A circadian rhythm in the level of carbon dioxide compensation inBryophyllum fedtschenkoiwith zero values during the transient
✍ Scribed by M. B. Jones; T. A. Mansfield
- Publisher
- Springer-Verlag
- Year
- 1972
- Tongue
- English
- Weight
- 764 KB
- Volume
- 103
- Category
- Article
- ISSN
- 0032-0935
No coin nor oath required. For personal study only.
✦ Synopsis
Detached shoots of iBryophyllum ]edtschenkoi maintained in a closed system in the light exhibited an endogenous circadian rhythm in CO 2 compensation. The rhythm was sensitive to changes in light intensity and temperature. At 15~ it damped rapidly in light of 78 J m -2 s -1, but at 10~ a rhythm of considerable amplitude was evident at this same light intensity. During the transient (i.e. the temporary state of the rhythm before it acquired its steady state) low compensation values between 0 and 5 ppm C02 were achieved. When the plants were maintained at a higher light intensity prior to the measurements, the period of low compensation during the transient was extended, and zero values were obtained under some conditions.
Studies of gas exchange at opposite phases of the rhythm revealed: (i) that the rate of uptake of 1~CO~ differed, both in light and darkness (the epidermis was removed during these observations to avoid interference from stomatal rhythms); (ii) 'photorespiration', estimated by extrapolation of the graph relating photosynthetic rate and CO 2 concentration, was highest during the peaks of the rhythm in CO 2 compensation; (iii) estimates of the capacity for 'photorespiration' by the glycine-l-14C assay indicated highest values during the troughs of the rhythm.
These findings are discussed in relation to the Ca-acid metabolism of this species. Low C02 compensation is probably due to the activity of phosphoenolpyruvate earboxylase and not to the absence of proeesses involving CO 2 evolution.