Two Steps of Gas Exchange in Leaf Photosynthesis (original) (raw)
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Oxygen Exchange in Leaves in the Light
Plant Physiology, 1980
Photosynthetic 02 production and photorespiratory 02 uptake were measured using isotopic techniques, in the C3 species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO2 and normal 02,02 production increased linearly with light intensity. At low 02 or low C02, 02 production was suppressed, indicating that increased concentrations of both 02 and CO2 can stimulate 02 production. At the CO2 compensation point, 02 uptake equaled 02 production over a wide range of 02 concentrations. 02 uptake increased with light intensity and 02 concentration. At low light intensities, 02 uptake was suppressed by increased CO2 concentrations so that 02 uptake at 1,000 microliters per liter CO2 was 28 to 35% of the uptake at the CO2 compensation point. At high light intensities, 02 uptake was stimulated by low concentrations of CO2 and suppressed by higher concentrations of C02. 02 uptake at high light intensity and 1000 microliters per liter CO2 was 75% or more of the rate of 02 uptake at the compensation point. The response of 02 uptake to light intensity extrapolated to zero in darkness, suggesting that 02 uptake via dark respiration may be suppressed in the light. The response of 02 uptake to 02 concentration saturated at about 30% 02 in high light and at a lower 02 concentration in low light. 02 uptake was also observed with the C4 plant Amaranthus edulis, the rate of uptake at the CO2 compensation point was 20% of that observed at the same light intensity with the C3 species, and this rate was not influenced by the CO2 concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of 02. Both 02 evolution and 02 uptake take place in leaves of C3 and C4 plants in the light (4, 8, 17, 21, 23, 24, 27, 28). 02 evolution is derived entirely from the water-splitting reaction of PSII, but three principal 02 uptake processes are presently recognized. These are: the oxygenase reaction of ribulose bisP carboxylase-oxygenase and the associated metabolism of P-glycolate (2, 4, 5, 18, 20); the Mehler reaction (22), which results in the direct photoreduction of 02 and may support ATP synthesis via pseudocyclic photophosphorylation (9, 13, 16); and the possibility that 02 uptake associated with mitochondrial respiration continues in the light (18). Volk and Jackson and their colleagues (17, 23, 24, 27, 28) have made substantial contributions to the study of 02 exchange in intact leaves, but only a limited range of conditions were em-This paper is Carnegie Institute of Washington publication No. 686.
New Phytologist, 2005
• Gas exchange is generally regarded to occur between the leaf interior and ambient air, i.e. in vertical (anticlinal) directions of leaf blades. However, inside homobaric leaves, gas movement occurs also in lateral directions. The aim of the present study was to ascertain whether lateral CO 2 diffusion affects leaf photosynthesis when illuminated leaves are partially shaded. • Measurements using gas exchange and chlorophyll fluorescence imaging techniques were performed on homobaric leaves of Vicia faba and Nicotiana tabacum or on heterobaric leaves of Glycine max and Phaseolus vulgaris. • For homobaric leaves, gas exchange inside a clamp-on leaf chamber was affected by shading the leaf outside the chamber. The quantum yield of photosystem II (Φ PSII) was highest directly adjacent to a light/shade border (LSB). Φ PSII decreased in the illuminated leaf parts with distance from the LSB, while the opposite was observed for nonphotochemical quenching. These effects became most pronounced at low stomatal conductance. They were not observed in heterobaric leaves. • The results suggest that plants with homobaric leaves can benefit from lateral CO 2 flux, in particular when stomata are closed (e.g. under drought stress). This may enhance photosynthetic, instead of nonphotochemical, processes near LSBs in such leaves and reduce the photoinhibitory effects of excess light.
New Phytologist, 2006
Gas exchange is generally regarded to occur between the leaf interior and ambient air, i.e. in vertical (anticlinal) directions of leaf blades. However, inside homobaric leaves, gas movement occurs also in lateral directions. The aim of the present study was to ascertain whether lateral CO 2 diffusion affects leaf photosynthesis when illuminated leaves are partially shaded. • Measurements using gas exchange and chlorophyll fluorescence imaging techniques were performed on homobaric leaves of Vicia faba and Nicotiana tabacum or on heterobaric leaves of Glycine max and Phaseolus vulgaris . • For homobaric leaves, gas exchange inside a clamp-on leaf chamber was affected by shading the leaf outside the chamber. The quantum yield of photosystem II ( Φ PSII ) was highest directly adjacent to a light/shade border (LSB). Φ PSII decreased in the illuminated leaf parts with distance from the LSB, while the opposite was observed for nonphotochemical quenching. These effects became most pronounced at low stomatal conductance. They were not observed in heterobaric leaves.
Plant, Cell and Environment, 2002
Photosynthesis is a complex process whose rate is affected by many biochemical and biophysical factors. Fortunately, it is possible to determine, or at least estimate, many of the most important parameters using a combination of optical methods and gas transient analyses. We describe here a computer-operated routine that has been developed to make detailed assessments of photosynthesis at a comprehensive level. The routine comprised the following measurements: steady-state light and CO 2 response curves of net CO 2 assimilation at 21 and 2 kPa O 2 ; transients from limiting to different saturating CO 2 concentrations at 2 kPa O 2 ; post-illumination CO 2 fixation transient; dark-light induction of O 2 evolution; O 2 yield from one saturating single-turnover flash; chlorophyll fluorescence F 0 , F s and F m during the light and CO 2 response curves; leaf transmission at 820 nm (P700 + ) during the light and CO 2 response curves; post-illumination re-reduction time of P700 + . The routine was executed on a two-channel fast-response gas exchange measurement system (A. Laisk and V. Oja: Dynamic Gas Exchange of Leaf Photosynthesis. CSIRO, Canberra, Australia). Thirty-six intrinsic characteristics of the photosynthetic machinery were derived, including quantum yield of CO 2 fixation ( Y CO2 ), time constant of P700 re-reduction ( τ τ τ τ ′ ′ ′ ′ ), relative optical cross-sections of PSII and PSI antennae ( a II , a I ), PSII and PSI density per leaf area unit, plastoquinone pool, total mesophyll resistance, mesophyll diffusion resistance, V m , K m (CO 2 ) and CO 2 /O 2 specificity of Rubisco, RuBP pool at CO 2 limitation (assimilatory charge). An example of the routine and calculations are shown for one leaf and data are presented for leaves of 8-year-old-trees of two birch clones growing in Suonenjoki Forest Research Station, Finland, during summer 2000. Parameters Y CO2 , basic τ τ τ τ ′ ′ ′ ′ , a II , a I , K m (CO 2 ) and K s varied little in different leaves [relative standard deviation (RSD) < 7%], other parameters scattered widely (RSD typically 10-40%). It is concluded that the little scattered parameters are determined by basic physico-chemical properties of the photosynthetic machinery whereas the widely scattered parameters are adjusting to growth condi-
Photosynthesis in lightfleck areas of homobaric and heterobaric leaves
Journal of Experimental Botany, 2010
Leaves within a canopy are exposed to a spatially and temporally fluctuating light environment which may cause lateral gradients in leaf internal CO 2 concentration and diffusion between shaded and illuminated areas. In previous studies it was hypothesized that lateral CO 2 diffusion may support leaf photosynthesis, but the magnitude of this effect is still not well understood. In the present study homobaric leaves of Vicia faba or heterobaric leaves of Glycine max were illuminated with lightflecks of different sizes, mimicking sunflecks. Photosynthetic properties of the lightfleck areas were assessed with combined gas exchange measurements and chlorophyll fluorescence imaging. Lateral diffusion in homobaric leaves with an interconnected intercellular air space stimulated photosynthesis and the effect was largest in small lightfleck areas, in particular when plants were under drought stress. Such effects were not observed in the heterobaric leaves with strongly compartmented intercellular gas spaces. It is concluded that lateral diffusion may significantly contribute to photosynthesis of lightfleck areas of homobaric leaves depending on lightfleck size, lateral diffusivity, and stomatal conductance. Since homobaric leaf structures have been reported for many plant species, it is hypothesized that leaf homobary may have an impact on overall plant performance under conditions with a highly heterogeneous light environment.
Photosynthetic pigments, morphology and leaf gas exchange
The effect of relative humidity (RH) and temperature on CO 2 assimilation (An), stomatal conductance (Sc), transpiration rate (Tr), chlorophyll content, fresh and dry weight, leaf length, leaf area, leaf width, formation of new root and survival rate have been assayed in Doritaenopsis in growth chamber after 1 month of acclimatization. Reduced growth was observed at below and above 25 • C whereas it was increased with increasing humidity. Relative water content (RWC) was decreased at 50% and 70% humidity after second day of transfer and recovered completely with the progression of acclimatization. RWC also reduced at high temperature but recovered slowly and a gradual decrease of RWC was observed at 15 • C. A visual symptom of severe leaf tip burn was observed at 50-70% humidity and at 35 • C during acclimatization. At 15 • C and 50% humidity sudden decrease of photosynthetic efficiency (F v /F m ) was observed, which could not recover in temperature treated plantlets during acclimatization period. Chlorophyll content increased with increasing humidity and at 15 and 35 • C chlorophyll content was decreased compared to 25 • C. Chlorophyll a/b ratio was unchanged while total chlorophyll/carotenoids ratio was increased from low to high temperature. Exposure of plantlets to high temperature led to a noticeable decrease in An, Sc and Tr, and at 15 • C they were more decreased whereas significant differences were not observed in the parameters tested under humidity after 25 days of acclimatization. During daytime at 15 • C, increase in An, Sc and Tr indicates the plantlets adaptability in the new environment. The peroxidase activity remained unaffected in all humidity stress whereas low temperature increased the peroxidase activity compared to high temperature. These finding suggests that photosynthetic properties was greatly affected by air temperature conditions with a reduction of An, Sc and Tr at 15 and 35 • C compared to humidity stress that played a greater role in limiting photosynthesis.
Comparison of Methods to Estimate Dark Respiration in the Light in Leaves of Two Woody Species
Plant physiology, 1994
Dark respiration in the light was estimated in leaves of two woody species (Heteromeles arbutifolia Ait. and Lepechinia fragans Greene) using two different approaches based on gas-exchange techniques: the Kok method and the Laisk method. In all cases, dark respiration in the light was lower (P < 0.05) than respiration in darkness, indicating that dark respiration was inhibited in the light. Rates of dark respiration in the light estimated by the Laisk method were 52% higher (P < 0.05) than those estimated by the Kok method. Differences between the methods could be explained by the low ambient CO2 concentrations required by the Laisk approach. The mean value of the inhibition of respiration by light for the two species, corrected for the ambient CO2 concentration effect, was 55%. Despite the differences in leaf characteristics between the species, values of the CO2 photocompensation point, at which the rate of photosynthetic CO2 uptake equaled that of photorespiratory CO2 evolu...