Postillumination burst of carbon dioxide in crassalacean Acid metabolism plants

Immediately following exposure to light, a postillumination burst of CO₂ has been detected in Crassulacean acid metabolism plants. A detailed study with pineapple (Ananas comosus) leaves indicates that the postillumination burst changes its amplitude and kinetics during the course of a day. In air, the postillumination burst in pineapple leaves generally is exhibited as two peaks. The postillumination burst is sensitive to atmospheric CO₂ and O₂ concentrations as well as to the light intensity under which plants are grown. We propose that the CO₂ released in the first postillumination burst peak is indicative of photorespiration since it is sensitive to either O₂ or CO₂ concentration while the second CO₂ evolution peak is likely due to decarboxylation of organic acids involved in Crassulacean acid metabolism.     

Some effects of chloramphenicol on the metabolism of chlorella

Summary A chloramphenicol concentration of 3 mg per ml inhibits uptake of ¹⁴C-labelled phenylalanine, lysine, and adenine by Chlorella cells. Incorporation into both the free pool and the TCA insoluble fraction is inhibited. The inhibition is not related to inhibition of protein synthesis since cycloheximide (a specific inhibitor of protein synthesis in Chlorella) does not inhibit uptake of the ¹⁴C-labelled amino acids. Uptake of ¹⁴C-uracil is not inhibited by chloramphenicol.Both chloramphenicol and 2.4-dinitrophenol stimulate endogenous respiration of Chlorella, but whereas the latter reduces the internal concentration of ATP, the former (in concentrations of 1–3 mg/ml) stimulates it about two-fold. Similar concentrations of chloramphenicol decreases slightly the concentration of ADP, and it is therefore suggested that in Chlorella, chloramphenicol concentrations of 1–3 mg per ml inhibit some energy-linked reactions by preventing ATP utilization.     

Flagellar adhesion and deadhesion in chlamydomonas gametes: Effects of tunicamycin and observations on flagellar tip morphology

The aggregation-dependent loss of flagellar adhesiveness in Chlamydomonas reinhardi has been correlated with changes in flagellar tip morphology during adhesion and deadhesion. As aggregating mt^? and impotent (able to adhere, but not fuse) mt⁺ gametes begin to disaggregate in the presence of the protein synthesis inhibitor cycloheximide, there is a concomitant change in flagellar tip morphology from the activated bulbous form to the nonactivated tapered shape. The requirement of protein-synthetic activity for the maintenance of flagellar adhesiveness during aggregation may be due in part to turnover of proteins involved in formation or stabilization of activated flagellar tips. Incubation of aggregating gametes with tunicamycin indicates that, like protein synthesis inhibitors, this inhibitor of glycosylation also causes adhering gametes to deadhere. The results suggest that protein glycosylation may be essential for maintenance of adhesiveness during aggregation.     

Year-round observations of the net ecosystem exchange of carbon dioxide in a native tallgrass prairie

An Ameriflux site was established in mid 1996 to study the exchange of CO₂ in a native tallgrass prairie of north‐central Oklahoma, USA. Approximately the first 20 months of measurements (using eddy covariance) are described here. This prairie, dominated by warm season C4 grasses, is typical of the central Kansas/northern Oklahoma region. During the first three weeks of the measurement period (mid‐July–early August 1996), moisture‐stress conditions prevailed. For the remainder of the period (until March 1998), however, soil moisture was nonlimiting. Mid‐day net ecosystem CO₂ exchange (NEE), under well‐watered conditions, reached a maximum magnitude of 1.4 mg CO₂ m^?2 s^?1 (flux toward the surface is positive) during peak growth (mid‐July 1997), with green leaf area index of 2.8. In contrast, under moisture‐stress conditions in the same growth stage in 1996, mid‐day NEE was reduced to near‐zero. Average night NEE ranged from near‐zero, during winter dormancy, to ? 0.50 mg CO₂ m^?2 s^?1, during peak growth. Most of the variance in average night NEE was explained by changes in soil temperature (0.1 m depth) and green leaf area. The daytime NEE measurements were examined in terms of a rectangular hyperbolic relationship with incident photosynthetically active radiation. The analysis showed that the quantum yield during peak growth was similar to those measured in other prairies and the y‐intercept, so obtained, can be potentially used as an estimate of night‐time CO₂ emissions when eddy covariance data are unavailable. Daily integrated NEE reached its peak magnitude of 30.8 g CO₂ m^?2 d^?1 (8.4 g C m^?2 d^?1) in mid‐July when the green LAI was the largest (about 2.8). In general, the seasonal trend of daily NEE (on relatively clear days) followed that of green LAI. Annually integrated carbon exchange, between prescribed burns in 1997 and 1998, was 268 g C m^?2 y^?1. After incorporating carbon loss during the prescribed burn , the net annual carbon exchange in this prairie was near‐zero in 1998.     

Post-illumination burst of carbon dioxide inPhaseolus vulgaris L. as affected by leaf temperature

The effect of leaf temperature on the post-illumination burst of CO₂ (PIB) in 15 day-old primary bean leaves (Phaseolus vulgaris L.) was studied by means of infrared gas analysis in a closed gas exchange system. The amplitude and kinetic of PIB was different with its own characteristic course for different temperature steps. The temperature optimum for the PIB at 21% O₂ near the carbon dioxide compensation concentration Λ (150 mg m^-3) was 33 °C while that for net photosynthetic rate (P _N) at 21% O₂ and 600 mg m^-3 CO₂ was 24.5 °C. The PIB was observed to 12…33 s after the darkening of leaves. No PIB was observed at 2% O₂. The applicability of PIB as an estimate of photorespiration rateR _p has been proved by comparing it with extrapolation of the relationship betweenP _n and CO₂ concentration to zero.     

Some effects of sugars and sugar phosphates on carbon dioxide fixation by isolated chloroplasts

1. Carbon dioxide fixation by isolated pea chloroplasts was stimulated by the addition of intermediates of the Calvin photosynthesis cycle and by some related compounds. 2. Ribose 5-phosphate and fructose 1,6-diphosphate consistently produced the largest effects; free sugars such as erythrose and sedoheptulose and acids such as glycollate and glyoxylate were largely ineffective or even inhibitory. 3. Small effects were produced by fructose and ribose but not by their isomers, glucose and xylose. 4. Maximal rates in the presence of ribose 5-phosphate varied between 10 and 50μmoles of carbon dioxide fixed/mg. of chlorophyll/hr.