Main description:

The acid metabolism of certain succulent plants, now known as Crassulacean Acid Metabolism (CAM) has fascinated plant physiologists and biochemists for the last one and a half centuries. However, since the basic discoveries of De Saussure in 1804 that stem joints of Opuntia were able to remove CO from the 2 atmosphere during the night, and of Heyne in 1815 (see Wolf, 1960) that organic acids accumulate in the leaves of Bryophyllum calycinum during the night, the two main aspects of CAM, diurnal CO gas exchange and metabolism of malic acid, 2 have first been studied nearly independently. Hence, it is not surprising that most research to elucidate the mechanism of CAM has been during the last 15 years since CO exchange and malate metabolism were studied and interpreted in its 2 context. These efforts finally resulted in a clear realization that the CAM phenom enon is a variation on the mode of how plants can photosynthetically harvest CO from the atmosphere. 2 The interpretation of CAM in this sense was stimulated by the discovery of another variant of photosynthesis, the C -pathway (see Black, 1973; Hatch and 4 Slack, 1970; Hatch, 1976). Because this newly discovered photosynthetic pathway is recognized to be very closely related to the CAM pathway, the work on the latter became intensified during these last years.

Contents:

Terminology.- 1. Taxonomy and Geographical Distribution of CAM Plants.- 1.1 Cactaceae.- 1.2 Crassulaceae.- 1.3 Euphorbiaceae.- 1.4 Aizoaceae (Mesembryanthemaceae).- 1.5 Bromeliaceae.- 1.6 Asclepiadaceae.- 1.7 Orchidaceae.- 1.8 Liliaceae.- 1.9 Agavaceae.- 1.10 Asteraceae.- 1.11 Vitaceae.- 1.12 Geraniaceae.- 1.13 Other Families.- 1.14 Conclusions.- 2. Morphology, Anatomy, and Ultrastructure of CAM Plants.- 2.1 What is a Succulent?.- 2.2 Quantitative Indices of Succulence.- 2.3 Succulence and the Occurrence of CAM.- 2.3.1 Succulent CAM Plants.- 2.3.2 Nonsucculent CAM Plants.- 2.3.3 Mesophyll Succulence (Sm) as a New Index of CAM Capacity?.- 2.4 The Presence of the Photosynthetic Apparatus as a Prior Condition for the Occurrence of CAM.- 2.5 The Architecture and Ultrastructure of CAM-Performing Cells.- 2.5.1 Light Microscope Observations.- 2.5.2 Electron Microscope Observations.- 3. The Metabolic Pathway of CAM.- 3.1 The Processes of the Dark Period.- 3.1.1 Early History.- 3.1.2 Dark CO2 Fixation and Its First Product.- 3.1.3 Secondary Products and Organic Acids Other Than Malic...- 3.1.4 The Active Chemical Species of "CO2".- 3.1.5 Generation of P-Enolpyruvate, the CO2 Acceptor in Dark CO2 Fixation.- 3.1.6 Depletion of Malate in the Dark.- 3.1.7 The Storage of Malic Acid.- 3.2 The Processes of the Light Period.- 3.2.1 Deacidiflcation and Malate Decarboxylation.- 3.2.2 The Fate of the Decarboxylation Products.- 3.2.2.1 Three-Carbon Fragments.- 3.2.2.2 Carbon Dioxide.- 3.2.3 Assimilation of Exogenous CO2 in the Light.- 3.2.4 Photorespiration in CAM Plants.- 3.3 Carbon Isotope Composition.- 3.4 The Proposed Total Carbon Flow in CAM.- 3.5 Comparison of CAM with Other Carboxylation Pathways in Plants.- 3.5.1 The Nonautotrophic C4 Pathway of CO2 Fixation.- 3.5.2 C3-Photosynthesis.- 3.5.3 C4-Photosynthesis.- 3.5.4 Conclusions.- 3.6 Translocation of CAM Products in the Plant.- 4. Control and Modification of CAM.- 4.1 Definitions.- 4.2 Metabolic Control of CAM.- 4.2.1 The CAM Enzymes.- 4.2.1.1 P-Enolpyruvate Carboxylase [Orthophosphate: Oxalacetate Carboxylase (Phosphorylating)].- 4.2.1.2 Malate Dehydrogenase (L-malate: NAD Oxidoreductase).- 4.2.1.3 Aspartate Aminotransferase (L-aspartate: ?-Oxoglutarate Aminotransferase).- 4.2.1.4 "Malate Enzyme" [L-malate: NADP Oxidoreductase (Decarboxylating)].- 4.2.1.5 P-enolpyruvate Carboxykinase [ATP: Oxalacetate Carboxylase (Transphosphorylating)].- 4.2.1.6 Pyruvate, Phosphate Dikinase.- 4.2.1.7 Alanine Aminotransferase (L-Alanine: ?-Oxoglutarate Aminotransferase).- 4.2.1.8 Riboluse-1.5-Bisphosphate Carboxylase/Oxygenase [3-phospho-D-glycerate Carboxylase (Dimerizing)].- 4.2.1.9 Phosphofructokinase (ATP-D-fructose-6-phosphate-1-phosphotransferase).- 4.2.1.10 Phosphorlyase (?-1.4-Glucan: Orthophosphate Glucosyltransferase).- 4.2.2 The Compartmentation of CAM Enzymes and Metabolites.- 4.2.2.1 Enzymes.- 4.2.2.2 Metabolites.- 4.2.2.3 Conclusions.- 4.2.3 Models of Metabolic CAM Control.- 4.2.3.1 Control of CAM During the Dark Period.- 4.2.3.2 Control of CAM During the Dark/Light Transient and During the Light Period.- 4.3 Modification of the Diurnal Malic Acid Cycle by External Factors.- 4.3.1 Effects of Temperature.- 4.3.2 Effects of Light.- 4.3.3 Effects of Ions.- 4.3.4 Effects of Water Relations and the Question of "Facultative" CAM Plants.- 4.3.4.1 Effects of Drought on CAM in "Obligate" CAM Plants.- 4.3.4.2 Induction of CAM in "Facultative" CAM Plants.- 4.3.5 Effects of Oxygen and Carbon Dioxide.- 4.3.5.1 Oxygen.- 4.3.5.2 Carbon Dioxide.- 4.4 Seasonal Control of CAM.- 4.4.1 Photoperiod.- 4.4.2 Thermoperiod.- 4.4.3 Hydroperiod.- 4.5 Developmental Control of CAM.- 4.6 Conclusions.- 5. Gas Exchange of CAM Plants.- 5.1 CO2 Exchange.- 5.1.1 History.- 5.1.2 General Phenomena of CO2 Exchange.- 5.1.3 Patterns of CO2 Exchange in the Dark.- 5.1.3.1 General Characteristics.- 5.1.3.2 Factors Affecting CO2 Exchange During the Dark Period.- 5.1.4 CO2 Exchange During the Light Period.- 5.1.4.1 General Characteristics.- 5.1.4.2 Factors Affecting CO2 Exchange During the Light Period.- 5.1.4.3 The Initial Burst of CO2 Uptake.- 5.1.4.4 Compensation Point, Effects of CO2 and O2 Concentration on CO2 Fixation in the Light.- 5.1.5 CO2 Exchange in Continuous Darkness or Continuous Light.- 5.1.5.1 Introduction.- 5.1.5.2 CO2 Exchange in Continuous Darkness.- 5.1.5.3 CO2 Exchange Under Continuous Illumination.- 5.1.5.4 Conclusions.- 5.2 Oxygen Exchange.- 5.2.1 History.- 5.2.2 Manometric Analysis.- 5.2.3 Polarographic Analysis.- 5.2.4 Paramagnetic Analysis.- 5.3 Water Vapor Exchange and Stomata of CAM Plants.- 5.3.1 Introduction.- 5.3.2 The Diurnal Cycle of Stomata Movements.- 5.3.2.1 Phenomenology.- 5.3.2.2 Coupling Between CAM and Movements of Stomata.- 5.3.2.3 Mechanism of Stomatal Opening.- 5.3.3 Gas Diffusion Resistances in CAM Plants.- 5.3.3.1 Gas Exchange Parameters.- 5.3.3.2 Boundary Layer Resistance (ra).- 5.3.3.3 Stomatal Resistance (rs).- 5.3.3.4 Cuticular Resistance (rc).- 5.3.4 Response of Stomatal Movements to the Age of the Plant and Environmental Factors.- 5.3.4.1 Age.- 5.3.4.2 Water Relations.- 5.3.4.3 Temperature.- 5.3.4.4 Light.- 5.3.5 Morphology of Stomata in CAM Plants.- 5.3.5.1 Number and Distribution of Stomata.- 5.3.5.2 Size and Shape of the Stomata.- 5.3.6 Thermal Consequences of Stomatal Behavior in CAM Plants.- 6. Ecology, Productivity, and Economic Use of CAM Plants.- 6.1 The Hypothesis: Ecological Advantage of CAM.- 6.2 Verification of the Hypothesis.- 6.2.1 CAM and Water Use.- 6.2.2 Observation of CAM in Situ.- 6.2.2.1 Gas Exchange and Acid Fluctuation.- 6.2.2.2 Estimations of ?13C Values in Samples Collected in the Field.- 6.2.2.3 Ecological Relevance of Optional CAM.- 6.2.3 Conclusions.- 6.3 Productivity.- 6.4 Economic Exploitation.- References.- Taxonomic Index.