Just like any other organism, plants can get stressed — think heat or drought.
When they’re stressed, plants might not grow as large or produce as much, so many scientists have tried genetically modifying plants to be more resilient.
But increasing stress tolerance often results in plants that produce less. It’s a difficult conundrum.
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I have been studying how the plant hormone ethylene regulates growth and stress responses in plants. In a study published in July, my lab made an unexpected and exciting observation. We found that when seeds are germinating in darkness, as they usually are underground, adding ethylene can increase both their growth and stress tolerance.
My lab focuses on how plants and bacteria sense ethylene and on how it interacts with other hormone pathways to regulate plant development. While conducting this research, my group made an accidental discovery.
We’d been running an experiment where we had seeds germinating in a dark room. We had exposed the seeds to ethylene gas for several days to see what effect it might have. We then removed the ethylene.
Normally, this is where the experiment would have ended. But after gathering data on these seedlings, we transferred them to a light cart. This is not something we usually do, but we wanted to grow the plants to adulthood so we could get seeds for future experiments.
Several days after placing the seedlings under light, some lab members made the unexpected and startling observation that the plants briefly gassed with ethylene were much larger. They had larger leaves as well as longer and more complex root systems than plants that had not been exposed to ethylene. These plants continued growing at a faster rate throughout their lifetime.
We tested the effects of short-term ethylene treatment on germinating tomato, cucumber, wheat and arugula seeds. All grew bigger.
But what made this observation unusual and exciting is that the brief ethylene treatment also increased tolerance to various stresses such as salt stress, high temperature and low oxygen conditions.
Long-term effects on growth and stress tolerance from brief exposure to a stimulus are often called priming effects. You can think of this much like priming a pump, where the priming helps get the pump started easier and sooner.
Since that first experiment, my lab group has tried to figure out what mechanisms allow for these ethylene-exposed plants to grow larger and tolerate more stress. We’ve found a few potential explanations.
One is that ethylene priming increases photosynthesis, the process plants use to make sugars from light.
Correlating with the increase in photosynthesis is a large increase in carbohydrate levels throughout the plant. This includes large increases in starch, which is the energy storage molecule in plants, and two sugars, sucrose and glucose, that provide quick energy.
More of these molecules in the plant has been linked to increased growth and a better ability to withstand stressful conditions.
Our study shows that environmental conditions during germination can have profound and long-lasting effects on plants that could increase both their size and their stress tolerance at the same time.
Understanding the mechanisms for this is more important than ever and could help improve crop production to feed the world’s population.
– Brad Binder is professor of biochemistry and cellular and molecular biology at the University of Tennessee. This is an excerpt of a column that first appeared as part of Reuters’ the Conversation.
