Category Archives: Links

Plant evolution: The inevitability of C4 photosynthesis

Photosynthesis Although atmospheric carbon dioxide (CO2) levels are currently rising, the last 30 million years witnessed great declines in CO2, which has limited the efficiency of photosynthesis. Rubisco, the critical photosynthetic enzyme that catalyses the fixation of CO2 into carbohydrate, also reacts with oxygen when CO2 levels are low and temperatures are high. When this occurs, plants activate a process known as photorespiration, an energetically expensive set of reactions that release one molecule of CO2.

C4 photosynthesis is a clever solution to the problem of low atmospheric CO2. It is an internal plant carbon-concentrating mechanism that largely eliminates photorespiration: a ‘fuel-injection’ system for the photosynthetic engine. C4 plants differ from plants with the more typical ‘C3′ photosynthesis because they restrict Rubisco activity to an inner compartment, typically the bundle sheath, with atmospheric CO2 being fixed into a 4-carbon acid in the outer mesophyll. This molecule then travels to the bundle sheath, where it is broken down again, bathing Rubisco in CO2 and limiting the costly process of photorespiration.

The evolution of the C4 pathway requires many changes. These include the recruitment of multiple enzymes into new biochemical functions, massive shifts in the spatial distribution of proteins and organelles, and a set of anatomical modifications to cell size and structure. It is complex, and it is also highly effective: C4 plants include many of our most important and productive crops (maize, sorghum, sugarcane, millet) and are responsible for around 25% of global terrestrial photosynthesis. A new paper in eLife examines how this process may have evolved, first to correct an intercellular nitrogen imbalance, and only later evolved a central role in carbon fixation.

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Leafsnap: An Electronic Field Guide

Leafsnap Leafsnap is the first in a series of electronic field guides being developed by researchers from Columbia University, the University of Maryland, and the Smithsonian Institution. This free mobile app uses visual recognition software to help identify tree species from photographs of their leaves.

Leafsnap contains high-resolution images of leaves, flowers, fruit, petiole, seeds, and bark created by the conservation organization Finding Species. The Leafsnap app is available in versions for the USA and for the UK. It’s pretty good – try it – go to the iTunes app store and search for Leafsnap.

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