Kolkata, West Bengal
"The grasshopper hopped around and landed on the leaf of the plant. Instantly, the leaf folded from the middle, trapping the insect tightly. I watched in astonishment as the interlocking 'teeth' created a cage from which there was no escape for the hapless grasshopper. I had never seen such a horrifying trap in nature before."
This chilling description comes from the renowned filmmaker, author, and artist Satyajit Ray. The above lines are an excerpt from his story Septopus-er Khidde (The Hunger of the Septopus), a science fiction tale about how carnivorous plants became predatory. In the story, a character wonders, "What guarantees that the insect will land on that particular leaf?"
There is a guarantee. Setting aside fiction, let's delve into science. The first question: How does the grasshopper leap onto the plant's leaf, even in darkness? This long-unsolved mystery has been unraveled by science.
Our discussion centers on a particular type of plant—carnivorous plants. These plants have unique adaptations, consuming insects to survive. The essential nutrient they obtain from their prey is nitrogen, extracted from the insects' bodies. But how do they capture insects? Plants can’t chase after their prey. So how do they do it?
Carnivorous plants employ various methods to trap insects. Some emit light to lure their prey. Scientists have proven that certain species of carnivorous plants emit a bright blue glow. Attracted by this light, insects land on the plants' leaves.
There are many types of carnivorous plants, including Sundews (Drosera), Venus Flytraps, Butterworts (Pinguicula), Bladderworts (Utricularia), and Pitcher Plants (Nepenthes).
Pitcher Plants (Nepenthes) are shaped like pitchers. The rim of the pitcher (Peristome) acts as a trap, emitting a bluish glow (Fig. 1). This glow is ultraviolet radiation at a specific wavelength (366 nm). While invisible to the human eye, it is detected by insects even in complete darkness. Once an insect is drawn to the light and lands on the rim, there’s no escape from the plant’s deadly trap.
Inside the Pitcher: The Inescapable Trap
Once an insect is trapped inside the pitcher, it suffocates, leading to its death. The plant then digests the insect, deriving essential nutrients from it.
The process that makes the pitcher’s rim glow is called fluorescence. Fluorescence is a type of light emission where the radiated light has lower energy than the incident light.
Fluorescence is found everywhere—in water, land, and even the sky. Many aquatic creatures and fish emit fluorescent light. Certain plants also possess fluorescent compounds in their flowers and leaves. Even diamonds can fluoresce in the dark, and the stars and sun exhibit fluorescence in space.
In everyday life, we see fluorescence in traffic signals, safety vests, modern communication systems, and counterfeit currency detection. When exposed to UV light, specific marks on genuine currency notes fluoresce, helping to differentiate them from counterfeits.
The Sticky Trap: Sundews
Returning to carnivorous plants, some use sticky substances to trap insects. For example, sundews (Drosera sp.), a genus of about 200 species, are commonly found worldwide, including in India. Sundews have sticky substances coating their flowers and leaves that trap insects upon contact, rendering escape impossible.
This natural adhesive is a subject of extensive research. Scientists have discovered that the adhesive consists of polysaccharides with calcium and magnesium ions, and it is 96% water.
Potential Applications of Sundew Adhesive
Researchers are exploring potential applications for this natural adhesive, particularly in cell culture processes. Cell culture involves growing animal, human, or microbial cells in laboratory conditions, often for drug development or biological research. The cells are grown in petri dishes, which are plastic or glass plates invented by German scientist Julius Richard Petri. These dishes are coated with substances like collagen or fibronectin to help cells adhere to the surface.
Could the adhesive from carnivorous plants like sundews be a viable alternative for cell culture applications? Scientists are optimistic, as natural adhesives could reduce production costs significantly.
Reality vs. Fiction
Unlike their portrayal in science fiction, carnivorous plants pose no threat to humans or large animals. Their diet is restricted to small insects, whose proteins provide the plants with necessary nutrients. These remarkable plants are fascinating examples of nature's ingenuity and hold promise for various scientific advancements.
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