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.

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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.

Stomata in hornworts and mosses

Photo credit: Google

Polytrichum juniperinum (Juniper Hair Cap)

Stomatal density and aperture in non-vascular land plants are non-responsive to above-ambient atmospheric CO2 concentrations

by Field K. J.Duckett J. G.Cameron D. D., Pressel S. (2015)

in Ann Bot (2015) 115 (6): 915-922.

doi: 10.1093/aob/mcv021

Abstract

Background and Aims Following the consensus view for unitary origin and conserved function of stomata across over 400 million years of land plant evolution, stomatal abundance has been widely used to reconstruct palaeo-atmospheric environments. However, the responsiveness of stomata in mosses and hornworts, the most basal stomate lineages of extant land plants, has received relatively little attention. This study aimed to redress this imbalance and provide the first direct evidence of bryophyte stomatal responsiveness to atmospheric CO2.

http://upload.wikimedia.org/wikipedia/commons/9/95/Anthoceros_agrestis_060910c.jpg
http://upload.wikimedia.org/wikipedia/commons/9/95/Anthoceros_agrestis_060910c.jpg

Methods A selection of hornwort (Anthoceros punctatus, Phaeoceros laevis) and moss (Polytrichum juniperinum, Mnium hornum, Funaria hygrometrica) sporophytes with contrasting stomatal morphologies were grown under different atmospheric CO2 concentrations ([CO2]) representing both modern (440 p.p.m. CO2) and ancient (1500 p.p.m. CO2) atmospheres. Upon sporophyte maturation, stomata from each bryophyte species were imaged, measured and quantified.

Funaria hygrometrica - http://www.anbg.gov.au/abrs/Mosses_online/images/DT_Funaria_hygro_1.jpg
Funaria hygrometrica – http://www.anbg.gov.au/abrs/Mosses_online/images/DT_Funaria_hygro_1.jpg

Key Results Densities and dimensions were unaffected by changes in [CO2], other than a slight increase in stomatal density in Funaria and abnormalities in Polytrichum stomata under elevated [CO2].

Conclusions The changes to stomata in Funaria and Polytrichum are attributed to differential growth of the sporophytes rather than stomata-specific responses. The absence of responses to changes in [CO2] in bryophytes is in line with findings previously reported in other early lineages of vascular plants. These findings strengthen the hypothesis of an incremental acquisition of stomatal regulatory processes through land plant evolution and urge considerable caution in using stomatal densities as proxies for paleo-atmospheric CO2 concentrations.

See the text: Ann. Bot.

BIBLIOGRAPHY OF STOMATA: ANTHOCEROTOPHYTA

Field K. J.Duckett J. G.Cameron D. D., Pressel S. (2015) – Stomatal density and aperture in non-vascular land plants are non-responsive to above-ambient atmospheric CO2concentrations – Ann. Bot. (2015) 115 (6): 915-922. (http://aob.oxfordjournals.org/content/115/6/915.short?rss=1) – (On our blog : https://plantstomata.wordpress.com/2016/04/10/stomata-in-non-vascular-land-plants-and-co2/)

Lucas J. R., Renzaglia K. S. (2002) –  Structure and function of hornwort stomata. – 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 – (On our blog : https://plantstomata.wordpress.com/2017/11/25/structure-and-function-of-hornwort-stomata/)

Pressel S., Goral T., Duckett J. G. (2014) – Stomatal differentiation and abnormal stomata in hornworts -Maney Online: Volume 36, Issue 2 (June 2014), pp. 87-103 – http://dx.doi.org/10.1179/1743282014Y.0000000103 – (http://www.maneyonline.com/doi/abs/10.1179/1743282014Y.0000000103) – (On our blog : https://plantstomata.wordpress.com/2015/01/30/stomata-of-hornworts-anthocerotophyta/).

Pressel S., Renzaglia K. S., Duckett, J. G. (2011) Hornworts: a new look at stomatal evolution. – In: XVIII International Botanical Congress, Melbourne, abstract book, pp. 237. – (No abstract found – Who can send us one ?)

Renzaglia K. S., Villarreal J. C., Piatkowski B. T., Lucas J. R., Merced A. (2017) – Hornwort Stomata: Architecture and Fate Shared with 400-Million-Year-Old Fossil Plants without Leaves – Plant Physiology, June 2017, Vol. 174, pp. 788–797 – (On our blog : https://plantstomata.wordpress.com/2017/06/07/architecture-and-fate-of-stomata-in-hornworts/)