University of Cambridge > > Plant Sciences Departmental Seminars > Pollen tube growth: of male gametophytes and the need for models

Pollen tube growth: of male gametophytes and the need for models

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Pollen is the male gametophyte of plants. From a dehydrated, quiescent organ in the atmosphere, pollen grains take up water from the female tissues in a matter of seconds, and in minutes develop a unique form of cellular outgrowth, the pollen tube. Pollen tubes are among the fastest growing cells in Nature, they achieve growth rates up to 4 um/sec, and in a matter of few hours can increase their volume up to 50 fold without division (1). Despite copious amounts of detailed physiological and molecular data, the mechanistic regulation of growth in pollen tubes still lacks an integrative model. While transcriptomics reveals the presence of about 7.000 genes, theoretical modeling shows that cooperation of all of these into two processes- wall surface and cytoplamic volume growth- is condition enough to generate apical growth as we know it. Spatial and temporal integration of extended biochemical and biophysical processes is mandatory, and in the past we have proposed and demonstrated that “ion dynamics” which we define specifically as the regulation of ion membrane fluxes and cytosolic free ion concentration- is maybe a common denominator of this integrative processes, and follow the behavior of a dynamical attractor on the space phase (2). In pollen tubes, ion fluxes are polarized, implying that carriers for protons, calcium, chloride and potassium show non-linear patterns in space (polarized distribution of carriers) and also in time (oscillatory and chaotic behaviors) (3). We thus are systematically cloning and GFP expressing the putative genes involved in ion dynamics. Recently we cloned the first proton pump P-ATPase from tobacco pollen (Nt AHA - Nicotiana H+ ATPase), which shows clear correlation with the flux patterns: NHA is excluded from the apex membrane by mechanisms involving polarized translation, the actin cytoskeleton and membrane recycling (4). Nt AHA gets polarized soon after hydration, and its absence is predictive of the germination pore. Information about fluxes and underlying molecular mechanisms are now being integrated in intracellular diffusion models which should allow us to test the adequacy of our model.

(1) Int.J.Dev.Biol. 49:595-614, 2005; Int.J.Dev.Biol. 49:615-632, 2005; (2) BioEssays, 23:86-94, 2001 (3) Int.J.Dev.Biol., doi:10.1387/ijdb.072296em, 2008; Sex.Plant Reprod., doi:10.1007/s00497-008-0076-x, 2008 (4) Plant Cell, 20:614-634, 2008.

This talk is part of the Plant Sciences Departmental Seminars series.

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