Department of Biological Sciences
Speaker: Prof. M. K. Mathew,
National Centre for Biological Sciences, Bangalore
Date/Time: Thursday, July 28, 2016 at 5:00 pm
Venue: L3, LHC
Title: Investigating Vesicle Trafficking in an Intact, Functioning Tissue: the
Arabidopsis Root
A critical process required for the sustenance of cells is a function called endocytosis. Among
other functions, endocytosis allows cells to engulf proteins and food or fluid matter from its
surroundings. Endocytosis can occur through several pathways – the most well-characterised of
these is mediated through a ‘coat protein’ (clathrin). Others, that do not require clathrin are
collectively termed clathrin-independent processes. The endocytic process and its various roles
have been extensively studied in animal systems. However, studies of these processes in plants
have been limited and largely restricted to clathrin-dependent endocytosis.
Most studies of endocytosis in any kingdom have been limited to cells in culture or on the
surface layer of tissues. Endocytic mechanisms may be expected to vary across cell types in an
intact, functional tissue and, moreover, be subject to differential regulation in response to diverse
physiological conditions. We have exploited the optical transparency and physical accessibility
of young Arabidopsis roots to explore the full panoply of endocytic mechanisms in different cell
layers. We observe a stratified distribution of endocytic processes, with different pathways
operating in different layers of the root. Saline stress induces a hitherto unreported pathway that
is clathrin-independent, catholic in its choice of cargo, and operates across all layers of the root.
Concomitantly, small acidic compartments in inner cell layers expand to form larger vacuole-like
structures.
Sequestration of Na+ in endomembrane structures energised by a H+ gradient has been implicated
in surviving salt stress. This requires both large endomembrane compartments and pH gradients
across their limiting membranes. The formation of the former appears to be correlated with the
induction of salt-induced endocytosis. Development of pH gradients is also induced by salt by
mechanisms that we are currently investigating.