Nigel Chaffey
One way of increasing crop productivity is to increase the amount of grain or other harvestable product that is actually harvested from the plant. To that end scarecrows were invented by human beings, although their success in that regard is inconsistent at best (is there a scientific study on the effectiveness of scarecrows just waiting to be done..?). However, another variation on the scarecrow theme aims to tackle productivity more directly, and shows quirkily that clues to above-ground productivity can come from ‘down-below’. Investigating any similarities between the endodermis in roots [‘the central, innermost layer of cortex in some land plants… a… ring of endodermal cells that are impregnated with hydrophobic substances (Casparian Strip) to restrict apoplastic flow of water to the inside’] and the sheath of mesophyll cells that surround the vascular bundles in leaves of C4 photosynthetic plants (the so-called Kranz anatomy, which is the site of net CO2 fixation into photosynthesis in those plants) such as maize, Thomas Slewinski et al. have discovered that a transcription factor called ‘SCARECROW’ is involved in development of both. [A transcription factor is a protein that ‘binds to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to m(essenger)RNA’.] Scarecrow is more usually associated with various issues of cell identity and cell-patterning in subterranean roots [ a ‘wiki’ that incidentally has the serious scientific credibility of combining ‘collaborative and largely altruistic possibilities of wikis with explicit authorship’ – Robert Hoffman]. So, establishing its role in above-ground Kranz anatomy is both interesting and testament to a high degree of molecular economy in plant design principles. But the real hope is that this knowledge can now be exploited to convert C3 photosynthetic plants into Kranz-bearing C4 ones, which are photosynthetically more efficient than their C3 poor-relations. Set against a backdrop of global concerns about the ability of current crops to provide enough food for a growing world population [‘food security‘], this C3 to C4 conversion is one of the holy grails (e.g. Richard Leegood; Udo Gowik and Peter Westhoff; Rowan Sage and Xin-Guang Zhu), if not the Grand Challenge (Sarah Covshoff and Julian Hibberd), of plant physiology, and doubtless has many more years to run. However, rather than add extra cell layers, etc, into C3 plants, might it not be easier to engineer the rather neat trick of having both C4 and C3 photosynthesis in the same cell, as naturally exists in such plants as the hydrophyte Hydrilla verticillata (e.g. Srinath K. Rao et al.)? Sadly, I can take no credit for that suggestion(!), but see the experiences of Mitsue Miyao et al. and their attempts to effect this in C3 rice. However, if you want to dabble in such areas, you’ll probably want to keep such work under wraps – or in the confines of the lab – since Hydrilla has been hailed as ‘the perfect aquatic weed’ by Kenneth Langeland. Which gives me an idea: if it is allowed to escape and colonise the rest of the planet’s waterways with regrettable – but necessary! – elimination of native flora we’d have converted huge areas of the planet to more productive C4 photosynthesis at a stroke. If only we can eat the stuff, future food security will have been secured..? Isn’t science and a little bit of imagination great!? Who said scientists can’t be creative?
[Please do not attempt to test mischievous Mr P. Cuttings’ ‘Hydrilla hypothesis’ at home; and certainly not outdoors! – Ed.]
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