membrane recycling as basis for graviperception and graviresponse (RootResponse)

abstract

Experiments under reduced gravity have been performed in drop tower, during parabolic flights and in the TEXUS programme. Control experiments on ground under different expositions of plants, normal vertical, horizontal and inverted position, as well as on clinostats (simulated weightlessness) and centrifuges (hypergravity) completed and ascertained results from flight experiments. With plants, for the first time extreme early signals have been shown which are triggered by microgravity. Using specific microelectrodes we were able to detect in roots of Zea mays changes in oxygen uptake, oxygen burst, reactive oxygen species (ROS), nitric oxide (NO) and hydrogen peroxide (H2O2) already 3 to 5 seconds after entering the microgravity environment (drop tower, parabolic flights). In addition, electrical patterns measured by multi electrode arrays (MEA) and action potentials have been identified exclusively in region of the transition zone as it was with early signals mentioned before. This specific zone is localised between the sites of graviperception and gravirepsonse and is structurally characterised by remarkable rearrangement of the actin cytoskeleton system. Immunolocalisation of diverse proteins in this zone, like PIN proteins, synaptotagmin, plasma membrane proton pump and motor protein myosin showed their specific arrangement at transversal cell walls. Here occurs highest activity of cytoskeleton dependent endocytosis, vesicle transport and membrane recycling. We therefore defined this cellular region as plant synapses. The recycling process is partially gravity dependent. From our results we can conclude that microgravity acts as stress factor for plants and furthermore that polar auxin transport can not explained exclusively by diffusion. We therefore propose in addition a model on the basis membrane recycling.

• Volkmann D, Baluška F (2007) Physiological responses of higher plants. In: Biology in Space and Life on Earth, Brinckmann E (ed), WILEY-VCH Verlag GmbH, pp. 53-70

• Baluška F, Barlow PW, Volkmann D, Mancuso S (2007) Gravity related paradoxes in plants: plant neurobiology provides the means for their resolution. In: Biosemiotics in Transdisciplinary Context, Proceedings of the Gathering in Biosemiotics 6, Salzburg 2006, Witzany G (ed), Umweb, Helsinky

• Volkmann D, Johnsson A, Baluska F (2009) The puzzle of plants. Looking up. Europe’s quiet revolution in micrgravity research. Sci Am Special Issue, 92-99

experiment year: 2008
number of drops: 12