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Phytochrome Physiology and Plant Perception of Far-Red Photons

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Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 8-2021 Phytochrome Physiology and Plant Perception of Far-Red Photons Paul Kusuma Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Plant Sciences Commons Recommended Citation Kusuma, Paul, "Phytochrome Physiology and Plant Perception of Far-Red Photons" (2021). All Graduate Theses and Dissertations. 8173. https://digitalcommons.usu.edu/etd/8173 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. PHYTOCHROME PHYSIOLOGY AND PLANT PERCEPTION OF FAR-RED PHOTONS by Paul Kusuma A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Plant Science Approved: _________________________ _________________________ Bruce Bugbee, Ph.D. Lawrence Hipps, Ph.D. Crop Physiology Biometeorology & Atmospheric Science Major Professor Committee Member _________________________ _________________________ Marc van Iersel, Ph.D. Lance Seefeldt, Ph.D. Plant Physiology Biochemistry Committee Member Committee Member _________________________ _________________________ Raymond Wheeler, Ph.D. D. Richard Cutler, Ph.D. Plant Physiology Interim Vice Provost for Committee Member Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2021 ii Copyright © Paul Kusuma 2021 All Rights Reserved iii ABSTRACT Phytochrome Physiology and Plant Perception of Far-red Photons by Paul Kusuma, Doctor of Philosophy Utah State University, 2021 Major Professor: Dr. Bruce Bugbee Department: Plant, Soils and Climate Plants evolved in the natural environment where resources are often scarce. Photons within the range of photosynthetically active radiation (PAR) are a critical resource that can be blocked by neighboring vegetation. As plants are shaded, they adjust their shape (stem length and leaf area) to either reach for the light and/or maximize photon capture. These responses are modulated through an array of photoreceptors that have evolved to perceive the photon flux from 280 to 800 nm. One spectral region with significant impacts on plant shape is far-red (FR), which is barely visible to the human eye. Photons in this range are minimally absorbed by chlorophyll, and are therefore transmitted through leaves and relatively enriched in canopy shade. Plants sense this enrichment through the photoreceptor phytochrome, which has two primary states: Pfr, which inhibits elongation in sunlight; and Pr, which cannot inhibit elongation and is abundant in the shade. The dynamic relationship between Pfr and Pr has been described by the phytochrome photoequilibrium (PPE), which is the ratio of Pfr/(Pr+Pfr). PPE is often predicted with photoconversion coefficients that are iv used to estimate the rates of Pr and Pfr conversion under a given spectral photon distribution. I describe shortcomings of this technique and provide a modified approach that incorporates spectral distortions in leaves. Due to the complexity of PPE, environmental metrics may be preferable for predicting morphology. The R:FR ratio is often used as an environmental metric, but it has shortcomings. Instead, the FR fraction [FR/(PAR+FR)] integrates plant responses to blue, green, red and far-red photons. Blue photons reduce plant size through cryptochrome, while green photons are hypothesized to induce shade avoidance responses by reversing this blue photon response. However, I show that green photons have minimal effects on morphology. The FR fraction is an intuitive metric and appears to be well correlated with morphology. Total photon intensity interacts with the FR fraction to predict morphology, especially leaf area – a crucial component of plant development that determines how many photons can be captured for photosynthesis. Under high photon intensities, FR increased lettuce leaf area, but under low intensities, FR decreases leaf area. (318 pages) v PUBLIC ABSTRACT Phytochrome Physiology and Plant Perception of Far-red Photons Paul Kusuma Photons are the primary energy source for most life on Earth, as they drive photosynthesis, a process that turns the CO2 in air into food. One crucial parameters for the optimization of growth is leaf area, which determines the ability of a plant to capture photons for photosynthesis. In order to gain access to photons in shaded environments, plants have evolved unique sensors, called photoreceptors, which respond to changes in the color and intensity of light. Far-red photons (photons at the edge of human vision that appear as dim red light) hold particular promise in regulating plant shape and photon capture. These photons are minimally absorbed by chlorophyll, and are thus enriched in the shade – making them a potent signal of the presence of shade. These photons have been shown to increase leaf area and stem elongation, which increase access to photons, and thus increase plant growth. Additionally, the lower energy of far-red photons make them particularly useful for reducing the massive requirement for electrical power in indoor agriculture. Here, I describes how far-red interacts with blue, green, and red photons to affect plant morphology. I compare traditional and newly developed models/metrics that predict the action of far-red through a photoreceptor called phytochrome. Additionally, I discuss their interactions with total photon intensity. vi ACKNOWLEDGMENTS I would have not made it nearly this far without the love from my family: my parents Lynda and David, as well as my siblings Sarah, Thomas and Timothy. I would also like to thank Drs. William Wheeler and Shuyang Zhen who had the misfortune of sharing an office with me over the course of my PhD program. I have received much assistance from members of the Crop Physiology Laboratory over the past five years, namely from Mitchell Westmoreland, Matthew Hardy, Wyatt Johnson, Jakob Johnson, Boston Swan, Erik Sargent, Kahlin Wacker, Logan Banner, Terri Manwaring, Alec Hay and other unnamed laboratory members. I am grateful for all of their help. Thanks to Dr. Morgan Pattison for his insight in writing manuscripts, and thanks to Dr. Kevin Folta who initially led me down this road. I thank my committee members, Dr. Lance Seefeldt, Dr. Raymond Wheeler, Dr. Marc van Iersel, Dr. Lawrence Hipps and Dr. Keith Mott, whose assistance and discussion in specific areas helped guide my understanding across various topics. Finally, I thank my major advisor, Dr. Bruce Bugbee who has been a guiding mentor throughout my program. I have spent many hours in his office talking through data, refining manuscripts and generally scheming. It has been a wild five years. Paul Kusuma vii CONTENTS Page ABSTRACT ....................................................................................................................... iii PUBLIC ABSTRACT ........................................................................................................ v ACKNOWLEDGMENTS ................................................................................................. vi LIST OF TABLES ........................................................................................................... xiii LIST OF FIGURES ......................................................................................................... xiv CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW .................................... 1 Introduction ...................................................................................................... 1 Literature review ............................................................................................... 2 1.2.1 General Effect of Specific Wavelengths ............................................................. 2 1.2.2 Photoreceptors ................................................................................................... 5 1.2.3 Photoconversion Coefficients .......................................................................... 10 Objectives & Hypotheses ............................................................................... 22 Literature Cited ............................................................................................... 25 CHAPTER 2 DOES GREEN REALLY MEAN GO? INCREASING THE FRACTION OF GREEN PHOTONS PROMOTES GROWTH OF TOMATO BUT NOT LETTUCE OR CUCUMBER................................................................... 30 Abstract ........................................................................................................... 30 Introduction .................................................................................................... 31 Material and Methods ..................................................................................... 35 2.3.1 Plant Material and Cultural Conditions .......................................................... 35 2.3.2 Treatments ........................................................................................................ 36 2.3.3 Plant Measurements ......................................................................................... 37 2.3.4 Statistical Analysis ........................................................................................... 39 Results ............................................................................................................ 40 2.4.1
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