Seeding the Passion

February 14, 2025

A plant sanctuary established in the Weizmann Institute greenhouses holds valuable lessons for survival and helps to instil a love for plant conservation.

When PhD student Gal Raviv thought of creating a sanctuary garden at the Weizmann Institute of Science, what she had in mind was saving endangered plants. But after the October 7 attack on Israel, the recently established garden became for her a refuge of serenity and strength.

“There’s something grounding about plants that keep growing no matter what happens around us. If they can do it, so can we,” she said.

“They represent what the land of Israel can produce and, in these difficult times, they symbolize our own roots in this land.”

Raviv came up with the idea of the garden after hearing a lecture on plant conservation at a conference that Professor Tamir Klein had organized at the institute. Klein, whose Weizmann lab specializes in tree research, was thrilled by her passion for the project.

In late summer of 2023, they set up the garden in Weizmann’s greenhouses, with full backing from Weizmann’s Institute for Environmental Sustainability.

Raviv’s doctoral research, conducted in Professor David Margulies’s lab, is unrelated to plants and focuses on molecular aspects of cancer therapy. Nonetheless, she volunteered to tend the garden, getting crucial help from the greenhouse staff and relying on their expertise.

“When people hear about endangered species, they usually think of a toad whose swamp has dried up, or other animals or birds. But at the basis of any ecosystem are plants: They are the very foundation of our existence,” Raviv said.

“Plant diversity supports diverse insects that in turn provide food for birds and animals. When plant species go extinct, their loss can disrupt the integrity of an entire ecosystem,” added Klein.

Of some 2,300 wild plants found in Israel, more than 400 are in danger of extinction according to the Red Book  of Israel’s Nature and Parks Authority. Plant species that are unique to Israel are particularly threatened: There are about 55 such species, and 35 of them are endangered.

“We have a global responsibility to preserve these plants,” Klein said.

The major threat to plants is habitat loss, which in Israel is especially acute along the Mediterranean. Sand dunes and other parts of the coastal plain are home to an unusually large proportion of wild plant species, yet to the plants’ misfortune, that’s also where humans love to settle. Less than 30 percent of the pristine coastal sands that used to line the Mediterranean in the early 20^th century remained undeveloped by the beginning of the 21st. These sands might disappear altogether if left unprotected.

There are several plant sanctuaries in Israel, but not all have the proper climate to grow coastal plants outdoors, whereas the Weizmann campus, with weather that’s similar to that of the coast, is well suited to this end. Raviv and Klein kept this in mind when compiling a list of plant species for the sanctuary and obtaining seeds from plant gene banks.

Now in its second year, Weizmann’s sanctuary garden holds some 20 endangered plants, a number of which are unique to Israel’s coastal plain; others also grow in neighbouring regions. Most are flowering annuals, but there are also perennials, as well as two species of ancient wheat, genetic relatives of today’s crop varieties. These plants are gradually revealing their preferences and personalities to Raviv and the greenhouse staff, while occasionally serving up challenges and surprises.

Becoming the bee
Soon after the sanctuary garden was established, it became apparent that some plants had pollination issues. Since the greenhouses have no bees or other natural pollinators, some of the plants bloomed but produced no seeds.

“So I became the bee,” Raviv said.

To help some species, she made adjacent flowers ‘kiss’, that is, touch in a way that pollen from one flower could get to the stigma, or ovary system, of another – a process known as self- pollination or cross-pollination, depending on whether the two flowers belong to the same plant or to different ones. She did that, for instance, for Erodium subintegrifolium, or makor hasida tamim in Hebrew, known as stork’s bill in Europe and heron’s bill in North America.

In other species – such as the perennial Salvia eigii, marvat eig in Hebrew, named for the botanist Alexander Eig – the reproductive organs are too deep inside the flower for the kiss method to work. Raviv came up with a creative solution. She collected whisker hairs shed by her three cats and used them to transfer pollen from one flower to the stigma of another.

Luckily for Raviv, however, most plants in the sanctuary garden manage to pollinate by themselves. Some even spread their seeds with no help from the garden staff.

Late bloomers
Silene modesta, tzipornit hofit in Hebrew, from a genus also known as campion or catchfly – an annual plant that grows in sandy soil on the coast and in the western Negev desert – thrived in the sanctuary garden from the start. However, even though it produced lots of flower buds, these seemed to dry up before getting a chance to bloom. Raviv dropped by the garden at all hours of the day but never saw any open flowers.

A plant conservation expert told her to open one of the dried buds to see if it contained seeds. Indeed, it did, which meant that it had bloomed at some point without being caught in the act. So Raviv went to the garden late at night and, sure enough, found the slender Silene in full bloom.

Keeping the bud closed after sunrise is the plant’s clever strategy for reducing water evaporation during the hot hours, while also protecting its flowers from the strong daytime coastal winds.

“I’d missed the bloom because the plant was ‘sleeping’ during the day,” Raviv said.

The discovery prompted Raviv to initiate a research project in which she compares Silene modesta with its gorgeous unendangered relative, Silene palaestina, or tzipornit eretz-israelit. The goal is to uncover the biochemical processes that ensure water conservation in the endangered plant.

In fact, a major goal of plant conservation is to preserve valuable properties that might be lost forever should their carriers disappear. Revealing the mechanisms behind such properties might in the future make it possible to transfer them to other plants to, for example, help them grow in arid conditions or otherwise adapt to the adversities of climate change.

Moving back home
Several of the sanctuary’s plants recently found an additional residence on campus outside the greenhouse, in the Clore Garden of Science, where they are on display as part of a dedicated exhibit. These plants will also form the basis of an environmental educational program that Klein and Raviv are currently developing with the Davidson Institute of Science Education. Both the exhibit and the program are intended to demonstrate the need for conservation and stimulate interest in native flora and in ecology.

“While our first goal in creating a sanctuary garden is conservation, our second goal is this: to raise awareness not only at Weizmann but around us, and to spread the enthusiasm for saving plants from extinction,” Raviv said.