Sharon Danielson is a plant ecology intern, supported by the Norweb Fellowship at The Holden Arboretum. She is currently working with Holden scientist Juliana Medeiros, PhD, to study water transport in rhododendrons. She recently had the opportunity to travel to the West Coast to conduct research at the University of California – Los Angeles and wrote about her experiences for the research department’s Adventures in Plant Sciences blog.
Studying Leaf Hydraulic Conductance in Genus Rhododendron: Botanical Escapades in the Lab
I recently had the opportunity to study leaf hydraulic conductance at the University of California, L.A. in the lab of Dr. Lawren Sack, who is a pioneer in the field. For those who may not be familiar with “leaf hydraulic conductance”, this is the measure of how easily water moves through the leaf. Transpiration is the process by which water moves from roots, through shoots, to leaves and exits the leaf via the stomata due to evaporation. If the plant is unable to replace the water that is lost during transpiration, they will desiccate and perish. Leaf hydraulics can be understood as the measure of the plants’ ability to replace the water in the leaf that is lost during transpiration and is represented as Kleaf. For our study, we are interested in the potential differences of leaf hydraulic conductance in the various types of leaves found in Rhododendrons and how this may provide clues to the types of climate they are found in.
Dr. Sack’s lab is bustling, filled with five PhD candidates, a post-doc, lab manager, and two visiting research interns (myself included). It is an incredible opportunity to be able to collaborate with different scientists and, Lawren was very gracious to invite us to learn the techniques for understanding water transport in plants. It is already a great experience getting to collaborate with other scientists but it is particularly fulfilling when you have the opportunity to work with people from all over the world. Dr. Christine Scoffoni, a postdoctoral researcher, and her intern, Justine, (pictured left to right) are both French natives working in the Sack lab. Christine is a very talented researcher who has done significant work studying water transport in plants. She spent a significant amount of her time providing us with helpful techniques to use in our study.
There are multiple different methods that can be used to study leaf hydraulic conductance but we have chosen to use the Evaporative Flux Method, or EFM, because it simulates the most natural process in the laboratory. Individual leaves are connected to water-filled tubing that is, in turn, connected to a graduated cylinder filled with water on a balance. Grow lights emitting photosynthetically active radiation (PAR) are placed over the leaves to induce photosynthesis. As the leaves photosynthesize, stomata open in order for the plant to gain access to the CO2 that is used during photosynthesis to produce sugars. When the stomata open, water evaporates from the surface of the leaf during transpiration and water flows through the plant system. The rate at which the water flows through the leaf is determined by weighing the water in the graduated cylinder at 30-second intervals for several minutes. It is very important to make sure that the leaves do not overheat so, water is placed between the lights and the leaves to absorb heat and the fans also help to cool the leaves. Here, two Rhododendron arboreum leaves are set up on the system.
Genus Rhododendron is a large and diverse group of plants of roughly 900 species. They vary in their climate and in their leaf sizes; therefore, we suspect that they will also vary in Kleaf. The three species of Rhododendron that I worked with were R. arboreum, R. makinoi, and R. kiusianum (pictured left to right). This makes Rhododendrons a very fascinating group of plants to study. However, as often happens in science, the most interesting organisms or questions are not always the easiest to study.
In the evaporative flux method, the system is akin to putting a person on IV fluids where pure water in a tube is the IV for the leaf. Just as an embolism is deadly to humans, a bubble entering the leaf can be detrimental to water flow in plants. The petiole has to be securely fastened to the tubing and no air can enter the tubing. Because Rhododendrons have wildly different petiole shapes and sizes (large, small, flat, round, semi-lunar etc.), a wide range of connectors with different sized tubing on them are necessary. Sometimes it can take a while and a few failed attempts before the tubing is securely attached to the leaf!
Exploring the Plants and Sites of Los Angeles: Botanical Escapades Outdoors
As a native Clevelander, I have grown to appreciate the beauty of each of our different seasons but even those of us who don’t mind the snow can use a break from the gray days in the middle of January. It was a tad disorienting to see plants in bloom in the middle of January but I felt the same excitement I do every time spring comes to Cleveland. I received a few perplexed glances as I stopped in the middle of the sidewalk to admire the various blooms, especially the Rhododendrons.
When I was younger, I only thought of Rhododendrons as the decorative shrubs that people often had in their gardens. Now that I am working with Rhodies, I have come to appreciate just how diverse the genus is and I am starting to notice them everywhere! Pictured above are two evergreen Azaleas in bloom. These are hardy plants that can tolerate heat—a very important characteristic for any shrub growing in Southern California.
When we were on our flight to California, I asked Juliana, “What are a few things that are different about California?” as you may expect a botanist to respond, she said, “The plants!”. If you have never been to Southern California or any other arid climate, the unique vegetation may surprise you. Because Southern California is prone to drought, many of the landscape and gardens are filled with drought-tolerant plants called succulents.
Above is a photo of a wall-mounted succulent planter on the side of a restaurant I visited during the weekend. The orange, pencil-like plant on the right side of the photo is a member of genus Euphorbia (family Euphorbiaceae). If you were to pull off a portion of the stem you would notice a white sap exuding from the end. The white sap is actually latex so if you have a latex allergy, steer clear! Succulents are one of my favorite plant forms and are incredibly easy to care for—they require plenty of light but they require little watering. If you’d like to see succulents growing at Holden, you can head on over to Lantern Court where a well-drained succulent garden is situated along the driveway and small potted succulents rest in the windows of the former home of Warren and Maud Corning.
Even though I thoroughly enjoyed my botanical escapades in and out of the laboratory, I wanted to take the time to explore some of the other natural sites of California. Over the weekend, my husband Scott came to visit and we visited with my best friend from childhood, Lauren, who relocated to Long Beach, CA two years ago. Lauren suggested that we go kayaking around the pier at Redondo Beach, roughly a 30-minute drive from the area where I was staying in West L.A. I had hoped to see some marine wildlife and I was not disappointed! There were plenty of sea lions basking on the rock barriers and even some on the docks. I mistakenly referred to them as seals but the locals explained that sea lions have small external earflaps whereas seals simply have an ear opening.
I managed to capture a photo from the kayak (a risky task, indeed!) of the sea lions basking on a barge that was specifically constructed for their use. These animals are very social and vocal. It was quite entertaining to watch how one pesky sea lion could upset the delicate balance of the pile whenever it needed to move. Needless to say, some of the snoozing sea lions were none too pleased with the one who opted to go for a swim.
In just a short walk down the coastline, I arrived at Hermosa Beach (Hermosa= the feminine form of “beautiful” in Spanish). After a cool, cloudy, and misty morning of kayaking at the Redondo Beach pier, the sun began to shine. While the winter storm Jonas was blasting the East Coast with several feet of snow, I couldn’t help but notice the disparity between the two coasts. I watched children sledding down a sand hill as opposed to a freezing cold snow pile!
On the southeast corner of the UCLA campus, next to the Life Sciences Building where I was working, was one of my favorite sites of all. The Mildred E. Mathias Botanical Garden at U.C.L.A. is a gorgeous garden with walking paths and benches that was founded almost 100 years ago. Because the garden has been around for so long, it is home to some of the largest trees in the area. Impressive Ficus (fig) trees are located on edge of the garden and I would pass by them each morning while walking to the campus from the bus stop. The sheer diversity of plant-life in the garden is stunning. Pictured above is a photo of a climbing aloe plant that covered what would otherwise be an unsightly chain-link fence. The bright orange tubular flowers are visited frequently by humming birds, which were certainly very active and vocal throughout the entire garden as I enjoyed an afternoon walk. Pictured to the right, is a Camelia, or Tea Flower, that is a member of the Theaceae family. This stunning botanical garden also features a long creek-like water feature that is the home to many koi and even a few turtles.
Just on the outskirts of the botanical garden are several large woody plants from the genus Burgansia. They were in full bloom while I was visiting UCLA and the large, yellow, trumpet-like flowers certainly caught my eye. I first became familiar with this genus while studying abroad in Costa Rica while I was an undergraduate student. There they refer to the plants as “Reina de La Noche”, Spanish for Queen of the Night, a fitting term as they are members of the family Solonaceae, or nightshades.
I am incredibly thankful that I had the opportunity to collaborate with such profound scientists. I had a blast exploring the diverse plant-life and natural sites around Los Angeles. But the fun isn’t over! Now that I have the techniques under my belt, I will continue our research on water transport in genus Rhododendron back at Holden with the support of grants provided by the Azalea Society of America and the American Rhododendron Society. And so, the botanical escapades continue on!
adventuresinplantscience 