Ullah Najeeb

Insights into cadmium induced physiological and ultra-structural disorders in Juncus effusus L. and its remediation through exogenous citric acid

This study appraised cadmium (Cd) toxicity stress in wetland plant Juncus effusus, and explored its potential for Cd phytoextraction through chelators (citric acid and EDTA). Cadmium altered morphological and physiological attributes of J. effusus as reflected by growth retardation. Citric acid in the presence of 100 μM Cd significantly countered Cd toxicity by improving plant growth. Elevated Cd concentrations reduced translocation factor that was increased under application of both chelators. Citric acid enhanced Cd accumulation, while EDTA reduced its uptake. Cadmium induced oxidative stress modified the antioxidative enzyme activity. Both levels of citric acid (2.5 and 5.0 mM) and lower EDTA concentration (2.5 mM) helped plants to overcome oxidative stress by enhancing their antioxidative enzyme activities. Cadmium damaged the root cells through cytoplasmic shrinkage and metal deposition. Citric acid restored structure and shape of root cells and eliminated plasmolysis; whereas, EDTA exhibited no positive effect on it. Shoot cells remained unaffected under Cd treatment alone or with citric acid except for chloroplast swelling. Only EDTA promoted starch accumulation in chloroplast reflecting its negative impact on cellular structure. It concludes that Cd and EDTA induce structural and morphological damage in J. effusus; while, citric acid ameliorates Cd toxicity stress.

Cadmium-induced functional and ultrastructural alterations in roots of two transgenic cotton cultivars.

The toxic effect of cadmium (Cd) at increasing concentrations was studied with special attention being given to the root morphological and ultrastructural changes in two transgenic cotton cultivars viz. BR001 and GK30 and their wild relative viz. Coker 312. In comparison to their respective controls, low concentration (10 and 100microM) of Cd greatly stimulated seed germination, while it was inhibited by highest concentration of Cd (1000microM) in case of two transgenic cultivars. However, in Coker 312 the seed germination percentage progressively decreased over the control at all Cd levels. Various physiological and morphological parameters of the root and whole plant in both transgenic cotton cultivars and their relative wild cotton genotype respond differently towards the Cd toxicity. Bioavailability of Cd was concentration-dependent where seedling root captured more Cd as compared to shoot. BR001 accumulated more Cd followed by GK30, while Coker 312 was less Cd accumulator. The ultrastructural modifications in the root tip cells of both the transgenic cotton cultivars and their wild relative were also dose-dependent. With the increase in Cd levels, the fine structures of their root cells also invariably changed. Increase in plasmolysis of the plasma membrane, greater number of nucleoli and vacuoles and enlarged vacuoles could be observed in both transgenic cotton cultivars. In comparison to them, Coker 312 showed relatively well developed ultrastructures of the root tips except enlarged vacuoles and greater number of mitochondria. Moreover, the accumulation of Cd in the form of electron dense granules and crystals both in vacuoles and attached to cell walls were visible in both transgenic cotton cultivars and their wild relative. These results suggest that both transgenic cotton cultivars and their wild relative cotton genotype responded positively towards Cd stress at seedling stage, the internal Cd-detoxification might be through apoplastic and symplastic binding. Moreover, as a whole BR001 proved to be sensitive whereas; GK30 and Coker 312 were found as tolerant.

Citric acid assisted phytoremediation of copper by Brassica napus L.

Use of organic acids for promoting heavy metals phytoextraction is gaining worldwide attention. The present study investigated the influence of citric acid (CA) in enhancing copper (Cu) uptake by Brassica napus L. seedlings. 6 Weeks old B. napus seedlings were exposed to different levels of copper (Cu, 0, 50 and 100µM) alone or with CA (2.5mM) in a nutrient medium for 40 days. Exposure to elevated Cu levels (50 and 100µM) significantly reduced the growth, biomass production, chlorophyll content, gas exchange attributes and soluble proteins of B. napus seedlings. In addition, Cu toxicity increased the production of hydrogen peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL) in leaf and root tissues of B. napus. Activities of antioxidant enzymes such as guaiacol peroxidase (POD), superoxide dismutase (SOD), catalases (CAT), ascorbate peroxidase (APX) in root and shoot tissues of B. napus were increased in response to lower Cu concentration (50µM) but increased under higher Cu concentration (100µM). Addition of CA into nutrient medium significantly alleviated Cu toxicity effects on B. napus seedlings by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in CA-treated plants seems to play a role in capturing of stress-induced reactive oxygen species as was evident from lower level of H2O2, MDA and EL in CA-treated plants. Increasing Cu concentration in the nutrient medium significantly increased Cu concentration in in B. napus tissues. Cu uptake was further increased by CA application. These results suggested that CA might be a useful strategy for increasing phytoextraction of Cu from contaminated soils.

Citric acid enhances the phytoextraction of manganese and plant growth by alleviating the ultrastructural damages in Juncus effusus L.

Chelate-assisted phytoextraction by high biomass producing plant species enhances the removal of heavy metals from polluted environments. In this regard, Juncus effusus a wetland plant has great potential. This study evaluated the effects of elevated levels of manganese (Mn) on the vegetative growth, Mn uptake and antioxidant enzymes in J. effusus. We also studied the role of citric acid and EDTA on improving metal accumulation, plant growth and Mn toxicity stress alleviation. Three-week-old plantlets of J. effusus were subjected to various treatments in the hydroponics as: Mn (50, 100 and 500 microM) alone, Mn (500 microM) + citric acid (5 mM), and Mn (500 microM) + EDTA (5 mM). After 2 weeks of treatment, higher Mn concentrations significantly reduced the plant biomass and height. Both citric acid and EDTA restored the plant height as it was reduced at the highest Mn level. Only the citric acid (but not EDTA) was able to recover the plant biomass weight, which was also obvious from the microscopic visualization of mesophyll cells. There was a concentration dependent increase in Mn uptake in J. effusus plants, and relatively more deposition in roots compared to aerial parts. Although both EDTA and citric acid caused significant increase in Mn accumulation; however, the Mn translocation was enhanced markedly by EDTA. Elevated levels of Mn augmented the oxidative stress, which was evident from changes in the activities of antioxidative enzymes in plant shoots. Raised levels of lipid peroxidation and variable changes in the activities of antioxidant enzymes were recorded under Mn stress. Electron microscopic images revealed several modifications in the plants at cellular and sub-cellular level due to the oxidative damage induced by Mn. Changes in cell shape and size, chloroplast swelling, increased number of plastoglobuli and disruption of thylakoid were noticed. However, these plants showed a high degree of tolerance against Mn toxicity stress, and it removed substantial amounts of Mn from the media. The EDTA best enhanced the Mn uptake and translocation, while citric acid best recovered the plant growth.

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.

Cadmium-induced ultramorphological and physiological changes in leaves of two transgenic cotton cultivars and their wild relative

The present study describes cadmium-induced alterations in the leaves as well as at the whole plant level in two transgenic cotton cultivars (BR001 and GK30) and their wild relative (Coker 312) using both ultramorphological and physiological indices. With elevated levels of Cd (i.e. 10, 100, 1000 microM), the mean lengths of root, stem and leaf and leaf width as well as their fresh and dry biomasses linearly decreased over their respective controls. Moreover, root, stem and leaf water absorption capacities progressively stimulated, which were high in leaves followed by roots and stems. BR001 accumulated more cadmium followed by GK30 and Coker 312. Root and shoot cadmium uptakes were significantly and directly correlated with each other as well as with leaf, stem and root water absorption capacities. The ultrastructural modifications in leaf mesophyll cells were triggered with increase in Cd stress regime. They were more obvious in BR001 followed by GK30 and Coker 312. Changes in morphology of chloroplast, increase in number and size of starch grains as well as increase in number of plastoglobuli were the noticed qualitative effects of Cd on photosynthetic organ. Cd in the form of electron dense granules could be seen inside the vacuoles and attached to the cell walls in all these cultivars. From the present experiment, it can be well established that both apoplastic and symplastic bindings are involved in Cd detoxification in these cultivars. Absence of tonoplast invagination reveals that Cd toxic levels did not cause water stress in any cultivars. Additionally, these cultivars possess differential capabilities towards Cd accumulation and its sequestration.

Haploid and Doubled Haploid Technology

The microspore culture technique has its wide applications in plant genetic research and breeding programmes in oilseed Brassicas due to its relative simplicity, efficiency in haploid and doubled haploid production, mutation and germplasm generation, and gene transformation. Various factors could influence microspore embryogenesis and haploid production including donor plant genotype, donor plant physiology, microspore developmental stage, culture conditions, culture environment and pretreatments. Stress is also an essential component during embryogenesis induction in microspore culture. Efficient plant regeneration from microspores mostly occurs through direct embryogenesis ensuring minimal occurrence of cytogenetic abnormalities. Appropriate stress conditions such as chilling, partial desiccation, cotyledon excision, and successive subculture of microspore-derived embryos could promote plant development in oilseed rape. Medium renovation, phytohormones and plant growth regulators, and chromosome doubling agents such as colchicine treatment also affect plant regeneration in Brassica species. Compared to colchicine treatments of microspore-derived embryos and plants, immediate colchicine treatment of isolated microspores results in high embryogenesis and diploidisation and low chimeric percentages. The ploidy level of microspore-derived plants of Brassica species could be estimated by different methods at various stages. Mutation breeding techniques are widely used in plant breeding for producing useful mutants and variants. Microspore culture also provides an ideal method for mutation because the mutated traits can be fixed in homozygous condition by chromosome doubling, which can enforce to obtain target mutation traits efficiently. Ultraviolet irradiation, mutagenic agents ethyl methane sulphonate and sodium azide could be applied to isolated microspores and the derived embryos of rapeseed. Utilization of microspore-derived embryos for production of desired traits such as the altered fatty acids, disease resistance and glucosinolate compositions through mutagenesis and selection is advancing and also discussed.

Consequences of waterlogging in cotton and opportunities for mitigation of yield losses

Cotton is a major world crop that is notoriously susceptible to waterlogging damage, particularly when cultivated on fine-textured soils. However, damage is also exacerbated because of inadequate acclimation of roots to low oxygen levels, and secondary effects on shoots. Despite the commercial importance of cotton, very little has been published when compared with waterlogged cereals. This review provides a comprehensive view of the constraints on cotton in low-oxygen conditions, including absence of aerenchyma and the inadequacy of fermentation to overcome waterlogging damage. We emphasise the possibilities of improved tolerance through management practices, manipulation of hormone pathways and gene technologies to modify perception and response to low-oxygen environments.

Induction of tetraploidy in Juncus effusus by colchicine

Tetraploidy was induced in vitro in mat rush (Juncus effusus L.) cultivar Nonglin-4 by exposure to colchicine (0, 50, 100 and 500 mg dm−3) for 6, 12 and 24 h. Flow cytometric analysis was used to confirm the ploidy level. Anatomical and ultrastructural analyses at cellular and subcellular levels in tetraploid and diploid control plants revealed differences between diploid and tetraploid plants. The leaf epidermis had larger stomata but lower stomatal density in tetraploid plants. In addition, mesophyll cells in tetraploid plants appeared more compact and showed less intercellular spaces along with increased size of vascular bundles. However, a significant reduction of chlorophyll content was observed in tetraploid plants that might be the result of structural modification in the lamellar membranes of chloroplasts.

Improved lentil production by utilizing genetic variability in response to phosphorus fertilization

Abstract A field experiment was undertaken for evaluating the performance of three lentil genotypes with phosphorus (P) fertilization at four rates: 0, 40, 60, and 80 kg P2O5 ha−1 under rain-fed conditions. Genotypes of lentil were: Masoor-93, Markaz-2001, and NARC-02/2. Masoor-93 showed the highest seed yield, crop-growth rate, net assimilation rate, and seed protein contents among all the tested cultivars. P applied at the highest rate (80 kg ha−1) caused the best positive response with respect to physiological traits, growth attributes, and yield components. Furthermore, the application of P-fertilizer was found to be feasible in economic terms, as the net return, value-to-cost ratio, and relative increase in income were enhanced successively at higher phosphorus rates. It was concluded that for maximum potential yield of lentil, genotype Masoor-93 is the best suited under rain-fed conditions provided that its P nutrition is enhanced. The pronounced genetic variability in lentil-yield traits suggests that nutrient-efficient germplasm can be screened through breeding programmes to promote lentil production.