The structure and plastochronic changes of the shoot apex, and the origin,
development, procambialization, and vascular relationships of the axillary bud in
Cuminum cyminium were investigated.
Pre-leaf initiation, leaf initiation, and post-leaf initiation phases of the shoot
apex are identified. The inflorescence is axillary. During flowering the main vegetative
shoot apex is semispherical, stratified, and devoid of any distinction between the central
and peripheral zones.
The vegetative axillary bud is differentiated from the peripheral zone of the
shoot apex at the second node. It is delimited by an arcuate shell zone which helps
in changing the apical position of the bud to foliar. The emergence of the bud is effected
by the meristematic activity of tunica and corpus cells. A single prophyll is formed at
right angles to the axillant leaf.
Usually the bud trace procambium is differentiated during prophyll initiation.
Occasionally it may be seen earlier, but not in connection with the earliest visible bud
meristem. There are four to six strands of the bud trace directly interconnecting not
only the strands of the prophyll and axillant leaf traces but also those of the second or
sometimes even the third bud leaf and the axillant leaf. The bud trace procambial
connection is formed by basipetal and acropetal differentiation of procambium in
which the bud meristem cells and vacuolated ground meristem cells below the bud are
involved. The cells of the peripheral zone of the bud apex below the prophyll primordium
procambialize in a basipetal direction. As a continuation from the strand of the axillant
leaf trace, the adjacent vacuolated ground meristem cells below the bud acropetally
differentiate into procambial cells in the direction of the basipetal procambium and
they make connection with it. All the strands of the bud trace are not simultaneously
developed.
The vegetative and inflorescence buds show varying vascular relationships
between the strands of the leaf traces and those of the bud traces. The node differentiated
during the vegetative phase of the plant is trilacunar and the one formed at flowering
time is tetra- or pentalacunar. The nature and number of bud trace strands, however,
suggest fundamental similarities between vegetative and inflorescence buds.
Histochemical and cytophotometric estimation of DNA, RNA and proteins in the shoot apex of Nicotiana tabacum Linn.
