SIGNIFICANCE OF FLUENCE-RESPONSE DATA IN PHYTOCHROME-INITIATED SEED GERMINATION |
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Authors: | Stephen O Duke |
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Institution: | Southern Weed Science Laboratory*, Agricultural Research Service, U.S. Department of Agriculture, Stoneville, MS 38776, U.S.A. |
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Abstract: | Abstract. A model was developed to describe changes in fluence-response kinetics in terms of total phytochrome level (Ptot), level of the factor X interacting with active phytochrome (Pfr), PfrX equilibrium constant, seed sensitivity to Pfr-X interaction, and variation in phytochrome sensitivity within the seed population. Under conditions of stable X levels and stable population variation, the model predicted that a change in any of the other components will result in a parallel fluence-response curve on a probit-logarithmic plot. The linearity of the subsaturation plot is dependent on the ratio of Ptot to X concentrations. The model showed that changes in threshold response fluences can result from many causes other than changes in total phytochrome Ptot>]. Changes in response-saturating fluences when maximal germination is less than 100% are predicted to be due to limiting levels of X. Changes in slope of fluence-response curves can be explained by changes in seed population variation by this model. Rumex crispus L. fluence-response data for germination is best explained by this model in terms of neither changes in Ptot nor X levels altering kinetics. |
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