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The Genetic Analysis of Heat Tolerance and Genotypic Difference on Heat Shock Response in Cucumber

Author: LiWeiGuan
Tutor: ChenJinFeng
School: Nanjing Agricultural College
Course: Olericulture
Keywords: Cucumber heat stress major gene plus polygene HSPs DNA methylation MSAP
CLC: S642.2
Type: Master's thesis
Year: 2009
Downloads: 32
Quote: 0
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Abstract


Cucumber (Cucumis sativus L.) is an important vegetable crop grown widely throughout the world. China is the biggest cucumber producing country in the world. Due to global warming, heat stress is one of the major environmental factors affecting plant growth and productivity. High temperature stress causes some physiological, biochemical and molecular changes in plant metabolism. The ability of crop plants to adapt to heat stress is potentially an important component of tolerance to heat stress under field conditions. Therefore, research on the mechanism of high temperature stress in cucumber has importance for future advances in cucumber breeding and improvement. In this experiment, the CSHSP70 expression and the DNA methylation level under heat stress was studeid, based on the genetic analysis of heat tolerance of cucumber genotypes. The results were summarized as follows:1. Major-polygene genetic analysis of heat tolerance at seedling stage in cucumberThe method of major gene plus polygene mixed inheritance model was used to analyze the genetics of heat tolerance traits at seedling stage in cucumber. The results showed that heat tolerance traits were controlled by two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects (the E-1 model). Heritability values of the major genes was from 31.49% to 66.67%, while those of polygenes was from 10.24% to 35.13%. Environment greatly effects heat tolerance gene expression, its’variance was 33.36%～46.19% of the total phenotype variance.2. CSHSP70 expression and physiological studies in different cucumber genotypes under heat stressThe CSHSP70 expression was detected by RT-PCR technique and some physiological parameters related to thermotolerance were also studied in cucumber seedlings under various thermal stresses. The results showed increased membrane permeability and MDA content. SOD activity and Proline content was significantly increased in all genotypes under various thermal stresses. The enhanced genotypic difference in HSP70 gene expression was also noted in present studies. 3. Analysis of cytosine methylation in response to heat stress in cucumberThe changes of cytosine methylation patterns and levels in response to heat stress in Cucumber genomes was studied by methylation sensitive amplification polymorphism(MSAP). The results showed levels of methylation was significantly increased under various thermal stresses and indicated difference between heat tolerance and sensitive varieties. Numbers of sequences changes were less than numbers of methylation pattern changes including de novo methylation, de-methylation, atyPical Pattern and no changes of methylation pattern in stastic of 14 MSAP profiles. Besides these, the results indicated number of de novo methylation sites were more than de-methylation’s, the ratio of de novo methylation in heat tolerance variety was higher than in heat sensitive variety, but the ratio of de-methylation was completely opposite.

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CLC: > Agricultural Sciences > Gardening > Vegetable gardening > Melons > Cucumber
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