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Wheat Information
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Number 72: 88-90 (1991)
Photosynthesis
and respiration in eu- and alloplasmic common wheat with cytoplasms
of Triticum and Aegilops
K. Kasai, C. Yamagami, Y. Kubota and C. Nakamura
Department of Plant Protection, Faculty of Agriculture, Kobe
University, Kobe 657, Japan
Genetic diversity in cytoplasms of Triticum and
Aegilops has been studied mainly using euand alloplasmic wheat
having the same nuclear genotypes. It has become clear that
cytoplasmic diversity manifests itself in various characters of the
alloplasmic lines (Tsunewaki 1988). We report our results on
cytoplasmic variability in photosynthesis and respiration, two of the
most important cytoplasmic functions.
Photosynthesis (maximum photosynthetic capacity) and respiration of
newly assimilated photosynthates (data not shown) in common wheat
(T. aestivum) cv Chinese Spring (CS) with 17 different
cytoplasms of Triticum and Aegilops (Table
1) were measured
based on the rates of 13CO2 assimilation and
consumption, respectively, by far-red spectrophotometry. The maximum
photosynthetic capacity in 3- and 10-week-old plants differed
significantly among eu- and alloplasmic lines. Interestingly, a
significant negative correlation was found between the photosynthetic
capacity and growth measured based on dry matter weights in these
lines. A similar negative correlation was reported in euplasmic
Triticum and Aegilops species between their
photosynthetic capacity and growth and/or yield (Evans and Dunstone
1970). This appareently paradoxical relationship therefore has its
basis not only on nuclear genomes but also on cytoplasmic genomes.
Groups of cytoplasms causing either growth depression or male
sterility in CS nuclei showed higther photosynthetic capacities than
euplasmic CS. No differences were found in the photosynthetic
capacity between cytoplasms having H- and L- type Rubisco large
subunits, which respectively show high and low in
vitro
Rubisco activity (Evans and Austin 1986).
All but C-type cytoplasms causing male sterility in CS nuclei and S
group of cytoplasms showed higher rates of respiratory consumption of
new photosynthates than CS, indicating that respiration in these
cytoplasms depends more on newly assimilated carbons.
Respiratory electron flows were measured based on the rates of oxygen
uptake using an oxygen electrode in the presence and absence of
respiratory inhibitors (1 mM KCN and 5 mM salicylhydroxamic acid) and
a uncoupler (2 and 10 microM carbonylcyanide m-chlorophenyl
hydrazone). The in
vitro
catalytic activity of cytochrome c oxidase (cox) was measured also by
an oxygen electrode. The total respiratory activity and capacity, the
activity and capacity of the cytochrome and alternative paths, and
the in
vitro cox
activity were all higher in 2-day-old seedlings than in 2-week-old
seedling leaves and roots (Fig.
1, capacity data
not shown). A significant negative correlation was found between the
cox activity in roots and growth among the cytoplasms. The highest
cox activity occurred in a A-type cytoplasm which caused the severest
growth depression and complete male sterility.
The cox activity significantly differed depending on the ages and/or
tissues: in 2-day-old seedlings the activity was higher in the
euplasmic CS, whereas in 2-week-old seedling leaves and roots it was
higher in the alloplasmic lines (data not shown). When growth
depression-causing cytoplasms and male sterility-casuing cytoplasms
were compared with the others, similar differential effects of plant
ages and tissues were observed in the cox activity.
Our results thus revealed a large genetic variability in the effects
of cytoplasms on photosynthesis and respiration, the parameters of
which varied at different ages and in different tissues among the 17
different cytoplasms of Triticum and Aegilops.
References
Evans LT and Dunstone RL (1970) Some physiological aspects of
evolution of wheat. Aust J Biol Sci 23: 735-741.
Evans JR and Austin RB (1986) The specific activity of ribulose-1,
5-bisphoshate carboxylase in relation to genotype in wheat. Planta
167: 344-350.
Tsunewaki K (1988) Cytoplasmic variation in Triticum and
Aegilops. Proc VII Int Wheat Genet Symp: 53-62.
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