Effects of temperature on the gas exchange of leaves in the light and dark

144

The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of 02 in the C3 species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of 02/CO2 in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of 02 and CO2 in the intercellular spaces of leaves as derived from whole (1,5,11,12,14,15,18,22 (1, 11,12,14,15,18,22) increased with increasing temperature although the absolute rate of 02 inhibition of photosynthesis (rate of photosynthesis at 1.5% 02 -rate of photosynthesis at 21 % 02) shows an optimum temperature. Generally only atmospheric levels of CO.2 and 02 have been considered in comparative studies on 02 inhibition of photosynthesis in various species and on 02 inhibition of photosynthesis as affected by temper.ature. In the present study the percentage inhibition of photosynthesis by O., was analyzed with several C3 species in relation to calculated intercellular levels of CO., and O., and solubility ratios of 02/CO2 in the leaf. Gas Exchange Measurements. Rates of photosynthesis and transpiration were measured simultaneously and continuously with a Barnes multispec IR CO., and water vapor analyzer in an open circuit system as described previously (18). The attached leaves were enclosed in a 180 cm:' Plexiglas chamber similar to that designed by Ku and Hunt (19). Eight ports in the sidewalls of the leaf chamber were connected to a closed and independent air-conditioning system which established the leaf temperature. The air recirculates in this system at 13 1/min which minimizes the boundary layer resistance of the leaves to water vapor and CO2 transfer. Using wet filter paper of similar size and orientation as the leaves, the boundary layer resistance to water vapor transfer was determined for each species under such conditions. Leaf temperature was measured with a 75-,ukm diameter chromel-constantan thermocouple held against the adaxial surface of the leaf, and was maintained within ±0.3 C of the desired leaf temperature without detectable fluctuation. Using an air conditioner, the temperature around the plant was also kept within +3 C of the leaf temperature. Irradiance was provided by a 400 w Lucolux lamp (General Electric) in the horizontal position, and was filtered through a 5-cm water tank. Light was measured using a quantum flux sensor (Lambda Instruments, Lincoln. Neb. MATERIALS AND METHODS

mentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Oxygen Inhibition of Photosynthesis

Ku¹,

Edwards²

1977

144

“…It is well documented (7,10) that photosynthesis of maize and other tropical grasses is very low at temperatures below 15 C and that chilling temperatures will cause visible lesions on the leaves of these plants (22); yet we are still unsure of the primary sites of temperature sensitivity.…”

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confidence: 99%

Plants under Climatic Stress

Taylor¹,

Rowley²

1971

156

“…Its CO2 compensation concentration (F ) approaches zero at temperatures less than 30 C (28,29,42) and is unaffected by 02 concentration (7,10); it releases little or no CO2 to CO2-free air (8,30) or even to C02-free oxygen (48); it fails to exhibit a CO, burst upon darkening (6,10,42); its net photosynthetic rate is not stimulated by lowering the ambient 02 concentration from 21 to 2% (3,5,7,14,18); and it does not depress the specific radioactivity of 14C during photosynthetic CO2 fixation (15,45). The absence of these external photorespiratory indices can be interpreted in two ways: maize either lacks photorespiration altogether, or it recycles photorespiratory CO2 with considerable efficiency.…”

mentioning

confidence: 99%

Photorespiratory Phenomena in Maize

Volk¹,

Jackson²

1972

Concurrent 02 evolution, 02 uptake, and CO2 uptake by illuminated maize (Zea maya) leaves were measured using 12CO2 and 802. Considerable 02 uptake occurred during active photosynthesis. At CO2 compensation, 02 uptake increased. Associated with this increase was a decrease in 02 release such that a stoichiometric exchange of 02 occurred. The rate of 02 exchange at CO2 compensation was directly related to 02 concentration in the atmosphere at least up to 8% (v/v).When illuminated maize leaves were exposed to saturating CO2 concentrations containing approximately equal amounts of 'CO2 and '3CO2, the latter was taken up more rapidly, thus depressing the atom % 13C in the atmosphere. Moreover, upon exposure to CO2 containing 96 atom % "3C, there occurred a directly measurable efflux of '2CO2 from the leaves for at least 15 minutes. During this period an equimolar evolution of 1602 and uptake of 12CO2 was observed. Thereafter, although the rate of 1602 evolution remained unchanged, the rate of "3CO2 uptake declined markedly, suggesting continual "3C enrichment of the photorespiratory substrate.It is concluded that a finite photorespiratory process occurs in maize and that the CO2 generated thereby is efficiently recycled. Recycling maintains the internal C02 concentration at a level difficult to detect by most photorespiratory assays.