Internship: Chlorophyll fluorescence to understand complex stress responses in plants

Talent Vharachumu, undergraduate student intern in 2019, used chlorophyll fluorescence to assess heat tolerance in citrus leaves.

Florida has several fascinating subtropical and tropical flora. The abundant sunshine and mild winter of Florida prolong the physiological activities of the plants leading to a longer growth season compared to other cooler landscapes. But too much sunshine than what is metabolically desired often leads to serious physiological stress. Evolution has led to plants that can handle such surplus light energy. But what happens under more complex stress situations? For example, Florida has been witnessing a progressive climatic warming, and new disease and pest outbreaks. Plant’s defense mechanisms face a stupendous challenge when handling such multiple stressors and failure to do so can threaten species long-term sustainability. At the Tree Physiology Laboratory at the University of Florida’s Citrus Research and Education Center (Lake Alfred, FL), we are studying how the tropical evergreen citrus trees respond to the complex agroclimatic niche of central Florida that includes warming events, high sunlight energy and greening (a systemic plant disease).

One of our approaches is to decode the chlorophyll fluorescence signals that citrus leaves emit back to nature while harvesting sunlight. These long wavelength, invisible fluorescence spectrums though emitted out, they carry valuable information on leaves bioenergetic processes and overall photosynthetic performance. We use different high throughput fluorometers to monitor real-time plant fluorescence emission signals, study signal patterns and use the signal-derived variables as biophysical markers for comparative stress physiology studies.

We are looking for undergraduate student interns who are excited to work with plants and interested in taking up short-term projects on plant stress physiology using chlorophyll fluorescence approaches. We do not expect the students to have a deep understanding of chlorophyll fluorescence or photobiology as our projects are designed for hands-on learning and gradual concept building. We will offer research projects that are either experimental (in field and controlled environment settings) or meta-analysis (literature review, data analysis, and interpretation) depending on student’s interest and the availability of lab projects. Please contact or if interested in joining us for the summer. Interns are paid. We will begin the selection process after April 16, so please contact us before then.

Talent Vharachumu

Talent Vharachumu was an undergraduate intern who is originally from Zimbabwe and attends university in Costa Rica. She is studying agricultural sciences and has become particularly interested in plant physiology, especially due to her time at the lab. Along with the work Talent did for the physiology lab, as is typical for an intern, she sometimes participated in work with other labs as well. She enjoyed this because it allowed her to learn many different things and meet more people. She hopes to be able to return to the lab to complete her masters. 


She enjoyed her work at the lab because she learned more about plant physiology. Our goal at the tree physiology lab is to improve general tree health and make strides in understanding tree physiology better and more completely. To accomplish this goal, we do research with a whole plant approach. One such experiment is on how different plants respond to and are affected by heat.  


Talent primarily worked on that experiment. She would collect leaves from a variety of trees in a variety of genotypes and perform a procedure on them to test how they tolerate the different temperatures. To do the experiment she used a machine that punches a piece of the leaf out, then placed the piece on a black disk that went inside a Ziplock bag, which was then placed in a container of water for 30 minutes. Then she’d record the chlorophyll fluorescence (photosynthetic energy conversion) of the leaves, given from a machine called the Fluoremeter. She also worked on another project with an infrared gas analyzer (Li-6800) machine to measure photosynthesis, gas exchange, and chlorophyll fluorescence. 

When I asked Talent why she believes this work is important and why she thinks people should care about it she explained that the data she’s gathering helps us better understand the way climate change is affecting the planet, different environments, and plants in general. People who work in agriculture can use the data about which plants tolerate heat better to determine which genotypes to grow, which hopefully will increase plant yield and agricultural efficiency as temperatures warm. Talent also said it “…can help them reduce losses from low production due to high temperatures that are being caused by global warming.” This is useful because it allows growers to make informed decisions about what kinds of crops to plant as the climate and planet continue to change. I asked specifically what she would say to people who think they don’t have a reason to care about plants and she said, “They don’t care about plants, but they care about eating.” 

Orlando goes to the field

PhD student, Orlando Li, and student intern Mikal Wegener classify flush in the field.

When I first spoke with Orlando Li he told me he wanted to work in the field with farmers; I knew I had the right candidate for my lab. Many students who contact me have an interest in biology that takes them to what we refer to as “lab work.”  But I sometimes tell folks that the word “lab” for our group is a bit of a euphemism.  What we have is more of a scientific field crew than a lab.  Orlando’s interests fit perfectly with our group and our research aims.

Orlando is just finishing his proposal and preparing preliminary experiments to address how citrus plants regulate flushing on a whole plant basis.  He’s looking into the environmental cues of flushing, relative timing of citrus root and shoot growth and of changes in carbohydrate movement, as well as what signals plants to make these changes happen.  

“What does this have to do with field and farmers?” you ask.

Flushing patterns determine when the two major citrus pests in Florida can reproduce.  Both Asian citrus psyllids and citrus leafminer lay their eggs on new flush, so if growers understood these cues they could use them to both manipulate them and to time other management decisions.  If a grower knew a major flush was coming insecticides could reduce adult insect populations before they could lay eggs- even better if the grower could force the flush to be concentrated and keep it from spreading out over time. The answers to Orlando’s questions will help us design grower practices that will contribute to managing the two major disease challenges Florida citrus growers face. Orlando, whose given name is Sheng-yang, earned his Master’s degree in horticultural sciences at the National Taiwan University working on pear fruit thinning. He subsequently worked in Belize helping develop a certified budwood source for citrus growers there. I expect his contribution to Florida citriculture to be even more impactful.