The photosynthesis of young Panicum C 4 leaves is not C 3 ‐like
Evidence is presented contrary to the suggestion that C 4 plants grow larger at elevated CO 2 because the C 4 pathway of young C 4 leaves has C 3 ‐like characteristics, making their photosynthesis O 2 sensitive and responsive to high CO 2 . We combined PAM fluorescence with gas exchange measurements...
Saved in:
Published in | Plant, cell and environment Vol. 21; no. 11; pp. 1123 - 1131 |
---|---|
Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
01.11.1998
|
Online Access | Get full text |
Cover
Loading…
Summary: | Evidence is presented contrary to the suggestion that C
4
plants grow larger at elevated CO
2
because the C
4
pathway of young C
4
leaves has C
3
‐like characteristics, making their photosynthesis O
2
sensitive and responsive to high CO
2
. We combined PAM fluorescence with gas exchange measurements to examine the O
2
dependence of photosynthesis in young and mature leaves of
Panicum antidotale
(C
4
, NADP‐ME) and
P. coloratum
(C
4
, NAD‐ME), at an intercellular CO
2
concentration of 5 Pa.
P. laxum
(C
3
) was used for comparison. The young C
4
leaves had CO
2
and light response curves typical of C
4
photosynthesis. When the O
2
concentration was gradually increased between 2 and 40%, CO
2
assimilation rates (
A
) of both mature and young C
4
leaves were little affected, while the ratio of the quantum yield of photosystem II to that of CO
2
assimilation (
Φ
PSII
/
Φ
CO2
) increased more in young (up to 31%) than mature (up to 10%) C
4
leaves.
A
of C
3
leaves decreased by 1·3 and
Φ
PSII
/
Φ
CO2
increased by 9‐fold, over the same range of O
2
concentrations. Larger increases in electron transport requirements in young, relative to mature, C
4
leaves at low CO
2
are indicative of greater O
2
sensitivity of photorespiration. Photosynthesis modelling showed that young C
4
leaves have lower bundle sheath CO
2
concentration, brought about by higher bundle sheath conductance relative to the activity of the C
4
and C
3
cycles and/or lower ratio of activities of the C
4
to C
3
cycles. |
---|---|
ISSN: | 0140-7791 1365-3040 |
DOI: | 10.1046/j.1365-3040.1998.00348.x |