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Parasitic Plant Waits for Host’s Signal Before Flowering

Dodders grow into tangled masses of leafless tendrils also called wizard’s net and strangleweed

Parasitic dodders use outgrowths called haustoria to leech water and nutrients from their host plants. (Jingxiong Zhang, Kunming Institute of Botany, Chinese Academy of Sciences, China)
smithsonianmag.com

Parasitic dodders are paradoxical plants. Most plants rely on their leaves to recognize the perfect time to flower. Dodders lack leaves—and roots, for that matter—but they still flower right on schedule.

Previous work has shown that when dodders siphon off their host’s nutrients and water, they also pick up the host’s chemical signals. A study published last month in the Proceedings of the National Academy of Sciences presents evidence that when the host’s leaves send out the signal that it’s time to flower, the dodder understands that signal and creates flowers, too, Ariana Remmel reports for Chemical and Engineering News.

There are 145 different species of dodders. Each dodder begins its life as a seed that sprouts one anchoring root into the ground and then sends another tendril into the air. The tendril grows outward until it reaches a larger plant, and then the dodder latches onto it with additional appendages called haustoria. Once the dodder has a tight grip on its host, the anchoring root withers away.

The dodder uses its haustoria, instead of leaves or roots, to leech water and nutrients out of its host. And it keeps growing larger, throwing out more spindly vines that grab on to more plants and more branches. Eventually a dodder looks like a tangled mess of vines that earn the parasite its more colorful names, like wizard’s net and strangleweed, per a statement.

Botanists had wondered about the dodder’s strategy for timing reproduction. If it waits too long, the host plant could die before the dodder manages to produce its flowers and seeds, Jonathan Lambert writes for Science News. If the dodder produces flowers too early in the season, it won’t produce as many seeds as dodders that waited.

But by paying attention to the host plant’s chemical network, the dodder can sense the perfect time to strike. The new research even suggests that dodders’ own flowering signals are disabled, forcing them to rely on the host plant to know when to reproduce.

“The dodder plant gave up its own flowering mechanism in order to gain ecological benefit,” syncing its reproductive timing up with its host in order to maximize its growth time, Jianqiang Wu, a botanist at the Chinese Academy of Sciences’ Kunming Institute of Botany tells Chemical and Engineering News.

To build their case that dodders mooch off of their hosts’ flowering signals, the researchers first attached one species of dodder to three different hosts. The hosts flowered at three different times, but each parasitic partner flowered in sync with its own host.

Next, the team created genetically modified hosts that don’t create a flowering signal, and paired them with dodders. Without the host’s flowering signal, neither the host nor the dodder flowered. Last, the researchers created a green fluorescent version of the flowering signal chemical, which provided visual evidence that dodder plant tissues can absorb the chemical and direct it to their flowering mechanisms.

“Dodder and host plant synchronization has never been so clearly shown as in this paper,” plant pathologist James Westwood of Virginia Tech tells Science News, but he adds that more research is necessary because “biology is rarely that simple.”

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