A lot of our understanding about starch initiation and formation in leaves has come from work on the model plant Arabidopsis thaliana. However, there is still a lot of work to do to understand granule initiation and formation within cereal grains. As cereals are one of the major food crops, and a major source of starch for industrial processes, understanding granule initiation and formation in grains is crucial.
At the John Innes Centre we are using a large mutant collection of wheat to investigate the granule initiation and have already isolated several promising mutants with radically altered starch granules. By investigating these further, we hope to identify key candidates involved in granule initiation in wheat, which may allow the development of new tools to improve crop quality and tailor starch production properties for different uses.
Professor Cathie Martin is to give two special lectures after being elected to be the Janaki Ammal Visiting Professor by the Indian Academy of Sciences for , as an outstanding woman in science.
Professor Cathie Martin has been awarded the prestigious Rank Prize for Nutrition for her globally significant research in making fruit and vegetables more nutritious.
In July, Dippy the Dinosaur arrived in Norwich, taking up residence in the Cathedral and this special Diplodocus has got everyone thinking and talking about evolution. Home Blog How do plants make starch? Carbohydrate chains, however, contain multiple connected simple carbohydrates. Starch contains multiple connected glucose molecules arranged as amylose in linear chains or amylopectin in highly branched chains. The orientation of these chains determines whether the glucose chains form starch for storage or cellulose for plant growth and structural support, says the Polymer Science Learning Center.
A glucose chain with an oxygen and hydrogen pair pointing downward is called an "alpha glucose," while a glucose chain with an oxygen and hydrogen pair pointing outward is called a "beta glucose. When the plant needs energy, a glucose molecule is taken from the starch molecule to be broken down for the stored energy. Cellulose, on the other hand, forms when beta glucose molecules connect into long chains that fit together like blocks to create the structure of the plant's cell walls.
These cellulose chains fit so tightly together that water molecules can't fit between them, making cellulose essentially waterproof. While some glucose remains stored in the leaf as starch grains where it formed, much of the glucose combines with fructose to form sucrose before moving through the plant to provide energy for metabolic processes in cells that don't have access to sunlight. The sucrose moves due to differences in sugar and water concentrations in the cells, states Georgia State University.
Special cells found in the phloem carry the sugar from the leaves to the other, nonphotosynthesizing parts of the plant, including flowers, fruit, seeds, branches and roots. Once the sucrose reaches these new locations, some of the sucrose is used immediately while the excess is converted to starch or cellulose.
Some plants, like sugar cane Saccharum officinarum, U. Department of Agriculture plant hardiness zones 8 through 12; and sugar beets Beta vulgaris, zones 4 through 8 , store higher concentrations of sucrose than do other plants. Sugar cane, for example, contains about 14 percent sucrose, while sugar beets contain about 19 percent sucrose.
Sugar storage in plants, especially in fruit, provides energy for the developing seed. Seeds, however, contain starch that provides nutrition for the new plant until the new plant grows leaves to begin photosynthesis. Under these conditions, sink strength decreases due to impaired sink tissue growth, thus increasing the carbon pool in source tissue which is stored as starch Fredeen et al. Elevated sucrose in the phloem functions as a signal for induction of phosphate starvation-related gene expression, rather than Pi deficiency directly affecting gene expression Hammond and White, In transient starch, only 0.
Nonetheless, potato tubers grown in soil of varied phosphorus concentrations resulted in commensurate changes to the amount of phosphate in starch Jacobsen et al. Unlike leaf starch which accumulates under Pi deficiency, low Pi in potato results in a decrease in tuber yield relative to total plant biomass Fernandes et al. Many studies have shown that altering source or sink metabolism in isolation, as a strategy to increase yield, is often ineffective, perhaps not surprisingly given their interconnection.
Source activity is limiting in many agronomic systems, and increasing photosynthetic rates may contribute to a significant improvement in crop yields. These include efforts to induce C 4 metabolism in rice Sage and Zhu, , engineering Rubisco to promote carboxylase and repress oxygenase activity Carmo-Silva et al. However, there is a need to better understand how to translate any gains in source metabolism most effectively into increased yield. Recent studies suggest that starch produced at the floral base, stem, and siliques transient starch sources which are not often targeted for modification are important for the development and initiation of normal seed set numbers and healthy viable seed Ishimaru et al.
It is possible that engineering localized increases in starch accumulation in these tissues may impact yield more effectively than targeting leaf or seed starch synthesis alone. Starch reserves associated with reproductive tissues support sugar metabolism directly at the point of need, and at critical periods, such as during seed set when the timing of source starch remobilization may be significant for the prevention of seed abortion.
Thus temporal, local increases in carbon availability to developing seeds may also increase yield. The potential for such gains needs, however, to be better understood in the context of interactions with macronutrient availability, particularly nitrogen and phosphorus, in different tissues.
Finally, despite the apparent wealth of information concerning the regulation of starch metabolism, little is known about how the molecular architecture of the granule affects remobilization, and how starch reserves in the cell are sensed. Given the importance of starch reserves in defining yield and productivity via provision of sugars, this should be a major focus of research aimed at crop improvement in the future. Protein—protein interactions among enzymes of starch biosynthesis in high-amylose barley genotypes reveal differential roles of heteromeric enzyme complexes in the synthesis of A and B granules.
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