Chapter 2 - Carbon dioxide assimilation and respiration

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Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is the most abundant single protein on earth and is pivotal for CO2 assimilation by all plants. In higher plants, the holoenzyme consists of eight large subunits, each with a molecular mass of 50-55 kD (identified in (b)), and eight small subunits of molecular mass 12-18 kD (not shown). Large subunits are encoded by a single gene in the chloroplast genome while a family of nuclear genes encode the small subunits.Any loss of catalytic effectivess or reduction in amount translates to slower photosynthesis and reduced growth. Tobacco plants (a) transformed with an antisense construct against Rubisco (anti-Rubisco) grow more slowly than wild types due to a 60% reduction in photosynthetic rate. Immunodetection of the large subunit polypeptide of Rubisco with an anti-Rubisco antiserum (b) shows that the anti—Rubisco transgenic plants contain less than 50% of the Rubisco detected in wild-type tobacco plants. Scale bar in (a) = 10 cm (Photograph courtesy Susanne von Caemmerer; original immunoblot courtesy Martha Ludwig)

How green plants obtain their supplies of carbon had been a mystery for many years, and the first investigator to discover any clue to the problem was the English divine, Joseph Priestley. In 1771 Priestley found that sprigs of mint were able to produce ‘dephlogisticated air’ i.e. oxygen, from an atmosphere vitiated by animal respiration…It remained for Ingen-Housz (1779) to show that it was only the green parts of plants that were able to purify the vitiated air…It was largely due to the German chemist Liebig (1840) that it came to be realized that the sole source of carbon in the green plant is the carbon dioxide of the air, and the humus theory was ultimately abandoned.

(E.C. Barton Wright (1937), General Plant Physiology, Williams and Norgate Ltd: London)