Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Factors affecting kernel yield in maize

08.12.2006
Understanding nitrogen metabolism is of critical importance to crop management, as nitrogen availability is one of the major factors limiting crop growth and yield.

All of the nitrogen in a plant, whether derived initially from nitrate, nitrogen fixation, or ammonium ions, is converted to ammonia, which is rapidly incorporated into organic compounds through a number of metabolic pathways beginning with the activity of the enzyme glutamine synthetase (GS), which catalyzes formation of the amino acid glutamine from ammonia and glutamic acid.

An individual nitrogen atom may pass many times through the GS reaction, following uptake from the soil, assimilation, remobilization, and delivery to growing roots and leaves, and ultimately, deposition in seed as storage proteins. Thus GS is likely to be a major check-point controlling plant growth and crop productivity.

In research reported in The Plant Cell, scientists Antoine Martin and Bertrand Hirel from the National Institute of Agronomic Research (INRA) in Versailles, France, together with colleagues from institutions in the U.K., Spain, and Japan, present new information on the roles of two forms (isoenzymes) of cytosolic glutamine synthetase (GS) in maize, which underscores the importance of this enzyme and nitrogen metabolism in cereal crop productivity. Improving nitrogen use efficiency of crop plants, i.e. reducing the amount of costly nitrogen fertilizer inputs that farmers need to apply to crops while at the same time maintaining and even improving yields, is an important goal in crop research. As noted by Dr. Hirel, “a more complete understanding of the roles of GS enzymes in nitrogen metabolism and grain yield in maize and other crop plants (including rice, wheat and barley) may lead to improvements in fertilizer usage and crop yield, thus mitigating the detrimental effects of the overuse of fertilizers on the environment“.

The roles of these two GS isoenzymes, products of the Gln1-3 and Gln1-4 genes, were investigated by examining the impact of knock-out mutations on kernel yield. GS gene expression was impaired in the mutants, resulting in reduced levels of GS1 protein and activity. The gln1-4 phenotype displayed reduced kernel size whereas gln1-3 had reduced kernel number, and both phenotypes were evident in the gln1-3 gln1-4 double mutant. Shoot biomass production at maturity was not affected in either the single mutants or double mutants, suggesting that both gene products play a specific role in grain production. Levels of asparagine increased in the leaves of the mutants during grain filling, most likely as a mechanism for circumventing toxic ammonium buildup resulting from abnormally low GS1 activity. Phloem sap analysis revealed that, unlike glutamine, asparagine is not efficiently transported to developing maize kernels, which could account for the reduced kernel production in the mutants. Constitutive overexpression of Gln1-3 in maize leaves resulted in a 30% increase in kernel number relative to wild type, providing further evidence that GS1 plays a major role in kernel yield.

Some of the major cereals, such as maize, sorghum, and sugar cane, exhibit C4 photosynthesis, which enhances the efficiency of photosynthesis at high temperature (most C4 plants originated in tropical climates). In standard C3 photosynthesis (present in rice, wheat, and most temperate crop plants), CO2 entering the leaf is converted to a 3-carbon compound via the C3 pathway, utilizing energy derived from the light reactions of photosynthesis. In plants that have C4 photosynthesis, the C3 pathway enzymes are localized in specialized “bundle sheath” cells which surround the vascular tissue in the interior of the leaf. CO2 entering mesophyll cells at the leaf surface initially is converted to a 4-carbon compound, which is shuttled into the bundle sheath cells and then decarboxylated to release CO¬2. CO2 released into bundle sheath cells then enters the standard C3 pathway. This CO2-concentrating mechanism allows plants in a hot and dry climate to take up CO2 at night and store it, and release it again inside bundle sheath cells during the day, thus solving the problem of how to maintain a high concentration of CO2 inside the leaf during the daylight hours, when stomata often must be kept closed to prevent water loss. Using cytoimmunochemistry and in situ hybridization, Martin et al. found that GS1-3 is present in maize mesophyll cells whereas GS1-4 is specifically localized in the bundle sheath cells. Thus the two GS1 isoenzymes play non-redundant roles with respect to their tissue-specific localization, and the activity of both is required for optimal grain yield. This work illustrates the close coordination between nitrogen and carbon metabolism in photosynthetic tissues, and reveals that nitrogen metabolism plays a critical role in optimizing grain yields.

Nancy Eckardt | EurekAlert!
Further information:
http://www.aspb.org
http://www.plantcell.org

Further reports about: CO2 GS1 Mutant glutamine kernel maize metabolism nitrogen photosynthesis

More articles from Life Sciences:

nachricht Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory

nachricht How cheetahs stay fit and healthy
24.03.2017 | Forschungsverbund Berlin e.V.

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>