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Heat stress tolerance studies in Tomato (Lycopersicon
esculantum Mill.)
By:
Shehzad Ahmad Kang, Department of Plant Breeding and
Genetics,University of Agriculture, Faisalabad, Pakistan-
38040
Esculantum is a diploid specie, belong to family solanaccae
and chromosome number is 2n=24.It is day neutral plant.
Tomato fruit commercially use for different purpose
i.e.cooking,salad,ketchup.The red color due to presence of
lycopene.It contain 93% water content and 1.9% protein
content. Normally best tomato plant growth at temperature
range 15-25 oC and flowering temperature 30 oC in Pakistan.
In 2011 tomato crop grown under the area of 53700 ha and
yield obtained 570.32MT. Average yield can be obtained 7-14
Ton /ha at field condition and 18-22 Ton /ha by cultivation
of hybrid varieties in tunnel farming in Pakistan. Nagina,
Roma, Garden delight, Naqeeb and Salaar F1 are partially
heat tolerance varieties under 40oC–50oC. Heat stress due to
increase temperature is a major agricultural problem in many
areas in the world. Constantly high temperature cause an
array of morpho-anatomical change in plant which effect the
seed germination, plant growth, flower shedding, pollen
viability, gametic fertilization, fruit setting ,fruit size
and fruit weight. These problems can also be minimizing by
the improvement of cultural practices and breeding
approaches. so there are different type of morphological
traits which help for heat tolerance in convential breeding
approaches.
1) Long root length which has good ability to uptake water
and nutrients from the soil surface.
2) Short life span which help to minimize the temperature
affect on plant.
3) Hairiness which provide partially shade to cell wall,
cell membrane and repel sun rays.
4) Small leave size that resist evaporation due to
shortening of stomata.
5) Leaf orientation enhance the photosynthetic activity and
produce tolerance against heat stress. Physiologically heat
stress enhance the kinetic energy and movement of molecule
across a membrane thereby breakage of chemical bond within
molecule of biological membrane. This makes lipid bilayer of
biological membrane more fluid by either denaturation of
protein so integrity and function of biological membrane are
sensitive to high temperature. The hormone play major role
in life stability and biosynthesis i.e. Abscisic acid and
ethylene are heat tolerant hormones which are involved to
regulate the many physiological role by acting as signal
molecules, and expression of different type of heat tolerant
proteins which soluble in water and therefore contribute to
heat stress tolerance by the hydration of cellular
structure. Several genes responsible for producing heat
shock protein and the expression of heat shock gene
influence when temperature exceed from 30oC. i.e. Heat shock
protein that influences such as embryogenesis, germination,
plant growth, flowering, pollen development, fruit formation
and fruit maturation in heat stress condition. General
response to heat stress involves signaling via redox system;
Ca+2 and plant hormone activate the genomic re-programming
via signal cascade. It is suggested that changing membrane
fluidity play a central role in the sensing and influencing
gene expression under low and high temperature. Modeling for
temperature sensing and regulation of heat shock response
integrates observed membrane alteration. So the thylakoid
membrane in plant acts as a heat sensor is physiologically
crucial. Recent research has suggested that plant
experiences oxidative stresses during the initial period of
adjustment to any stress. Each gene show specific response
to specific stress. However genomic in plant including
genetics (direct mutation) and epigenetic (methylation,
chromatin remodeling, histone acecylation), transfer of gene
in plant response to heat stress tolerance. Physiological
genetic investigation indicate that heat tolerance traits
are complex (polygenic),it means that traits are controlled
by more than one gene and they are highly influence by
environmental variation. With the improvement through
convential breeding scientist select two cultivars which
both desire characters i.e. heat tolerance and high yielded
genes and hybridize it and select desirable plants from
segregating generation. However scientists use molecular and
biotechnological strategies for the purpose of heat
tolerance in tomato by using such techniques i.e. Genetic
engineering use to transfer of heat tolerant gene in plant
cell which have all other desirable characters is called
genetic engineering, High temperature tolerance has been
genetically engineered in plants mainly by over-expressing
the heat shock protein genes or indirectly by altering
levels of heat shock transcription factor proteins. Apart
from heat shock proteins, thermo tolerance has also been
altered by elevating levels of osmolytes, increasing levels
of cell detoxification enzymes and through altering membrane
fluidity. It is suggested that HSPs may be directly
implicated in thermo tolerance as agents that minimize
damage to cell proteins. Tissue culture technique use to
make plant from transformed cell. Molecular / genetic marker
used to identify the gene in plant cell or in F2 generation
that has ability to tolerance against high temperaure.Now a
days biotechnology contributed significantly to better
understanding of heat tolerant gene and heat tolerance
mechanism in tomato plants. Biotechnology play positive role
to take genetic homozygosity in plant in very short period
to make model plant for mankind.
Corresponding author’s email:
shehzadpbg@gmail.com |
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