JXB Advance Access published online on September 17, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm192
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Trends in leaf photosynthesis in historical rice varieties developed in the Philippines since 1966
1Division of Agricultural and Environmental Science, School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, Leicestershire LE12 5RD, UK
2Crop and Environmental Sciences Division, International Rice Research Institute (IRRI), Los Baños, Philippines
3Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
4South China Institute of Botany, Academia Sinica, Leyiju, Guangzhou 510650, PR China
* To whom correspondence should be addressed. E-mail: Erik.murchie{at}nottingham.ac.uk
Crop improvement in terms of yield is rarely linked to leaf photosynthesis. However, in certain crop plants such as rice, it is predicted that an increase in photosynthetic rate will be required to support future grain yield potential. In order to understand the relationships between yield improvement and leaf photosynthesis, controlled environment conditions were used to grow 10 varieties which were released from the International Rice Research Institute (IRRI) between 1966 and 1995 and one newly developed line. Two growth light intensities were used: high light (1500 µmol m–2 s–1) and low light (300 µmol m–2 s–1). Gas exchange, leaf protein, chlorophyll, and leaf morphology were measured in the ninth leaf on the main stem. A high level of variation was observed among high light-grown plants for light-saturated photosynthetic rate per unit leaf area (Pmax), stomatal conductance (g), content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), and total leaf protein content. Notably, between 1966 and 1980 there was a decline in Pmax, g, leaf protein, chlorophyll, and Rubisco content. Values recovered in those varieties released after 1980. This striking trend coincides with a previous published observation that grain yield in IRRI varieties released prior to 1980 correlated with harvest index whereas that for those released after 1980 correlated with biomass. Pmax showed significant correlations with both g and Rubisco content. Large differences were observed between high light- and low light-grown plants (photoacclimation). The photoacclimation ‘range’ for Pmax correlated with Pmax in high light-grown plants. It is concluded that (i) leaf photosynthesis may be systematically affected by breeding strategy; (ii) Pmax is a useful target for yield improvements where yield is limited by biomass production rather than partitioning; and (iii) the capacity for photoacclimation is related to high Pmax values.
Key words: Acclimation, biomass, historical, improvement, irradiance, morphology, photosynthesis, rice, Rubisco, variation
Received 20 February 2007; Revised 11 July 2007 Accepted 24 July 2007