Download Powerpoint: Flooding Response in Shoots

Flooding effects: Shoots
Messages



Substances
POSITIVE:
increase in messages
from roots to shoots

Toxins (Mn2+, Fe2+, S-)

Nutrients
NEGATIVE:
decrease in messages
from roots to shoots

Photosynthate (starches
and sugars)

Water

Hormones
ACCUMULATIVE:
build up of substances
in the roots and shoots
Hormones

Hormones act as intermediates between environmental
signals and the plants responses to these stimuli.



Ethylene – involved in cell elongation, Associated with
Local Growth. (Abscission, hypertrophy,
aerenchyma)
Auxin – Made in the shoot tip; Cell elongation; photo
and geotropism; apical dominance; prevents
abscission
Gibberellin – Made in apical portion of shoots and
roots; Stem and leaf elongation, delays
senescence
Hormones

ABA (Abscisic Acid) –
Stomatal closure, leaf elongation. Associated
with Root Growth

Cytokinin –
Made in the roots; prevents senescence,
promotes cell division, promotes lateral
branching; stomatal opening, controls shoot
extension; delays senescence .
Inhibition of Growth
 Inhibition

Major causes: nitrogen deficiency and build
up of ethylene
 Inhibition

of Leaf Growth
of Stem Extension
Caused by negative messages (e.g. lack of
gibberellin) as well as water stress, toxins etc.
 Inhibition
of Photosynthesis
Reorientation of Growth

Vertical Growth of Stolons


Stimulation of cell extension
Epinastic curvature of leaf petioles



An acceleration of growth and elongation of leaf
petiole causing leaves to turn downward
Positive message caused by ethylene build up
Possibly minimizes radiation loading
Senescence

Deterioration that gives rise to the death of part
or all of the plant.

Negative Messages



Hormone deficiency
Nitrogen Deficiency
Positive Messages – P, H2S and Fe
Abscission


Leaf drop
Occurs most rapidly in the presence of ethylene (not
abscisic acid)



Senescence is probably a precursor to abscission
Senescing leaves produce a lot of ethylene and produce little
auxin.
Adaptive advantage




Form of self pruning
Reduce transpiration load
Prevent spread of microbial infection
Maintain root to shoot ratio
Wilting
 “flopping”,
 Principal


loss of turgor
cause
Rapid wilting is a consequence of higher
resistance to the mass flow of water through
the roots of flooded plants
Wilting is relieved by stomatal closure
Promotion of Extension Growth

Occurs in aquatics
and emergents


Such as water lilies
Shoot Elongation

Cell wall extension
caused by ethylene
build up and lack of
Gibberellin
Hypertrophy

Swelling of the stem base
or hypocotyls

Lenticels

Result of increase in
ethylene, photosynthate
and auxin at the plant
base

Induced in rising water
Adventitious Rooting

Roots that arise from the
stem in flood tolerant
trees and herbaceous
species just above the
anaerobic zone.

Adaptive Significance
and Features

Causes
Adventitious Roots
Shoot/Root Adaptations