Effects of Plant growth

1. Growth:
Environmental
Effects

2. Chemical Regulators
The best known regulators are the auxins, giberellins, kinins,
and phytochrome.
• commonest plant hormones
-regulate growth & other
physiological processes in plants
-produced by root tip / shoot tip
-they affect the elongation region of
the tip
AUXINS

3. 1. Auxin is produced principally in the growing
shoot apex of plant.
2. It moves downward under the influence of
gravity.
3. It moves away from its region of synthesis by
diffusion or by directional transport.
4.It is driven by undirectional light from an
illuminated side to a darker side of a plant.
5.A very low concentration of auxin in a stem
stimulates cellelongation, but the same
concention in a root inhibit cell elongation.

4. Tropisms
- a growth response which a plant
makes with respect to a directional
stimulus is a tropism.
Negative geotropism
- The bending of a shoot away
from the pull of gravity.
Positive geotropism
- The bending of a root toward the
center of the earth

5. Gibberellins
- are a group of plant hormones responsible for
growth and development. Chemically speaking,
gibberellins are actually acids. They are
produced in the plastids of plant cells and are
eventually transferred to the endoplasmic
reticulum of the cell, where they are modified
and prepared for use.

6. KININS
Can stimulate cell divisions, cause lateral buds to grow,
inhibit growth of adventitious roots, and increase leaf
growth.

7. Phytochrome
One of the most intensively studied of the light
sensitive compounds in plants.
Still incompletely characterized protein, bluish in color,
and capable of regulating plant growth in a variety of
ways.

8. Phytochrome actions
are:
1. Germination
2. Control of entiolation
3. Photoperiodism
GERMINATION
Some varieties of seeds will not germinate unless
they receive a minimal dose of red light. Daylight
contains enough red to cause germination. If kept
in the dark or irradiated with far-red, the seeds
remain doramant.

9. CONTROL OF ETIOLATION
When grown in the dark or in far-red light,
seedlings become etiolated, that is, thier
leaves do not expand, the internodes
elongate excessively, the chloroplasts do
not develop chlorophyll, and a sharp bend
in the stem just below the growing point
keeps its curvature.

10. PHOTOPERIODISM
Some plants make only flowers only when days are short in
comparisons to the length of nights. Other plants flower
only during long days.
SHORT DAY PLANTS
Will flower if they recieve the following treatments: long, uninterrupted
dark periods; or long dark ods interrupted by a short light period,
provided the light “flash” is followed by a “flash” or far-red light.
LONG DAY PLANTS
Will flower if they receive; short dark periods; or long dark
periods which are interrupted by a ‘flash’ of light.

12. OTHER PLANT MOVEMENTS
TROPISMS
Other than geo- and phototropism are thigmotropism and
hydrotropism. Thigto touch motropism, a response to touch, is
demonstrable in tendrils (a growth reaction) an in special leaves,
such as Venus fly-trap and the sensitive Mimosa.
NASTIC MOVEMENTS
These are movements of leaves and petals, caused by unequal
growth of either the upper layers of an organ growing faster than
the lower, causing the organ to bend downward (epinasty), or vice
versa (hyphonasty.
TAXIC RESPONSES
These are the movements of entire plants, such as
motile cells of algae, fungi,sperm cells, etc.

13. NASTIC MOVEMENTS