Regulatory mechanisms that control photosynthetic responses to developmental processes in Xanthium strumarium

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Title: Regulatory mechanisms that control photosynthetic responses to developmental processes in Xanthium strumarium
Author: Gordon, Elizabeth P
Abstract: Photosynthetic adjustments to developmental changes (e .g . flowering , fruiting and senescence ) are frequently attributed to a source :sink feedback mechanism . This mechanism may be driven by changes in leaf soluble sugar content that in turn induce changes in the activity of key photosynthetic enzymes . Quantifying plant response and enzyme function in terms of age and nutrient supply can help define the relationship between growth and physiology , as well as elucidating the interactions of plant function from the cellular to whole plant level . This study used the model plant Xanthium strumarium to explore these functional interactions through two separate nutrient experiments focusing on nitrogen and phosphorus before , during , and a change in photoperiod , which was used to transition the plants from the vegetative to the reproductive growth phase . Parameters examined were biomass allocation and amount , elemental content (nitrogen and phosphorus ) , photosynthetic rate and capacity (Asat , Amax , Vcmax , and Jmax ) , chlorophyll content , total nonstructural carbohydrate amount (sugar , starch , and total TNC ) , and the enzyme activities of Rubisco , invertase , and sucrose phosphate synthase . Results indicated that changes in nutrient availability negatively affected enzyme activity and source :sink relationships , and specifically demonstrated that during conditions of nutrient limitation , sink activity was reduced due to limited source activity . Results also indicated that increasing age and changing developmental stage exacerbated nutrient limitation effects as well as causing effects that were independent of nutrient limitation . In both experiments , increasing plant age decreased photosynthetic rate and capacity as well as chlorophyll content and enzyme activity while it increased TNC amounts and overall biomass as well as biomass allocation . Increasing plant age increased root TNC content as well as invertase activity and root allocation . Our results indicate that decreasing nutrient supply and increasing plant age are linked processes that have feedback effects not only on overall plant function , but also on each other .
URI: http : / /hdl .handle .net /2346 /8788
Date: 2008-05

Citation

Regulatory mechanisms that control photosynthetic responses to developmental processes in Xanthium strumarium. Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /8788 .

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