Reproductive development in dwarf mistletoes (genus Arceuthobium): the male's tale, explosive seed discharge, and 'environmental' microscopy.

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Dwarf mistletoes (genus Arceuthobium, Santalaceae) are parasitic flowering plants that infect economically important conifers, seriously compromising their health. As effective maturation of pollen, its dispersal, and seed dissemination all govern the success of Arceuthobium as a parasite, understanding developmental and dispersive events will identify key stages toward which a control program may ultimately be devised. The proposed work will use Arceuthobium americanum (the lodgepole pine dwarf mistletoe) collected near Kamloops, British Columbia and target three short-term objectives. In Objective 1, pollen development will be delineated using advanced tools for microscopy. My students and I will employ light microscopy (LM) and transmission electron microscopy (TEM) to explore developmental anatomy and morphology of anthers and pollen. We will also use fluorescence microscopy (FM) and TEM in conjunction with specific antibodies to determine changes in pollen cell wall chemistry. In Objective 2, the role of aquaporins (membrane water channels) in seed dispersal will be defined in collaboration with Dr. Ralf Kaldenhoff at Technische Universität Darmstadt, Germany and Dr. Carl Douglas at the University of British Columbia. Arceuthobium species are standouts among flowering plants, as they forcibly discharge their single seed from the fruit via hydrostatic pressure. We will identify aquaporin genes in Arceuthobium and monitor their expression using real-time PCR and in situ localization. In Objective 3, real-time changes in dehiscing anthers, intercepted pollen, discharging fruit, and released seeds will be examined with 'environmental" scanning electron microscopy (SEM). Through the Canada Foundation for Innovation, my lab has acquired an SEM capable of imaging living specimens under varying pressures, temperatures, and relative humidity. This powerful tool will enable critical questions regarding real-time events in anthers, germinating pollen, mature fruit, and seeds to be answered. The proposed work will train 13 undergraduate and 3 graduate students as well as contribute information that can be used to shape management decisions regarding this notorious forest pest.