Variations in guard cell wall composition reflect different physiological activity of stomata in land plants

 

 

Contrasting pectin polymers in guard cell walls of Arabidopsis and the hornwort Phaeoceros reflect physiological differences

by Merced A., Renzaglia K. S. (2018)

Amelia Merced,  Karen S. Renzaglia,

===

in Annals of Botany, mcy168 – https://doi.org/10.1093/aob/mcy168 –

https://academic.oup.com/aob/advance-article-abstract/doi/10.1093/aob/mcy168/5092734?redirectedFrom=fulltext

Abstract

Background and Aims

In seed plants, stomata regulate CO2 acquisition and water relations via transpiration, while minimizing water loss. Walls of guard cells are strong yet flexible because they open and close the pore by changing shape over the substomatal cavity. Pectins are necessary for wall flexibility and proper stomata functioning. This study investigates the differences in pectin composition in guard cells of two taxa that represent key lineages of plants with stomata: Arabidopsis, an angiosperm with diurnal stomatal activity, and Phaeoceros, a bryophyte that lacks active stomatal movement.

Methods

Using immunolocalization techniques in transmission electron microscopy, this study describes and compares the localization of pectin molecule epitopes essential to stomata function in guard cell walls of Arabidopsis and Phaeoceros.

Key Results

In Arabidopsis, unesterified homogalacturonans very strongly localize throughout guard cell walls and are interspersed with arabinan pectins, while methyl-esterified homogalacturonans are restricted to the exterior of the wall, the ledges and the junction with adjacent epidermal cells. In contrast, arabinans are absent in Phaeoceros, and both unesterified and methyl-esterified homogalacturonans localize throughout guard cell walls.

Conclusions

Arabinans and unesterified homogalacturonans are required for wall flexibility, which is consistent with active regulation of pore opening in Arabidopsis stomata. In contrast, the lack of arabinans and high levels of methyl-esterified homogalacturonans in guard cell walls of Phaeoceros are congruent with the inability of hornwort stomata to open and close with environmental change. Comparisons across groups demonstrate that variations in guard cell wall composition reflect different physiological activity of stomata in land plants.

Advertisements

A lack of physiological regulation of stomatal movements in hornworts compared with tracheophytes

hornwortyoung
Introduction to the Anthocerotophyta (UCMP), Berkeley Above, you can see pictures of the hornwort Phaeoceros. On the left is a plant with young sporophytes beginning to elongate from the top of the gametophyte. (http://www.ucmp.berkeley.edu/plants/anthocerotophyta.html)

 

 

Hornwort stomata do not respond actively to exogenous and environmental cues

by Pressel S., Renzaglia K. S., Clymo R. S., Duckett, J. G. (2018) 

Silvia Pressel, Karen S. Renzaglia, Richard S. (Dicky) Clymo, Jeffrey G. Duckett

 

in Annals of Botany, mcy045 –  https://doi.org/10.1093/aob/mcy045

https://academic.oup.com/aob/advance-article-abstract/doi/10.1093/aob/mcy045/4979633?redirectedFrom=fulltext

Abstract

Backgrounds and Aims

Because stomata in bryophytes occur on sporangia, they are subject to different developmental and evolutionary constraints from those on leaves of tracheophytes. No conclusive experimental evidence exists on the responses of hornwort stomata to exogenous stimulation.

 

Methods

Responses of hornwort stomata to abscisic acid (ABA), desiccation, darkness and plasmolysis were compared with those in tracheophyte leaves. Potassium ion concentrations in the guard cells and adjacent cells were analysed by X-ray microanalysis, and the ontogeny of the sporophytic intercellular spaces was compared with those of tracheophytes by cryo-scanning electron microscopy.

 

Key Results

The apertures in hornwort stomata open early in development and thereafter remain open. In hornworts, the experimental treatments, based on measurements of >9000 stomata, produced only a slight reduction in aperture dimensions after desiccation and plasmolysis, and no changes following ABA treatments and darkness. In tracheophytes, all these treatments resulted in complete stomatal closure. Potassium concentrations are similar in hornwort guard cells and epidermal cells under all treatments at all times. The small changes in hornwort stomatal dimensions in response to desiccation and plasmolysis are probably mechanical and/or stress responses of all the epidermal and spongy chlorophyllose cells, affecting the guard cells. In contrast to their nascent gas-filled counterparts across tracheophytes, sporophytic intercellular spaces in hornworts are initially liquid filled.

 

Conclusions

Our experiments demonstrate a lack of physiological regulation of opening and closing of stomata in hornworts compared with tracheophytes, and support accumulating developmental and structural evidence that stomata in hornworts are primarily involved in sporophyte desiccation and spore discharge rather than the regulation of photosynthesis-related gaseous exchange. Our results run counter to the notion of the early acquisition of active control of stomatal movements in bryophytes as proposed from previous experiments on mosses.

==================

https://www.botany.one/2018/07/hornwort-stomata-are-not-actively-regulated/

Hornwort stomata are not actively regulated

Stomata, pores in the plant epidermis that regulate gas exchange, are a key innovation that enabled freshwater algae to colonize Earth’s landmasses some 500 Mya. Because stomata in bryophytes occur on sporangia, they are subject to different developmental and evolutionary constraints from those on leaves of tracheophytes. No conclusive experimental evidence exists on the responses of hornwort stomata to exogenous stimulation.

Hornwort stomata

Pressel and colleagues investigate stomatal behaviour in hornworts. They investigated responses of hornwort stomata to abscisic acid (ABA), desiccation, darkness and plasmolysis and compared these with those in tracheophyte leaves. Potassium ion concentrations in the guard cells and adjacent cells were analysed by X-ray microanalysis, and the ontogeny of the sporophytic intercellular spaces was compared with those of tracheophytes by cryo-scanning electron microscopy.

They show that there are no potassium fluxes associated with hornwort stomata, and that these do not respond to external factors (abscisic acid, desiccation, darkness and plasmolysis), which cause stomatal closure in other land plants. Their results run counter to the notion that active stomatal control was acquired early in the evolution of land plants, and support the alternative hypothesis of gradual acquisition of active control mechanisms.

Hornwort Stomata (Anthoceros)

Screen Shot 2018-02-07 at 21.21.43

 

Anatomy, Ultrastructure and Physiology of Hornwort Stomata

by Lucas J. R. (2000)

Jessica Regan Lucas,  Southern Illinois University Carbondale

========

in  Honors Theses. Paper 136 –

http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1142&context=uhp_theses

Screen Shot 2018-02-07 at 21.24.07

Conclusions;

The development of hornwort stomata is very simple. This is indicated by the single longitudinal division of the guard cell precursor, pectinous ledges, lack of subsidiary cells, and lack of radial micellation. Gas exchange seems to be a likely function of hornwort stomata, but the absence of vascular tissue makes water transport improbable. Histochemical stains for malate and potassium indicate that guard cells localize ions for a short time- after the differentiation of the epidermis and before spore dispersal.

Diurnal guard cell movements do not occur in hornworts. Neither dehydration or ABA treatment effects the guard cells in respect to movement. It is still unclear whether or not hornwort stomata are homologous to stomata of vascular plants. The prominent chloroplast, the localization of ions, and the role of stomata in gas exchange suggest that anthocerote stomata are related to those of other embryophytes.

However, the lack of vascular tissue and stomatal movement counter the homologous theory. Also in opposition to this paradigm is the distinct wall structure of hornwort guard cells. A multilayered wall and ledges of pectin have only been reported for a few other plants. In the future to elucidate the homology of these structures, the effect of ABA should further be studied. Also the guard cells’ ability to transport ions, which is essential for movement, should be determined.

Structure and function of hornwort stomata.

Photo credit: Google

The hornwort Phaeoceros

Structure and function of hornwort stomata.

by Lucas J. R., Renzaglia K. S. (2002)

Jessica R. Lucas, Karen S. Renzaglia, Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901

in Microscopy and Microanalysis 8, Supplement 2: 10901. – DOI 10.1017.S143192760210701X –

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/86FDD369AEC9E488CBBE7529D424D8A7/S143192760210701Xa.pdf/div-class-title-structure-and-function-of-hornwort-stomata-div.pdf

As minute structures that open and close in response to environmental cues, stomata are key adaptive innovations of land plants [1]. In vascular plants, stomata function in gas exchange in photosynthetic tissue and in facilitating nutrient transport through the transpirational stream. In bryophytes, the basal most land plants, stomata are restricted in occurrence and are poorly characterized in regards to structure-function relationships.

This study was undertaken to evaluate the microanatomy and physiology of stomata in hornworts, the oldest living lineage of plants that possess stomata. Protocols for SEM and TEM follow Renzaglia et al. [2]. To assess the osmotic regulation of stomatal functioning, we performed cytochemical localizations of potassium with Macullum’s reagent [3] and organic ions with Fast Violet B solution [4].

In hornworts, stomata occur scattered among elongated epidermal cells in the sporophyte. Mature stomata each consist of two bean-shaped guard cells subtended by an air-filled cavity (Figs. 1-3). In cross section, guard cells are larger than epidermal cells and they each contain a large starchfilled chloroplast (Figs. 1, 2).

Aside from prominent ledges on the outer and inner walls where the cells meet, the guard cell wall is thin throughout (Fig. 1). Extensive fibrous and flocculent material is associated with the outer ledge where the pore forms (Figs. 1, 3). The large chloroplasts in the underlying photosynthetic tissue are invariably positioned adjacent to air spaces, indicating a role of stomata in gas exchange (Fig. 4).

In contrast, the lack of an internal conducting system in hornworts suggests that stomata are not involved in nutrient transport or in regulating the transpirational flow as they are in plants with vascular tissue. Stomata examined in immature regions of the sporophyte are closed, while in mature regions, the stomata are typically opened.

Examination of sporophytes collected during dark and light periods indicates that there are no diurnal movements, i.e., guard cells in hornworts do not open and close in response to light. Further experiments with abscisic acid, a hormone that results in stomatal closure in vascular plants, resulted in no change in the pore (not illustrated).

In immature regions, both K+ and malate exhibit general localization in all epidermal cells (Figs. 5, 7). In mature tissue, these ions are localized in guard cells and are interpreted as functioning as osmoticum that is responsible for water influx and the creation and maintenance of stomatal pores (Figs. 6, 8).

These results coupled with the structural observations above support the concept that hornwort stomata open once through osmotic changes and remain open during the duration of physiological activity of the sporophyte. It appears that unlike vascular plants, the primary role of stomata in hornworts is in providing a passageway for gas exchange.

Architecture and fate of stomata in hornworts

Photo credit: Renzaglia et al. (2017)

Figure7. Presenceandlossofcollapsedstomatainhornworts(greentags).Stomataareplesiomorphicinhornworts,withstomata lost in two clades, Notothylas and the crown group Megaceros/Nothoceros/Dendroceros. The earliest fossil stomata from the Silurian (yellow tag) exhibit the collapsed condition. Among other bryophytes (orange tags), liverworts lack stomata and mosses exhibit all three conditions; Sphagnum has collapsed stomata, and other mosses either possess or have lost stomata. All tracheophytes (blue tags) have green, living stomata. Without a resolution of bryophyte relationships, represented here as a polytomy, it is im- possible to determine if stomata are plesiomorphic in embryophytes.

Hornwort Stomata: Architecture and Fate Shared with 400-Million-Year-Old Fossil Plants without Leaves

by Renzaglia K. S., Villarreal J. C., Piatkowski B. T., Lucas J. R., Merced A. (2017)

Karen S. Renzaglia, Juan Carlos Villarreal, Bryan T. Piatkowski, Jessica R. Lucas, and Amelia Merced

Department of Plant Biology, Southern Illinois University, Carbondale, Illinois 62901-6509 (K.S.R., J.R.L.);

Département de Biologie, Université Laval, Quebec, Quebec, Canada G1V 0A6 (J.C.V.);

Smithsonian Tropical Research Institute, Ancon, 0843-03092 Panama, Republic of Panama (J.C.V.);

Department of Biology, Duke University, Durham, North Carolina 27708 (B.T.P.);

Institute of Neurobiology, University of Puerto Rico, San Juan, Puerto Rico 00901 (A.M.)

 

 

in Plant Physiology, June 2017, Vol. 174, pp. 788–797

Screen Shot 2017-06-07 at 21.07.21

Abstract

As one of the earliest plant groups to evolve stomata, hornworts are key to understanding the origin and function of stomata.

Hornwort stomata are large and scattered on sporangia that grow from their bases and release spores at their tips. We present data from development and immunocytochemistry that identify a role for hornwort stomata that is correlated with sporangial and spore maturation.

We measured guard cells across the genera with stomata to assess developmental changes in size and to analyze any correlation with genome size. Stomata form at the base of the sporophyte in the green region, where they develop differential wall thickenings, form a pore, and die.

Screen Shot 2017-06-07 at 21.09.21

Guard cells collapse inwardly, increase in surface area, and remain perched over a substomatal cavity and network of intercellular spaces that is initially fluid filled. Following pore formation, the sporophyte dries from the outside inwardly and continues to do so after guard cells die and collapse.

Spore tetrads develop in spore mother cell walls within a mucilaginous matrix, both of which progressively dry before sporophyte dehiscence.

A lack of correlation between guard cell size and DNA content, lack of arabinans in cell walls, and perpetually open pores are consistent with the inactivity of hornwort stomata.

Stomata are expendable in hornworts, as they have been lost twice in derived taxa. Guard cells and epidermal cells of hornworts show striking similarities with the earliest plant fossils.

Our findings identify an architecture and fate of stomata in hornworts that is ancient and common to plants without sporophytic leaves.

An architecture and fate of stomata in hornworts that is ancient and common to plants without sporophytic leaves.

 

Hornwort stomata: Architecture and fate shared with 400 million year old fossil plants without leaves

by Renzaglia K. S., Villareal J. C., Piatkowski B. T., Lucas J. R., Merced A. (2017)

Karen_Renzaglia
Karen S Renzaglia, Southern Illinois University C… , Carbondale, USA
Juan_Villarreal2
Juan Carlos Villarreal, Laval University , Québec, Canada

Bryan Thomas Piatkowski

Jessica Regan Lucas

 

in Plant physiology · April 2017 – DOI: 10.1104/pp.17.00156 – 

https://www.researchgate.net/publication/316247209_Hornwort_stomata_Architecture_and_fate_shared_with_400_million_year_old_fossil_plants_without_leaves

Abstract
As one of the earliest plant groups to evolve stomata, hornworts are key to understanding stomata origin and function.
Hornwort stomata are large and scattered on sporangia that grow from their bases and release spores at their tips.
We present data from development and immunocytochemistry that identify a role for hornwort stomata that is correlated with sporangial and spore maturation. We measured guard cells across the genera with stomata to assess developmental changes in size and to analyze any correlation with genome size.
Stomata form at the base of the sporophyte in the green region, where they develop differential wall thickenings, form a pore and die. Guard cells collapse inwardly, increase in surface area and remain perched over a substomatal cavity and network of intercellular spaces that is initially fluid filled. Following pore formation, the sporophyte dries from the outside inwardly and continues to do so after guard cells die and collapse.
Spore tetrads develop in spore mother cell walls within a mucilaginous matrix, both of which progressively dry before sporophyte dehiscence. A lack of correlation between guard cell size and DNA content, lack of arabinans in cell walls, and perpetually open pores are consistent with inactivity of hornwort stomata.
Stomata are expendable in hornworts as they have been lost twice in derived taxa. Guard cells and epidermal cells of hornworts show striking similarities with the earliest plant fossils.
Our findings identify an architecture and fate of stomata in hornworts that is ancient and common to plants without sporophytic leaves. 

Drought and stomatal resistance

 

Changes in Photosynthesis, Stomatal Resistance and Abscisic Acid of Vitis labruscana Through Drought and Irrigation Cycles

by Liu W. T., Pool R., Wenkert W., Kriedemann P. E. (1978)

in Am. J. Enol. Viticult. 29, 239–246 (1978). –

http://www.ajevonline.org/content/29/4/239

http://eurekamag.com/research/004/910/004910418.php

Abstract

Concord grapevines (Vitis labruscana) grown in pots under natural climate fluctuations were followed through drought and irrigation cycles to study the changes in abscisic and phaseic acid and the effect on stomatal and photosynthetic activity.

When leaf water potential reached -16 bars, stomatal closure was essentially complete (15 to 25 sec•cm-1), and photosynthesis was minimal (1 to 5 mg CO2 dm-2 hr-l).

Small pot grapevines had a prehistory of mild, repetitive, water stresses which, relative to the large pots, was associated with lower photosynthesis rate at light saturation (26 compared to 32 mg CO2 dm-2 hr-1), and higher abscisic acid (0.33 compared to 0.14 mg kg-1 fresh weight) and hydrolyzable abscisic acid (0.14 compared to 0.04 mg kg-1 fresh weight).

A prolonged (more than two weeks) and/or severe stress (leaf water potential less than -16 bars) led to large increase of ABA content (2.5 mg kg-1) and incomplete recovery of photosynthetic potential despite reopening of stomata on restoring plant water status for rewatering.

The plant water status of grape leaves affects stomatal opening and thus photosynthesis. With increasing water stress other biochemical processes become affected such as an increase in abscisic acid.