AsianScientist (Nov. 21, 2016) – In a study published in Science Advances, researchers from Nagoya University have shown that contents of the pollen tubes can increase the size of seeds even without fertilization. Their findings could be useful in developing crops that can produce seeds in unfavorable environmental conditions were fertilization does not readily occur.
In mice, the seminal fluid is essential for fertilization, as mice that lack a particular seminal fluid protein are unable to induce fertilization. The contents of the pollen tube, which grows inside the plant pistil to deliver sperm cells to the egg cells in the ovule, are analogous to seminal fluid but relatively less well understood.
In the present study led by Professor Tetsuya Higashiyama of Nagoya University’s Institute of Transformative Bio-Molecules (ITbM), researchers have found that release of pollen tube contents (PTC) in the ovule leads to cell division, ovule enlargement and seed coat formation, even in the absence of sperm.
“The most difficult part of this research was to make sure that fertilization does not occur in order to identify the function of PTCs,” said study first author Dr. Ryushiro Kasahara.
To do this, Kasahara and colleagues conducted hybridization experiments using mutants of the model plant Arabidopsis thaliana that can release PTCs into the ovule even when fertilization does not occur. They found that ovules that had accepted PTCs but were not fertilized did not show gene expression of the embryo and the endosperm but showed expression of genes that induce cell expansion and division, as well as seed coat formation.
“This new observation overturns the common principle that ovules need to fertilize for enlargement to occur,” Kasahara added.
By using mutant A. thaliana strains where pollen tubes burst at a certain rate to release PTCs, Kasahara and team were able to compare the ratio of ovules that increased in size without fertilization to ovules where the pollen tube ruptures to release PTCs.
“We were delighted to see that the percentage of ovules that become enlarged and the percentage of ovules accepting PTCs showed a good match,” said Kasahara. “This shows evidence that PTCs contribute to ovule enlargement.”
The researchers have named this new phenomenon POEM, which stands for “pollen tube dependent ovule enlargement morphology.”
“We are currently interested in what kind of molecules in the PTCs are responsible for triggering POEM,” Kasahara said. “We hope we can find key molecules, which can be constantly expressed in ovules so that the endosperm can be formed without fertilization. This is expected to be highly useful for producing crops in various climates, where fertilization does not readily occur.”
Source: Nagoya University; Photo: Pixabay.
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