- Title
- Regulation of pollen germination and pollen tube elongation and response to heat stress by cell wall invertase
- Creator
- Astija
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The pollen tube is a single haploid cell carrying two sperm to fertilize the egg and the central cell of the female gametophyte to form the endosperm and embryo, respectively. As such, pollen grain germination and pollen tube elongation are critical reproductive processes for successful seed and fruit production in most crop species. These processes are underpinned by significant changes in metabolism, cytoskeletal rearrangement and gene expression and are highly sensitive to abiotic stress such as heat. Pollen grains and pollen tubes are symplasmically isolated from surrounding style tisssues. Thus, sugars required for their germination and elongation respectively must come from the cell wall space shared by these cells and the adjacent transmitting tissues of the styles, once pre-stored starch is depleted in the pollen grain. Emerging evidence indicates that cell wall invertase (CWIN) hydrolysing sucrose in the apoplasm may play a major role in pollen grain germination and pollen tube elongation. However, there is a lack of direct evidence of whether and how genetically altering CWIN catalytic activity may influence pollen growth. To address this important question in plant reproductive biology, we investigated the potential roles of CWIN on the regulation of pollen grain germination and pollen tube elongation both in vitro (in a culture medium) and in vivo (in pistilous tissues) under normal and heat stress conditions. By using two sets of transgenic tomato plants with their CWIN activity either down- or up- regulated (CWIN-RNAi and cell wall invertase inhibitor ((INH)-RNAi), we obtained compelling evidence that pollen grain germination and pollen tube elongation are positively regulated by CWIN-mediated sucrose metabolism. Down regulation of CWIN reduced pollen tube growth whereas up regulation of CWIN increased the process and conferred heat tolerance. The latter was shown by improved pollen grain germination percentage and pollen tube elongation under heat stress when CWIN activity was genetically elevated. Our biochemical and gene expression studies revealed that the observed reduced or increased pollen grain germination and pollen tube elongation is due to decreased or enhanced CWIN activity which may regulate: (1) Sucrose hydrolysis in the extracellular space, thereby affecting cellular glucose and fructose concentrations; (2) The expression of hexose transporters (HT1-3) and H⁺ATPase, thereby likely enhancing energy-dependent hexose uptake by germinating pollen grains and elongating pollen tubes; (3) The expression of sucrose phosphate synthetase (SPS) and sucrose synthase (SUS3), which allows sucrose to be resynthesized in the cytoplasm for SUS to cleave into fructose and UDP glucose. The latter product could be utilized for cellulose and callose synthesis, a key feature of pollen tube elongation. This is indicated by the up regulated expression of callose synthase (GSL1) in the CWIN-elevated pollen tubes and (4) The expressions of heat shock genes directly responsible for protecting against cellular damage from heat stress (HSP17.4-CII, HSP17.6-CII). These novel findings suggest that CWIN positively regulates pollen grain germination and pollen tube elongation by controlling sucrose hydrolysis and providing hexoses as metabolites and signals to modulate expression of some major genes involved in sugar metabolism and heat stress responses under both normal and heat stress conditions.
- Subject
- cell wall invertase; pollen germination; pollen tube elongation
- Identifier
- http://hdl.handle.net/1959.13/1309756
- Identifier
- uon:21941
- Rights
- Copyright 2015 Astija
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Abstract | 65 KB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Thesis | 3 MB | Adobe Acrobat PDF | View Details Download |