Influence of Light and Darkness upon Carbon Dioxide Fixation.

Abstract

For plants sensitive to photoperiodism light is generally essential for flowering, and the requirement for CO2 with the light indicates a photosynthetic function for the light period (21, 10). There appears to be an additional role of light in which it apparently alters a photoreceptor pigment controlling floral initiation (22).Evidence has been advanced recently that CO2 is also essential during the dark period for floral initiation in some short day plants (13) conditions. It has long been accepted that some materials synthesized in a high intensity light process are utilized in the long dark period essential for flowering of short day plants (9). This suggests that .a ttlIy of C*02 fixation in light and darkness during the period of photoperiodic induction with the aid of chromatographic and autoradiographic techniques may yield useful information regarding the biochemistrv of the photoperiodic reactions. MATERIALS AND METHODS Two short day species-Biloxi Soybean (Glycine Max L.) and Cocklebur (Xanthium pensylvanicum Wallr.), and one long day species-Wintex barley (Hordeum vulgare L.), were used. These were grown on gravel beds with nutrient solutions. Induction treatment was begun when the plants were at least 3 weeks o0l(. Short and long day species were maintaine(l in the vegetative condition by subjecting them to 16-and is leaves) when only the roots were removed. The leaves of soybean and cocklebur were selected to have a midrib length of 6 to 8 cm; for cocklebur such young leaves have been shown to have the maximum sensitivity (11). The leaves were cut under water and the petioles were then dipped in a complete nutrient solution. The method of application of CO2 was as described previously (13). The concentration of CO2 in the experimental atmospheres was 0.25 %, and the radioactivity was approximately 25 Mc/l of air. Where comparisons of 3 species are made in the tables, all 3 were exposed to the C*0, simultaneously in the same chamber.In the experiments on photosynthesis, the photosynthetic chamber was immersed in a glass water bath to minimize temperature changes inside the chamber. The chamber was evacuated briefly with an air circulating pump before C*02, was introduced. The C*02 was generated previously in a closed weighing bottle fitted with stop-cocks and forming a part of the assembly, and was swept into the experimental chamber with natural air when the stopcocks were opened. The light on the leaf surfaces was ca 3000 fc in intensity and was supplied by a 150 w reflector flood lamp for 15 minutes in all experiments.The plant material was weighed before introduction into the chamber, and immediately after cessation of the experiment was dropped into boiling 80 % ethanol and extracted on a water bath for 20 minutes. The alcoholic extract was decanted, and the tissues further crushed and extracted with fresh 80 % ethanol on a Waring Blendor for 5 minutes and the extract filtered. The combined filtrates and washings were concentrated under vacuum to a small volume, and then diluted with water t...

Dark Fixation of CO2 by Tobacco Leaves.

“…We have been unable to detect any radioactivity associated with the carbohvdrate or phosphorylated carbohydrate fractions in tobacco leaves exposed to C'402 in the dark for 5 hours. Sen and Leopold (14) report a rather significant carhohydrate fraction, 7 to 77 %, of the C"402 fixed in the The presence of an active Krebs cycle in photosynthesizing tissues has been an elusive problem for a long time. Recently, Snmillie (15) (20) Serine incorporated C'4 prior to glycine in tobacco leaves, as has been observed with Bryophyllum (13).…”

Dark Fixation of CO2 by Succulent Leaves: Conservation of the Dark Fixed CO2 Under Diurnal Conditions.

“…The other inhibitors were prepared in 0.05 M phosphate buffer and then adjusted to pH 4.5. Insoluble phosphorus was determined by the method of Krotkov and Helson (8) and nitrogen was determined by the semi-…”