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February 19, 2013

Touchy, feely, moving.....plants?


 Staying Overnight at Xiaosha Stream
Trees, laced in mountain mist,
patch broken clouds;
the wind scatters a rainstorm of fragrant petals.
The green willows, it is said, are without feeling-
why then do they try so hard to touch the traveler
with their catkins?
Poem by Yang Wanli (1127-1206)
Translated by Jonathan Chaves

Plants can seem simple and inanimate.  They are rather silent and seem to sway passively in the evening wind.  When winter comes it is hard to tell if the deciduous trees are dead, alive, aware, or unconscious without their leaves. 



   
Through my studies in biology, however, I’ve realized that complexity found is proportional to how closely and attentively one looks.  That which seems “lesser, simpler or primitive” in passing, in reality, is just different upon closer observation.  
                                                                                                                                                            
I began reading a book by Dr. Daniel Chamovitz, director of the Manna Center for Plant Biosciences @ Tel Aviv University in Israel (http://en.wikipedia.org/wiki/Tel_Aviv_University), called "What a Plant Knows" (http://www.whataplantknows.com/) and came to realize that though plants are different from us in how they survive and thrive, there is an eerie complexity to their behavior.
A good example from the book is a plant called Cuscuta pentagona (http://en.wikipedia.org/wiki/Cuscuta), commonly known as dodder.  It lacks the ability to use the sun’s energy to make food—it has little or no chlorophyll to perform photosynthesis.  Rather, Cuscuta gets its energy from other plants—it is a parasite of other plants!  

Not only is Cuscuta a parasite, but it also has its preferences; when given choices it chooses consistently.  When amongst wheatgrass and tomato plants—tomato plants being the favorite—Cuscuta moves its stem about in circles not just to feel its surroundings, but also to “sniff” its surroundings until it picks up the scent of its beloved tomato plant at which point it will grow towards it to feast.  How it can distinguish between different species of plants is not well understood, but it is known that when tomato plant extract is put on a stick at any position in a room the dodder will seek it out; the volatile chemicals of its victim acting as an attractant, probably, amongst other signals.

When it has found a host Cuscuta begins winding its way around and up the stem putting spigot-like haustoria (http://www.thefreedictionary.com/haustoria) in along the way to obtain nutrients to grow.  When the haustoria are in place and a steady flow of nutrients are coming from the host, Cuscuta’s roots die though it continues to grow upward and onward, potentially, to many other hosts.
To get a feel for just how active and deliberate dodders are check out this video:
 
Plants lack a nervous system, but that doesn’t mean that they can’t sense their environment.  On the contrary plants, as exemplified by Cuscuta pentagona, act upon the information they obtain with complex behavior.  They can “smell” their neighbors and move toward or away from them; they can feel what they touch and in the case of dodder can accurately pierce their haustoria to where the nutrient-rich sap of their host is.  Plants are also known to be responsive to light and shadow, time, temperature, gravity, touch, chemicals from insects and other plants, and probably many other stimuli not yet discovered.   

One departing, unscientific thought/question that arose in my head while reading “What a Plant Knows”:  Just as animals exhibit behavior and communicate through movement, do plants exhibit similar behaviors and expression through growth? 

Post by: Seth Commichaux

Sources used:
Chamovitz, Daniel.  What a Plant Knows.  New York: Scientific American, 2012.
“Cuscuta.”  Wikipedia.  12 Feb. 2013.
                                                                                                                                       

                

1 comment:

Anonymous said...

thanks for share...