title: Submergence-induced morphological, anatomical, and biochemical responses in a terrestrial species affect gas diffusion resistance and photosynthetic performance.
abstract: Gas exchange between the plant and the environment is severely hampered when plants are submerged, leading to oxygen and energy deficits. A straightforward way to reduce these shortages of oxygen and carbohydrates would be continued photosynthesis under water, but this possibility has received only little attention. Here, we combine several techniques to investigate the consequences of anatomical and biochemical responses of the terrestrial species Rumex palustris to submergence for different aspects of photosynthesis under water. The orientation of the chloroplasts in submergence-acclimated leaves was toward the epidermis instead of the intercellular spaces, indicating that underwater CO(2) diffuses through the cuticle and epidermis. Interestingly, both the cuticle thickness and the epidermal cell wall thickness were significantly reduced upon submergence, suggesting a considerable decrease in diffusion resistance. This decrease in diffusion resistance greatly facilitated underwater photosynthesis, as indicated by higher underwater photosynthesis rates in submergence-acclimated leaves at all CO(2) concentrations investigated. The increased availability of internal CO(2) in these "aquatic" leaves reduced photorespiration, and furthermore reduced excitation pressure of the electron transport system and, thus, the risk of photodamage. Acclimation to submergence also altered photosynthesis biochemistry as reduced Rubisco contents were observed in aquatic leaves, indicating a lower carboxylation capacity. Electron transport capacity was also reduced in these leaves but not as strongly as the reduction in Rubisco, indicating a substantial increase of the ratio between electron transport and carboxylation capacity upon submergence. This novel finding suggests that this ratio may be less conservative than previously thought.
authors.affiliation: Department of Experimental Plant Ecology , Radboud University Nijmegen, The Netherlands. l.mommer@science.ru.nl
authors.forename: Liesje
authors.initials: L
authors.lastname: Mommer
authors.forename: Thijs L
authors.initials: TL
authors.lastname: Pons
authors.forename: Mieke
authors.initials: M
authors.lastname: Wolters-Arts
authors.forename: Jan Henk
authors.initials: JH
authors.lastname: Venema
authors.forename: Eric J W
authors.initials: EJ
authors.lastname: Visser
mesh_terms: D000064:Acclimatization; D002245:Carbon Dioxide / Q000378:metabolism*; D019069:Cell Respiration / Q000187:drug effects; D004058:Diffusion / Q000187:drug effects; D004777:Environment; D005740:Gases / Q000378:metabolism*; D008027:Light; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000187:drug effects / Q000378:metabolism*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D031804:Rumex / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D014867:Water / Q000494:pharmacology
chemical_list: D005740:Gases; D014867:Water; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase