Crassulacean acid metabolism enhances underwater photosynthesis and diminishes photorespiration in the aquatic plant Isoetes australis.
• Underwater photosynthesis by aquatic plants is often limited by low availability of CO(2), and photorespiration can be high. Some aquatic plants utilize crassulacean acid metabolism (CAM) photosynthesis. The benefits of CAM for increased underwater photosynthesis and suppression of photorespiration were evaluated for Isoetes australis, a submerged plant that inhabits shallow temporary rock pools. • Leaves high or low in malate were evaluated for underwater net photosynthesis and apparent photorespiration at a range of CO(2) and O(2) concentrations. • CAM activity was indicated by 9.7-fold higher leaf malate at dawn, compared with at dusk, and also by changes in the titratable acidity (μmol H(+) equivalents) of leaves. Leaves high in malate showed not only higher underwater net photosynthesis at low external CO(2) concentrations but also lower apparent photorespiration. Suppression by CAM of apparent photorespiration was evident at a range of O(2) concentrations, including values below air equilibrium. At a high O(2) concentration of 2.2-fold the atmospheric equilibrium concentration, net photosynthesis was reduced substantially and, although it remained positive in leaves containing high malate concentrations, it became negative in those low in malate. • CAM in aquatic plants enables higher rates of underwater net photosynthesis over large O(2) and CO(2) concentration ranges in floodwaters, via increased CO(2) fixation and suppression of photorespiration.
School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia. opedersen@bio.ku.dk
Ole
O
Pedersen
Sarah Meghan
SM
Rich
Cristina
C
Pulido
Gregory Robert
GR
Cawthray
Timothy David
TD
Colmer
D000388:Air; D059001:Aquatic Organisms / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects*; D001315:Australia; D044002:Bryophyta / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D002245:Carbon Dioxide / Q000494:pharmacology; D019069:Cell Respiration / Q000187:drug effects / Q000528:radiation effects; D019015:Geologic Sediments; D008027:Light; D008293:Malates / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D013997:Time Factors; D017186:Titrimetry; D014867:Water
D008293:Malates; D014867:Water; D002245:Carbon Dioxide; C030298:malic acid; D010100:Oxygen