Understanding the Behavior and Function of Plant Leaves to Increase Growth

Using novel experimental plant systems to identify the factors that affect the rate of leaf growth

Leaves are central to a plant’s function and survival. Fundamental to all ecosystems, they act as a plant’s food source, enabling it to absorb sunlight, make sugars, and carry water and nutrients through their veins. Understanding how leaves grow on a cellular level has very important implications in agricultural production. However, the process is complex and not widely understood. Dr. Elizabeth Van Volkenburgh, Professor in the Biology Department at University of Washington is exploring the physiological regulation of leaf growth to identify factors that drive or limit the rate at which they grow. Because leaves act as food that feed the plants we harvest, limits in their growth or performance can lead to a decrease in crop yield. Identifying how they tolerate environmental stressors will lead to the improvement of agricultural plant production for both breeders and farmers. 

Understanding leaf growth provides a basic lens through which the health of any plant system can be studied. Dr. Van Volkenburgh and her team of graduate and undergraduate researchers, principal co-investigators, and an associated Lecturer collaborate globally with researchers and breeders from the International Center for Tropical Agriculture (CIAT), a Colombian bean breeding station. Together, they focus on understanding how light stimulates leaf growth, how droughts limit growth, the significance of leaf shape, and the way plants behave collectively. They’ve developed model experimental systems to look at the rate of leaf expansion, as well as the molecular physiology and behavior of both major crops, native plants, and beans. 

Current research includes:

  • Identifying How Beans Develop Tolerance To Drought - Dr. Van Volkenburgh and her team seek to understand how droughts limit leaf expansion and leaf function (photosynthesis and exported sugars). They compare different lines of beans in order to identify which are drought-tolerant. Then they try to understand how those beans are capable of that resilience. They use various bean types from CIAT, growing them in greenhouses and growth chambers. Dr. Van Volkenburgh and her team take pieces of leaves, float them in solution, and measure the cellular properties. They identify the rate at which the leaves expand, their photosynthetic function, and how many beans a plant produces. They also look at the “abortion” of flowers and bean pods—a process that leads to crop yield loss—and monitor the mechanism that promotes leaf growth rate. This project, initiated 10 years ago, is collaboration with CIAT researchers. They aim to complete the study within 10 more years. 
  • Understanding How Blue Light Affects Leaf Growth - Light stimulates the growth of leaves. Dr. Van Volkenburgh and her team are studying the way blue light interacts with phototropin (a photoreceptor) in order to make leaves grow faster. This photoreceptor works very effectively in stomate guard cells and causes plants to bend toward toward the light. It helps regulate stomates—the gas-exchange valves on the surface of leaves—and the speed by which different cell layers in the leaf expand. However, until now, few have studied how it works in growing leaves. In their biochemistry and biomolecular experiments, phototropin enables Dr. Van Volkenburgh and her team to untangle the regulatory processes that control the growth rate in leaves. They use arabidopsis (a model plant) and mutants in the phototropin gene, with the intent of later applying their findings to beans. This project has been ongoing for 10 years and is expected to reach completion in four years. 
  • Identifying Various Tomato Leaf Shape Functions - Dr. Van Volkenburgh and her team want to understand the functional significance of leaf shapes in tomatoes. Tomato plants have leaves with diverse edges; some are lobed, smooth, or have teeth. Traditionally thought to be an adaptive feature in plants, leaf shapes have been correlated with temperature since prehistoric times. Tooth and lobe-shaped leaves are usually found in temperate zones, and smooth leaves are found in the tropics. However, the way these different leaf shapes affect leaf function is unknown. Dr. Van Volkenburgh and her team collaborate with medical and zoological labs that use innovative CT-scanning microscopes to look inside tomato leaves with different shapes. By observing the photosynthetic rate and transpiration—two major processes in leaves—they will identify the rate of sugar flow coming out of and into leaves through its veins. Their findings may enable the breeding of different leaf shapes in crops to promote successful growth in different environments. They have worked on this project for four years, and will finish it in four more.
  • Understanding Plant Behavior and Collective-Decision Making - Dr. Van Volkenburgh and her team—in collaboration with colleagues studying animal behavior and plant cognition—are investigating collective plant behavior and how leaves react to stressors. First, they want to know if plants make collective decisions together. Factoring in the influence of soil nutrients and water availability, they look at how an individual plant’s root “decides” which direction to grow in. Then they compare these findings to a group of roots. With more than one input, they want to identify whether or not these roots make a different decision together. Additionally, Dr. Van Volkenburgh and her team are looking at the collective behavior of bean leaves in a canopy to understand how it functions when stressed. Leaves point themselves toward light under good conditions, and fold up to shield themselves when stressed. Their goal is to better understand how plants work and publicize the sensitive nature and ability of plants to respond to their environment. Farmers and breeders will then be able to better protect plants and support their growth in natural ecological settings.

Bio

Dr. Elizabeth Van Volkenburgh is very interested in how people learn about biology. She first became interested in biology in high school, after she took a biology and chemistry from two wonderful teachers. However, she entered college with the intention to become a lawyer, focusing her studies in economics and political science. She soon found that she enjoyed and excelled in the biology course she was concurrently taking. It was then that she decided to switch her major to botany and became fascinated with plant biology and function.

Directly out of college, Dr. Van Volkenburgh became a technician and began her work looking at how plants regulate their growth. Two years later, one of her compelling advisors encouraged her to go to grad school to continue this work. She decided to pursue her research, entering grad school with a question on leaf growth, which she formed during her time as a technician. Upon hearing her question, a professor merged their interests and together they figured out how leaves grow, using a mechanism the professor developed for stems. This was the first time anyone had ever looked at this mechanism in leaves. That work rapidly propelled her research forward. From there, she obtained her Ph.D. in Plant Physiology at University of Washington. 

At first, and now more recently, she wanted to help "feed the world.” But she was also interested in how plants make sense of their world, respond to environmental input, and adapt. Physiology inspires Dr. Van Volkenburgh because so much is still unknown. Her appetite to discover how plants work is further whetted by the talented experimenters, curious inquisitors, and fascinating story tellers she has met along the way.

Outside of the lab, Dr. Van Volkenburgh enjoys spending time with her family, sailing, swimming, and traveling. She is married to a retired high school physics teacher engaged in professional development in STEM.  Their daughter is an elementary school teacher and their son is in construction management.  Their shared love of education leads to many creative family trips and projects (they all live in “fixer-upper houses,” because they love to experiment with the best designs).