The phloem is one of the central tissues in the plant. It is notoriously difficult to access and to investigate, because it is usually covered by a thick layer of opaque tissues. Other tissues that are deeply embedded in the plant body can often be isolated for cell biological investigations with good results, because individual cells remain functional when separated. The phloem, in contrast, forms a network of tubes of low resistance throughout the plant, and the driving forces for long distance transport and unloading are generated in distant organs. Detachment from either sink or source leads to an instant cessation of transport function and the emergence of structural artifacts. Yet, the phloem is a key player in plant performance. Virtually all terrestrial energy-rich substances that form the basis of human food sources (including cereals, fruits, roots and tuber crops) as well as nearly all carbon sequestered in forest ecosystems are translocated via the phloem. In addition, the phloem serves as the primary channel for long-distance signaling and communication between plant organs, transmitting information about biotic and abiotic stresses and enabling coordinated systemic responses. Co-evolution has led to an armada of pests and pathogens exploiting the phloem network. Piercing insects such as aphids directly feed on the nutritional phloem sap. Plant viruses, bacteria and phytoplasma utilize sieve tubes for systemic spread and infection, leading to massive crop losses every year.

Although considerable efforts have been devoted to improving photosynthetic activity, corresponding increases in crop yield have not been achieved. Limited knowledge of phloem-mediated loading, transport, and unloading of photoassimilates represents an important constraint for further productivity gains. Similarly, our capabilities of fighting devastating diseases such as huanglongbing and others are very limited as the interaction with the sieve element and it’s organelles are practically unknown.

We have developed multiple in situ techniques to study phloem structure/function relations and plant pest interactions. In addition, we study plasmodesmata as their function is closely related to phloem function.

Find out more about our research.

Selection of publications (click publications for a full list)

•  Howell AH, James V, Christensen AH, Vasina VV, Jensen KH, Foley J, Evans JE, Stone HA, Peters WS, Knoblauch M (2026) The influence of electrical charge on plasmodesma conductivity. Proceedings of the National Academy of Science USA 123 (15). doi:ARTN e2527879123
• Howell AH, Volkner C, McGreevy P, Jensen KH, Waadt R, Gilroy S, Kunz H-H, Peters WS, Knoblauch M (2023) Pavement Cells Distinguish Touch From Letting Go. Nature Plants https://doi.org/10.1038/s41477-023-01418-9
• Liu Y, Vasina VV, Kraner ME, Peters WS, Sonnewald U, Knoblauch M (2022) Proteomics of isolated sieve tubes from Nicotiana tabacum: sieve element-specific proteins reveal differentiation of the endomembrane system. Proceedings of the National Academy of Science. doi: 10.1073/pnas.2112755119.
• Benjamin T Julius, Tyler J McCubbin, Rachel A Mertz, Nick Baert, Jan Knoblauch, DeAna G Grant, Kyle Conner, Saadia Bihmidine, Paul Chomet, Ruth Wagner, Jeff Woessner, Karen Grote, Jeanette Peevers, Thomas L Slewinski, Maureen C McCann, Nicholas C Carpita, Michael Knoblauch, David M Braun (2021) Maize Brittle Stalk2-Like3, encoding a COBRA protein, functions in cell wall formation and carbohydrate partitioning. The Plant Cell
• Knoblauch J, Knoblauch M, Vasina VV, Peters WS, 2020. Sieve elements rapidly develop ‘nacreous walls’ following injury− a common wounding response? The Plant Journal102, 797-808.
• Timothy J Ross-Elliott, Kaare H Jensen, Katrine S Haaning, Brittney M Wager, Jan Knoblauch, Alexander H Howell, Daniel L Mullendore, Alexander G Monteith, Danae Paultre, Dawei Yan, Sofia Otero, Matthieu Bourdon, Ross Sager, Jung-Youn Lee, Ykä Helariutta, Michael Knoblauch, Karl J Oparka. (2017) Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle. eLife 2017;6:e24125
• Knoblauch, M., J. Knoblauch, D.L. Mullendore, J.A. Savage, B.A. Babst, S.D. Beecher, A.C. Dodgen, K.H. Jensen, and N.M. Holbrook. (2016). Testing the Münch hypothesis of long distance phloem transport in plants. eLife. 5:e15341
• Knoblauch M, Vendrell M, de Leau E, Paterlini A, Knox K, Ross-Elliot T, Reinders A, Brockman SA, Ward J, Oparka K. (2015) Multispectral phloem-mobile probes: properties and applications. Plant Physiology 167 1211-1220
• Knoblauch J, Mullendore DL, Jensen KH, Knoblauch M (2014) Pico gauges for minimally invasive intracellular hydrostatic pressure measurements. Plant Physiology 166, 1271-1279
• Knoblauch M, Froelich DF, Pickard WF, Peters WS (2014) SEORious business: structural proteins in sieve tubes and their involvement in sieve element occlusion. Journal of Experimental Botany 65 1879-1893.
• Dettmer J, Ursache, R, Campilho, A, Miyashima, S, Belevich, I, O’Regan, S, Mullendore, DL, Yadav, SR, Lanz, C, Beverina, L, Papagni, A, Schneeberger, K, Weigel, D, Stierhof, YD, Moritz, T, Knoblauch, M, Jokitalo, E, Helariutta, Y…More. (2014) CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication. Nature Communications 5, 1-11
• Knoblauch M, Oparka KJ (2012) The structure of the phloem–still more questions than answers. The Plant Journal. 70 (2012) 147-156
• Froelich DF, Mullendore DM, Jensen KH, Ross-Elliott TJ, Anstead JA, Thompson GA, Pelissier H, Knoblauch M (2011) Phloem Ultrastructure And Pressure Flow: Sieve-Element-Oclussion-Related Agglomerations Do Not Affect Translocation. The Plant Cell, 23
• Knoblauch M, Peters WS (2010) Münch, morphology, microfluidics – our structural problem with the phloem. Plant, Cell, Environment 33, 1439 – 1452
• Mullendore D, Windt CW, Van As H, Knoblauch M. (2010) Sieve tube geometry in relation to phloem flow. The Plant Cell 22, 579-593
• Pelissier, HC, Peters WS, Collier R, Van Bel AJE, Knoblauch M (2008) GFP Tagging of Sieve Element Occlusion (SEO) Proteins Results in Green Fluorescent Forisomes. Plant and Cell Physiology, 49 (11), 1699-1710
• Knoblauch M, Noll GA, Müller T, Prüfer D, Schneider-Hüther I, Scharner D, van Bel AJE, Peters WS (2003) ATP-independent contractile proteins from plants. Nature Materials 2, 600-603
• Knoblauch M, Peters WS, Ehlers K, van Bel AJE (2001) Reversible calcium-regulated stopcocks in legume sieve tubes. The Plant Cell 13, 1221-1230
• Knoblauch M, Hibberd JM, Gray JC, van Bel AJE (1999) A galinstan expansion femtosyringe for injection of eukaryotic organelles and prokaryotes. Nature Biotechnology 17, 906-909
• Knoblauch M, van Bel AJE (1998) Sieves tubes in action. The Plant Cell 10, 35-50