Transcript Molecular Adaptations Made by Plants to Improve Flood Tolerance

Molecular Adaptations Made by
Plants to Improve Flood
Tolerance
Nikkita M. Keelen
Florida A&M University
April 20, 2004
Key Terms
Waterlogging
 Flooding Tolerance
 Anaerobic Conditions
 Molecular Strategies
 Crop Plants

Introduction
Waterlogging in crop plants occurs often
 Mainly due to unfavorable weather
conditions, sub-optimal soil and poor
irrigation techniques

Introduction cont’d

When plants experience flooding they also
experience a lack of oxygen.

Due to their immobility, plants have
evolved mechanisms that allow them to
adapt to low oxygen levels
Introduction cont’d

When crop plants are
unable to adapt to low
oxygen levels,
substantial crop loss
occurs.
www.gartenbau.uni-hannover.de/.../ WESONGA.HTM
Introduction cont’d

Crop loss is a major
economical and
agricultural dilemma.
www.gartenbau.uni-hannover.de/.../ WESONGA.HTM
Introduction cont’d
A healthy gas
exchange between
plants and the
atmosphere is vital to
all life on Earth.
 O2 is an essential part
of cellular respiration.

www.elmhurst.edu/.../chm110/ outlines/atmos.html
Introduction cont’d

Experiments have been conducted to
determine the mechanisms used by plants
to adapt to low oxygen stress

Additionally, by figuring out these
mechanisms, we plan to manipulate plants
on a molecular level to facilitate the
adaptation process
Materials and Methods

Arabidopsis was used
as a model system

Cotton and Rice were
used as examples of
flood-sensitive and
flood-tolerant species
respectively
www.rib.okayama-u.ac.jp/mol.gen/ z-kenkyunaiyo.htm
Materials and Methods
A seedling survival test was developed in
Arabidopsis.
 Three-week old seedlings were subjected
to hypoxic stress (0.1% O2 for 24-48h)
 They were immediately transferred to
agar plates and the position of the root tip
was marked.

Materials and Methods
Plants were incubated in aerobic conditions
and their root growth scored.
 In order to test whether increasing the
levels of ADH and/or PDC or early
induction of these enzymes would protect
plants from hypoxic stress, a
pretreatment was applied.

Materials and Methods
In cotton, this study focused on the
alcohol fermentation pathway
 Cotton was grown hydroponically in clear
plastic cylinders.
 The cylinders were fitted with an airstone at the bottom.
 Root growth was observed daily through
transparent tubes.

Materials and Methods

In rice, the rice PDC gene and ADH
production are being tested for tolerance
to oxygen deficiency under submergence.
Results

In Arabidopsis, it was found that the
hypoxic treatment greatly improved
survival of subsequent extremely low
oxygen conditions(0.1% oxygen) in both
roots and shoot.

Results suggest that the prior induction of
ANPs enhance survival
Results

In cotton, plants containing the cotton
ADH cDNA showed a 10-30 fold increased
ADH activity

Also showed a significant increase in the
rate of ethanol fermentation
Results

Rice plants over-expressing PDC do not
show increased tolerance to submergence

Reduction of ADH activity in rice led to
the inability of seeds to germinate under
low oxygen conditions
Results
Discussion
Three main fermentation pathways are
active in plants during flooding: ethanol,
lactic acid and a plant-specific pathway.
 presence during low oxygen conditions
suggests a role in the low oxygen survival
mechanism.

Discussion

www.polk.cc.fl.us/.../BSC1005/ Respiration.html
Plants which are more
flood tolerant have a
more active alcohol
fermentation pathway
Discussion

asm.wku.edu/pix/Pix.htm
Fermentation of
carbohydrate enables
the plant to maintain
ATP production in the
absence of oxygen.
Discussion

The entire response to waterlogging is
divided into three stages: 0-4h, 4-24h and
24-48h.

In each of these stages, more complex
molecular adaptations to flooding are
made.
Results
Results
Two methods of manipulating the normal
three stage process have been proposed
 The first involves the over expression of
the fermentation pathway genes.
 The second involves manipulating the signal
transduction cascade using transcription
factor AtMYB2.

Conclusion
The presence of lactic acid, ethanol and plantspecific fermentation pathways play a vital role
in a plant’s ability to adapt to flood tolerance.
 Induction of an ANP hypoxic pre treatment
enhances flood tolerance in Arabidopsis.
 ADH is essential for germination and growth of
rice seeds under submerged conditions.
 In cotton a 10-30 fold increase of ADH activity,
as well as an increase in the rate of ethanol
fermentation occurred in order to improve flood
tolerance.

Conclusion
Manipulating flood tolerance in plants is still not
totally possible due to lack of knowledge of the
molecular basis of the problem.
 The fact that anaerobic proteins are involved in
many other cellular processes further complicate
this matter.
 Experiments continue to be conducted to develop
an answer to this problem

Further Study
Manipulating water
logging tolerance
 Hypoxic stress
 Anaerobic Conditions
 The effect of water
logging on plants

Sources




Molecular Strategies for Improving Waterlogging
Tolerance in Plants By: E.S. Dennis
A Comparative Molecular-Physiological Study of
Submergence Response in Lowland Deepwater Rice
By: Dominique Van Der Straeten
Sugarcane Cultivar Response to High Summer Water
Tables in the Everglades
By: Barry Glaz
Physiological and Morphological Changes Made by
Wetland Plants that Contribute to the Adaptations
Permitting Flood Tolerance.
By: Marnie E. Ort
Acknowledgements
Florida A&M University Biology
Department
 Dr. Gokhan Haci-Salihoglu
 Coleman Library
 Science and Research Library
