I love transfer cells. They are plant cells (which is great), but with a difference; they are ‘specialized parenchyma cells that have an increased surface area, due to infoldings of the plasma membrane. They facilitate the transport of sugars from a sugar source, mainly leaves, to a sugar sink, often developing fruits. They are found in nectaries of flowers and some carnivorous plants’. Those plasma membrane infoldings are the result of cell wall ingrowths and transfer cells (TCs) appear to have been present in angiosperms for over 50 million years.
The term ‘transfer cell’ was coined in recognition of proposed general functions in transferring solutes between interconnected protoplasts (symplast) and non-living spaces (apoplast) in or surrounding the plant. TCs are found in many widely dispersed plant types and their importance probably lies in their role in nutrient distribution, as they facilitate high rates of transport at sites that might otherwise present ‘bottlenecks’ for apo-/symplasmic solute exchange; e.g. crop yield in many species may ultimately depend as much upon proper functioning of internal TCs as it does on externally applied fertiliser(!). So, the more that is known about development, etc, of TCs the better for all of us. Well, good news then that Kiruba Chinnappa et al. have developed phloem parenchyma TCs in Arabidopsis as an experimental system to identify transcriptional regulators of wall ingrowth formation. Exploiting this system, they’ve so far identified ‘master switches’ that respond to various inductive signals to co-ordinate wall ingrowth deposition in TCs. Ultimately, the hope is that manipulation of this process may provide new opportunities for improving crop yield. I’m sure we can all wish them well in that noble endeavour.
[Ed. – And, if your appetite for TCs has now been whetted, these curious cells will feature in a future Research Topic in Frontiers of Plant Physiology to be edited by David McCurdy and Gregorio Hueros. But, if you can’t wait until then, Felicity Andriunas et al.’s article “Intersection of transfer cells with phloem biology—broad evolutionary trends, function, and induction” is available now…]