STUDENT QUESTION: relationship between senescence and

Oliver Sparrow ohgs at chatham.demon.co.uk
Wed Mar 2 11:51:18 EST 1994


You want to read up on cytokinins. The roots of a vigorous plant
produce hormones which suppress senscence, which seems the otherwise
natural lot of leaf tissue. This has some interesting dynamic 
consequences:

Roots, being the bottom end of the source-sink pecking order, get
starved when major sinks switch on. You may have wondered why cereal
plants become sensescent and mobilise up to half their physical mass
so that this can be loaded into the developing seed. The answer seems to
be that the roots get straved, the hormone flow stops: off the system
goes.

Mild drought lowers leaf turgor and stops cells from swelling (as do
other mechanisms) What assimilate there is, therefore, is less sharply
sought and roots do well: that is, in dry conditions, roots grow, leaves
do not. Adaptive, no? But under sharp stress, roots starve too; so leaves
become sensescent, remobilise reserves by which the core of the plant 
survives, then drop off and so reduce water loss. 

This comes back to your gene. Does it fit with all of this complex embedded
behaviour? If not, think hard about your hypothesis.
_________________________________________________

  Oliver Sparrow
  ohgs at chatham.demon.co.uk



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