Flooding effects: Shoots Messages  POSITIVE: increase in messages from roots to shoots  NEGATIVE: decrease in messages from roots to shoots  ACCUMULATIVE: build up of substances in the roots and shoots Substances  Toxins (Mn 2+, Fe 2+, S - )  Nutrients  Photosynthate (starches and sugars)  Water  Hormones

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) 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 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 Gibberellin – Made in apical portion of shoots and roots; Stem and leaf elongation, delays senescence

Hormones ABA (Abscisic Acid) – ABA (Abscisic Acid) – Stomatal closure, leaf elongation. Associated with Root Growth Cytokinin – Cytokinin – Made in the roots; prevents senescence, promotes cell division, promotes lateral branching; stomatal opening, controls shoot extension; delays senescence.

Inhibition of Growth  Inhibition of Leaf Growth Major causes: nitrogen deficiency and build up of ethylene Major causes: nitrogen deficiency and build up of ethylene  Inhibition of Stem Extension Caused by negative messages (e.g. lack of gibberellin) as well as water stress, toxins etc. 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 Stimulation of cell extension  Epinastic curvature of leaf petioles An acceleration of growth and elongation of leaf petiole causing leaves to turn downward An acceleration of growth and elongation of leaf petiole causing leaves to turn downward Positive message caused by ethylene build up Positive message caused by ethylene build up Possibly minimizes radiation loading Possibly minimizes radiation loading

Senescence  Deterioration that gives rise to the death of part or all of the plant.  Negative Messages Hormone deficiency Hormone deficiency Nitrogen Deficiency Nitrogen Deficiency  Positive Messages – P, H 2 S and Fe

Abscission  Leaf drop  Occurs most rapidly in the presence of ethylene (not abscisic acid) Senescence is probably a precursor to abscission Senescence is probably a precursor to abscission Senescing leaves produce a lot of ethylene and produce little auxin. Senescing leaves produce a lot of ethylene and produce little auxin.  Adaptive advantage Form of self pruning Form of self pruning Reduce transpiration load Reduce transpiration load Prevent spread of microbial infection Prevent spread of microbial infection Maintain root to shoot ratio Maintain root to shoot ratio

Wilting  “flopping”, loss of turgor  Principal cause Rapid wilting is a consequence of higher resistance to the mass flow of water through the roots of flooded plants 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 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