temperature effect

1. EFFECT OF TEMPERATURE ON
REGULATION OF GIBBERELLIN
Presented by Ayesha Tariq
BS-B-14-33
BZU (Multan)

2. WHAT ARE GIBBERELLINS?
Gibberellins are a group of plant hormones responsible for growth
and development. Chemically speaking, gibberellins are actually
acids. They are produced in the plant cell's plastids or the double
membrane-bound organelles responsible for making food and are
eventually transferred to the endoplasmic reticulum of the cell where
they are modified and prepared for use .Gibberelllin is mostly found
in plant roots and young leaves.

3. CHEMISTRY OF GIBBERELLINS
Gibberellins are tetra cyclic diterpene acids. There are two classes based on the
presence of either 19 or 20 carbons. The 19-carbon gibberellins, such as
giberellic acid have lost carbon 20 and in place possess a five-member lactone
bridge that links carbons 4 and 10. The 19-carbon forms are in general, the
biologically active forms of gibberellins.
Hydroxylation also has a great effect on the biological activity of the
gibberellins. In general, the most biologically active compounds are
dihydroxylated gibberellins, which possess hydroxyl groups on both carbon 3
and carbon 13. Giberellic acid is a dihydroxylated gibberellins. The bioactive
GAs are GA1, GA3, GA4, and GA7.

5. FUNCTIONS OF GIBBERELLINS
Gibberellins (GAs) are plant hormones that
regulate growth and influence
various developmental processes including
• Stem elongation
• Seed germination
• Breaking dormancy
• Flowering
• Fruit ripening
• Help plants with dwarf varieties grow to normal
size

6. REGULATION OF GIBBERELLLIN BY TEMPERATURE
What is temperature?
Temperature is a primary factor affecting the rate of plant growth and
development. It influence the rate of growth within a certain range (0-30°C).
Temperature can also effect the activity of gibberellins in plant growth.
Gibberellins are produced in greater mass when the plant is exposed to cold
temperatures.
 A prolonged period of chilling or moist condition (stratification) is required to
seed germination.
 In winter annuals, a prolonged period of cold (Vernalization) is required to
promote flowering the following spring.

7. stratification is a period of
moist-chilling (also known as
cold, moist) or moist-warm
conditions that overcomes
physiological dormancy
requirements in seeds of some
plant species. Cold, moist
stratification is required for
some native plants, like
milkweeds

8. Vernalization is a period of
cold temperatures required by
some plant species to induce
flowering. Many biennials –
plants with a two year life cycle
of seed to plant to flower to seed
– and some perennials require
vernalization.

9. LOW TEMPERATURE RESPONSE TOWARD PLANT
SIZE:
When Arabidopsis have grown at low (<4°C) temperatures, reductions in plant
size are accompanied by the expression of genes that include (CBF). Plants
constitutively expressing CBF transcription factors display both enhanced
freezing tolerance and a severe reduction in growth. This growth retardation has
recently been shown to involve CBF-mediated stabilization of the DELLA
family of growth repressing proteins, through reductions in the level of the plant
hormone GA. Gibberellins regulate growth through targeting DELLA proteins
for proteosome -mediated degradation.

11. LOW TEMPERATURE RESPONSE TOWARD SEED
GERMINATION :
Temperature is crucial external cue that
controls seed germination. In many plant
species including A. thaliana, exposure of
seeds to low temperatures (typically 2 to
5°C) immediately after imbibition
promotes germination. Although such
cold treatment, often called stratification.
Gibberelllin (GA) biosynthesis genes
were upregulated in response to low
temperature(4°C) resulting in an increase
in the level of bioactive GAs.

12. INHIBITION OF GROWTH AND NITROGEN UPTAKE AT
SUBOPTIMAL ROOT-ZONE TEMPERATURE BY
GIBBERELLLIN:
Suboptimal temperature stress suppressing plant growth during winter and early
spring. Giberellic acid (GA) has been reported to be involved in plant growth and
acquisition of mineral nutrients plants under conditions of short-term suboptimal root-
zone temperatures (Tr). Exposure of cucumber seedlings to a Tr of 16°C led to a
significant reduction in root growth, and this inhibitory effect was reversed by exogenous
application of GA.
Expression patterns of several genes encoding key enzymes in GA metabolism were
altered by suboptimal Tr treatment, and endogenous GA concentrations in cucumber
roots were significantly reduced by exposure of cucumber plants to 16°C Tr, suggesting
that inhibition of root growth by suboptimal Tr may result from disruption of endogenous
GA homeostasis.

13. To further explore the mechanism underlying the GA-dependent
cucumber growth under suboptimal Tr we studied the effect of
suboptimal Tr and GA on nitrate uptake, and found that exposure of
cucumber seedlings to 16°C Tr led to a significant reduction in nitrate
uptake rate and exogenous application GA can alleviate the down-
regulation by up regulating the expression of genes associated with
nitrate uptake.

15. EFFECT OF TEMPERATURE ON FLOWER
INITIATION:
Gibberellins (GAs) have been found to induce flower formation in many plants
under non-inductive conditions. Many plants with a long-day requirement for
flowering (long-day plants, LDP) and many cold-requiring plants (including
crucifers, members of the family Brassicaceae) grow as rosettes prior to
receiving the flowering stimulus.

16. In plants with a rosette stage of development and a vernalization response,
one of the earliest detectable events following thermo induction of flowering is
the rapid increase in the level of endogenous gibberellins By applying exogenous
GAs, flower formation can be induced in many LDP with a rosette stage,
suggesting that GA may be limiting under short days (SD). There have been a
number of studies of the relationship between GAs and environmental stimuli in
the induction of flowering

18. EFFECT OF TEMPERATURE ON STEM
ELONGATION:
The effect of day/night temperature on stem elongation and on the content of
endogenous gibberellins (GAs) in vegetatively propagated plants of Campanula
isophylla Compared with a constant temperature regime at 18°C (18/18°C), stem
and internode elongation was enhanced significantly by a combination of high
day/low night temperature (21/15°C) and inhibited by an opposite regime
(15/21°C). Gibberellins A1, A19, A44, A53, and A97 were identified as endogenous
components in Campanula. Quantitative analysis of the endogenous GAs
indicates that temperature regimes that stimulate elongation growth are
accompanied by an increase in the level of GA1, GA19, and GA44. On the other
hand, in plants grown under conditions that reduced stem elongation growth,
there was an increased level of GA97.

20. EFFECT OF TEMPERATURE ON POTATO
TUBERISATION:
The potato is remarkably adaptable crop. Its production is, however restricted by
the fact that tuber formation is more or less completely prevented by high
temperature.
The responses of potato plants (Solanum tuberosum) to high temperatures (32
day/28 °C night or 32/18 °C) and gibberellin are similar, in that they promote
haulm growth and suppress tuber production, whereas low temperatures (22/18
°C have the opposite effect, promoting tuber production and reducing the growth
of the haulms.
Endogenous levels of gibberellins in potato plants are high in non-inductive
conditions (high temperatures and long photoperiod) and decrease under
conditions of induction tuberisation

22. THE EFFECTS OF TEMPERATURE AND GIBERELLIC
ACID ON GROWTH OF FRUIT:
The effect of temperature and giberellic acid (GA3) applications on fruit have been
determined by
• Measurements of fruit size and
• Shape
• Mesocarp cell number
• Endogenous gibberelllin.
Application of heat during the first 10 nights after anthesis increased the initial
growth rate of fruit and of cells in the mesocarp and produced more rapid cell
division in this tissue. It did not affect final fruit size or the number and
diameter of cells in the mesocarp.

23. GA3 perfused into branches before anthesis produced an increased drop of
flower buds and fruit, raised the ratio of flower buds to leaf buds initiated that
season, and resulted in elongated pedicels. Initially, fruit growth rate was
increased by GA3 but subsequently it was depressed and final size was below
normal. These effects on fruit size were mainly due to effects on the rate of cell
division. Some differences were noted in the dimensions of cells but final radial
cell diameter did not differ from untreated fruit. GA3-treated fruit ripened sooner
than controls.