Heat stress tolerance studies in Tomato (Lycopersicon esculantum Mill.)
January 02, 2013
Shehzad Ahmad Kang
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.
Tomato Plant and Fruits
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.
By Shehzad Ahmad Kang, Department of Plant Breeding and Genetics, University of
Agriculture, Faisalabad, Pakistan- 38040
Corresponding author’s email: firstname.lastname@example.org
Zarai Media Team