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Low sink demand limits photosynthesis under P(i) deficiency
A J Pieters1, M J Paul, D W Lawlor
1Biochemistry and Physiology Department, IACR-Rothamsted, Harpenden, Hertfordshire AL5 2JQ, UK.
Journal of Experimental Botany
|July 4, 2001
Summary
Phosphate deficiency severely limits photosynthesis in plants. Reduced demand for carbon sugars (sink strength) exacerbates this, restricting sucrose export and synthesis, ultimately limiting plant growth.
Area of Science:
- Plant Physiology
- Biochemistry
- Photosynthesis Research
Background:
- Phosphate (P(i)) is crucial for plant energy metabolism and photosynthesis.
- The regulation of photosynthetic carbon assimilation (Pn) by carbon demand (sink strength) is not fully understood, especially under nutrient stress.
Purpose of the Study:
- To investigate how sink demand influences photosynthetic carbon assimilation in phosphate-deficient tobacco plants.
- To determine if sink limitation exacerbates P(i) deficiency effects on photosynthesis.
Main Methods:
- Manipulated phosphate supply and sink strength (via partial leaf darkening) in tobacco plants.
- Measured photosynthetic rates (Pn), P(i) content, metabolites, enzyme activities (Rubisco, phosphoribulokinase), and sucrose export.
Main Results:
- Phosphate withdrawal reduced Pn by 75%, decreasing P(i), ATP, and key photosynthetic intermediates.
- Reduced sink strength (partial darkening) in P(i)-deficient plants delayed photosynthetic decline.
- Partial darkening increased sucrose export and synthesis, suggesting P(i) recycling and sustained Pn.
Conclusions:
- Low sink strength is a primary limitation on photosynthesis in phosphate-deficient plants.
- Sink limitation restricts sucrose export and synthesis, leading to end-product inhibition of photosynthesis.
- Maintaining sink activity can mitigate the negative impacts of phosphate deficiency on plant carbon assimilation.