Pollen is produced by trees, grasses, and weeds, and it's a way for plants to reproduce by disseminating their genetic material. Male pollen grains are often carried by the wind or insects, and when they land on the female part of a plant, fertilization happens. The male pollen grain can become several thousand times longer as it seeks a female egg cell to transfer its sperm cells to. Researchers have now learned more about the growth of these pollen tubes, which may teach us more about other aspects of biology like growth in human neurons. They determined that the extension of this plant erection is driven by a proton pump-powered electrical circuit. The findings have been reported in Nature Communications.
"We were taken aback by how extremely advanced the plant's fertilization mechanism really is. From textbooks, we understand that pollen tubes grow and push forth by continually building additional floors upon the cell skeleton, like a growing scaffold. However, very little was known about the underlying mechanisms of this enormous growth. Our work has made the world a bit wiser," said Professor Michael Broberg Palmgren from the Department of Plant and Environmental Sciences.
The pollen tube can 'sniff out' an egg cell that lies inside the female receptor to create a seed. The probing of the tube is called tip growth, where continuous extension occurs. In a weed called the thale cress, it reached about three millimeters a day. "The pollen tube is not a rigid tube. It is dynamic and can redirect as it searches for an egg," explained Michael Broberg Palmgren.
In this study, the researchers altered a group of plant genes called AHA, which generate the proton pumps. These structures control a balance of acids and bases to generate voltage across the membrane of cells. The scientists turned various combinations of the genes off and studied the outcome.
"In experiments, we were able to see that the 'mutant pollen tubes,' in which we had switched off the genes, were dramatically delayed in their growth and had difficulty finding their way," noted Professor Palmgren.
In this type of basic research, we may be able to predict what it will tell us about other aspects of biology in the future. But, the mechanisms underlying tip growth may provide insight into the growth of nerves, suggested the investigators.
"Very little is known about what controls nerve growth—which is hugely important for recovery from nerve or brain damage. Here, our result might prove useful for better understanding the process of tip growth, which is how the human nervous system grows as well," said Palmgren. "The more we investigate, the more advanced plants turn out to be. There are no arguments to suggest that plants are any less than us humans."