Planta
Planta 134, 1 2 7 - 1 3 2 (1977)
9 by Springer-Verlag 1977
Influence of Certain Environmental Factors on Photosynthesis and Photorespiration in Simmondsia chinensis G. J. Collatz* Department of Environmental Biology, Research School of Biological Sciences, Australian National University, Canberra City, A.C.T. 5601, Australia
Abstract. The response of net photosynthesis and apparent light respiration to changes in [O2] , light intensity, and drought stress was determined by analysis of net photosynthetic CO 2 response curves. Low [O2] treatment resulted in a large reduction in the rate of photorespiratory CO 2 evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO23. These results indicate that [CO2] , [O2] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO 2 uptake decreased in low [O23 and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO 2 compensation point or the [CO2] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.
Key words: Gas exchange - Oxygen inhibition Photorespiration - Photosynthesis - S i m m o n d s i a Water stress.
Introduction
In many environments, plant productivity is determined at least in part by the rate of net photosynthesis * Present address: Department of Biological Sciences, Stanford University and Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA Abbreviations: C~ intracellular CO 2 concentration; F~ros~ gross photosynthesis; F,, t net photosynthesis; I light intensity; R L light respiration rate; rc carboxylation resistance; rg leaf gas-phase resistance; r~ intracellular resistance; to CO 2 uptake: r~ resistance to CO 2 flux between the intercellular spaces and the carboxylation sites; TL leaf temperature; ~v leaf water potential, F CO2 compensation point.
(Fnet) and is, therefore, subject to environmental constraints placed on Fnet. The efficiency with which CO 2 is fixed and the rate of CO 2 produced by respiration in the light (RL), determine Fnet. The efficiency of CO 2 uptake is here defined as the inverse of the total resistance to CO z flux which is composed of gas-phase, liquid-phase, and metabolic resistances in series (Jarvis, 1971). Carbon-dioxide evolution in the light has been estimated to be 25-75 % ofFnet (Zelitch, 1975), and thus Fnet should show sensitivity to changes in R L. In attempting to understand how the physical environment controls F.et it is necessary to take into account the response of both the resistance to CO 2 and RL. By analyzing the response of F.e, to CO 2 under differing experimental conditions, gas exchange parameters such as the CO 2 compensation point (F), RL, and CO 2 transfer resistances can be examined separately in terms of their response to changes in the physical environment. The relative importance of each of these parameters in determining Fnet can then be studied. This approach was taken using an evergreen xerophyte S i m m o n d s i a c h i n e n s i s (Link) Schneid. (family, Buxaceae), native to the Sonoran desert of North America and capable of withstanding extreme high leaf temperature and severe water stress (A1-Ani et al., 1972). The photosynthetic response of a plant adapted to a stressful environment should provide information concerning the genetic flexibility of the photosynthetic apparatus when compared with the well-documented response of C-3 agricultural mesophytes (Laing et al., 1974; Troughton and Slatyer, 1969). Comparisons of gas exchange in the leaves of S. c h i n e n s i s and other C-3 plants with in-vitro data on the activity of ribulose-l,5-diphosphate (RuDP) carboxylase are analyzed, and environmental control of photosynthesis and photorespiration at the subcellular level is discussed.
128
G.J. Collatz: Environment, Photosynthesis and Photorespiration in Simmondsia
Material and Methods Seedlings of Simmondsia chinensis, 8 months old, were obtained from the C.S.I.R.O. phytotron in Canberra and were transplanted in 25-cm (diameter) pots filled with soil. The plants were exposed for 3 months to a warm, dry summer in Canberra, and they received intermittent watering. The largest and healthiest seedling was then selected for gas-exchange analyses. The upper 8 leaves of a shoot which had developed over the summer were enclosed in an assimilation chamber similar to that described by Jarvis and Slatyer (1966). Net photosynthesis was measured as described by Slatyer (1970). Leaf area was measured with a leaf-area meter (Lambda Instr., Lincoln, Neb., USA) and did not change during the course of the experiments. Intracellular CO 2 concentrations (C~) and leaf gas-phase resistances (%) were calculated from transpiration measurements (see Slatyer, 1970). Intracellular resistance to CO z uptake (ri) was determined by the following relationship: AC w Afn~t where A C,jAF,,,t is the inverse of the initial slope derived from a
plot of Fn~t versus C~. The response of F.et to Cw was determined at ambient (21 ~o) and low (
Planta 134, 1 2 7 - 1 3 2 (1977)
9 by Springer-Verlag 1977
Influence of Certain Environmental Factors on Photosynthesis and Photorespiration in Simmondsia chinensis G. J. Collatz* Department of Environmental Biology, Research School of Biological Sciences, Australian National University, Canberra City, A.C.T. 5601, Australia
Abstract. The response of net photosynthesis and apparent light respiration to changes in [O2] , light intensity, and drought stress was determined by analysis of net photosynthetic CO 2 response curves. Low [O2] treatment resulted in a large reduction in the rate of photorespiratory CO 2 evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO23. These results indicate that [CO2] , [O2] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO 2 uptake decreased in low [O23 and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO 2 compensation point or the [CO2] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.
Key words: Gas exchange - Oxygen inhibition Photorespiration - Photosynthesis - S i m m o n d s i a Water stress.
Introduction
In many environments, plant productivity is determined at least in part by the rate of net photosynthesis * Present address: Department of Biological Sciences, Stanford University and Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA Abbreviations: C~ intracellular CO 2 concentration; F~ros~ gross photosynthesis; F,, t net photosynthesis; I light intensity; R L light respiration rate; rc carboxylation resistance; rg leaf gas-phase resistance; r~ intracellular resistance; to CO 2 uptake: r~ resistance to CO 2 flux between the intercellular spaces and the carboxylation sites; TL leaf temperature; ~v leaf water potential, F CO2 compensation point.
(Fnet) and is, therefore, subject to environmental constraints placed on Fnet. The efficiency with which CO 2 is fixed and the rate of CO 2 produced by respiration in the light (RL), determine Fnet. The efficiency of CO 2 uptake is here defined as the inverse of the total resistance to CO z flux which is composed of gas-phase, liquid-phase, and metabolic resistances in series (Jarvis, 1971). Carbon-dioxide evolution in the light has been estimated to be 25-75 % ofFnet (Zelitch, 1975), and thus Fnet should show sensitivity to changes in R L. In attempting to understand how the physical environment controls F.et it is necessary to take into account the response of both the resistance to CO 2 and RL. By analyzing the response of F.e, to CO 2 under differing experimental conditions, gas exchange parameters such as the CO 2 compensation point (F), RL, and CO 2 transfer resistances can be examined separately in terms of their response to changes in the physical environment. The relative importance of each of these parameters in determining Fnet can then be studied. This approach was taken using an evergreen xerophyte S i m m o n d s i a c h i n e n s i s (Link) Schneid. (family, Buxaceae), native to the Sonoran desert of North America and capable of withstanding extreme high leaf temperature and severe water stress (A1-Ani et al., 1972). The photosynthetic response of a plant adapted to a stressful environment should provide information concerning the genetic flexibility of the photosynthetic apparatus when compared with the well-documented response of C-3 agricultural mesophytes (Laing et al., 1974; Troughton and Slatyer, 1969). Comparisons of gas exchange in the leaves of S. c h i n e n s i s and other C-3 plants with in-vitro data on the activity of ribulose-l,5-diphosphate (RuDP) carboxylase are analyzed, and environmental control of photosynthesis and photorespiration at the subcellular level is discussed.
128
G.J. Collatz: Environment, Photosynthesis and Photorespiration in Simmondsia
Material and Methods Seedlings of Simmondsia chinensis, 8 months old, were obtained from the C.S.I.R.O. phytotron in Canberra and were transplanted in 25-cm (diameter) pots filled with soil. The plants were exposed for 3 months to a warm, dry summer in Canberra, and they received intermittent watering. The largest and healthiest seedling was then selected for gas-exchange analyses. The upper 8 leaves of a shoot which had developed over the summer were enclosed in an assimilation chamber similar to that described by Jarvis and Slatyer (1966). Net photosynthesis was measured as described by Slatyer (1970). Leaf area was measured with a leaf-area meter (Lambda Instr., Lincoln, Neb., USA) and did not change during the course of the experiments. Intracellular CO 2 concentrations (C~) and leaf gas-phase resistances (%) were calculated from transpiration measurements (see Slatyer, 1970). Intracellular resistance to CO z uptake (ri) was determined by the following relationship: AC w Afn~t where A C,jAF,,,t is the inverse of the initial slope derived from a
plot of Fn~t versus C~. The response of F.et to Cw was determined at ambient (21 ~o) and low (
