The talking trees: unraveling the secret language of plants

Do we know about the secret language of plants?

Introduction

In the quest for comfort, we always listen to our instincts whenever we face less-than-ideal situations like scorching heatwaves, freezing cold snaps, torrential downpours, or those pesky swarms of biting insects. We are hardwired to find solutions to stay cozy and protected e.g., when the sun blazes, we turn on that trusty fan, and when the rain pours, we pop open an umbrella. And let us not forget our secret weapon against pesky bugs – a liberal slathering of insect repellent to keep those unwanted bites at bay! It is all about making the best of any situation and ensuring our comfort no matter what problems come on our way. But have we ever thought how plants would deal with such problems in their daily life being alive and sessile in nature? Talking of unfavorable conditions for plants, they too encounter extreme heat, cold, rain, pest attack, and need to compete with neighboring plants for food and nutrition. Plants, like us, may adapt to challenging conditions by making use of resources in their immediate environment. It is fascinating that through secret language of plants can communicate with their surrounding environment and with each other as these green creatures have their own language. Interestingly, such language is not based on spoken or audible medium but through the science of chemical signaling. In this article, we shall delve into the fascinating realm of plant communication to see how these organisms interact with one another and other groups of organisms to collaborate or compete for their survival.

Ways of plant communication

      With the advancement in science & technology, scientists around the world have successfully decoded the secret language which plants use to communicate with their surroundings. Plants use specific chemical languages in the form of “odors” for communication, which resembles to instant “messaging” or “calling out for help” in plants. These odors are commonly known as volatile organic compounds (VOCs) which can travel far as gasses. Plants produce a variety of VOCs to communicate with neighboring plants, microbes, pollinators, seed dispersers, herbivores, and their natural enemies, as well as to guard against abiotic stressors such as extreme light and temperature. For example, when a caterpillar feeds on plant leaves, the plant in response releases Methyl jasmomate (MeJA) as major VOCs that serve as a distress signal. Upon ‘smelling’ the threat (MeJA), nearby plants also prepare themselves against upcoming attack through a process known as “priming” and subsequently release VOCs to repel the intruders. It is somewhat similar to imagine someone using a very strong unpleasant perfume. Similarly, when plants are attacked by pathogens and certain herbivores, particularly aphids, they secrete Methyl salicylate, which is chemically similar to the human painkiller, aspirin. These chemical communications can be seen either in between the same (conspecifics) or different species (heterospecifics) of plants which experience any danger approaching to them.

Allelopathy

        Plants can interact with one another not only in the aboveground, but they are also actively involved in belowground communication. They produce “allelochemicals” in the rhizosphere (area around the roots in soil) to control their neighbors to avoid competition for resources or fight against a pathogen by a process called “allelopathy”. Allelopathy can be defined as a biological phenomenon where plants produce one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. For example, plants like sorghum (Jowar) and wheat produces ‘sorgoleone’ and ‘benzoxazinoids’, respectively from their root hairs, which does not allow unwanted plants viz., weeds to grow near them. Similar results are seen in rice plants, which produces an allelochemical called “momilactone” to suppress competing weeds and fight fungal infection. According to research, typical paddy weeds like barnyard grass may grow more successfully when they are near rice plants that cannot make momilactone, as opposed to when they are close to rice plants that can produce momilactone. This allelochemical disrupts essential biochemical processes in barnyard grasses, interfering with cell metabolism, enzymes, and hormone signaling, all of which are required for germination and growth (fig: 1&2). By this strategy, these crop plants can obtain more nutrition for themselves from the soil. Recent research efforts have focused on identifying and isolating these allelochemicals so that they can be used commercially as alternatives to artificial pesticides and herbicides in the agricultural fields.

Figure 2: Normal germination and growth of a plant

Figure 3: Rice plant secrets momilactone in its vicinity to inhibit growth and germination of neighboring plants/seeds

         So next time when you are out in a garden or a field, pause for a second. If you happen to see any caterpillar munching its snacks on leaves, pay close attention to what a plant must be trying to tell. You may also sniff the chewed leaves and observe whether they have a distinct aroma from the unchewed ones. Or try planting a seedling next to another plant to see whether they get along or if their roots clash, and one plant will emerge victorious. This way, you too will be able to decode their language and communicate with them.

 Allelochemicals

         Those chemical compounds generated by plants that influence the growth and behavior of other organisms, especially other competing plants. These chemicals are essential in plant interactions throughout ecosystems, regulating competition, defense, and plant communication. Allelochemicals generated by plants disrupt many cellular processes of neighboring plants, preventing germination and development. Allelochemicals released into the environment disrupt neighboring plants’ biological processes, such as cell division, nutrient uptake, photosynthesis, enzyme activity, and hormone signaling. Most allelochemicals inhibit seed germination of the other plants. When seeds receive water from the soil, the germination process begins. This water intake causes metabolic changes inside the seed, activating enzymes that break down stored nutrients to enable early development. If allelochemicals are present in the surrounding soil or environment, they may interact with the seed and prevent it from imbibing.  Some well-studied examples of allelochemicals generated by various plants include: Cinnamic acid, which is released by sunflower roots, inhibits the germination and growth of nearby plants. Our early knowledge on allelopathy was based on juglone, which is released by black walnut trees. It interferes with processes such as photosynthesis and nutrient uptake in susceptible plants. Similarly, catechin, which is released by loblolly pine needles, can inhibit seed germination and early seedling growth of understory plants.