What is pattern formation ? or gases (ethylene. Plant are
substances. plant hormotrs
can be broadly divided into two groups based on their
functions in a living plant body. one group growth
promoting activities. such as cell division. cell pattern
. flowering. fruiting and formation These
are also called plant growth promoters _ e.g. auxins. and
cytokinins. pc,Rs of the other group play an role plant
responses to Wounds and stresses of biotic abiotic tn-igin. They are
also involved in Various grOwth inhibiting activities such as dormancy
and abscission. The PC.R abscisic acid belongs to this group.
PGR_ ethylene. could fit either of the groups. but it Is largely an
of growth activities.
15.4•.2 The Discovery of Plant Growth Regulators
Interestingly. the discovery or each 01 the five
major groups of PGRs have been accidental.
All this started with the observation of Charles
and his Francis Darwin when they
that the coleoptiles Of canary grass
responded to unilateral illumination by
*rowing towards the light sourceß
fmotropisrnJ. After a series of experiments.
It Vas that the tip Of coleoptile was
ute transmittable influence that caosed
1 S. 10
trnding of the entire colecvtile (Figure
m. Auxin isolated by F. W. Went
lips of coleoptiles of oat