Different Water States and Locations in Pollen Grains

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Research Proposal
DIFFERENT WATER STATES AND LOCATIONS IN POLLEN GRAINS

• Principal investigator, visiting scientist

Ettore Pacini

Nationality: Italian
Position: professor of Botany
Place of work: Dipartimento di Biologia Ambientale, Sezione Botanica, Universitá di Siena, Via P.A. Mattioli 4, 53100 SIENA Italy. Phone –39 0577 232863; Fax –39 0577 232860; E-mail pacini@unisi.it

Partecipating researchers

* Massimo Nepi

Nationality: Italy
Position: Laboratory technician
Place of work: Dipartimento di Biologia Ambientale, Sezione Botanica, Universitá di Siena, Via P.A. Mattioli 4, 53100 SIENA Italy. Phone –39 0577 232867; Fax –39 0577 232860; E-mail nepim@unisi.it

* C.J. Keijzer

Place of work: Laboratory of Experimental Plant Cytology Arboretumlaan 4, 6703 BD WAGENINGEN The Netherlands
* H. Van As
Wageningen NMR Centre and Lab of Molecular Physics
Dreijenlaan 3, 6703 HA WAGENINGEN The Netherlands
• Requested support
- Variable field machine (Maran). Period of measurements: 10 days - NMR imager. Period of measurements: 10 days
• Length of fellowship
one months

• Project description
1. Introduction
Mature pollen of different species are dehydrated to different degrees at dispersal. In most cases, they become very dehydrated, with a water content of 10-20% on average. Pollen of this type is usually small (longitudinal diameter 30-60 µm), prolate and tricolpate or tricolporate. Less frequently pollen are only slightly dehydrated with a water content above 50%. This type of pollen is usually large, spherical and uni- or polyporate. The mean life of a pollen grain is strongly influenced by its water content at dispersal: the lower the water content, the longer the mean life. Very dehydrated pollen usually has a high cytoplasmic mono-, oligo- and polysaccharide content and no starch, unlike only slightly dehydrated pollen which contains starch and variable quantities of cytoplasmic mono-, oligo- and polysaccharides. The high content of osmotically active molecules (such as mono and oligosaccharides) reduces the risk of water loss, and in the case of sucrose has been shown to protect the cell membrane. Hence the mean life of pollen also depends on the types of reserve carbohydrates it contains. In addition to physiological and cytological factors, pollen viability is also influenced by environmental factors such as temperature and relative humidity. In a previous research water state and location inside the pollen grain was investigated in Cucurbita pepo and Petunia by mean of NMR and Cryo-Sem. Cucurbita pepo (Cucurbitaceae) has large spherical pollen with a water content of approximately 43% of its fresh weight; the polysaccharide reserve is starch, traces of mono-, olygo- and polysaccharides are also present. Petunia hybrida (Solanaceae) has small, very dehydrated pollen with a water content of 10% of its fresh weight at dispersal; reserves consist of cytoplasmic mono-, olygo- and polysaccharides, starch is absent. NMR measurements and data analysis revealed that water is present in different states inside the two types of pollen. The largest water component is in a glassy state (T2 around 100 µs) in Petunia pollen. The glassy state is never reached in Cucurbita even at a water content comparable to that of Petunia pollen. In Cucurbita pollen the largest water component has a T2 value of 6.5 ms. Cryo-Sem observations demonstrated that water containing vesicle like structures are present both in Cucurbita and Petunia. In Cucurbita pollen these structures are no more detectable after 90 min. of exposure to RH 30%, instead in Petunia are present also after 360 min. of exposure to the same RH.

2. Research aims
The research is performed in order to clarify some of the features pointed out in the previous study. In particular we intend: 1) to study the glassy state of water inside the pollen of Petunia...
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