As climate change continues to promote extreme weather conditions across the globe, it becomes necessary to examine what will happen to plants under these conditions, specifically under high temperatures. Under high temperatures and an excess of greenhouse gases accumulation, plants will have to devise new strategies to cope with these new environments.
However, many plant breeds are under threat because high heat does not just mean water loss -- under high heat, some proteins may denature, especially the important enzyme Rubisco, used in photosynthesis. If the problem is not just water loss, which can be prevented by adding more loss, the inability to use essential proteins will be disastrous if a plant cannot photosynthesize. In order to understand more about this phenomenon, it becomes necessary to examine current methods used in drought-resistant plant breeds, and how heat affects Rubisco.
How It Is Normally Done
In the carbon fixation stage of the most common form of photosynthesis (C3 fixation), Rubisco is an essential protein in fixating carbon to glyceraldehyde 3-phosphate (Ga-3P) molecules to form carbohydrates. However, in arid conditions, many plants have developed mechanisms to increase the efficiency of Rubisco without that much water. One of these mechanisms is Crassulacean acid metabolism (CAM), which is named after the Crassulaceae group of desert plants. During the night time, these plants open up their stomata in order to diffuse oxygen out while consuming carbon dioxide, which will be used to create oxaloacetate, a necessary molecule used in the citric acid cycle. During the day time, the stomata then close again, allowing for the plant to perform the rest of the citric acid cycle in order to create the necessary carbohydrates it needs to survive (Lüttge, 2003).
The CAM cycle is most commonly used in desert plants, such as many cacti and the jade plant, and has been known for some time now already (Smith et al., 1984). Most of these plants also use another method called C4 fixation where carbon dioxide is stored clustered with Rubisco around the plant at all times, therefore trying to maximize the efficiency of carbon fixation without the need of much water and excess amount of light. Many scientists have already begun developing new plant breeds that mimic desert plants, such as the drought-resistant corn (McFadden et al., 2019).
Current Methods & Discussion
With the rise in temperature, many staple crops are vulnerable to dealing with new environmental conditions. For example, corn is an important crop that feeds people in industrial food, flour, oil, and livestock. In many states of the United States, the temperature is expected to rise in the next decade to temperatures that will cause many crops to die. Corn, however, can only survive optimally in the ten-degree range of 85 to 95 degrees Fahrenheit. As a result, many scientists have been working on creating drought-resistant and heat-resistant corn.
Of these new breeds of corn, the genetically modified corn breeds use genes from the bacterium species Bacillus subtilis that is commonly found in soil which can withstand extreme temperatures. This bacteria is commonly found in soil and is not harmful to humans. They are well-studied for their known heat resistance. It seems that once it is too hot, water no longer becomes necessary, and the bacteria will lose water in order to prevent proteins from denaturing. Water molecules will move, which will create more heat that may be harmful to the bacteria, and some studies have observed that proteins will appear immobile in bacteria dealing with high heat (Cowan et al., 2003).
However, more research is needed to understand what types of chemicals are needed in order to prolong heat resistance and why some chemicals are worse than others to help the bacteria survive (Gerhardt and Marquis 1989). Much of the current research is outdated, and there now needs to be more information in order for current agricultural scientists to develop more heat-resistant crops. It seems in bacteria, the first to be a problem when dealing with heat resistance is loss of water, then membrane damage, and then finally, DNA and protein damage. In plants, it is required that more research is done to target the first part of the plant to defend when trying to adapt to new climate circumstances.
Citations
Cowan A.E., Koppel D.E., Setlow B., Setlow P. 2003. A soluble protein is immobile in dormant spores of Bacillus subtilis but is mobile in germinated spores: Implications for spore dormancy. Proceedings of the National Academy of Sciences. 100 (7) 4209-4214; DOI:10.1073/pnas.0636762100
Gerhardt, P. and Marquis, R.E. (1989) Spore Thermoresistance Mechanisms. In: Slepecky, R.A. and Setlow, P., Eds., Regulation of Prokaryotic Development, American Society for Microbiology, Washington DC, 43-63.
McFadden J., Smith D., Wechsler S.J., & Wallander S. 2019. Development, Adoption, and Management of Drought-Tolerant Corn in the United States, ERS.
Smith, S., Didden-Zopfy, B., & Nobel, P. (1984). High-Temperature Responses of North American Cacti. Ecology,65(2), 643-651. doi:10.2307/1941427
U. Lüttge, PHOTOSYNTHESIS AND PARTITIONING : CAM Plants, Encyclopedia of Applied Plant Sciences, Elsevier, 2003, Pages 688-705, ISBN 9780122270505, https://doi.org/10.1016/B0-12-227050-9/00096-X.
Zhibo Wang, Guofang Li, Hanqing Sun, Li Ma, Yanping Guo, Zhengyang Zhao, Hua Gao, Lixin Mei. 2018. Biology Open. 7: bio035279 doi: 10.1242/bio.035279 Published 22 November 2018
