Spring cold stress is a problem for wheat crops at heading and also may be damaged some other parts of this plant. The aim of this study was the investigation of spring cold stress on the physiological traits, plant pigments (total, a and b chlorophyll and Carotenoid) and cell membrane damage at the reproductive stage with the artificial conditions. For this purpose an experiment with 20 varieties of wheat with four treated cold level of stress (8 (control), +2, 0, 2 Celsius) in factorial arrangement in a randomized completely design implemented. Results of variance analysis showed the effects of interaction between cultivars spring cold levels is signification at the 5% level. Comparison between the interaction of all of traits showed the tolerant cultivars have more little cell membrane leakage and more plant pigments at the different levels of artificial Spring cold stress and PISHTAZ and AZAR 2, are the most tolerant cultivars andBECK CROSS.ROSHAN is the most susceptible cultivar. The results showed different reactions between cultivars and therefore these cultivars have considerably genetic diversity.

Plants are often exposed to a wide range of abiotic stresses, which have adverse effects on the survival, growth, quality, and quantity of crops. Coldness is one of these stresses that the late spring cold can cause great damages to the crop (cereal) planting during the reproductive period. The purpose of this research was to investigate the effect of spring cold on the physiological traits, associated with stress toleration including proline amino acid, and pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid) in the reproductive stage.To this end, an experiment was conducted in a controlled condition (greenhouse) with a combined analysis model based on a completely randomized design in four media (control temperature level of +8°C, +2°C, 0°C, and -2°C)for 20 cultivars of barley and three replicationin the Faculty of Agriculture of Tarbiat Modarres University, Iran, in 2016-17. The results of the analysis of variance showed that cold stress levels, cultivar, and interaction of cultivar on cold were significant for all the traits at 1% probability level.Cold-tolerant cultivars had higher levels of proline (Jolgeh cultivar) and plant pigments (Yousef and Nik) at different levels of cold stress. The cluster analysis was performed through the Ward method using the Euclidean distance coefficient to determine the genetic relationships between the studied cultivars, and the studied cultivars were divided into five groups at the control and severe stress (-2°C) levels and tolerated cultivars were grouped together. 12 pairs of microsatellite primers were used to study the genetic diversity in the molecular segment and the average polymorphism content information was estimated as much as 0.38. The cultivars were grouped through the Dice similarity coefficient as well as cluster analysis via the UPGMA model, and 20 cultivars of barley were divided into 4 groups. The results of correlation analysis through stepwise regression analysis showed a high correlation (highest coefficient of explanation) for Bmag0337 indicator with proline (R2=0.43), Bmac0518 indicator with chlorophyll a and total chlorophyll (R2=0.29), EBmac0602 indicator with chlorophyll b (R2=0.15), and Bmag0375 (R2=0.44) with carotenoid trait.

Plants are usually exposed to a range of environmental stresses. These stresses have undesirable effects on survival create growth, quantity and quality of agriculture products. Chilling stress is one of them that can damage cereals at the reproductive stage. The aim of present study was investigation of chilling effects on physiological traits, plant pigments (total, a and b chlorophyll and Carotenoid), proline content and ion leakage at reproductive stage under artificial conditions. To reach to this aim na experiment with 20 bread wheat cultivars with four levels of chilling stress ( (control), , 0, -2 Celsius) using factorial arrangement based on a completely randomized design was implemented. Results of variance analysis showed that cold levels, cultivars and effects of interaction signification at the 1% level. Comparison of means effects of interaction showed that the tolerant cultivars have little cell membrane leakage and more plant pigments and proline content at different levels of artificial chilling stress. Oroom and Aflak were known as the most tolerant cultivars and Line A and Mv17 as the most susceptible cultivars According to these criteria. Totally, this research showed that ion leakage, plant pigments and proline content can suitable traits for assessment of chilling stress.

Food productivity is declining due to the effect of different abiotic stresses. Stress is the result of abnormal physiological processes that influence by one or a combination of biological and environmental factors. Cold, salinity and drought are important among the other stresses. Three types of cold stress has been identified that include: Frost, Freezing and Chilling Stress. The relationship between plant growth and climate change is a seemingly contradictory event. In fact, warming increases danger of cold stress. In the spring, at the same time of started wheat growth, it is increase its sensitivity to low temperatures and it damaged. This model of cold stress called rapidly falling temperatures in the spring or in short term called "chilling". Chilling stress reduced leaf expansion, wilting, chlorosis (yellowing of leaves) and may lead to necrosis (death of tissue) and strongly disturbed the reproductive development of plants. Low temperature stress limit the grain production in cold and ultra-cold climates and makes high damages in some years. Therefore produce resistant cultivars is necessary. Management of genetic resources, and knowledge of the genetic diversity are tow important principles of breeding projects. This study examines the genetic diversity of some of bread wheat cultivars for some physiological characteristics associated with chiling stress using multivariate statistical methods and compare these methods.
This survey performed in 2013 at the Faculty of agriculture, Tarbiat Modares University. In this study an experiment with 20 varieties of wheat with four treated cold levels of stress (8 (control), , 0, -2 Celsius) in factorial arrangement in randomized completely design implemented. In early of reproductive stages (Zydaky code 50 to 68), the plant transferred to growth chamber under 14/10 hours and 16/8 °C day/night photoperiod. To impose stress, temperature reduced 2°C per one hours from 8 °C then the pots were placed for 2 h under stress in each of stress temperature levels (2, 0 and -2 °C). After stress, temperature up to 8 °C with ramp 2 °C per hours. Sampling was done after 24 h and then electrolyte leakage, chlorophyll (a, b, ab and cartenoids), proline and fructan, were assessed.
The results of this study showed that the effects of interaction between gentopyes and chiling stress were significant at 1% level. Based on results of the cluster analysis twenty genotypes were classified into four groups in -2 celsius temperature and two groups in control temperature. The principal component and principal coordinate ,confirmed grouping created based on of cluster analysis. The principal component analysis decrease all treats in to 3 components in control (with cumulative of variance 80) and sever stress (with cumulative of variance 85). Also the principal coordinate analysis decrease all component to 3 components with cumulative variance 94.11 (for control) and 96.59 (for sever stress). Based on cluster analysis Pishgam and Aflak genotypes in control condition and Alvand and Sivand in -2°C had the maximum genetic distance. The minimum genetic distance was observed between Mv17 and Navid genotypes (in control condition) and Kaskojen and Pishgam (sever stress).
(1) Chiling stress detects the diversity amoung studied gentopyes; (2) In order to grouping of genotypes, cluster analysis provided more accurate grouping than principal component analysis and principal coordinate analysis ; (3) Alvand and Sivand cultivars can be use as potential parents to provide the necessary population in classical breeding programs, in order to detect of QTLs for chiling tolerance and also for marker assisted selecion.

Genetic diversity is necessary for breeding program and increasing genetic gain of selection in crop plants. With the onset of spring growth, Spring cold stress is a problem for wheat crops at heading and also may be damaged some other parts of this plant. The aim of this study is the investigation of genetic diversity duo to artificial cold stress on the physiological traits, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid and cytoplasmic membrane stability at the reproductive stage. For this purpose an experiment with 20 cultivars of bread wheat and four levels of cold stress, (8 (control), +2, 0 and -2 Celsius) was performed in factorial arrangement in a completely randomized design. Results of variance analysis showed the effects of interaction between cultivars and cold stress levels is significant at the 5% level which showed the existence of genetic diversity between studied cultivars.. There were significant correlations between chlorophyll a, b, total and carotenoid. In order to determination of genetic relation between cultivars, cluster analysis using was performed Ward method and cultivars were divided into 5 groups at -2 °C and 4 groups at +8 °C. Discriminate function and principal component analysis confirmed the results of cluster analysis. The third group of -2 °C including of GHODS, TAJAN and PISHTAZ had the lower level of ion leakage and higher level of plant pigments.

Genetic diversity is a necessary factor for breeding programs and increasing genetic gain of selection in crop plants. Molecular markers have been successfully used for analysis of genetic diversity in various crops. For this purpose the 20 bread wheat cultivars were in a completely randomized design and five physiological traits, total chlorophyll, chlorophyll a, chlorophyll b, carotenoids and their stability was assessed in the cytoplasm membrane. Study of genetic diversity accomplished by 12 SSR marker primers. In order to determine genetic relation between cultivars, cluster analysis in Ward method was performed and cultivars were into four groups. The association between 40 microsatellite bands of 12 primer pairs and 5 physiological traits recorded on 20 wheat bread cultivars. Polymorphic information contents (PIC) of loci were in the range of 0.32 (Xgwm10) to 0.725 (Xgwm33). By multiple regression stepwise relationship of each 5 physiological traits and the 40 polymorphic markers were studied. The result of stepwise regression analysis showed the significant relationship of 2 markers with 5 physiological trait at the contort temperature and also 6 marker with those physiological marker at the severe level of spring cold stress, may facilitate preliminary selection of these traits for breeding purposes. Moreover, our results showed that some of the markers were related to more than one trait, implying close linkage and/or peliotropy of these genes on chromosomes.

Late spring frost damage is the main factor that limits apricot production in Iran. This research was aimed to evaluate the damage of freezing in two apricot cultivar flowers: ʽʽNasiriʼʼ and ʽʽNori-Dirrasʼʼ during spring 2011. Reproductive organs of these cultivars at two phenological stages، popcorn and full bloom، were transferred to programmable freezer with temperature touch down from 5°C to -10°C. Temperature were detected by the mean of thermocouple and recorded by a data logger connected to a PC Computer. According to the results، differences between two cultivars and interaction of cultivar and phenological stages were not significant، whereas the effect of phenological stage was significant. The lowest supercooling temperature was -6. 1°C and recorded at full bloom stage in ʽʽNori-Dirrasʼʼ. More than 30% of ʽʽNori-Dirrasʼʼ buds and more than 60% of its flowers showed less supercooling than -5°C. According to this result، ʽʽNori-Dirrasʼʼ showed lower supercooling temperature than ʽʽNasiriʼʼ.

Studying the phenomenon of frost and chilling is one of the fundamental researches in the field of Agroclimatelogy and knowing how and when they occur, could be useful significantly in the agricultural sector. Climate change which causes changes in temperature parameters influences the frost. To this end, a research was done so that the beginning of the first frost and chilling in autumn, the last frost and chilling in spring and also period of the frost and freezing at three weather stations in Tabriz, Qazvin and Mashhad would be checked during 1961-2005 as the basis period and during 2005-2050 as the future period. The data of the future period was produced based on output of Hadcm3, under the scenario A1B, using the software of data generator LASR-WG. Then time series of the dates of the first and last frost and chilling in autumn and spring was formed for each year during the periods of the study and the best statistic distribution was fitted for each of them and the possibilities of their happening were calculated. The results showed that at all stations affected by the climate change, the first frost and chilling in autumn will occur earlier and the last frost and chilling in spring will occur earlier and length of frost and chilling period will decrease.

Increasing of wood demand is currently one of the most important problems in our society. Different clones of Populus nigra from salicacea as a native fast-growing species have a good potential for planting in wide scale. But because of the ecological differences in the field, especially. Temperature alterations, segregation of the cold resistant clones in relation to in seedling stage establishment is very important. Peroxidase enzyme as one of the most sensitive physiological factors to environmental stresses, especially low temperature was used to compare the ability of cold resistance of five clones of this species. Quantitative and qualitative activities of this biochemical marker (POD) were studied during five months from September till May. The result indicated that P. nigra 62.231 and 64.13 clones had the best ability of early autumn cold resistance and P. nigra 56.52 clone had the best ability of late spring cold resistance. Also, P. nigra 62.171 and 64.13 clones the best winter cold resistance.

Cold is one of the most significant abiotic stresses which restrict crop growth and productivity worldwide. In order to investigate how spring barley (Hordeum vulgare L.) seedlings adapt to short-term periods of low temperature, the present study explored proteomic changes in leaves. Cold stress at 4 °C was applied to barley seedlings for 48 hours; third leaves were harvested and compared with seedlings grown in normal conditions (25° C). The proteomic analysis was conducted by twodimensional electrophoresis (2-DE) and the Coomassie blue staining procedure. Fifteen reproducible protein spots showing a significant difference between the control condition and cold stress were identified; 10 of the spots demonstrated an increase in expression while 5 spots showed a decrease under 4 °C cold stress for 48 hours. By applying MALDI-TOF analysis, 7 spots were identified. These responsive proteins were involved in the Calvin cycle, photosynthetic electron transport, light reaction, and signal transduction. The upregulation of proteins involved in the regulation of the chloroplast system, the integrity of chloroplasts, energy metabolism, antioxidant defense, and photosynthesis has probably acclimatized the plant to cold stress. These findings indicate that there was greater cold stress affecting photosynthesis in spring barley and it is of crucial importance to maintain the efficiency of photosynthesis under cold stress.