ACKNOWLEDGEMENT

I would like to express my thanks and gratitude to our

Principal Mr. Murali sir for giving me the golden
opportunity to do this wonderful Project on the topic
“Apical dominance in potato and coleus” which has
helped me in doing a lot of research. I would extend my
heartiest thanks to my Biology teacher Mrs. Sumaiya mam
for providing me with all the support I required at all times.
I would like to gratefully thank my parents for providing
me with all the facilities and a favourable environment at
home.
I would also thank my friends who have given me support
and helped me in finalizing the project in the given time
frame.

Thank You
 INDEX

S.no Topic

1 Introduction

2 Apical dominance

3 Apical dominance and illustrating

correlative effects of hormones

4
Auxin

5 Cytokines

6 Pruning

7 Apical dominance in potato

8 Apical dominance in coleus

9 Bibliography
 INTRODUCTION

Plants, like animals, produce hormones to regulate plant

activities, including growth. They need these hormones to
respond well to their environment and to sustain growth,
development, and dispersal. Plant biologists recognize
five major groups of plant hormones: auxins, gibberellins,
ethylene, cytokinins, and abscisic acid. Find out in this
guide the importance of each hormone in the life of a plant
(•) Apical dominance: It is the phenomenon by which the
presence of apical buds does not allow the nearby lateral
or axillary buds to grow.
(•) Apical bud secretes auxin which inhibits the growth of
lateral buds.
(•) If the apical bud is removed (Decapitation), the lateral
buds sprout i.e., start growing.
(•) However, if a paste containing auxin is applied on the
cut portion of the decapitated shoot, the lateral buds
remain inhibited in the similar way when apical bud is
present.
(•)The removal of apical bud is done for the preparation
of hedges and bushy growth in certain plants. For
example, when the apical bud of tea plants is removed, the
lateral buds start developing into branches. It is done to
produce a greater number of leaves so that yield can be
increased.
(•) In this phenomenon the central branch is dominant
over the side branches.
(•) It is the phenomenon in which control is exerted by
apical portions of shoot towards the outgrowth of lateral
buds.

Note: Auxin hormones maintain apical dominance, they

increase the growth of shoot and inhibit the growth of
lateral buds. When lateral bud present in the axil of the
leaves does not grow to form branches it is known as
apical dominance. It is caused due to apical bud.
Apical Dominance & Some Other Phenomena Illustrating
Correlative Effects of Hormones

Apical Dominance Varies with Species and Cultivars

Apical dominance is genetically based and varies with
species and cultivars. Some species show strong apical
dominance [e.g., Helianthus annuus (sunflower),
Tradescantia sp.]. Fieldgrown sunflower plants, 4 feet tall,
may show little or no lateral branching in intact plants. In
a nursery or greenhouse, by suitable gibberellin treatment,
they can be made to grow 7-8 feet tall and still show no
branching. Other species show an intermediate or partial
apical dominance, i.e., there is some branching [e.g.,
Phaseolus vulgaris (common bean), Vicia faba (broad
bean), Pisum sativum (pea), Ipomoea nil (Japanese
morning glory)], whereas still others show very weak or
no apical dominance— they show substantial and
continuing branching in intact plants (e.g., Coleus,
Arabidopsis). Apical Dominance Varies with Species and
Cultivars Apical dominance is genetically based and
varies with species and cultivars. Some species show
strong apical dominance [e.g., Helianthus annuus
(sunflower), Tradescantia sp.]. Fieldgrown sunflower
plants, 4 feet tall, may show little or no lateral branching
in intact plants. In a nursery or greenhouse, by suitable
gibberellin treatment, they can be made to grow 7-8 feet
tall and still show no branching. Other species show an
intermediate or partial apical dominance, i.e., there is
some branching [e.g., Phaseolus vulgaris (common bean),
Vicia faba (broad bean), Pisum sativum (pea), Ipomoea
nil (Japanese morning glory)], whereas still others show
very weak or no apical dominance— they show
substantial and continuing branching in intact plants (e.g.,
Coleus, Arabidopsis). Auxin: Auxin as a plant growth
hormone . This hormone is responsible for the growth and
elongation of the shoot. There is apical dominance
observed in presence of auxin. This results in the growth
of the central stem which is dominant and supresses the
growth of the lateral buds such phenomena is called apical
dominance . The auxins are produced at the tips . The
pruning of the tips is done where the braches are cut
periodically in mariculture . This allows the lateral buds
to grow and form braches . This help to grow and form
branches . This help to make the plant busty.
The affect of apical dominance can be overcome by which
of the following hormone? Presence of cytokinin in an
area causes preferential movement of nutrients towards it
When applied to lateral buds, they help in their growth
despite the presence of apical bud. They thus act
antagonistically to auxin which promotes apical
dominance. Therefore cytokinin can overcome apical
dominance.
Pruning
 Pruning is an invigorating process, stimulating
regrowth in proportion to pruning severity. Light
annual pruning is better than periodical severe
pruning.
 The two basic types of pruning cuts are heading and
thinning. Thinning cuts are the least invigorating type
of cut and are the most effective pruning cut for
maintaining woody plants in their natural form.
 Pruning, particularly heading cuts, stimulates
regrowth very close to the pruning cut. Heading cuts,
such as topping, dehorning and hedging, often are
misused and destroy the natural shape of plants
because they stimulate regrowth near pruning cuts.
 Bench cuts, pruning upright limbs back to flat limbs,
result in vigorous regrowth and weak limbs. Instead,
 thin out limbs leaving those oriented at a 45° to 60°
angle from vertical.
 Pruning time should be dictated by specific
requirements or characteristics of the plant such as
flowering date, susceptibility to cold weather, etc.
 Wounds heal fastest when pruning does not disturb
important areas of cambium such as the bark ridge
and branch collar. Wound dressing is cosmetic and
does not promote healing.
 All too often, improper pruning techniques seriously
damage or kill woody plants. If you wish to have
woody plants properly maintained, personally
supervise or conduct the pruning operation.
Potato (Solanum tuberosum) tuber, a swollen
underground stem, is used as a model system for the study
of dormancy release and sprouting. Natural dormancy
release, at room temperature, is initiated by tuber apical
bud meristem (TABmeristem) sprouting characterized by
apical dominance (AD). Dormancy is shortened by
treatments such as bromoethane (BE), which mimics the
phenotype of dormancy release in cold storage by
inducing early sprouting of several buds simultaneously.
We studied the mechanisms governing TABmeristem
dominance release. TAB-meristem decapitation resulted
in the development of increasing numbers of axillary buds
with time in storage, suggesting the need for autonomous
dormancy release of each bud prior to control by the apical
bud. Hallmarks of programmed cell death (PCD) were
identified in the TAB-meristems during normal growth,
and these were more extensive when AD was lost
following either extended cold storage or BE treatment.
Hallmarks included DNA fragmentation, induced gene
expression of vacuolar processing enzyme1 (VPE1), and
elevated VPE activity. VPE1 protein was semipurified
from BE-treated apical buds, and its endogenous activity
was fully inhibited by a cysteinyl aspartate-specific
protease-1-specific inhibitor NAcetyl-Tyr-Val-Ala-Asp-
CHO (Ac-YVAD-CHO). Transmission electron
microscopy further revealed PCD-related structural
alterations in the TAB-meristem of BE-treated tubers: a
knoblike body in the vacuole, development of
cytoplasmic vesicles, and budding-like nuclear
segmentations. Treatment of tubers with BE and then
VPE inhibitor induced faster growth and recovered AD in
detached and nondetached apical buds, respectively. We
hypothesize that PCD occurrence is associated with the
weakening of tuber AD, allowing early sprouting of
mature lateral buds.
AD in Sprouting Tubers: We checked whether the tuber
exhibits classical stem-like behavior and investigated the
role of bud AD in determining lateral bud dormancy
release and sprouting. Removing the apical bud after 30,
60, and 90 d in cold storage resulted in sprouting of an
average of one, two, and nine buds, respectively (Fig. 3,
A–C). Aging in cold storage resulted in the sprouting of
more buds due to removal of the apical bud, suggesting
the need for each bud to reach maturity and autonomous
dormancy release before it can be controlled by the TAB-
meristem.
Altering Bud Dormancy and AD by Aging in Cold Storage
and BE Treatment
We observed three main types of loss of AD in stored
potato (Fig. 1): loss of dominance of the apical buds over
those situated more basipetally on the tuber (type I); loss
of dominance of the main bud in any given eye over the
subtending axillary buds within the same eye (type II);
and loss of dominance of the developing sprouts over
their own branching, meaning that side stems emerge not
from the base of the sprout as in type II (type III).
Detection of PCD in TAB-Meristem Induces Loss of AD
Since both aging in cold storage and BE decrease
AD, we suspected that the viability of some of the
meristem cells is altered, possibly as a result of induced
PCD. We checked whether there is a correlation between
the incidence of PCD in the TAB-meristem and the loss
of AD (type I) during aging in cold storage. We
hypothesized that the effect of excess PCD of the
meristem cells would be similar to that of decapitation of
the apical bud on AD. A specific feature of PCD is the
cleavage of genomic DNA at internucleosomal sites by
endogenous nucleases. To detect fragmented nuclear
DNA in situ, a terminal deoxynucleotidyl transferase-
mediated dUTP nick end labeling (TUNEL) procedure
was applied. TAB-meristem isolated from cv Nicola
tubers at harvest showed no symptoms of DNA
fragmentation, either within the apical meristem or,
initially, in the leaf primordium covering the TAB-
meristem (Fig. 4, top panel). After 30 and 45 d at 20°C,
when AD was still in place, initial DNA fragmentation
could be detected in the TAB-meristem (Fig. 4, AD).
Incubating the tubers at 6°C for 60 d, which results in the
loss of AD, induced widespread and more extensive DNA
fragmentation. After 90 d, the fragmentation had spread
throughout the TAB-meristem (Fig. 4, ND), and the bud
developed more slowly as compared with the dominant
apical bud.
An axillary bud is an embryonic or organogenic shoot
which lies dormant at the junction of the stem and petiole
of a plant. [1]:18  It arises exogenously from outer layer
of cortex of the stem. Axillary buds do not become
actively growing shoots on plants with strong apical
dominance (the tendency to grow just the terminal bud on
the main stem). Apical dominance occurs because the
shoot apical meristem produces auxin which prevents
axillary buds from growing. The axillary buds begin
developing when they are exposed to less auxin, for
example if the plant naturally has weak apical dominance,
if apical dominance is broken by removing the terminal
bud, or if the terminal bud has grown far enough away for
the auxin to have less of an effect.[2] Apical bud is the
dominant bud found in the apex of the plant. Axillary bud
is a lateral bud, which remains dormant under the
influence of auxin produced by the apical meristem. It
allows plants to develop branches.
The Mechanism of Apical Dominance in Coleus
The development of lateral buds in isolated stems of
Coleus blumei is inhibited by low concentrations of
indoleacetic acid or other auxins, just as in other plants.
The inhibition can be fully reversed by kinetin, about 3
times as much kinetin as IAA being needed. However, the
outgrowth of the same lateral buds on intact Coleus plants
is sensitive to environmental conditions, wellnourished
plants in full daylight often showing little inhibition by
applied auxin. It is shown that (a) the solvent used for
IAA, (b) the light intensity and (c) the nitrogen and
phosphorus nutrition, all control the sensitivity of the
buds to auxin inhibition. Using water instead of lanolin,
lowering the light intensity or decreasing the supply of
either nitrogen or phosphorus all increase the degree of
apical dominance.
Thank You
 BIBLIOGRAPHY

https://www.researchgate.net/publication/221859163_
https://www.tandfonline.com/doi/full/10.4161/psb.21324
https://www.semanticscholar.org/paper/Release-of-Apical-Dominance-in-
Potato-Tuber-Is-by-Teper-Bamnolker-
Buskila/2570dde8deac341c6f4c8493103ce545b67e865e
https://www.jnsciences.org/component/content/article.html?id=71:physiolo
gy-of-potato-sprouting