A recent spate of books – e.g. Daniel Chamovitz’s “What a plant knows”, Richard Karban’s “Plant Sensing & Communication”, and “Brilliant Green” by Stefano Mancuso and Alessandra Viola – have opened up our imaginations to the sensory capabilities of plants. In identifying plant equivalents of the five traditionally recognised human senses – touch, taste, hearing, smell, and sight – those volumes challenge us to re-examine the ways in which plants ‘find out’ about their environments.* However, and as uncomfortable as that invitation seems to be – particularly for those who see in such investigations threatening notions of plant intelligence, etc. – I don’t think any of those texts have gone as far as Frantisek Baluška and Stefano Mancuso.
In their article on plant vision, these notable plant neurobiologists posit the notion that plants are able to sense shapes and colours via plant-specific ‘ocelli’. For leaves, they propose that the cuticle acts like a cornea, and the epidermis as a lens, focussing light onto the light-sensitive mesophyll cell layer. And for roots (which live in soil that is not completely devoid of light, and whose apices are highly specialised in light-sensing…), they envisage light-focussing by the epidermis onto the light-sensitive sub-epidermal cells. Such use of light is therefore deemed to be harnessing its informational content rather than its capacity as an energy source – as in photosynthesis.
As is typical of papers that consider plants as more than just receivers of environmental stimuli (and for which views the burden of proof/provision of supporting evidence seems to be so much higher than for more mainstream hypotheses…), this synthesis draws upon the older – and oft-forgotten/ignored/overlooked… – plant biology literature and the most up-to-date contributions. Thus, the work of such greats of plant science as Gottlieb Haberlandt, Francis (son of Charles…) Darwin, and Harold Wager is skilfully tied in with studies that consider cyanobacteria to act as micro-lenses, and the remarkable leaf-mimicry ability of Boquila trifoliolata.
This article – no doubt provocative and far too outlandish for some – is appropriately billed by the journal as a Forum piece. And just like the forum of the Roman Empire (which is appropriate since co-author Mancuso is based at the University of Florence, in Italy) this refers to a space wherein discussion of ideas took place. So, let’s add to the debate, where do you stand on plant senses? Are you ‘for ‘em’, or ‘agin’ ‘em’…?
* And represent approaches that really help to impress upon phytoaverse, zoochauvinists how interesting – animal-like if you will – plants are…[Ed. – for readers who like to be further challenged, and are open to exploring the more ‘sensitive’ side of plants, may we suggest Ratnesh Chandra Mishra et al’s Opinion Paper “Plant acoustics: in the search of a sound mechanism for sound signaling in plants”? And, Ritesh Ghosh et al.’s paper that examines how “exposure to sound vibrations lead to transcriptomic, proteomic and hormonal changes in Arabidopsis”. You might also be intrigued by Olivier Hamant and Bruno Moulia’s Tansley Insight that considers how plants might have a sense of self.]