Peter Hepler University of Massachusets. PETER K. HEPLER is the Ray Ethan Torrey Professor, Emeritus in the Biology Department at the University of Massachuses, Amherst, MA. He has been invesgang the cytoskeleton in plants for over 50 years. He also studies the role of calcium and protons during signal transducon, and is parcularly interested in the interplay between these ions and the cytoskeleton. Earlier work focused on the mechanism and control of cell division, with parcular emphasis on cytokinesis. More recently aenon has been given to studies on the mechanism and regulaon of pollen tube growth. In his work Dr. Hepler uses a variety of microscopical methods and approaches including both light and electron microscopy. In more recent years an emphasis has been given to the examinaon of structures and dynamic processes as observed in living cells. He and co-workers have been involved in developing the methods and use of fluorescent analog cytochemistry, and as well as transient expression of fluorescent reporters to examine the cytoskeleton in living plant cells. He has also championed the use of raometric ion imaging for examining the locaon and dynamics of calcium and protons during plant growth and development. Talk: Polarized growth of the pollen tube: a role for ions and acn. Peter K. Hepler Biology Department, University of Massachuses, Amherst, MA 01003. Pollen tubes are polarized, p-growing cells that deliver sperm cells to the egg apparatus in higher plants. Their growth is essenal for sexual reproducon, and for the development of the fruits, nuts and seeds that we eat. Herein I report on the mechanism of lily pollen tube growth. Rapid, polarized growth depends on the synthesis and localized secreon of cell wall components, which are packaged in vesicles, and transported apically along acn microfilaments. Controlling factors include acn, which is organized as a corcal fringe in the pollen tube p, plus apical gradients of calcium and pH. All these factors demonstrate an oscillatory behavior that correlates with the oscillaon in growth rate. Quantave studies indicate that increases in secreon, the alkaline band, and acn polymerizaon ancipate the increases in growth rate, whereas increases in the calcium gradient follow the increases in growth rate. To gain further insight we reversibly inhibited growth with KCN, and followed the effects on calcium, pH, secreon and the apical acn fringe. During recovery the calcium gradient reappears ≈2.5 minutes before growth restarts. However the alkaline band precedes the increase in calcium. Secreon follows a paern similar to the alkaline band, re-emerging before KCN has been removed. KCN also degrades the acn fringe. Secreon, which restarts in the absence of the fringe, inially lacks focus and causes ballooning of the apex. However, with the re-appearance of the fringe, growth becomes polarized. I suggest that the acn fringe delivers vesicles to their secretory locus, thereby giving polarity to the growing pollen tube, while the proton ATPase establishes the membrane potenal and ion gradients that control the transport of nutrients necessary for growth. Luis Cárdenas Instuto de Biotecnología, UNAM. LUIS CÁRDENAS is a tenured professor at the Instute of Biotechnology (IBT) of the Naonal Autonomous University of México (UNAM) and a researcher at the Plant Molecular Biology Department. He earned his PhD from IBT-UNAM and then visited Peter K. Hepler´s lab in the USA for a postdoctoral training. He described that Nod factors (NFs) from Rhizobium induced an extensive fragmentaon of the acn cytoskeleton in living root hair cells. This study, which was as a cover story in Plant Physiology, has been cited over 100 mes and is emerging as a benchmark for further work on the structure of acn in response to NFs. These studies formed the basis for a review in Plant Physiology in 2000, which was highlighted as an Editors' Choice in Science. Perhaps his most insighul work was the discovery that reduced NAD, an important energy co-enzyme associated with mitochondria, oscillated during pollen tube growth, with oxidized NAD ancipang the increase in growth rate. These studies led to the hypothesis that oscillaons in metabolism iniate cell growth. This work was published in Plant Physiology and connues to be an emerging interesng aspect of plant cell growth. This contribuon was singled out by Faculty of 1000 as an important contribuon. He was awarded with the Alfonso Caso medal from UNAM as the best PhD student of his generaon, and his thesis awarded the Weisman prize from the Mexican Academy of Science. He was also awarded an American Society of Microbiology (ASM) fellowship to do summer training in Simon Gilroy's lab. At the moment he is interested in life cell imaging, polar growth, differenaon, and plant– microbe interacon. His work is fully supported by DGAPA UNAM and CONACyT, the two main sources for financial support. Talk: Reacve oxygen species in plant root hair cells as key regulators of the symbioc interacons and in pollen tubes as growth rate modulators. Cárdenas, L.1, Hernández-Barrera, A.1, Velarde-Buendía, A., Sánchez, R.1, Johnson E.2, Wu, H.M.2, Quinto, C.1, Cheung, A.2. 1Instuto de Biotecnología, Universidad Nacional Autónoma de México, Ap. Postal 510-3 Cuernavaca, Morelos, México. [email protected] 2Department of Biochemistry and Molecular Biology, University of Massachuses, Amherst. In plant cells ROS accumulaon have been involved in several processes such as: development, hypersensive response, hormonal percepon, gravitropism and stress response. In guard cells from Vicia faba it has been shown to regulates the opening of stomata and in root hair cells from Arabidopsis ROS levels generate and maintain an apical calcium gradient and it has been proposed to play a key role in the cell wall remodeling during polar growth in pollen tubes and other p growing cells. NADPH oxidases have emerged as the main source of ROS to sustain the polar growth since mutaons in this genes impairs the ROS generaon and root hair development. Furthermore, ROS have emerged as a key regulator during the mutualisc interacons and silencing or overexpression of ROS generang enzymes such as NADPH oxidases affect the onset of nodulaon and mycorrhizaon. Pollen tubes and root hairs exhibit an oscillatory growth with phase of high and low growth rate. It has been shown that extracellular ROS producon also oscillate with a similar frequency, but out of phase. However, a clear analysis of intracellular ROS dynamic has not been depicted. Herein we report a new molecular probe to depict the ROS dynamic during root hair cell and pollen tube apical growth. Hyper is a new generated GFP fused to the OxyR domain that result in a hydrogen peroxide specific probe. This molecular probe was expressed in root hair cells from Arabidopsis and tobacco pollen tubes . By using high resoluon microscopy we depicted an apical H₂O₂ gradient at the p dome where the polar growth occur, furthermore we were able to visualize dynamic ROS oscillaons in root hair cells, which are couple to growth. In pollen tubes we also found a parcular ROS distribuon, with clear oscillaons couple to growth fluctuaons. In both p growing cells, the apical regions are the site where the more dynamic ROS changes were observed, furthermore we describe the localizaon of the NADPH oxidase in membrane lipid ra, suggesng a pivotal role in polar growth. Reinhard Fischer Karlsruhe Instute of Technology. REINHARD FISCHER is a Full Professor at the Karlsruhe Instute of Technology (KIT) in Karlsruhe, Germany. He is leading an independent research group on fungal molecular biology since 1994 and is internaonally well-recognized. He and his research team analyzes different aspects of fungal biology. Main fields are the photoresponse of Aspergillus nidulans, where he discovered a role for phytochrome in fungi. Another focus is the cell- and molecular biological analysis of polarized growth. In an applied research field, he analyzes the secondary metabolism of Alternaria alternata to discover novel compounds and understand the genec regulaon of the involved genes. Recently, he started a new line of research with the analysis of the molecular biology of nematode-trapping fungi. Reinhard Fischer has served as editor or associate editor for several journals such as Fungal Genecs and Biology (2000-2012), Molecular Microbiology (since 2005), FEMS Microbiol. Leers (2005-2007), Molecular Genomics and Genecs (since 2006), Eukaryoc Cell (2013-2015), mSphere (since 2016), and mBio (since 2016). He was the organizer of the annual meeng of the German Microbiological Society (VAAM)(1500 parcipants) in 2011 and of the internaonal meeng on Fungal Biology (FBC)(300 parcipants) in 2013. He is elected member of the grant review panel for Microbiology, Immunology and Virology at the German Science Foundaon (DFG) since 2012, re-elected 2016. He is liaison professor of the Studiensung des deutschen Volkes since 2009. He has educated 35 Ph.D. students and more than 40 Diploma- or Master students. Talk: Septal microtubule-organizing centers of Aspergillus nidulans share proteins with the outer plaque of spindle pole bodies and are anchored at septa through the disordered protein Spa10. Ying Zhang1, Xiaolei Gao1, Raphael Manck1, Marjorie Schmid1, Aysha H. Osmani2, Stephen A. Osmani2, Norio Takeshita1, 3 and Reinhard Fischer11* 1Karlsruhe Instute of Technology (KIT) - South Campus, Instute for Applied Biosciences, Dept. of Microbiology Hertzstrasse 16 D-76187 Karlsruhe Phone: +49-721-6084-4630 Fax: +49-721-6084-4509 E-mail: reinhard.fi[email protected] homepage: www.iab.kit.de Microtubule-organizing centers (MTOCs), such as centrosomes or spindle-pole bodies (SPBs) of fungi, are large, mul-subunit protein complexes. In the model fungus Aspergillus nidulans septum-associated MTOCs (sMTOCs) nucleate microtubules in addion to SPBs. The structure of sMTOCs is poorly understood and how they are targeted to septa is unknown.