The effects of irradiance and CO2 on the activity and activation of ribulose-1, 5-bisphosphate carboxylase/ oxygenase in the aquatic plant Spirodela polyrhiza |
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Authors: | Martindale Wayne; Bowes George |
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Abstract: | The activation of ribulose1, 5-bisphosphate carb-oxylase/oxygenase(Rubisco, EC 4.1.1.39
EC]
) from the floating angiosperm Spirodelapolyrhiza (L.) Schleid. (giant duckweed) grown at a photon irradianceof 200 or 400 mol photons m2 s1 was consistentlylow, in the range of 5662%. Similarly low values wereobserved with four other emergent aquatic species growing underfull sun irradiance. Transference of Spirodela plants for short(minutes) or long (days) periods to the higher or lower irradianceincreased or decreased, respectively, the activation by onlyabout 15%. Activation was not greatly altered by exposure ofthe plants to full sun irradiance of >2000 mol photons m2s1 or CO2 concentrations in air of 0 and 1170 mol mor1but darkness caused a slow decline to 20% activation. Transientoscillations were observed following a change in irradianceor CO2 concentration indicating that Rubisco was responsiveto environmental perturbations. The low Rubisco activation wasnot due to the tight binding of inhibitors such as carboxyarabinitol-1-phosphate.It is concluded that a substantial proportion of the Rubiscoprotein in these naturally-occurring species may not be usedfor CO2-fixation at any given moment. Key words: Rubisco |
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