Rates Of Photosynthetic Carbon Fixation Research Articles

Inorganic Carbon Requirements of Natural Populations and Laboratory Cultures of Some Chesapeake Bay Phytoplankton

The rates of photosynthetic carbon fixation for some natural populations of Chesapeake Bay phytoplankton and for unialgal cultures of species isolated from those populations follow hyperbolic saturation kinetics with respect to total inorganic carbon concentrations. The apparent half-saturation constants, Kc, measured by 14C uptake are close to and in some cases larger than ambient concentrations of total inorganic carbon, indicating that inorganic carbon can be a limiting nutrient in eutrophic systems. Addition of bicarbonate ion to incubation bottles increased the measured 14C uptake rates by factors as high as 2.5 for natural samples and 4.5 for laboratory cultures.

Photosynthesis in relation to growth and dormancy in Ceratophyllum demersum

Growth and photosynthetic activity in the different development stages of Ceratophyllum demersum L. were measured with particular reference to the physiological maxima of these processes and the factors influencing the carbon fixation rates. The elongation of the main axis and growth of the adventitious buds were used as parameters for growth. The rate of photosynthesis was determined by measuring the uptake of radioactivity from 14C-bicarbonate labelled medium. The growth of directly harvested and preconditioned plant material was measured under standard laboratory conditions. In the directly harvested plants, maximum elongation was observed in February, whereas sprout growth occurred particularly in April. Subsequently, the growth slowed down until November and the plants went into innate dormancy. In the preconditioned plants, the sequence of development events and the increase in photosynthetic activity happened earlier. The photosynthetic carbon fixation rate of Ceratophyllum plants was measured in several stages of post-dormancy under standard conditions. From the dormant period up to the spring, the rate of photosynthesis increased steadily. A sharp increase occurred in spring after the maximum development in elongation and the sprout growth. In the preconditioned plants, variations in length of the incubation period did not affect the carbon fixation rates, though such variations caused significant differences in full-grown plants. When the plants were adapted for 24 h to the standard conditions, the carbon fixation rates were, however, affected. In the preconditioned plants adapted for a long period to standard conditions, respiration rate was much higher in the dark than in the light, indicating efficient refixation of the 14CO 2 evolved in the light. In directly harvested, full-grown plant material, however, the fixation rate was much higher than that in preconditioned plants, which might explain the decrease in the carbon fixation rate commonly reported in midsummer. Only a small percentage of the released radioactivity from the plants consisted of the excreted non-gaseous organic products.

Physiological basis for salt tolerance in Tamarix ramosissima

Tamarix ramosissima Ledeb cuttings were grown in solution culture with different levels of NaCl to determine some of its physiological responses t salinity. Yields, mineral composition, and gas exchange rates for CO 2 and H 2O were determined. Levels of NaCl of 10 to 200 mequiv./l tended to depress yields of leaves, stems, and roots. Most of the Na transported to leaves was excreted from the leaves via salt glands as revealed by analyses of washed and unwashed leaf samples. 25% or more of the K, Ca, Cu, Mn, B, Al, Si, Ti, Mo, Sr and Ba also was readily washed from leaves. Sodium was accumulated in large quantities when present in high concentrations in the nutrient substrate and Na appeared to decrease uptake of both K and Ca. The Na concentration in roots and stems was much lower than in leaves. Rates of photosynthetic carbon fixation and transpirational water loss changed very little with increasing salt treatment indicating that the observed growth decreases were due to energy losses through increased respiration and/or salt pumping.

The association between chloroplasts ofCodium fragileand the molluscElysia viridisII. Chloroplast ultrastructure and photosynthetic carbon fixation inE. viridis

WhenCodium fragilechloroplasts in cells ofElysia viridiswere examined by electron microscopy, no structural damage or alteration was observed beyond a general change in shape from ellipsoid in the plant to more oval in the animal; outer chloroplast envelopes were always intact. Some chloroplasts in animal cells were enclosed by a membrane external to the envelope but others were not; the origin of this membrane is unclear. Neither the mechanism of entry nor the ultimate fate of chloroplasts in animal cells is fully understood. Rates of photosynthetic carbon fixation by chloroplasts inElysiaandcodiumwere of a similar order. The pathways of photosynthetic14C fixation inElysiawere not restricted compared to isolated chloroplasts. InCodium, incorporation of14C into sucrose occurs outside the chloroplast, as does incorporation into galactose inElysia. Substantial incorporation into galactose inElysiadoes not begin until about 20 to 30 min after the start of14C fixation, although a certain amount of14C galactose is detectable after 5 to 8 mins, indicating rapid release from chloroplasts. Chloroplasts isolated fromCodiumrelease only 2% of their fixed14C to the medium, mainly as glycolic acid. In animal homogenates, release of fixed14C from chloroplasts rises to 40%, mostly composed of glucose with some glycolic acid. In intact animals, at least 36% of the fixed carbon is released from the chloroplasts. Chloroplasts inElysia, unlike those inCodium, were not able to incorporate14C from CO2or other precursors into chlorophyll. InCodium, incorporation from CO2ceased in the presence of cycloheximide or choramphenicol, suggesting that complete biosynthesis of chlorophyll depends upon DNA in both the plant nucleus and the chloroplast. Incorporation from CO2into glycolipids and sulpholipids could not be detected inElysia. Chloroplasts inElysiaare unlikely to be completely autonomous.

Estimation of the rates of mass carbon transfer by leaves of sugar beet

Estimates of the rate of translocation of carbon, T, from sugar beet leaves were made from simultaneous determinations of CO2 exchange and dry weight change. For an illuminated leaf in a constant environment, T increased to a maximum during the first 2 h and was constant for the next 10 h. On darkening, T decreased rapidly in the first 2 to 4 h to a constant minimal value which could continue for as long as 24 h. The average value of T for nine leaves in the light was 4.2 ± 0.4 mg C dm−2 leaf surface h−1, while in the dark the average value for five leaves over 10 h was 1.2 ± 0.2 mg C dm−2 h−1. Generally T was about three-quarters of the net rate of photosynthetic carbon fixation.

The effect of radiocarbon on the rate of carbon dioxide utilization during photosynthesis

In view of the wide application of radioactive carbon dioxide in tracer experiments together with a reported anomalous effect of the isotope content on the tracer behavior, we have investigated the effect of varying specific activity of the carbon dioxide on both the rate and pattern of photosynthetic carbon fixation. We have found no effect of the carbon-14 other than the ordinary mass effect in both algae and higher plants.