Amjad Hameed

Alleviation of cadmium toxicity by silicon is related to elevated photosynthesis, antioxidant enzymes; suppressed cadmium uptake and oxidative stress in cotton

Biotic systems face immense environmental hazards such as accumulation of heavy metals, particularly in agricultural ecosystems that might cause deterioration of yield and quality of crops. In this study, we evaluated the role of silicon (Si) in alleviating the heavy metal (Cd) stress tolerance in cotton by analyzing the induced Physio-chemical changes. Cotton plants were grown in hydroponic culture with three different Cd levels (0, 1 and 5μM) along with two Si treatment levels (0 and 1mM). The data showed that Cd alone reduced the plant growth as well as the efficiency of antioxidant activity as compared to control plants. Plant growth, gas exchange characteristics (net photosynthetic rate, stomatal conductance, transpiration rate, water use efficiency) chlorophyll contents, and carotenoids as well as the performance of antioxidant enzymes were improved by the exogenous application of Si. The adverse effects of Cd on plant growth were alleviated by the exogenous application of Si. It was observed that Si effectively mitigated the adverse effects of Cd on cotton plants and markedly enhanced the growth, biomass and photosynthetic parameters while decreased the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and electrolytic leakage (EL). The antioxidant enzyme activities in cotton leaves and roots increased significantly, when Si was added to control as well as Cd stressed plants. In conclusion, Si improved the growth and photosynthesis attributes of cotton plants by mitigating the adverse effects of Cd stress through reduced EL, MDA and H2O2 contents and improved activities of antioxidant enzymes.

Differential changes in antioxidants, proteases, and lipid peroxidation in flag leaves of wheat genotypes under different levels of water deficit conditions

Changes in enzymatic antioxidants and oxidative injury were evaluated in flag leaves of seven wheat genotypes under well watered (WW), medium watered (MW), low watered (LW) and soil stored moisture (SSM) conditions maintained in lysimeters through neutron moisture prob. Genotypes behaved differentially in terms of antioxidant response and stress induced injury under above indicated water deficit levels. In general, antioxidant enzymes were rarely enhanced under MW condition, often increased under LW condition while remained unchanged, elevated or diminished under SSM condition (severe stress). Higher CAT and POD activities were observed in NR-234 and in Pfau followed by FD-83 respectively under LW conditions. Under SSM condition, APX and POD increased significantly in Nesser and Pfau and CAT in NR-234, Nesser and Pfau, while remained at control level or decreased in other genotypes. In NR-234, SOD activity enhanced only under LW condition. However, SOD rose in Nesser, FD-83 and Sarsabz while remained unaffected in NR-241, Sitta and Pfau under all water deficit conditions. Lipid peroxidation increased significantly in FD-83 only under MW condition along with raised protease activity and protein contents. However, peroxidation of lipids was significantly enhanced in all genotypes under LW and SSM conditions. It was concluded that response of genotypes vary under different levels of water deficit. Hydrogen peroxide scavenging system was more actively involved in detoxification of oxidative stress induced by water deficit. Raised antioxidants (CAT, POD) resulting in comparatively lower lipid peroxidation in Pfau under SSM condition and in Sitta under LW condition confer stress tolerance in these genotypes.

Citric acid improves lead (pb) phytoextraction in brassica napus L. by mitigating pb-induced morphological and biochemical damages.

Phytoextraction is an environmentally friendly and a cost-effective strategy for remediation of heavy metal contaminated soils. However, lower bioavailability of some of the metals in polluted environments e.g. lead (Pb) is a major constraint of phytoextraction process that could be overcome by applying organic chelators. We conducted a glasshouse experiment to evaluate the role of citric acid (CA) in enhancing Pb phytoextraction. Brassica napus L. seedlings were grown in hydroponic media and exposed to various treatments of Pb (50 and 100 μM) as alone or in combination with CA (2.5mM) for six weeks. Pb-induced damage in B. napus toxicity was evident from elevated levels of malondialdehyde (MDA) and H2O2 that significantly inhibited plant growth, biomass accumulation, leaf chlorophyll contents and gas exchange parameters. Alternatively, CA application to Pb-stressed B. napus plants arrested lipid membrane damage by limiting MDA and H2O2 production and by improving antioxidant enzyme activities. In addition, CA significantly increased the Pb accumulation in B. napus plants. The study concludes that CA has a potential to improve Pb phytoextraction without damaging plant growth.

Drought induced programmed cell death and associated changes in antioxidants, proteases, and lipid peroxidation in wheat leaves

Two wheat (Triticum aestivum L.) genotypes with varying degree of drought tolerance were used to analyze programmed cell death (PCD) and related biochemical changes under drought stress. Drought induced PCD in leaves, as evident by internucleosomal nDNA fragmentation, was observed in sensitive genotype Nesser. Drought tolerant genotype (FD-83) showed higher peroxidase, superoxide dismutase, and catalase activities and ascorbate content under drought stress compared to sensitive genotype. Total phenolic content increased whereas lipid peroxidation remained un-changed under drought in FD-83. In contrast, drought enhanced the proteases and ascorbate peroxidase activities and lipid peroxidation (MDA content) in Nesser.

Heat Stress-Induced Cell Death, Changes in Antioxidants, Lipid Peroxidation, and Protease Activity in Wheat Leaves

Six wheat genotypes were evaluated for heat tolerance in terms of seedling growth, antioxidant response and cell death. Based on the heat susceptibility index (HSI), response of the genotypes varied from heat tolerant (Inqilab-91) to heat sensitive (Sitta) along with moderately tolerant (Nesser and Sarsabz) and sensitive (Fareed and FD-83). Heat stress-induced programmed cell death (probably necrosis) in wheat leaves was evident by DNA smear. MDA content increased above twofold in most of genotypes under heat stress, with the lowest increase in the heat-tolerant genotype Nesser. Catalase activity diminished under heat stress in all genotypes. Peroxidase, superoxide dismutase (SOD), protease, and ascorbate peroxidase (APX) activities increased under heat stress. Apparently, heat stress-induced reduction in catalase activity was compensated by a parallel increase in peroxidases to quench H2O2. Heat stress-induced decrease (%) in catalase and increase in protease activities showed significant positive correlations, whereas increase (%) in APX activity showed a significant negative correlation with HSI or relative heat tolerance of genotypes. All these correlations signify that catalase, protease and ascorbate peroxidase can be used efficiently as biochemical markers to assess the relative heat stress tolerance of wheat genotypes at the seedling stage. In conclusion, using a multiparametric approach involving morphophysiological and biochemical assays, the sensitivity of wheat genotypes to heat stress could be evaluated to a sufficient level of certainty at the seedling stage.

Silicon alleviates nickel toxicity in cotton seedlings through enhancing growth, photosynthesis, and suppressing Ni uptake and oxidative stress

Cotton (Gossypium hirsutum L.) is a well-known and economically most beneficial crop worldwide while nickel (Ni) toxicity is a widespread problem in crops grown on Ni-contaminated soils. We investigated the response of silicon (Si) in cotton under Ni stress with respect to growth, biomass, gas exchange attributes, enzymatic activities, and Ni uptake and accumulation. For this, plants were grown in hydroponics for 12 weeks with three levels of Ni (0, 50, and 100 µM) in the presence or absence of 1 mM Si. Results showed that Ni significantly reduced the plant growth, biomass, gas exchange attributes, and pigment contents while Si application mitigated these adverse effects under Ni stress. Nickel stress significantly decreased antioxidant enzymes’ activities while increased malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolyte leakage (EC) in leaves and roots. The application of Si enhanced the activities of antioxidant enzymes and reduced MDA, H2O2, and EC in plants. Nickel application significantly increased Ni concentration and accumulation in leaf, stem, and roots while Si application significantly decreased Ni in these plant parts. The present study indicates that Si could improve cotton growth under Ni stress by lowering Ni uptake and reactive oxygen species (ROS) and by increasing antioxidant enzymes activities.

Biochemical alterations in leaves of resistant and susceptible cotton genotypes infected systemically by cotton leaf curl Burewala virus

Leaf curl disease caused by Cotton Leaf Curl Burewala virus (CLCuBuV) has been recognized as serious threat to cotton in Indian subcontinent. However, information about cotton–CLCuBuV interaction is still limited. In this study, the level of phenolic compounds, total soluble proteins, and malondialdehyde (MDA) and the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POX), catalase (CAT), proteases, superoxide dismutase (SOD), and polyphenol oxidase (PPO) were studied in leaves of two susceptible (CIM-496 & NIAB-111) and two resistant (Ravi and Co Tiep Khac) cotton genotypes. Disease symptoms were mild in the resistant genotypes but were severe in highly susceptible genotypes. The results showed that phenolic compounds, proteins, PAL, POX, CAT, proteases, SOD, PPO, and MDA play an active role in disease resistance against CLCuBuV. The amount of total phenols, proteases, MDA, and PPO was significantly higher in leaves of CLCuBuV-inoculated plants of both resistant genotypes as in non-inoculated plants, and decreased in CLCuBuV-inoculated plants of both susceptible genotypes over their healthy plants. POX, protein content, SOD, and PAL activities showed lower values in resistant genotypes, while they decreased significantly in susceptible genotypes as compared to the noninoculated plants except PAL, which showed non-significant decrease. CAT was found to be increased in both susceptible and resistant genotypes with maximum percent increase in resistant genotype Ravi, as compared to non-inoculated plants. The results showed significantly higher concentrations of total phenols and higher activity of protease, MDA, SOD, and PPO in resistant genotype Ravi after infection with CLCuBuV, suggesting that there is a correlation between constitutive induced levels of these enzymes and plant resistance that could be considered as biochemical markers for studying plant-virus compatible and incompatible interactions.

Evaluation of seedling survivability and growth response as selection criteria for breeding drought tolerance in wheat

Detection of genotypic variation in response to water stress at seedling stage could help in escalating selection intensity in breeding drought tolerant varities. Nine genotypes were tested for seedling survivability under drought stress. Four genotypes, i.e. ‘Sarsabz’, ‘Sitta’, ‘Fareed’ and ‘FD-83’, showed complete survival on resumption of irrigation after drought stress. These genotypes were late dying as they withered slowly under drought. Percent wilting and percent survival on resumption of irrigation were negatively correlated. Six genotypes were selected on the basis of seedling survivability (late and early dying) and evaluated for seedling growth response under drought. Root length and dry weight increased significantly under stress in ‘Sitta’, ‘FD-83’ and ‘Fareed’. Drought stress also increased the root-to-shoot length ratio in ‘FD-83’ and ‘Fareed’. However, seedling fresh and dry weight significantly reduced in ‘Nesser’ and ‘Inqalab-91’ under stress. In ‘FD-83’, seedling fresh and dry weight increased over control under stress. Results indicated that seedling survivability, root-to-shoot length ratio, root length and dry weight were most important traits for screening drought tolerance at seedling stage. On the basis of these indices, ‘Sitta’, ‘Fareed’ and ‘FD-83’ were classified as drought tolerant, ‘Sarsabz’ and ‘Nesser’ as moderately tolerant and ‘Inqalab-91’ as sensitive genotypes. Collectively, results suggested that selection by combining seedling survivability, growth response, RWC and leaf water potential can be efficiently used for rapid evaluation of drought tolerance in wheat breeding.

Evaluation of genetic diversity among bread wheat varieties and landraces of Pakistan by SSR markers

Genetic diversity of 48 Pakistani wheat varieties and 12 landraces was assessed, loss of genetic diversity in bread wheat during the change from traditional landraces (LVs) to modern breeding varieties was examined, and recent trends of national wheat breeding programmes were identified. A total of 29 SSR markers, representing at least one marker from each chromosome of wheat, were used to analyze the genetic diversity. A total of 80 alleles were generated by the 29 loci with an average of 2.76 alleles per marker. A significant loss of genetic diversity was observed from LVs to elite cultivated varieties. Average genetic similarity between landraces was 61% while varieties released after 1990 showed 73% similarity. Range of genetic distance observed between all possible pairs was from 1.41 to 4.90. It was also observed that most of the varieties released from one source showed comparatively lower diversity indicating the utilization of common elite breeding material or interbreeding of released varieties.

PHYSIOLOGICAL RESPONSE OF COTTON LEAF CURL BUREWALA VIRUS-INFECTED PLANTS OF TOLERANT AND SUSCEPTIBLE GENOTYPES OF DIFFERENT GOSSYPIUM SPECIES

The effect of Cotton leaf curl Burewala virus (CLCuBuV) on cotton growth, yield, photosynthetic gas exchange, chlorophyll fluorescence and chlorophyll contents was studied in susceptible (CIM-496 and NIAB-111 from Gossypium hirsutum) and tolerant (Ravi from G. arboreum and Co Tiep Khac from G. herbaceum) cotton genotypes under glasshouse condition through artificial inoculation. Compared to the non-inoculated plants, the inoculated plants of susceptible genotypes showed stunted growth, reflected as significant decrease in plant height, internode length, number of leaves per plant, leaf area, number of bolls per plant, boll weight and yield per plant. Upon virus inoculation, transpiration rate decreased significantly in both susceptible genotypes while water use efficiency (WUE) was enhanced in CIM-496 compared to the non- inoculated plants. However, overall plant growth, net photosynthetic rate, leaf transpiration, stomatal conductance and WUE remained unaffected by CLCuBuV-infection in tolerant genotypes. Moreover, chlorophyll b and total chlorophyll content increased in one of the tolerant genotypes (Ravi) in response to CLCuBuV-infection while remaining unaffected in all other genotypes. Level of chlorophyll a and chlorophyll fluorescence (Fv/Fm) was not affected by CLCuBuV-infection in all genotypes. In conclusion, CLCuBuV infection adversely affected the overall plant growth and yield in susceptible genotypes while tolerant genotypes were able to maintain the growth and yield in the presence of infection. Reduced transpiration rate and increased WUE in susceptible genotypes and increased chlorophyll b and total chlorophyll content in tolerant genotypes on virus inoculation provided evidence for their significant involvement in CLCuBuV-tolerance mechanism in cotton.