Dynamics of starch breakdown during rice development and drought stress
2007
Estenor, L. | Liao, R. Q. | Oane, R. H. | Bennett, J., International Rice Research Inst., Los Banos, Laguna (Philippines). Plant Molecular Biology, Plant Breeding, Genetics and Biotechnology Div.
Starch is a major form of carbon storage in plants such as rice and the major source of calories for human nutrition. Short-term storage takes place in the chloroplast of leaf blades during the day and is followed by starch breakdown at night, longer-term storage occurs in the leaf sheaths, stem internodes and other tissues, such as the ovary and the pollen, and terminal storage occurs in the endosperm, which provides carbon for seed germination or human nutrition. Several distinct enzymes catalyze different types of starch breakdown and there are multiple genes encoding most of those enzymes. In addition to starch breakdown occurring during plant development, mobilization of starch reserves is important for surviving and recovering from stresses such as drought. However, it is not clear which genes are responsible for the many developmental and stress-related instances of starch breakdown. Here the authors examines the dynamics of starch mobilization in response to developmental events and drought stress at the reproductive stage and compare them with transcript levels for genes of the Alpha-amylase. Beta-amylase and other enzyme families implicated in starch breakdown. The authors measure drought stress in terms of the relative water content of the flag leaf, they use 1k1 staining for microscopic localization of starch, and the anthrone method for chemical assays of starch and sugars, and they assay transcript with gene-specific reverse transcription-polymerase chain reaction(RT-PCR). The most rapid breakdown of starch occurs in pollen after they land on the stigma and is associated with the expression of two Alpha-amylase genes. The most dynamic changes in starch level in response to drought stress and re-watering occur at the base of leaf sheaths. The authors conclude that drought-arrest of peduncle elongation is more likely due to impediments in sucrose transport than in starch mobilization.
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