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 civince@ufl.edu or anirbanguha@ufl.edu 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.

Mark Keeley

Mark Keeley turned a lifelong passion for plants into work that hopefully will help us better understand the way HLB affects Florida citrus trees. He worked in citrus research before starting his Master’s, but said he’s always been interested in plants and has been playing around with them for as long as he can remember. He made his way to plant research after trying out several undergrad degrees that didn’t fit quite right. Eventually, to no one’s surprise he told me, he joined the UF Horticultural Sciences Department. From there he had several jobs before landing one at a private agricultural research station. He likes his job because he said it’s, “Me and orange groves 4 or 5 days a week. Me and the plants, it’s quiet. Calming.” Through this job he decided to pursue a Masters in Agronomy. When asked why he’s pursuing his masters and working full-time for the private lab he laughed and said it was mostly for selfish, personal reasons. As a part of his master’s program he’s working with the tree physiology lab on a project that’s attempting to show a relationship between photosynthesis and citrus greening.

At the tree physiology lab, we hope to improve citrus growth based on understanding its environmental physiology. This particular experiment’s goal to describe the effects of HLB on photosynthesis. Part of this experiment also includes looking at the difference between shoot photosynthesis and leaf photosynthesis. This photosynthetic activity can’t be translated between leaf and tree, so we are trying to determine why. Studying photosynthesis on the leaf level can help garner understanding for the effects of photosynthesis on the whole canopy, but we need to understand what causes differences, too. Mark explained, “[We are] specifically looking at impacts of greening on photosynthesis as well as the amount of photosynthesis acquired from the leaf material and the stem material and what those impacts are over time on maturation.” In terms of the importance of this work for management, “It’s no longer preventing the bacteria from being there; it’s more how do we support the tree in [spite] of the bacteria,” he explained. This would be helpful because Mark believes the current approach to managing HLB isn’t working, so this could open the door to try other approaches.

The project uses an infared gas analyzer (affectionately called “IRGA”) called Li-Cor 6800. The machine cycles a known amount of CO2 and water over the leaf and measures how the concentrations change after they pass over to determine how much CO2 is being taken in and how much water is being released by the plant. This allows us to measure photosynthetic activity. Doing this in the lab with a known amount of light allows us to see the direct impacts of disease or other treatments over time without having to contend with clouds, different radiation intensities, etc. Eventually Mark would like to do work like this in the field, but while he’s still developing the methods, inside the lab is the best opt

The project uses an infared gas analyzer (affectionately called “IRGA”) called Li-Cor[RV1]  6800. The machine cycles a known amount of CO2 and water over the leaf and measures how the concentrations change after they pass over to determine how much CO2 is being taken in and how much water is being released by the plant. This allows us to measure photosynthetic activity. Doing this in the lab with a known amount of light allows us to see the direct impacts of disease or other treatments over time without having to contend with clouds, different radiation intensities, etc. Eventually Mark would like to do work like this in the field, but while he’s still developing the methods, inside the lab is the best option. 


 

 

When I asked why he believes this work is important he said, “Fascination for me. I keep going down the rabbit hole more than anything. I think it will be important if we find some of these relationships with the infection level and the tree. Like I said, it’ll change the way we culturally try to manage the disease [HLB]. Other than that, it’s more of a curiosity.”