AOBPreview originally published online on October 17, 2007
Annals of Botany 2007 100(7):1475-1481; doi:10.1093/aob/mcm253
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Pollination Drop in Juniperus communis: Response to Deposited Material
1 Department of Environmental Sciences "G. Sarfatti", University of Siena, Via P.A. Mattioli 4, 53100 Siena, Italy
2 Department of Nature Protection, Environmental Protection and Technical Services Agency (APAT), Via Curtatone 3, 0085 Roma, Italy
* For correspondence. E-mail pacini{at}unisi.it
Received: 22 May 2007 Returned for revision: 13 July 2007 Accepted: 20 August 2007 Published electronically: 17 October 2007
Background and Aims: The pollination drop is a liquid secretion produced by the ovule and exposed outside the micropyle. In many gymnosperms, pollen lands on the surface of the pollination drop, rehydrates and enters the ovule as the drop retracts. The objective of this work was to study the formation of the pollination drop in Juniperus communis, its carbohydrate composition and the response to deposition of conspecific pollen, foreign pollen and other particulate material, in an attempt to clarify the mechanism of pollination drop retraction.
Methods: Branches with female cones close to pollination drop secretion were collected. On the first day of pollination drop exposure, an eyelash mounted on a wooden stick with paraffin was used to collect pollen or silica gel particles, which were then deposited by contact with the drop. Volume changes in pollination drops were measured by using a stereomicroscope with a micrometer eyepiece 3 h after deposition. The volume of non-pollinated control drops was also recorded. On the first day of secretion, drops were also collected for sugar analysis by high-performance liquid chromatography.
Key Results: The pollination drop persisted for about 12 d if not pollinated, and formed again after removal for up to four consecutive days. After pollination with viable conspecific pollen, the drop retracted quickly and did not form again. Partial withdrawal occurred after deposition of other biological and non-biological material. Fructose was the dominant sugar; glucose was also present but at a much lower percentage.
Conclusions: Sugar analysis confirmed the general trend of fructose dominance in gymnosperm pollination drops. Complete pollination drop withdrawal appears to be triggered by a biochemical mechanism resulting from interaction between pollen and drop constituents. The results of particle deposition suggest the existence of a non-specific, particle-size-dependent mechanism that induces partial pollination drop withdrawal. These results suggest that the non-specific response may decrease the probability of pollen landing on the drop, reducing pollination efficiency.
Key words: Juniperus communis, female cone, gymnosperm reproduction, pollen, pollination drop withdrawal
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  M. Nepi, P. von Aderkas, R. Wagner, S. Mugnaini, A. Coulter, and E. Pacini Nectar and pollination drops: how different are they? Ann. Bot., May 28, 2009; (2009) mcp124v1. [Abstract] [Full Text] [PDF]
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