Brainstorming by some of the world’s top plant scientists, including two from UCLA, results in the ideas described in paper recently published in the Proceedings of the National Academy of Sciences (PNAS).
The paper titled “Redesigning Photosynthesis to Sustainably Meet Global Food and Bioenergy Demand” was published in the July 14th issue of PNAS. The ideas discussed in the paper were the result of a 2013 workshop organized by UCLA Professor Sabeeha Merchant and Professor Donald Ort from the University of Illinois at Urbana-Champaign. The paper’s co-authors, including UCLA Professor Todd Yeates, are the scientists who attended the workshop.
“The inspiration for the workshop came from the Banbury Center at Cold Spring Harbor Laboratory” said Prof. Merchant. “They invited us to organize a an all-expenses paid meeting involving participants with expertise in engineering, physical sciences and, both molecular as well as organismal life sciences, to think about game-changing ideas for dealing with demand for products of photosynthesis for the food and fuel needs of the future. The conference was special because it offered the participants, ranging in experience from junior independent investigators to senior professors, the opportunity to exchange and criticize ideas with a spirit of open-ness and collaboration. Some of the ideas are already being tested while others, like the “smart canopy”, are longer-term designs.”
The world population, which stood at 2.5 billion in 1950, is predicted to increase to 10.5 billion by 2050. It's a stunning number since it means the planet's population has doubled within the lifetimes of many people alive today.
At the same time, arable land is shrinking and crop productivity is stagnating.
The last time population outran agricultural productivity, we were rescued by the Green Revolution, an increase in the harvest index (the amount of the plant's biomass partitioned into grain) achieved through classical plant breeding. Today's ears of corn are huge compared to those harvested in the 1920s.
But the harvest index can be pushed only so far; a plant can't be 100-percent grain. And as the harvest index approaches its theoretical limit, gains in crop productivity have plateaued.
Is there another rabbit plant scientists can pull out of the hat? One possibility is to redesign photosynthesis, the process by which plants convert sunlight and carbon dioxide into sugar and the ultimate source of all food, unless you're a chemosynthesizing bacterium.
Photosynthesis, scientists will tell you, is stunningly inefficient. "We expect the solar cells we put on our rooftops to be at least 15- or 20- percent efficient," said Robert Blankenship, PhD, the Lucille P. Markey Distinguished Professor of Arts and Sciences at Washington University in St. Louis. "A plant is at best one-percent efficient."
In an optimized canopy (right), leaves at the top, which receive too much light, might tilt vertically and have smaller and fewer light-gathering antennas (green cones) feeding many reaction centers. Those lower in the canopy would have larger antennas feeding fewer reaction centers. The leaves at the top would have a variant of RuBisCO, an important enzyme in photosynthesis, that had high catalytic activity but not be particularly good at distinguishing carbon from oxygen, whereas those at the bottom might have RuBisCO variants that were slower but less inclined to pick up oxygen instead of carbon. Credit: Zhu et al