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Exploring fig trees’ chemical tricks and reviving ancient date palms

by Katherine Bourzac
October 10, 2020 | A version of this story appeared in Volume 98, Issue 39


Houseplants are brilliant chemists

A photo of a ficus leaf.
Credit: Katherine Bourzac/C&EN
COVID-19 companion: New growth on a well-loved Ficus elastica Tineke

If you’re like some of the Newscripts gang, you might have brightened your home with some new houseplants—or, let’s face it, several of them—during the COVID-19 lockdowns. Some of the most popular, in the genus Ficus, have beautiful, delicate leaves, and watching them unfurl and grow to full size is fascinating.

Scientists are fascinated by ficus too. These plants, which include rubber plants and fig trees, like the fiddle-leaf fig, are well known for their mutual relationship with wasp pollinators. They’re also some of the plant kingdom’s fastest photosynthesizers.

After about 8 years of work, a team of biologists and optical physicists at the Weizmann Institute of Science now has evidence tying ficus’ photosynthetic prowess to some serious chemical flair. The plants’ leaves are dotted with microscopic amorphous calcium carbonate crystals called cystoliths. Weizmann structural biologist Steve Weiner tells Newscripts in an email that these crystals are “a most unusual, highly unstable mineral that is somehow stable in the leaf.” Weiner says these structures were probably first identified in the 19th century, but until recently, their function was unknown.

Weiner’s previous research showed that cystoliths scatter light and might help illuminate tissue deep within the leaf to boost plant productivity. His group worked with Weizmann botanist Tamir Klein to test this idea. Comparing six species with different distributions of cystoliths, Klein’s group assessed the plants’ photosynthetic rates by measuring carbon dioxide uptake and probing the leaves with micro–computed tomography, “which is like a 3-D X-ray, as used in hospitals,” he explains.

This work, which is not yet peer reviewed, shows that cystoliths do indeed boost photosynthetic rates (bioRxiv 2020, DOI: 10.1101/2020.04.08.030999). Weiner says it might be possible to bioengineer crop plants with ficus cystolith genes to boost their productivity. Meanwhile, he’s enjoying the company of a Ficus microcarpa, given to him by Assaf Gal, the grad student who initiated this research.


Reviving an ancient treat

Fig trees are native to Israel—and so are date palms. Since 2005, the Newscripts crew has been drooling over a project to revive the region’s ancient Judaean dates, which are praised in ancient texts but have been replaced by different varieties and were lost for centuries.

This is a photo of date fruits on a date palm.
Credit: Elaine Solowey
Ancient harvest: Judaean dates were made by reviving seeds about 2,000 years old.

Just in time for Rosh Hashanah (the Jewish New Year), a team of scientists picked the first crop of fruits made by breeding two trees sprouted from 2,000-year-old seeds found on an archaeological dig in the 1970s. The scientists, including Elaine Solowey, who directs the Center for Sustainable Agriculture at the Arava Institute for Environmental Studies in Kibbutz Ketura, Israel, have been working to revive ancient dates for the past 15 years.

Reached via email, Solowey explains that she used a bottle warmer to rehydrate the ancient seeds and treated them with gibberellic acid and an enzymatic fertilizer. The first tree to sprout, called Methuselah, was male. The scientists bred that tree with a modern date and made fruits. But to know the true taste of Judaean dates, they needed to revive a female seed and breed the resulting tree with Methuselah. Among the next group of revived trees was Hannah, a female. The New York Times reports that Solowey “painstakingly” gathered pollen from Methuselah and applied it to Hannah’s flowers (Sci. Adv. 2020, DOI: 10.1126/sciadv.aax0384).

The resulting dates, Solowey tells Newscripts, were “big, with a honey aftertaste.”

“I am very excited and thrilled that I was able to revive the Judaean date after so much ancient destruction and neglect,” Solowey says. So far, only a few people have been able to taste the fruits. But they may become more widely available thanks to Solowey’s work. “We may make a genetic line from Hannah through tissue culture,” she says. “She also has four offshoots.”

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