Knox genes are the main genes involved in the regulation of development in compound leaves. Whereas abiotic stress is the nonorganic type of stress. This presentation ill help to get a brief idea about both the topics in a compressed form.

1. SEMINAR
PRESENTED BY:
SOUGATA GANGULY
M.Sc. APPLIED GENETICS

3.  Simple vs. Compound leaves
 KNOX genes
 KNOX-BELL interaction
 Abiotic Stress
 Stress resistance
 Water deficit stress
 Heat stress
 Summary
 References

4. Simple Leaf:-
• Simple leaves are
those in which single
blade or lamina is
present.
• E.g.- Mango, Peepal,
Papaya
Compound Leaf:-
• Compound leaves are those in which the leaf blade or lamina is
divided into number of segments known as leaflets or pinnae.
• The leaflets never bear axillary buds in their axil.

6.  The shoot apical meristem (SAM) of seed plants is an
indeterminate structure that maintains itself and is the
source of cells that give rise to determinate organs, such as
leaves and flowers.
 Indeterminacy during vegetative and reproductive
development is controlled by a suite of genes that function
at different stages in the SAM.
 The role of meristem genes, the indeterminate SAM is
characterized by the expression of the Class 1
KNOTTED1-LIKE HOMEOBOX (KNOX1) genes.

7.  The Arabidopsis genome contains four Class I KNOX
genes: STM, BREVIPEDICELLUS (BP), Kn1-like in
Arabidopsis thaliana2 (KNAT2) and KNAT6.
 STM is the first KNOX gene expressed during early
embryogenesis and its expression marks the entire SAM.
 KNAT6 is expressed in the embryonic SAM once bilateral
symmetry is established and later marks the SAM boundaries.
 KNAT2 is expressed during embryogenesis and marks the base
of the SAM.

8. FIG: ROLE OF KNOX1 GENES IN COMPOUND LEAF DEVELOPMENT

9.  KNOX proteins interact with another group of TALE
proteins, the BEL1-like homeodomain family (BELL or
BLH), in a highly connected, complex network that
determines not only high-affinity KNOX target selection
but also their subcellular localization.
 This protein interaction network also includes Arabidopsis
thaliana OVATE family proteins (AtOFP), which
negatively control the activity of TALE protein dimers by
causing their relocalization from the nucleus, where they
are functional, to the cytoplasmic space.

10. ABIOTIC STRESS

11. o STRESS : Factors of environment interfering the complete
genotypic potential.
o ABIOTIC STRESS : The negative impact of non-living
factors on the living organisms in a specific environment.
o Abiotic stress factors or stressors are naturally occurring,
often intangible factors.
o The four major abiotic stresses – drought, salinity,
temperature and heavy metals, cause drastic yield reduction
in most crops.

12.  Water-logging and drought
 Excessive soil salinity
 High or low temperatures
 Ozone
 Low oxygen
 Phytotoxic compounds
 Inadequate mineral in the soil
 Too much or too little light

13. I. Unpredictable occurrence
II. Some stresses are impossible to manage
III. One stress may increase or decrease the level of another stress
IV. Differential response of plant sp. to a given stress
V. Effects generated by one abiotic stress may overlap with some
effects or another stress

14. Source: Biochemistry & molecular biology of plants 2007,22 1158-1159.

15.  Mechanism that permit stress survival are termed
stress resistance mechanisms.
 Stress resistance mechanisms can be grouped into
three categories---
 Avoidance mechanism : Which prevent exposure to stress.
 Tolerance mechanisms : Which permit the plant to
withstand the stress
 Acclimation stress : Alter the physiology in response

16.  A stress response is initiated when plant recognizes stress
at the cellular level.
 Stress recognition activates signal transduction pathways
that transmit information within the individual cell and
throughout the plant.
 Changes in gene expression may modify growth and
development and may even influence reproductive
capabilities.

17.  Water related stresses could affect plants if the
environment contains insufficient water to meet basic
needs.
 Water logging
 Drought condition

18. When soil is completely saturated with water is in general
referred to the water logging
Water logging cause :-
• Hypoxia i.e. shortage of oxygen
• Anoxia i.e. total lack of oxygen
Which causes the reduced growth, inhibits the metabolic
processes and finally reduces the yield of plant

19.  Drought:-
A prolonged period of abnormally low rainfall, leading to
a shortage of water.
 Mechanism of drought resistance:-
a) Drought escape : mature early
b) Drought avoidance : maintain water balance
c) Drought tolerance : higher yield even under low water
potential

20. PHYSIOLOGICAL RESPONSE TO DROUGHT
 Photosynthetic efficiency is reduced due to chloroplast
damage
 Reduced transpiration and reduced respiration losses
 Stomatal behavior
BIOCHEMICAL RESPONSE TO DROUGHT
 Accumulation of compatible solutes
 Increase in ABA and Ethylene
 Protein synthesis
 Nitrate reductase activity

21.  In response to dehydration or osmotic stress a series of
compatible solutes/osmolytes are accumulated for osmotic
adjustment, water retention and free radical scavenging.
 The cell actively accumulates solutes and as a result the solute
potential(ψs) drops, promoting the flow of water into the cell.
Few osmolytes:-
• Proline
• Glycine betaine
• Mannitol
• Osmotin
• D-Pinitol

23.  Generally resistant varieties have low yield; Do not have
much adaptability.
 Drought resistant genes may have linkage with undesirable
genes.
 Drought resistant traits may reduce yield.
 Transfer of resistant genes from wild types may pose a
problem.
 Creation of controlled moisture stress environment is a
problem, selection require considerable resources.

24. Heat stress is often defined as a period in which temperatures are hot
enough for a sufficient period of time to cause irreversible damage to
plant function or development. Plants can be damaged by either high
day or high night temperatures and either by high air or soil
temperatures.

25.  Heat stress is a decrease in the synthesis of normal
proteins, accompanied by an accelerated transcription band
translation of new proteins known as Heat Shock
Proteins(HSPs).
 Heat stress has been shown to cause problems in
mitochondrial functions and can result in oxidative
damage. Activators of heat stress receptors and defenses
thought to be related to ROS.

26. None of the mechanisms by which higher plants perceive abiotic stresses has
been elucidated. Progress in this crucial area will advance substantially our
knowledge of stress initiated signal transduction events stress related signal
propagated by several different agents in some cases, these signal transduction
events involve at least one of the five best hormones ABA, Auxin, Cytokinins,
Ethylene, and Gibberellins.
However, perhaps signaling molecules not yet identified also
participate in controlling plant response to the environment.

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