CAPP

Combining Algal and Plant Photosynthesis

The Research Dept.

Innovative CAPP research undergone at Cambridge University’s Plant Sciences department wouldn’t be possible without the combined efforts of scientists:

Professor Howard Griffiths

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Stable isotopes provide non-invasive biological and ecological markers of metabolic and atmospheric transformations of water and carbon dioxide, coupling plant carbon uptake and sequestration into biomass as a function of water availability and use (Griffiths & Jarvis 2005; Griffiths et al 2000; Tcherkez et al. 2007). We are evaluating plant growth under marginal habitats for the selection of drought tolerant cultivars and perennial biomass crops, such as Miscanthus, and their impact on canopy water use. Armed with a framework of quantitative models which allow plant gas exchanges to be modelled from the scale of leaf to crop (or forest) canopy, we can partition 13C/12C and 18O/16O to reveal net carbon sequestration over a plantation crop, as a function of soil respiratory losses. We use real-time, dynamic models of stable isotopes to monitor such exchanges (Tcherkez et al. 2007; Kromdijk et al 2008). Furthermore, with for every 3 CO2 entering a leaf, 2 retro-diffuse to create an isotopic imprint in atmospheric CO2, then the equivalent inward flux of water vapour must be 10 or 100 times greater at high humidity: Helliker and Griffiths, 2007) .                                                                                     Finally, an enduring interest in carbon concentrating mechanisms (CAM (Griffiths et al 2007), C4 (Marshall et al 2007), and the biophysical CCM in algae, cyanobacteria, lichens and hornworts has led us to investigate the structure, function and molecular basis to the chloroplast pyrenoid (Meyer et al 2008).

Moritz Meyer

image_normal2Central to my research project are the observations that a pyrenoid (an aggregation of active Rubisco) is found in the chloroplast of many hornworts, and that most pyrenoid-containing species possess a single chloroplast, characters which are not found in any other group of land plants. This suggests that hornworts may have retained genetically heritable algal-like features from the times when plants moved ashore, which were lost in all other terrestrial plants, or alternatively, have independently evolved an analogous mechanism more recently.

The hornwort pyrenoid had been associated with the existence of an active biophysical carbon concentrating mechanism (Smith and Griffiths, 1996), and the CCM activity is correlated with the presence and structure of pyrenoids (Hanson et al., 2002). It has been proposed early land plants probably owe their success to the development of less costly fixation mechanisms involving freely diffusing CO2 to internalised gas exchange surfaces (Griffiths et al., 2004).

My experimental programme starts with physiological methodologies on selected liverworts and hornworts, in order to determine the influence of thallus structure, ventilation and pyrenoid-presence/absence on gas exchange and isotope discrimination characteristics. Next, I will use molecular methodologies to identify essential components of the hornwort pyrenoid. My overall objective is to synthesise my findings into a model of evolution of CCMs in higher green algae and primitive land plants, and to clarify whether the hornwort pyrenoid is ancestral or not.

Maddie C. Mitchell

image_normalCarbon concentrating mechanisms (CCMs) occur in most aquatic photosynthetic organisms to compensate for Rubisco kinetic constraints and limited availability of CO2(aq). In Chlamydomonas reinhardtii, the CCM is composed of the active uptake of inorganic carbon, carbonic anhydrases to facilitate the interconversion of CO2 and HCO3-, and the localisation of Rubisco to a chloroplast microcompartment called the pyrenoid. An understanding of the molecular regulation of such a CCM is now critical, since perhaps 15% of global net productivity is mediated by such mechanisms, and because such knowledge would underpin strategies to maximise algal productivity in the context of global food and fuel security. I am investigating components of, and the relationship between, the CCM and chloroplast pyrenoid using both physiological and molecular biology approaches.

Oliver D. Caspari 

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Rachel Purdon

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Jess Finch

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Richard Perez-Storey

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Additionally, the CAPP project has included undergraduate student interns:

Oliver Terrett

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Ninghui Shi

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Charlie Whittaker

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