Plant talk: Learning the language
Fall 2016 | Jeremy Heath
The relentless increase in the human population has placed huge demands on worldwide food production. To make matters worse, climate change is creating a hotter and more variable environment, intensifying further the chronic difficulty of growing sufficient food. Although recent projections predicting that the human population will stabilize at around 8 to 10 billion by the year 2100 are encouraging, a more efficient system of food production is still needed if the persisting food shortages are to be addressed. In response to the shortage numerous solutions have been tested in an attempt to increase the yield of food. But although important improvements have been made over the years, the proposed solutions are not straightforward and are often riddled with complications.
One approach that has already been implemented is the manipulation of agricultural systems to achieve an increase in food production beyond what would be naturally possible. The Green Revolution, an ambitious program during the middle of the last century designed to inflate crop yields worldwide, achieved this by increasing fertilization and irrigation, distributing newly developed crop varieties with higher yields, frequently using pesticides, and broadening the use of agricultural machinery. The overall aim of these improvements was to simplify the agricultural system, which would ostensibly make it more manageable. Although the goal was achieved to some extent, the solution was not flawless.
The simplification instigated by the Green Revolution resulted in the drastic reduction or complete loss of essential insects and pollinators, as well as a sudden rise environmental and human health issues. Since analyzing the repercussions of the Green Revolution, scientists and the public have become increasingly aware of the indirect negative impact that large-scale mechanized agriculture has on the environment. As part of the response to this, the perceived and real adverse effects of pesticides on both human health and the environment have led to environmental advocates stepping up the pressure by campaigning for the avoidance or discontinuation of unnecessary pesticides, especially in the developed world.
As important as this is, however, the advances achieved during the Green Revolution cannot be completely abandoned – this would risk thwarting agricultural improvements in underdeveloped countries. Instead, more efficient and environmentally benign agricultural technologies must now be developed, optimized and enforced, which will hopefully allow developing countries to leapfrog the tried-and-tested, and potentially damaging, tools. This is a huge challenge, and one that will involve pursuing many avenues of inquiry while retaining as priorities the increase of food production, safety, nutrition and health.
The circumvention of artificial pesticides might feel like applying a brake to the agricultural improvements already achieved, but have no fear. Plants are remarkable organisms. Despite lacking the same sensory organs possessed by animals, plants are capable of perceiving the same range of sensations: taste, touch, hearing, sight and smell. This sensing ability is utilized by the plants in many ways, including communicating with their own extremities and appendages, as well as with their neighbors. One particularly useful example of plant communication is their ability to initiate a warning system. When under attack by a pest, plants respond with a flood of their own naturally produced pesticides. Impressively, neighboring plants that are not being fed upon can “smell” their neighbor’s pesticidal response and initiate their own defensive chemical production before the pest reaches them.
As another form of protection, some plants also synthesize biochemical rewards and odors to attract beneficial insects such as ants and parasitic wasps. These insects act as the plant’s own personal bodyguards against pests and parasites and also fulfill vital roles as invaluable pollinators.
In terms of developing new solutions to agriculture problems, plant productivity can potentially be increased by harnessing this “chemical ecology” to manipulate plants into producing more food, while concomitantly reducing the use of artificial pesticides. By taking over a plant’s natural defense systems we can take the decision-making away from the plant and switch their defense responses either on or off whenever we decide it is appropriate.
Today, in a world experiencing large fluctuations in climate, protecting plants from pests is not the only challenge of food production. A significantly larger and potentially more crippling problem is climate change, and breeding new varieties of plants that are drought tolerant, for instance, is no longer sufficient. Yields of plant growth and food production must be maintained at a high level, but with the advance of climate change, plants must not lose their crucial ability to adjust to an increasingly hotter and unpredictably variable environment. While plants have a capacity to adapt rapidly to environmental change, something they do innately each growing season, excessive breeding and the narrowing of gene pools to select for crop varieties with specific traits, suitable for precise environments has meant that a lot of this adaptive flexibility has been lost. Finding a solution to this problem is challenging, but here also, harnessing plant communication could play a significant role.
Many of the chemicals that plants use to communicate exist in two very similar states. Some chemicals evaporate from the tissue and are transported in the air, while others flow through the “veins” of the plant, exerting various hormonal effects. These hormones are functionally no different to those found in animals; the hormones act as signaling molecules to control a huge variety of physiological functions. For instance, plant hormones regulate the immune system, growth and reproduction, nutrient allocation and escape mechanisms, to name but a few. Importantly, the airborne and soluble states in which plant hormones exist are interchangeable; a plant hormone can be released as a spray of airborne particles, travel by air to the plant, and upon contact can enter the plant and be converted into the soluble form for fluid transport around the organism. By exploiting this biological phenomenon and treating plants with specific airborne hormones, we hope to control the various functions of the plant whenever we need to. For instance, during the best weeks of the growing season we may want to encourage plants to allocate more of their limited resources to making seeds, which could later be harvested. Correspondingly, during the tough weeks, months, or years we may need to push plants into increasing their pest defenses or water conservation mechanisms to obtain any harvest at all.
This new method of manipulating plant behavior and growth is a potentially powerful agricultural tool that could sidestep many of the existing complications caused by traditional crop breeding, and in this critical age of extreme climate change, helping plants cope with variable environments is more important than ever. My first investigations into these ideas are currently underway, and I hope to report back on my results in a following issue of Verve. Stay tuned.
Jeremy Heath is a postdoctoral fellow in the Department of Entomology and Plant Pathology at NC State University, funded by the National Institute of Food and Agriculture. He received his undergraduate degree from Acadia University in Canada, his Master’s degree from Ohio State University, and his PhD from Wright State University in Ohio.
Heath’s published work can be found in New Phytologist, Ecological Entomology, Arthropod- Plant Interactions, Entomologia Experimentalis et Applicata, Plant Disease, Environmental Entomology, and the Journal of Chemical Ecology. His current research focuses on exploiting the biochemical mechanisms of plant communication to improve worldwide agriculture and food production.