Running Head: Control and Adjustment of the Rate of Photosynthesis Above Present CO{sub 2} Levels Page: 6 of 30
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
Abstract
The adjustment of photosynthesis to different environmental conditions and especially to
elevated CO2 is often characterized in terms of changes in the processes that establish (limit)
the net C02 assimilation rate. At slightly above present ambient pCO2 light-saturated
photosynthetic responses to CO2 depart limitation by the catalytic capacity of tissue rubisco
content. An hypothesis attributing this departure to limited thylakoid reaction/electron transport
capacity is widely accepted, although we find no experimental evidence in the literature
supporting this proposition.. The results of several tests point to the conclusion that the
capacity of the thylakoid reactions cannot be generally responsible for the deviation from
rubisco limitation. This conclusion leaves a significant gap in the interpretation of gas
exchange responses to CO2. Since the inputs to the photosynthetic carbon reduction cycle
(CO2 and photon-capture/electron-transport products) do not limit photosynthesis on the
shoulder of the A=f(c1) curve, the control of photosynthesis can be characterized as: due to
feedback. Several characteristics of gas exchange and fluorescence that occur when steady-
states in this region are perturbed by changes in CO2 or 02 suggest significant regulation by
conditions other than directly by substrate RuBP levels. A strong candidate to explain these
responses is the triose-phosphate flux / inorganic phosphate regulatory sequence, although not
all of the gas exchange characteristics expected with "TPU-limitation" are present (e.g. oxygen-
insensitive photosynthesis). Interest in nitrogen allocation between rubisco and light capture /
electron transport as the basis for photosynthetic adjustment to elevated CO2 may need to be
reconsidered as a result of these findings. Contributors to the feedback regulation of
photosynthesis (which may include sucrose phosphate synthase and fructose bisphosphatase
activities, phloem loading, and "sink-strength") may play a large role in the adjustment of
photosynthesis to elevated CO2. The continuing rise in atmospheric CO2 elevates the need to
understand the regulation of photosynthesis that is not related to rubisco capacity.4
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Ball, J. Timothy. Running Head: Control and Adjustment of the Rate of Photosynthesis Above Present CO{sub 2} Levels, report, December 1, 1996; United States. (https://digital.library.unt.edu/ark:/67531/metadc718383/m1/6/: accessed April 30, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.