High Tech Harvest by Paul Lurquin

Author:Paul Lurquin [PAUL F. LURQUIN]
Language: eng
Format: epub
Publisher: Basic Books
Published: 2012-01-18T05:00:00+00:00

Boosting Yields Through Enhanced Photosynthesis

Increasing the yield of crop plants is probably as old an objective as agriculture itself. Classical breeding techniques, based on Mendel’s laws, have been extremely successful in producing high-yield plants like wheat, barley, rice, and corn. To achieve this result, breeders make crosses between different varieties that belong to the same species or that are closely related (sexually compatible). Then, often after years of work, they select the most desirable offspring of these crosses and release them as new varieties. The difficulty with a trait such as grain production is that it is not under the control of a single Mendelian gene. Rather, many genes are involved, and this multiplicity is what makes the production of high-yielding varieties so time-consuming and arduous. Further, gene transfer technology that deals with multiple genes is still in its infancy. For this reason, the transfer of yield-determining genes has not yet been achieved through genetic engineering. To complicate matters further, it may well be that the current plant gene pool has been mined as much as it can be. In other words, it may be that classical breeding is approaching its limits because all the high-yield genes available have already been used for breeding purposes. The gene pool may well have been exhausted. What, then, can be done to improve yields further?

Maurice Ku, a researcher at Washington State University, in collaboration with his Japanese colleagues, used an entirely new approach to tackle this problem—with rice. They based their reasoning on the fact that biochemical reactions of photosynthesis that convert atmospheric carbon dioxide into sugars are inefficient in rice plants and potentially could be improved. Indeed, rice is part of a group of plants (called C3 plants) that absorb carbon dioxide from the air much less efficiently and use more energy than most other plants (called C4 plants, corn being one example) to achieve the same result, the conversion of carbon dioxide into sugars mediated by sunlight. Ku and his colleagues hypothesized that transferring key genes from a C4 plant into rice could potentially enhance carbon dioxide fixation. Interestingly, rice possesses these genes but they are silent. Ku’s group cloned three genes from corn, coding for the three C4 enzymes, NADP-malic enzyme, phosphoenolpyruvate carboxylase and pyruvate, orthophosphate dikinase, and transferred them, one at a time, into rice, using a high-level expression vector. Normally, one would expect that addition of a single gene would not drastically enhance carbon dioxide fixation. Yet, this is what happened: All three transgenic lines showed enhanced carbon dioxide utilization and a 20 percent increase in rates of photosynthesis. What is more, the yield of these lines, in terms of grain production, was increased by 10 percent to 35 percent (as shown in Figure 5.2). The precise reasons why single genes have such an important effect on these transgenic plants are still under investigation, but this discovery bodes very well for the productivity of this all-important crop. High-yielding transgenic rice is not yet available to the public, however.

Figure 5.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.