic and Evolutionary Botany, and Department of Palaeobotany, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing 100093, P. R. China.
The stomatal density and index of fossil Ginkgo leaves (Early Jurassic to Early Cretaceous) have been investigated to test whether these plant fossils provide evidence for CO(2)-rich atmosphere in the Mesozoic. We first assessed five sources of natural variation in the stomatal density and index of extant Gingko biloba leaves: (1) timing of leaf maturation, (2) young vs. fully developed leaves, (3) short shoots vs. long shoots, (4) position in the canopy, and (5) male vs. female trees. Our analysis indicated that some significant differences in leaf stomatal density and index were evident arising from these considerations. However, this variability was considerably less than the difference in leaf stomatal density and index between modern and fossil samples, with the stomatal index of four species of Mesozoic Ginkgo (G. coriacea, G. huttoni, G. yimaensis, and G. obrutschewii) 60-40% lower than the modern values recorded in this study for extant G. biloba. Calculated as stomatal ratios (the stomatal index of the fossil leaves relative to the modern value), the values generally tracked the CO(2) variations predicted by a long-term carbon cycle model confirming the utility of this plant group to provide a reasonable measure of ancient atmospheric CO(2) change.
We have applied evolutionary comparatise methods to control for phylogenetic relationships between species in order to determine if three recently proposed relationships between leaf structure and function are upheld, using a large database comprising a wide range of species from tropical and temperate ecosystems.
The three hypotheses tested were:
(i) leaf thickness is positively correlated with total stomatal density (adaxial and abaxial values summed);
(ii) amphistomatous leases {stomata present on the upper and lower surfaces) have a higher maximum stomatal conductance than hypostomatous (stomata on the lower surface only) leaves, and
(iii) changes in the stomatal density on upper and lower leaf surfaces are regulated in a compensatory manner.
The results showed that, contrary to several mathematical modelling studies, thicker leaves were not associated with more stomata either in species from lowland tropical rain forests or from central Europe. .
4mphistomatous leaves had a higher maximum stomatal conductance, indicatmg that one aspect of previous modelling work is correctly underpinned after accounting for relatedness.
Finally, we found no evidence that the stomatal densities on upper and lower leaf surfaces are closely regulated. These three physiological traits are discussed with reference both to the modelling of leaf gas exchange and to plant function in relation to microclimate.
A recent high‐resolution record of Late‐glacial CO2 change from Dome Concordia in Antarctica reveals a trend of increasing CO2 across the Younger Dryas stadial (GS‐1).
These results are in good agreement with previous Antarctic ice‐core records. However, they contrast markedly with a proxy CO2record based on the stomatal approach to CO2 reconstruction, which records a ca. 70 ppm mean CO2 decline at the onset of GS‐1.
To address these apparent discrepancies we tested the validity of the stomatal‐based CO2reconstructions from Kråkenes by obtaining further proxy CO2 records based on a similar approach using fossil leaves from two independent lakes in Atlantic Canada.
Our Late‐glacial CO2 reconstructions reveal an abrupt ca. 77 ppm decrease in atmospheric CO2 at the onset of the Younger Dryas stadial, which lagged climatic cooling by ca. 130 yr.
Furthermore, the trends recorded in the most accurate high‐resolution ice‐core record of CO2, from Dome Concordia, can be reproduced from our stomatal‐based CO2 records, when time‐averaged by the mean age distribution of air contained within Dome Concordia ice (200 to 550 yr).
If correct, our results indicate an abrupt drawdown of atmospheric CO2 within two centuries at the onset of GS‐1, suggesting that some re‐evaluation of the behaviour of atmospheric CO2 sinks and sources during times of rapid climatic change, such as the Late‐glacial, may be required.
1. The results of Salisbury (1927) with regard to interspecific patterns of stomatal density have lead to much theorizing as to the causes for the apparent differences. However, Salisbury treated each species as an independent data point, a practice which may not be valid given that similarity can result from taxonomic relatedness independent of ecological effects.
2. In reanalyses of Salisbury’s data for stomatal number, we found that the patterns upon which Salisbury based his conclusion that stomatal density is correlated with the degree of ‘exposure’ of a species were not upheld when taxonomic relatedness was taken into account.
Specifically, we found stomatal density to be greater in shrubs than trees, in trees than herbs and in marginal herbs than understorey herbs, but no significant difference between shrubs and herbs, or woody plants (trees and shrubs pooled) and non-woody plants from the same habitat type.
3. In an additional analysis using data only for one life-form from one habitat type (herbs from the forest margin), we found no difference in stomatal density between amphi- and hypostomatous species.
The moss Physcomitrella patens genome encodes orthologues of the basic helix loop helix (bHLH) transcription factors regulating stomatal development in flowering plants (a) Developing P. patens sporophyte, arrow indicating region of stomatal placement, and (b) excised sporophyte with stomata (orange/brown pores) forming a ring around the base. (c) Close-up of the sporophyte epidermis with single celled guard cells and central pores. (d and e) Bootstrapped Maximum Likelihood phylogenies of the SMF gene family comprising the FAMA, SPCH and MUTE subfamilies and the SCRM/ICE gene family in sequenced land plants. Internal node names in bold red indicate inferred subfamily ancestry. Internal nodes are coloured to indicate either duplication (red), speciation (green) or haplotype (blue) origin of the descendant nodes. Edge values represent bootstrap values. External node names comprise species abbreviations, original accession numbers of the protein sequences and accepted gene names of experimentally studied representatives in bold red. Species abbreviations in five-letter-code: Arabidopsis thaliana, Populus trichocarpa, Oryza sativa, Sorghum bicolor, Selaginella moellendorffii and Physcomitrella patens. (f, g and h) Relative expression of PpSMF1, PpSMF2 and PpSCRM1 in the developing sporophyte (grey bars) and protonema tissue (black bars) analysed by qRT-PCR. Error bars indicate standard error of the mean. Three replicates per tissue type were used. The scale bar in a = 100μm, in b = 100μm, in c = 25μm.
Origin and function of stomata in the moss Physcomitrella patens
by Chater C. C., Caine R. S, Tomek M., Wallace S., Kamisugi Y., Cuming A. C., Lang D., MacAlister C. A., Casson S., Bergmann D. C., Decker E., Frank W., Gray J. E., Fleming A., Reski R., Beerling D. J. (2016)
PpSMF1 and PpSCRM1 are required for stomatal development in the moss Physcomitrella patens (a) Stacked UV fluorescence images (upper panel), scanning electron microscope images (middle panel) and bright field images (bottom panel) showing the spore capsule base and epidermal close-ups from P. patens wild-type, ΔPpSMF1, ΔPpSMF2 and ΔPpSCRM1 knock-out mutants, respectively. The top panel wild-type representative is from Villersexel K3 ecotype of P. patens, the middle panel wild-type representative is from the Gransden D12 ecotype and the bottom panel wild-type relates to the Gransden 2004 ecotype. There were no discernible differences between the sporophytes of the different background lines. For both of the ΔPpSCRM1 lines generated we observed one such instance of aborted stomata (see bottom right panel) in the 7 capsules of each line surveyed. (b) Number of stomata formed per sporophyte in two independent lines of each genotype versus wild-type controls. Error bars indicate one standard error of the mean. For ΔPpSMF1 and ΔPpSCRM1 and the corresponding wild-types, n = 7 capsules of each line were analysed. For ΔPpSMF2 and wild-type background, 5 capsules were surveyed. A One-way ANOVA was performed to test for differences between the wild-type and ΔPpSMF2 lines and no significant differences (denoted ns) were found. (c) RT-PCR to confirm loss of the respective transcript in each of the P. patens knock-out lines (top panel). A Rubisco (RBCS) control was run to verify the integrity of the produced cDNA (Bottom panel). For labelling purposes the wild-types Villersexel K3, Gransden D12 and Gransden 2004 are denoted Vx, GrD12 and Gr04. For PpSMF2 two bands were amplified in the control for which the smaller 239bp product represents the size expected for PpSMF2. Scale bars in a = 50 μm in the top and middle panels, in the bottom panel = 15 μm.
Abstract
Stomata are microscopic valves on plant surfaces that originated over 400 million years (Myr) ago and facilitated the greening of Earth’s continents by permitting efficient shoot-atmosphere gas exchange and plant hydration1.
However, the core genetic machinery regulating stomatal development in non-vascular land plants is poorly understood2-4 and their function has remained a matter of debate for a century5.
Here, we show that genes encoding the two basic helix-loop-helix proteins PpSMF1 (SPEECH, MUTE and FAMA-like) and PpSCREAM1 (SCRM1) in the moss Physcomitrella patens are orthologous to transcriptional regulators of stomatal development in the flowering plant Arabidopsis thaliana and essential for stomata formation in moss.
Targeted P. patens knockout mutants lacking either PpSMF1 or PpSCRM1 develop gametophytes indistinguishable from wild-type plants but mutant sporophytes lack stomata.
Protein-protein interaction assays reveal heterodimerization between PpSMF1 and PpSCRM1, which, together with moss-angiosperm gene complementations6, suggests deep functional conservation of the heterodimeric SMF1 and SCRM1 unit is required to activate transcription for moss stomatal development, as in A. thaliana7.
Moreover, stomata-less sporophytes of ΔPpSMF1 and ΔPpSCRM1 mutants exhibited delayed dehiscence, implying stomata might have promoted dehiscence in the first complex land-plant sporophytes.
Stomatal density is known to respond to CO2 levels during leaf development. Current interest in the increasing concentration of atmospheric CO2 has stimulated much experimentation on the responses of plants to relatively short‐term exposure in artificially high CO2 levels.
Attempts to extrapolate from short‐term to long‐term responses raise fundamental questions concerning evolutionary change in response to rising global CO2levels. We consider the improved water use efficiency observed under elevated CO2 levels to be the main driving force of natural selection affecting the genotypic component controlling stomatal density.
Whether a response is merely phenotypic or becomes incorporated into the genotype depends on two factors: (i) the time scale of exposure and (ii) the generation time of a species. Measurements of stomatal density on fossil leaves of Salix herbacea through a glacial cycle covering the last 140000 years have shown a decrease in stomatal density in response to the rising CO2 levels of this period.
This accords with the shorter‐term observations on leaves of trees seen in herbarium specimens where the stomatal density has decreased in response to the rising CO2 levels of the last 200 years.
The results indicate that natural selection over the 140000‐year period may have favoured a similar response to that shown by trees phenotypically over the last 200 years.
Since there is now some evidence for the genetic control of stomatal density, the role of natural selection affecting it must be considered when translating responses from short‐term experiments to predict how stomatal density will be affected by long‐term climatic and atmospheric change.
PLANT STOMATA ENCYCLOPEDIA 
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