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. – (No abstract found – Who can send us one ?)

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/)

Stomata of hornworts (Anthocerotophyta)

Photo credit: Google

Hornwort: Anthoceros punctatus

Stomatal differentiation and abnormal stomata in hornworts

by Pressel S., Goral T., Duckett J. G. (2014)

Silvia Pressel, Tomasz Goral

Jeffrey G. Duckett item21720

in Maney Online: Journal of Bryology, Volume 36, Issue 2 (June 2014), pp. 87-103

http://www.tandfonline.com/doi/pdf/10.1179/1743282014Y.0000000103

This light and electron microscope study reveals considerable uniformity in hornwort stomata morphology and density in contrast to common spatial and developmental abnormalities in tracheophytes and mosses.

Stomata arise from a median longitudinal division of sporophyte epidermal cells morphologically indistinguishable from their neighbours apart from the retention of a single chloroplast whilst those in the other epidermal cells fragment. Chloroplast division and side-by-side repositioning of the two daughter chloroplasts determines the division plane in the stomatal mother cell. The nascent guard cells contain giant, starch-filled chloroplasts which subsequently divide and, post aperture opening, regain their spherical shape. Accumulation of wall material over the guard cells and of wax rodlets lining the pores follows opening.

http://www.redorbit.com/media/gallery/national-science-foundation-gallery/medium/183_3a7118b1fc33363e96bafb88b27576fe.jpg
http://www.redorbit.com/media/gallery/national-science-foundation-gallery/medium/183_3a7118b1fc33363e96bafb88b27576fe.jpg

While the majority of stomata are bilaterally symmetrical those lining the dehiscence furrows display dextral and sinistral asymmetry due to differential expansion of the adjacent epidermal cells.

The ubiquity of open stomata suggests that these never close with the maturational wall changes rendering movement extremely unlikely. These structural limitations, a liquid-filled stage in the ontogeny of the intercellular spaces, and spores already at the tetrad stage when stomata open, suggest that their primary role is facilitating sporophyte desiccation leading to dehiscence and spore dispersal rather than gaseous exchange.

Stomata ontogeny and very low densities, like those in Devonian fossils, suggest either ancient origins at a time when atmospheric carbon dioxide levels were much greater than today or a function other than gaseous exchange regulation. We found no evidence for stomatal homology between hornworts, mosses and tracheophytes.

See also: Maney Online