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Wheat Information Service
Number 85: 25-30 (1997)
Research article
Rubisco activity vs photosynthetic CO2
assimilation rate in the alloplasmic hybrids of common wheat cv.
Chinese Spring
Kazue Kasai1, Chiharu Nakamura1,2,*, Naoki
Mori1 and Naotsugu Uchida1,3
1 Graduate School of Science and Technology,
Kobe University, 1 Rokkodal-cho, Nada- ku, Kobe 657, Japan.
2 Laboratory of Plant Genetics, Faculty of Agriculture,
Kobe University, 1 Rokkodai-cho, Nada- ku, Kobe 657, Japan.
3 Laboratory of Tropical Botany, Faculty of Agriculture,
Kobe University, 1 Rokkodai-cho, Nada-ku, Kobe 657, Japan.
Summary
In vitro Rubisco activity was measured in 15 alloplasmic
lines of common wheat (Triticum aestivum L.) cv.
Chinese Spring (CS) based, on the rate of incorporation of
NaH14C03 in acid-precipitable fraction. Five
alloplasmic lines with cytoplasms of T. boeoticum, Ae.
heldreichii, Ae. uniaristata, Ae. speltoides, and T
timopheevi showed significantly higher Rubisco activities than
CS. Rubisco activity was compared with the available data on the
photosynthetic capacity that was measured by the rate of
incorporation of 13CO2. The comparison showed
no correlation between the two parameters. A possible experimental
approach to solve this inconsistency between in vitro Rubisco
activity and in vivo photosynthetic C02
assimilation rate was discussed.
Key words: Rubisco activity, C02 assimilation
rate, Triticum, Aegilops, alloplasmic lines
Introduction
Photosynthesis is the most important function of the chloroplast
genome, that is regulated through the interaction with the nuclear
genome. In wheat, there are two forms of large subunit of
ribulose1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39,
abbreviation: Rubisco); one with the lower isoelectric point (L-type)
and the other with higher isoelectric point (H-type) (Chen et al.
1975; Hirai and Tsunewaki 1981). L-type is found in diploid species
with A or D genomes, while H-type is found in some diploid
Aegilops species of the section Sitopsis and in all tetraploid
and hexaploid species with B or G genomes. Evans and Seemann (1984)
and Evans and Austin (1986) showed an association of in vitro
Rubisco activity with the isoelectric property of its large subunit:
Rubisco with L-type large subunit shows low in vitro speciflc
activity, while that of H-type is high. Terachi et al. (1987) further
suggested, based on the sequences, of the genes (rbcL)
encoding L- and H-type large subunits, that the replacement of
glutamine in L-type by lysine in H-type is responsible for the higher
in vitro specific activity of Rubisco with H-type than L-type
subunit.
It was, however, shown that the higher in vitro Rubisco
activity did not result in different in vivo C02
assimilation rate measured under light-saturated and
C02-limiting conditions (Austin et al. 1984; Evans 1986).
In vivo maximum rate Of C02 assimilation measured
by the rate of 13CO2 incorporation also showed
no correlation with the large subunit types in alloplasmic common
wheat (Nakamura et al. 1991). In this communication, we report the
result of re-examination ofin vitro Rubisco activity using the
same set of alloplasmic lines and compared it with the previous data
on the C02 assimilation rate (Nakamura et al. 1991).
*Corresponding author: nakamura @ kobe-u.acjp
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