Ageing in plant cells

christian hartleben prophit at
Tue Dec 13 07:12:22 EST 1994

W.G.VAN.DOORN at wrote:
: 	In our institute (of the Netherlands Department of Agriculture, located
:      in Wageningen) we study both the fundamental and applied aspects of plant 
:      senescence.

:      	Plant senescence is now generally thought to be related to an increase 
:      in free radicals, due to a decrease in the activity of scavenging molecu-
:      les. The free radicals then result in a decreased phospholipid content of 
:      membranes, which would explain why the cells show increased leakage of
:      solutes. 
   Would an increase in exposure to radiation, specifically ultra violet 
wavelengths in the 300-400nm range inhibit selectively the molecules with 
conjugated pi orbitals, be responsible for the decrease in activity of 
the so-called scavaging molecules ?   I have been contemplating similar 
issues over the last month, which explains why I have such a hypothesis 
to offer.  
	The organic chemistry text which i have open before me points out 
that mono- and sesquiterpenes (resonance at shorter wavelengths), but 
also longer chains of carbons in adjacent pi-bonds like beta-carotene 
(lambda max = 455nm).  It would seem that such molecules would be 
disfavored under conditions of exposure to a modified spectrum.  This 
would be akin to moving a plant to latitudes where the wavelengths and 
their respective intensities and durations caused the failure of 
coordinated maturation processes as well as issues of repair (of which i 
have never had a clear concept).
	I have a posting to an agricultural discussion by an australian 
whose cauliflower florets became necrotic this season.  Furthermore, I 
understand from a Japanese news broadcast that the hot pepper crop in 
South Korea this last fall was so extremely spicy as to indicate that the 
plant had matured in a substantially different fashion.  The butterflies 
have failed to arrive in Santa Cruz, CA this fall, as they do during 
their seasonal migration.
	I would like to continue this exchange, but it is rather early 
where I am, and I need some sleep.  You make think me mad for the above 
collection of ideas; there certainly is a lot of confusion about.  But I 
have yet to find any other way to consider these events, and so i find it 
necessary to ask your consideration and appraisal.

chris hartleben

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