Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 4, 2000
Publication Date: N/A
Interpretive Summary: Plants are exposed to different light conditions in the course of a day. More energy is available to the plant during the day than during the night. Some of this energy is stored in seeds in the form of chemicals called polysaccharides. Polysaccharides make up the majority of the seeds in cereal crops, so they are agriculturally important. If seeds become limited din their ability to store polysaccharides, yield could be decreased. Because it takes energy to store polysaccharides, we set out to determine how much energy is in the seed in the course of a day, and also how much energy is available at different stages of development. This study indicates that seeds have less energy during the day, probably because it takes so much energy to store polysaccharides. They also have less energy as they mature. We also measured levels of the molecules that are converted into polysaccharides. The levels of these polysaccharide precursors did not change in the same way that energy availability did, so energy availability may not effect the seed's ability to store polysaccharides. The energy availability could affect other processes, however. This information will be important to consider when engineering plants to produce novel compounds in the seed. These novel pathways would best be used at night when the plant has sufficient energy to meet the needs of these novel pathways.
Technical Abstract: Maize endosperm is dependent on source tissues to supply the energy and carbon required for development. This supply varies during the course of each day and also throughout development. We examined the impact of these variations on the metabolism of developing endosperm by determining the energy status of the endosperm throughout the course of a day. The adenylate energy charge decreased as the tissue matured, and exhibited a distinct diurnal pattern, reaching a minimum in the afternoon, when the flux of photosynthate is the highest. The minimum value observed was similar to the adenylate energy charge in tissues under mild stress. As the endosperm matured, the adenylate energy charge decreased steadily. The levels of the polysaccharide precursors ADPG and UDPG did not reflect the daily fluctuations in adenylate energy charge by did exhibit similar long- term behavior in the latter half of development, decreasing steadily after 21 DAP. Similarities in the metabolic patterns of adenylate and uridylate nucleotide levels are discussed in terms of the analogous roles of these compounds starch and cellulose biosynthesis respectively. These data provide insight into the metabolic rhythms occurring during endosperm development, and provide a framework for efforts directed to metabolic engineering.