Plant & zo
The science of plants and more
Pollen discrimination
When visiting flowers pollinators bring a wide variety of pollen, coming from a range of plants. From plants of the same species, but also from those that are not related at all. Plants are picky, to prevent spending their energy on the production of unviable offspring. Only pollen that are recognised as compatible are allowed to fertilise a flower. The plant stops all the others. The question is how. Now Chinese and American researchers have found out.
The receptor SRK helps the plant to recognise unwanted pollen. Recognises SRK a protein on the pollen coat, then SRK gets hold of it. At that moment a chain reaction to prevent pollen tube formation gets underway. Preventing fertilisation of the flower.
To analyse what happens the researchers compared how the plant reacted to wanted and unwanted pollen. They noticed that, only in the case of unwanted pollen, that there was lots of reactive oxygen species present. Bot only when SRK was there. Was SRK absent, then there was also no reactive oxygen species in the presence of unwanted pollen, these could go ahead and fertilise the flower.
Nitrate oxide is enabling pollen tube formation
But what about when wanted pollen arrived on the stigma? Recognising these, the researchers noted, was done by a second receptor, FER. In absence of FER the wanted pollen could not form a pollen tube. Making it two receptors that are sorting the pollen, one for wanted and one for the unwanted ones.
The researchers observed that nitrate oxides are produced by the chain reaction that FER initiates. Nitrate oxide then prevents the formation of reactive oxygen species, and as such enabling pollen tube formation. To analyse if the presence of nitrate oxide allows the unwanted pollen access, the researchers treated the plants with GSNO, that is substance that is mimicking nitrate oxide. It turns out, that it allowed unwanted pollen to fertilise the flowers.
Nitrate oxide is enabling pollen tube formation. This knowledge could plant breeders use to cross distantly related species. Something that is often wanted, but in reality, is difficult to do, because plants pollen from distant relatives often not recognise as compatible. But through misleading the plants, breeders can now cross them.
Literature
Huang, J., Yang, L., Yang, L. et al. (2023) Stigma receptors control intraspecies and interspecies barriers in Brassicaceae. Nature 614, 303–308. https://doi.org/10.1038/s41586-022-05640-x
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