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Nectar: properties, floral aspects, and speculations on origin
Erick De la Barrera1, Park S Nobel
1Department of Organismic Biology, Ecology, and Evolution, University of California, Los Angeles, CA 90095-1606, USA.
Trends in Plant Science
|April 23, 2004
Summary
The evolutionary origin of nectar, vital for pollinators, is explored. Two hypotheses suggest nectar arises from
Area of Science:
- Plant Biology
- Evolutionary Biology
- Biochemistry
Background:
- Nectar is essential for pollinator survival and plant reproduction.
- The evolutionary origins of nectar secretion remain largely unexplored.
- Nectar shares similarities with phloem sap, including high sugar concentrations.
Purpose of the Study:
- To investigate the evolutionary origins of nectar.
- To propose novel hypotheses for nectar formation based on plant physiology.
Main Methods:
- Comparative analysis of phloem and nectar composition.
- Physiological reasoning based on plant vascular systems and transpiration.
Main Results:
- Nectar and phloem sap exhibit comparable high solute concentrations (10-30%).
- Phloem, not xylem, supplies water to flowers.
- Phloem sap's primary solute is sucrose; nectar contains sucrose, fructose, and glucose.
Conclusions:
- The 'leaky phloem' hypothesis posits nectar originates from phloem exudation due to internal pressure and tissue vulnerability.
- The 'sugar excretion' hypothesis suggests nectar forms from solute accumulation driven by high flower transpiration rates.