Foliar Anthocyanins in Coleus and Ornamental Grasses: Accumulation, Localization, and Function A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Jennifer Kay Boldt IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY John E. Erwin and Mary H. Meyer, advisers April 2013 © Jennifer Kay Boldt 2013 Acknowledgments I would like to thank my co-advisors, Drs. John Erwin and Mary Meyer, for their guidance and support. I would also like to thank Drs. Jerry Cohen, Cindy Tong, and Jeannine Cavender-Bares for serving on my graduate advisory committee and providing thoughtful feedback and critical review of my research. I wish to acknowledge all who have shared 440 Alderman Hall with me the past four years. You have helped me see my research from alternative perspectives, and have shared in my joys and frustrations. Thanks also to Chris Currey, Jonathon Hensley, and Laci Holbrook for helping care for my plants on weekends. In addition, I also thank Esther Gesick, Roger Meissner, and Doug Brinkman for their assistance with greenhouse and growth chamber issues. I would like to thank Dr. David Clark at the University of Florida, Emerald Coast Growers, EuroAmerican Propagators, and Pleasant View Gardens for donations of plant material. I wish to acknowledge Bill and Hella Hueg for their support of graduate research and education – it is an honor to be the first recipient of the Bill Hueg Landscape Arboretum Fellowship! Lastly, I would like to thank my family for their unwavering love and support. My parents introduced me to the world of floriculture, taught me the importance of hard work, and have provided unwavering support of all of my endeavors. And lastly, I wish to thank my twin sister, Jessica, for being my best friend and biggest supporter - you have encouraged me through this entire process! i Dedication This dissertation is dedicated to Mom and Dad, for initially exposing me to the wonderful world of plants. ii Abstract Anthocyanins provide red coloration in plants. The research objectives were to (1) investigate the influence of environmental factors on anthocyanin accumulation, (2) compare photosynthetic rates of red and green leaves, (3) determine anthocyanin localization in leaves, and (4) determine anthocyanin function(s) in leaves. Coleus (Solenostemon scutellarioides) and ornamental grasses, commonly cultivated for their foliage coloration, were selected as model plants. Irradiance and temperature influenced anthocyanin content in red coleus. Anthocyanin content increased with increasing irradiance, although photobleaching occurred in some cultivars at the highest irradiance. Exposure to low temperature (12 °C) resulted in maximum anthocyanin content in two cultivars but minimal anthocyanin content in another. In switchgrass and purple fountaingrass, anthocyanin content in individual leaves and the percent red leaves increased with increasing irradiance. Intensified seasonal leaf coloration in red-leaved grasses (Imperata cylindrica, Panicum virgatum, Pennisetum advena, Pennisetum purpureum, and Schizachyrium scoparium) resulted from increased anthocyanins and decreased chlorophyll. Anthocyanins were negatively correlated with average daily temperature and daily light integral (DLI) and positively correlated with total growing degree days and total DLI. Annual and non-native grasses had minimal seasonal fluctuations in pigmentation relative to native grasses (P. virgatum and S. scoparium), and this seasonal increase in anthocyanins might be an adaptive mechanism. At saturating irradiance, neither leaf color had a distinct advantage. Maximum photosynthetic rates (Amax) in red and green coleus were similar per area, higher in red iii per fresh or dry weight, and higher in green per unit chlorophyll. Amax in switchgrass was higher in green leaves per area, fresh, or dry weight, and similar in red and green leaves per unit chlorophyll. Anthocyanins in coleus and switchgrass localized in epidermal cells. They were ideally situated to provide a photoprotection role as light attenuators. Anthocyanins offered minimal photoprotection in switchgrass and their presence may simply be due to selection for desired ornamental attributes. Photoprotection by anthocyanins was most evident in coleus during low temperature/high irradiance stress. Red coleus exhibited less of a decline in Fv/Fm, photosynthesis, electron transport rate, and effective quantum yield than green coleus, and Fv/Fm and photosynthetic rate recovered to pre-stress levels more quickly. iv Table of Contents List of Tables…………………………………………………………………………….vii List of Figures……………………………………………………………………..............x List of Abbreviations……………………………………………………………………xiii Chapter 1: Anthocyanins: A Horticultural Review ............................................................. 1 Introduction .................................................................................................................... 2 Plant Pigments ............................................................................................................... 3 Anthocyanins ........................................................................................................ 3 Betalains ................................................................................................................ 3 Carotenoids ........................................................................................................... 5 Anthocyanins in Flowers and Fruits .............................................................................. 7 Foliar Anthocyanins ....................................................................................................... 8 Localization........................................................................................................... 9 Classification....................................................................................................... 10 Anthocyanin Biosynthesis and Regulation .................................................................. 11 Biosynthesis ........................................................................................................ 11 Transcriptional Regulation.................................................................................. 13 Color Modification.............................................................................................. 14 Degradation ......................................................................................................... 15 Physiological Basis for Occurrence ............................................................................. 16 Herbivory Defense .............................................................................................. 16 Photoprotection ................................................................................................... 18 Antioxidant ......................................................................................................... 22 Osmoregulator..................................................................................................... 24 Increase Leaf Temperature ................................................................................. 25 Specialized Functions ......................................................................................... 26 Anthocyanins Affect Photosynthetic Rate ................................................................... 27 Environmental Factors and Anthocyanin Accumulation ............................................. 29 Irradiance ............................................................................................................ 29 UV-B Radiation .................................................................................................. 33 Temperature ........................................................................................................ 35 Nutrients .............................................................................................................. 39 Drought/Salinity .................................................................................................. 40 Carbohydrates ..................................................................................................... 41 Plant Growth Regulators ..................................................................................... 42 Future Research ........................................................................................................... 43 v Chapter 2: Anthocyanin and Chlorophyll Show Seasonal Variation in Grasses .............. 48 Introduction .................................................................................................................. 49 Materials and Methods ................................................................................................. 51 Results .......................................................................................................................... 53 Discussion .................................................................................................................... 57 Chapter 3: Solenostemon scutellarioides and Panicum virgatum Cultivars Vary in Photosynthetic Responses to Short-Term Irradiance, Carbon Dioxide, and Temperature Fluctuations ................................................................................................. 73 Introduction .................................................................................................................. 74 Materials