What You Need to Know About Fruit Acclimation to Heat Stress
Posted by Tara Zimmerman | August 27, 2019
Written by Antoinette Avorgbedor, Intern at Washington State University’s Tree Fruit Research and Extension Center and the Center for Sustaining Agriculture and Natural Resources
Did you know that people indigenous to the hotter equatorial regions have much lower sweat rates than people in cooler regions of the world? Similar to the ability of the human body to adjust to different climatic conditions, plants have evolved various mechanisms to survive extreme weather conditions. Besides long-term evolutionary modifications, plants have been found to develop quick short-term tolerance to extreme environmental conditions. Many different plant species have been reported to develop “memory” to stress, which then helps protect against future adverse conditions. I found this topic pretty interesting. What types of benefits could be derived from a deeper understanding of how plants “acclimate” when experiencing physical stress factors? And could understanding this ability be useful for improving their tolerance to stress, so they can avoid some of the impacts of stress on fruit production?
First, some terminology. “Acclimation” is a general term used to the describe how plants respond to extreme environmental conditions like drought, excessive heat, extremely low temperature or even excessive salinity in soil, leading to long term developmental adjustments (Huner et al. 1998). Researchers have been exploring this topic and have begun to apply their discoveries on crops systems. Beyond that, there is not much research specifically on tree fruit acclimation to various types of stress. But by learning what goes on internally during the acclimation process, we could likely develop strategies to augment desirable traits or encourage growing practices that complement this natural hardening of fruit trees.
As a summer research intern involved in apple tree and fruit physiology, I have worked with Dr. Jessica Waite, who is conducting her postdoctoral research at Washington State University’s Tree Fruit Research and Extension Center. She is working to better understand the process of apple acclimation to heat and light stress. She hopes that discoveries in apple fruit acclimation will be useful in developing predictive tools and horticultural practices to avoid sunburn and decrease crop losses in climates with increasingly high heat and light extremes, such as Washington’s apple-producing region (I discuss current practices in a recent AgClimate.net article). Furthermore, this research can form a basis for understanding the pathways of other fruits’ reaction to environmental stress as well.
Waite’s work is highly relevant because fruit loss due to environmental stress is a major problem for fruit producers (Gunders and Bloom 2017). The challenge with her field of study, however, is that it can be difficult to conduct experiments in an uncontrolled atmosphere, as we experience in the field, that tease apart the roles of different stresses and different genes in influencing sunburn tolerance and fruit yield. When we understand the pathways involved in tree acclimation to stress, it should be possible to fine-tune practices we have in place to favor the development of fruit, especially in regions like the Pacific Northwest which experience high temperatures that can adversely affect apple development. And if we identify the genes that govern acclimation, that could help in the development of new apple varieties with heightened ability of withstand poor environmental conditions, especially as the climate continues to change. Note that there are known genes associated with heat tolerance, thus tracking the response of these genes through experimentation will be essential for understanding apple acclimation to heat stress.
Since Jessica Waite’s goal is to test and observe the dynamics of acquired heat tolerance in apples, her current approach is to subject early-stage developing apples to different kinds of temperature treatments in the early season. The principle behind this “pre-treatment” is to expose the young apples to high temperatures (but not yet sunburn-instigating temperatures) in order to condition the fruit to induce its own defense mechanism against higher temperatures of late summer (which are sunburn-instigating). It is similar to the basic effect of a vaccine on an organism: you expose the organism to a weakened virus, and it gets its defenses ready. So, when it is exposed again, naturally, it does better at fighting the virus. The progress of fruit growth during the season—its physiology or functioning, and its genetics—will then be monitored. The molecular, biochemical, and physiological information derived will then be linked back to the different temperatures that were administered to fruit in order to determine which treatments induced heat stress acclimation and prevented sunburn in the apples later in the season.
I am always excited to see new areas of knowledge being expanded by cutting-edge research. The possibility that apple acclimation to heat stress can be well-understood in arid areas like Eastern Washington could help us develop, in advance, agricultural strategies or models that help growers reduce fruit sunburn as annual temperatures rise and climatic conditions change.
Gunders, Dana, and Jonathan Bloom. Wasted: How America Is Losing Up To 40 Percent of Its Food from Farm to Fork to Landfill. 2nd Ed., Policy Publications, 2017.
Huner, Norman P.A, Öquist Gunnar and Sarhan Fathey. “Energy Balance and Acclimation to Light and Cold.” Trends in Plant Science, vol. 3, no. 6, 1998, pp. 224–230.