Chapter 14
Photosynthesis and Metabolism in Seagrasses
at the Cellular Level
Anthony W. D. Larkum
∗
School of Biological Sciences, University of Sydney, NSW 2006, Australia.
Email: alark@mail.usyd.edu.au
Edward A. Drew
21 Bishop St., Belgian Gardens, Townsville, Qld 4071, Australia.
Email: edrew1@austarnet.com.au
Peter J. Ralph
Institute of Water and Environmental Resource Management and Department of
Environmental Sciences, University of Technology, Sydney, Westbourne Street,
Gore Hill, NSW 2065, Australia. Email: peter.ralph@uts.edu.au
I. Introduction
Seagrasses are marine angiosperms from the
Families Potamagetonaceae and Hydrocharitaceae
(Chapter 1). These are by origin land plants that
developed both aerial photosynthesis and aerial
flowering and then returned to a successful fully
submerged marine habitat, from where their algal
forbears derived. Following the evolution of land
plants there have been few developments in terms of
photosynthesis: the only outstanding developments
being adaptations to arid conditions, such as the
development of C 4 photosynthesis in semi-arid
plants and Crassulacean Acid Metabolism (CAM)
in plants from desert regions (Bowes et al. 2002).
These adaptations affect morphological changes
(Kranz anatomy) in C 4 plants, as well as adaptation
of the initial carboxylation pathways (C 4 and
CAM plants) – with, in the case of CAM plants, a
Corresponding Author: email: alark@mail.usyd.edu.au
Contribution number 202 of the Institute for Water and Environmental Resource Management, UTS.
temporal shift in daily uptake of CO 2 (Keeley, 1982).
In both cases the Benson-Calvin Cycle is retained
together with a conventional set of photoreactions
(photosystem I, photosystem II and Chlorophyll
a/b light-harvesting complexes), as the primary
mechanism of photosynthesis.
While seagrasses are unique in having returned to
the sea, there are many plants that have evolved into
freshwater hydrophytes (Sculthorpe, 1967; Bowes
et al., 2002). Since they both live in an aqueous environment, there are close parallels in many respects
between seagrasses and freshwater hydrophytes,
such as the presence of a diffusive boundary layer
around the leaves, a photosynthetic epidermis, loss
of stomata and development of aerenchyma. Hydrophytes are found in both Potamagetonaceae and
Vallisneriaceae and therefore there are also close
phylogenetic relationships to consider. Much work
has been carried out on freshwater hydrophytes
(see e.g. Bowes et al. 2002; Maberly and Madsen, 2002) and this review will take this work into
account.
A recent review of photosynthesis in seagrasses
is that of Touchette & Burkholder (2000).
323–345.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
c
2006 Springer. Printed in the Netherlands.
Photosynthesis and Metabolism in Seagrasses
at the Cellular Level
Anthony W. D. Larkum
∗
School of Biological Sciences, University of Sydney, NSW 2006, Australia.
Email: alark@mail.usyd.edu.au
Edward A. Drew
21 Bishop St., Belgian Gardens, Townsville, Qld 4071, Australia.
Email: edrew1@austarnet.com.au
Peter J. Ralph
Institute of Water and Environmental Resource Management and Department of
Environmental Sciences, University of Technology, Sydney, Westbourne Street,
Gore Hill, NSW 2065, Australia. Email: peter.ralph@uts.edu.au
I. Introduction
Seagrasses are marine angiosperms from the
Families Potamagetonaceae and Hydrocharitaceae
(Chapter 1). These are by origin land plants that
developed both aerial photosynthesis and aerial
flowering and then returned to a successful fully
submerged marine habitat, from where their algal
forbears derived. Following the evolution of land
plants there have been few developments in terms of
photosynthesis: the only outstanding developments
being adaptations to arid conditions, such as the
development of C 4 photosynthesis in semi-arid
plants and Crassulacean Acid Metabolism (CAM)
in plants from desert regions (Bowes et al. 2002).
These adaptations affect morphological changes
(Kranz anatomy) in C 4 plants, as well as adaptation
of the initial carboxylation pathways (C 4 and
CAM plants) – with, in the case of CAM plants, a
Corresponding Author: email: alark@mail.usyd.edu.au
Contribution number 202 of the Institute for Water and Environmental Resource Management, UTS.
temporal shift in daily uptake of CO 2 (Keeley, 1982).
In both cases the Benson-Calvin Cycle is retained
together with a conventional set of photoreactions
(photosystem I, photosystem II and Chlorophyll
a/b light-harvesting complexes), as the primary
mechanism of photosynthesis.
While seagrasses are unique in having returned to
the sea, there are many plants that have evolved into
freshwater hydrophytes (Sculthorpe, 1967; Bowes
et al., 2002). Since they both live in an aqueous environment, there are close parallels in many respects
between seagrasses and freshwater hydrophytes,
such as the presence of a diffusive boundary layer
around the leaves, a photosynthetic epidermis, loss
of stomata and development of aerenchyma. Hydrophytes are found in both Potamagetonaceae and
Vallisneriaceae and therefore there are also close
phylogenetic relationships to consider. Much work
has been carried out on freshwater hydrophytes
(see e.g. Bowes et al. 2002; Maberly and Madsen, 2002) and this review will take this work into
account.
A recent review of photosynthesis in seagrasses
is that of Touchette & Burkholder (2000).
323–345.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
c
2006 Springer. Printed in the Netherlands.