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Carbon dioxide fixation by detached cereal caryopses.
1Department of Agricultural Biochemistry, School of Agriculture, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JG, Scotland.
Plant Physiology
|June 1, 1988
Summary
Immature barley and wheat caryopses can fix external carbon dioxide (CO2) in light or dark conditions. This CO2 fixation contributes a small but significant amount to the developing grain.
Area of Science:
- Plant Physiology
- Cereal Science
- Biochemistry
Background:
- Immature cereal grains are crucial for yield, but their early carbon assimilation capabilities are not fully understood.
- Investigating CO2 fixation in detached caryopses provides insights into early grain development and carbon metabolism.
Purpose of the Study:
- To determine if immature barley and wheat caryopses can fix external carbon dioxide (CO2).
- To identify the tissues within the caryopsis responsible for CO2 fixation.
- To elucidate the biochemical pathways involved in CO2 assimilation.
Main Methods:
- Incubation of detached immature barley and wheat caryopses with supplied (14)CO2 in light and dark conditions.
- Quantification of (14)C-labeled material distribution within different caryopsis tissues (cross cells, testa, transparent layer, endosperm/embryo).
- Analysis of carboxylating enzyme activities (phosphoenolpyruvate carboxylase, ribulose-1,5-bisphosphate carboxylase-oxygenase) in specific tissues.
Main Results:
- Detached immature caryopses of barley and wheat demonstrated the ability to fix external (14)CO2 in both light and dark.
- The majority of fixed (14)C was localized in the green cross cells and testa, with some in the transparent layer and endosperm/embryo.
- The transparent layer appeared to act as a barrier to CO2 uptake, as more (14)C was recovered when it was removed.
- Significant dark CO2 fixation occurred, and fixation was light-dependent in the chlorophyll-less mutant 'Albino lemma'.
- Enzyme assays suggested phosphoenolpyruvate carboxylase activity in the transparent layer and both phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase-oxygenase in the cross cells.
Conclusions:
- Intact immature cereal caryopses possess the capacity for external CO2 fixation and translocation of assimilated carbon to the endosperm/embryo.
- CO2 fixation by caryopses can contribute a small percentage (approx. 2%) to the final starch content of mature grains.
- Understanding these early carbon assimilation processes is vital for improving cereal crop productivity.