Physiological and morphological responses of two barley varieties and their progenies to toxic effects of Lead

Heavy metal contamination in soil caused by human activities, such as mining and industrial activities. Is a serious problem all over the world. Lead (Pb) is one of the major heavy metals that tend to accumulate in the surface ground layer and its concentration decreases with soil depth. Soils contaminated with Pb cause sharp decreases in crop productivity thereby posing a serious problem for agriculture.Toxic effects of lead on plants can be attributed chlorosis, reduced growth, blackening of root system, upsets mineral nutrition and water balance, changes in hormone status and effects on the structure and permeability of the membrane. This study was conducted to evaluate several morphological and physiological traits of barely genotypes under lead contamination stress.

In this research, morphological effects of three different densities of lead nitrate (1000,1500,2000ppm) and a control sample on two barley genotypes (Rec and Dom) were investigated in a completely randomized design with five replications. Traits of stem length, root length, leaf number and number of yellow leaves shoot fresh weight, root fresh weight, stem dry weight, root dry weight and ultimately the dry and fresh biological performances for the control and different treatments were measured. After observing the difference between the two parents in response to lead poisoning, on October 16, 2017, 94 inbred lines from Dom and Rec were planted in a completely randomized design with three replications in towenty-cm diameter pots. Then at 2- to 3-leaf stage, seedlings were treated by 0-2000 ppm density lead nitrate.

The results showed that there was a significant difference between Rec and Dom genotype in 2000ppm density respecting the lead resistance, and Dom showed a higher resistance compared to another parent. Stem length, leaf number, number of yellow leaves, stem dry weight; dry and fresh biological performances were affected by lead more than the other traits. The results of the experiment showed that in all morphological and physiological traits, there was a significant difference between the lines in the probability level of 1%. Based on genotypic correlation, there was a positive and significant correlation between photosynthesis and transpiration traits, stomatal conduction, CO2 Concentration, and plant greenness. In addition, there was a positive and significant correlation between fresh and dry biological performance and stem height, root length, shoot fresh weight, root fresh weight, root dry weight, and the number of green leaves. Based on the studied traits and by using cluster analysis, barley inbred lines were divided into 3 and 4 clusters under normal and stress conditions, respectively. The lines 24, 40, 41, 44, 78, 80 with the highest mean of morphological and physiological traits, were placed in cluster 3 under stress condition. These genotype sareamong the lead resistant genotypes. The lines 1, 7, 8, 15, 21, 25, 50, with the lowest mean of morphological and physiological traits, were put in cluster 2 under stress condition and were considered as the genotypes sensitive to lead.

Since tension with heavy metals causes’ significant disruption to plants, so it is essential to understand the traits that are affected by this tensions and relationships existing between them. In this study, photosynthesis, transpiration, stomatal conductance, stem length, number of yellow leaves, fresh and dry stem weight, fresh and dry Biological yield, affected by stress than other traits.