Vol. 16—1962 - NorthEastern Weed Science Society

27
CELLSTRUCTUREANDPLANTGROWTHCRMONEACTION
ArthlW W. Galston l
The Chemical control of pJ.Qil groWth is largeJg.~ empirical art which
has only occasionally approached the level of a pre~table science. This
empiricism is largely a consequence of our imperfeot unqerstanding of the
nature of· the action of growth reg~ator,y chemical~ .such as the auxins.and
gibberellins. It is a constant source of embarrassment to plant physiologists
and biochemists that roughly 35",~s after the disoove1'!Y of auxins we are .
still completely unable to. describe their mode of. &lotion in plant cells.
Lest we become too humble and emba;rrasaed about this sta!te of affairs, it 1s
well to recall that nowhere in biochemistr,y or phys1010gf :l,.sthere complete
understanding of the mode of action of any honnone} even such well known
systems as insulin have not been definitely pin-pointed biochemically. This
has caused some people to wonder whether if, in invelitigating the mechanism
of hormone action, we have not been barking up the wrong tree. All of us
have been looking for chemical effects, and in order to lilXPlain the ver,y
great efficacy of very few molecules of the honnone,we have tended to assume
that the hormone either becomes part of an enzyme systelll; or controls the
action of an enzyme system. Only in this way, it has been believed, can we .
get the proper amplification to pe:nnit relatively large biological effects
to be produced by a small number of molecules. Nonetheless, this line of.
reasoning has been most unrewarding in the past and In fact we still know
of no honnone whose action can be oompletely explained with reference to ~
partioular enzyme system.
Perhaps a part of the reason for our ignorancElof the mode of action .
of honnones lies in the fact that we are only now beg!nntng to understand
the structure of the ver,y complexl1llichine which we call the living cell.
Just as one could not hope to understand the funotioning of an automobile
engine without knowing in detail the structure of its component parts, M
the student of any aspect of cell physiology cannot hope to be able to
supply definitive answers without an intimate knciwledge .of the structure of
the cell and of its component parts, In recent years a revolution in our
understanding of cell structure has resulted from. 1;tle systematic applicat+on
of electron miorosoopy and ultra-thin sectioning to tJ1e ,study of various
cell types. BeeauseI believe that this new info~t:l,.on is basic to any
discussion of oell physiology and of auxin action, ! shall preface IIl;y
remarks with a brief description of our modern view of tpe plantoell. In
so doing, I would like to remind you that while the o~nar,y light mioroscope
is able to give us magnifioations in the range. of 1,000 diameters
with a resolution dOlm to '.2 mierons, the eleotron lIIicrosoope has already
given us olear pictures at 150,000 diameters magnif1~ation with a resolutipn
of 0.003 microns. In faot the theoretical limit of resolution, being based
on the wave length of the radiation employe~ can be imprpved still further
by two orders of magnitude , This clearly brings us liown to the range of
molecular dimensions. We should therefore expeot ~t ~thin the next
several decades, the ~stematic improvement of elec~onMicroscopy and
related. techniques will permit us to have a fairly qetailed view of the