Download Photoperiodic induction involves phytochrome

PHOTOPERIODIC
INDUCTION INVOLVES
PHYTOCHROME

Phytochrome – pigment involved in a number of growth
processes such as germination of some seeds.
PHOTOPERIODIC INDUCTION

Phytochrome – pigment involved in a number of growth
processes such as germination of some seeds.

Pr – absorbs red light at a wavelength of 660nm

Pfr – absorbs far-red light at a wavelength of about 725nm.
PHOTOPERIODIC INDUCTION

Phytochrome – pigment involved in a number of growth
processes such as germination of some seeds.

Pr – absorbs red light at a wavelength of 660nm

Pfr – absorbs far-red light at a wavelength of about 725nm.

When Pr absorbs light it is converted to Pfr and vice versa.
PHOTOPERIODIC INDUCTION

Sunlight contains both red and far red light so both reactions
would be expected to occur at the same time.

Sunlight contains both red and far red light so both reactions
would be expected to occur at the same time.

However, there is more red light than far-red so red light is
dominant.

Most plant responses are in anticipation of environmental
change as a result of slowing changing external factors –
daylength.
ADAPTIVE ADVANTAGES OF
PHOTOPERIODISM

Most plant responses are in anticipation of environmental
change as a result of slowing changing external factors –
daylength.

Photoperiodism allows plants to:
- Reach sexual maturity to coincide with pollinators being most
active and present in greatest numbers  increase chances of
cross-pollination or reproduce asexually when conditions are
optimal.
ADAPTIVE ADVANTAGES OF
PHOTOPERIODISM

Photoperiodism allows plants to:
- Expend energy and resources producing leaves etc when
daylength and light intensities are at their maximum for growth and
production of seeds.
ADAPTIVE ADVANTAGES OF
PHOTOPERIODISM

Photoperiodism allows plants to:
-
Expend energy and resources producing leaves etc when
daylength and light intensities are at their maximum for growth
and production of seeds.
-
Drop leaves to reduce transpiration when soil water may be
frozen, and develop buds that resist damage by frost/snow.
ADAPTIVE ADVANTAGES OF
PHOTOPERIODISM

Trees in temperate climates (oak and ash) short days trigger off
winter bud formation.
BUD DORMANCY

Trees in temperate climates (oak and ash) short days trigger off
winter bud formation.

These remain tiny and protected until spring – this period of
dormancy can only be broken by chilling temps.
BUD DORMANCY

Trees in temperate climates (oak and ash) short days trigger off
winter bud formation.

These remain tiny and protected until spring – this period of
dormancy can only be broken by chilling temps.

Therefore the factor that breaks dormancy (chilling) is different
from the factor that induces it (short days).
BUD DORMANCY

Not passive absence of growth – it is actively maintained by a
growth inhibitor called abscisic acid (ABA)
BUD DORMANCY

Not passive absence of growth – it is actively maintained by a
growth inhibitor called abscisic acid (ABA)

Chilling breaks dormancy by increasing the amount of gibberellin
which stimulates the growth again.
BUD DORMANCY

Not passive absence of growth – it is actively maintained by a
growth inhibitor called abscisic acid (ABA)

Chilling breaks dormancy by increasing the amount of gibberellin
which stimulates the growth again.

Without chilling, a plant may be late in resuming growth the next
season.
BUD DORMANCY

Leaf fall is preceded by abscission – complex process to do with
changes in the layer of cells at the base of the leaf.
LEAF FALL (ABSCISSION)

Leaf fall is preceded by abscission – complex process to do with
changes in the layer of cells at the base of the leaf.

When the leaf falls, a layer of cork seals off the leaf.
LEAF FALL (ABSCISSION)

Leaf fall is preceded by abscission – complex process to do with
changes in the layer of cells at the base of the leaf.

When the leaf falls, a layer of cork seals off the leaf.

Although short days act as an external stimulus, the internal
chemical signals are complex and involve interactions between
several stimulus.
LEAF FALL (ABSCISSION)