Bioremediation is gaining a lot of importance in recent times as an alternate technology for removal of elemental pollutants in soil and water, which require effective methods of decontamination. ...Phytoremediation—the use of green plants to remove, contain or render harmless environmental pollutants—may offer an effective, environmentally nondestructive and cheap remediation method. The use of genetic engineering to modify plants for metal uptake, transport and sequestration may open up new avenues for enhancing efficiency of phytoremediation. Metal chelator, metal transporter, metallothionein (MT), and phytochelatin (PC) genes have been transferred to plants for improved metal uptake and sequestration. Transgenic plants, which detoxify/accumulate cadmium, lead, mercury, arsenic and selenium have been developed. A better understanding of the mechanisms of rhizosphere interaction, uptake, transport and sequestration of metals in hyperaccumulator plants will lead to designing novel transgenic plants with improved remediation traits. As more genes related to metal metabolism are discovered, facilitated by the genome sequencing projects, new vistas will be opened up for development of efficient transgenic plants for phytoremediation.
Bacopa monnieri L. plants exposed to 10, 50, 100 and 200
μM cadmium (Cd) for 48, 96 and 144
h were analysed with reference to the accumulation of metal and its influence on various enzymatic and ...non-enzymatic antioxidants, thiobarbituric acid reactive substances (TBARS), photosynthetic pigments and protein content. The accumulation of Cd was found to be increased in a concentration and duration dependent manner with more Cd being accumulated in the root. TBARS content of the treated roots and leaves increased with increase in Cd concentration and exposure periods, indicating the occurrence of oxidative stress. Induction in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) was recorded in metal treated roots and leaves of
B. monnieri. In contrast, a significant reduction in catalase activity in Cd treated
B. monnieri was observed. An increase was also noted in the levels of cysteine and non-protein thiol contents of the roots of
B. monnieri followed by a decline. However, in leaves, cysteine and non-protein thiol contents were found to be enhanced at all the Cd concentrations and exposure periods. A significant reduction in the level of ascorbic acid was observed in a concentration and duration dependent manner. The total chlorophyll and protein content of
B. monnieri decreased with increase in Cd concentration at all the exposure periods. Results suggest that toxic concentrations of Cd caused oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However,
B. monnieri is able to combat metal induced oxidative injury involving a mechanism of activation of various enzymatic and non-enzymatic antioxidants.
Cadmium (Cd) is a major heavy metal pollutant which is highly toxic to plants and animals. Vast agricultural areas worldwide are contaminated with Cd. Plants take up Cd and through the food chain it ...reaches humans and causes toxicity. It is ideal to develop plants tolerant to Cd, without enhanced accumulation in the edible parts for human consumption. Glutathione transferases (GST) are a family of multifunctional enzymes known to have important roles in combating oxidative stresses induced by various heavy metals including Cd. Some GSTs are also known to function as glutathione peroxidases. Overexpression/heterologous expression of GSTs is expected to result in plants tolerant to heavy metals such as Cd.
Here, we report cloning of a glutathione transferase gene from Trichoderma virens, a biocontrol fungus and introducing it into Nicotiana tabacum plants by Agrobacterium-mediated gene transfer. Transgenic nature of the plants was confirmed by Southern blot hybridization and expression by reverse transcription PCR. Transgene (TvGST) showed single gene Mendelian inheritance. When transgenic plants expressing TvGST gene were exposed to different concentrations of Cd, they were found to be more tolerant compared to wild type plants, with transgenic plants showing lower levels of lipid peroxidation. Levels of different antioxidant enzymes such as glutathione transferase, superoxide dismutase, ascorbate peroxidase, guiacol peroxidase and catalase showed enhanced levels in transgenic plants expressing TvGST compared to control plants, when exposed to Cd. Cadmium accumulation in the plant biomass in transgenic plants were similar or lower than wild-type plants.
The results of the present study suggest that transgenic tobacco plants expressing a Trichoderma virens GST are more tolerant to Cd, without enhancing its accumulation in the plant biomass. It should be possible to extend the present results to crop plants for developing Cd tolerance and in limiting Cd availability in the food chain.
► Transgenic plants expressing a
TvGST gene were tested for tolerance, uptake and degradation of anthracene. ► Transgenic plants were more tolerant to anthracene and take up more anthracene from soil ...and solutions compared to control plants. ► Using
in vitro T
1 seedlings, we showed that anthracene—a three fused benzene ring compound was phytodegraded to naphthalene derivatives, having two benzene rings. ► This is the first time that a transgenic plant was shown to have the potential to phytodegrade anthracene.
Plants can be used for remediation of polyaromatic hydrocarbons, which are known to be a major concern for human health. Metabolism of xenobiotic compounds in plants occurs in three phases and glutathione transferases (GST) mediate phase II of xenobiotic transformation. Plants, although have GSTs, they are not very efficient for degradation of exogenous recalcitrant xenobiotics including polyaromatic hydrocarbons. Hence, heterologous expression of efficient GSTs in plants may improve their remediation and degradation potential of xenobiotics. In the present study, we investigated the potential of transgenic tobacco plants expressing a
Trichoderma virens GST for tolerance, remediation and degradation of anthracene—a recalcitrant polyaromatic hydrocarbon. Transgenic plants with fungal GST showed enhanced tolerance to anthracene compared to control plants. Remediation of
14C uniformly labeled anthracene from solutions and soil by transgenic tobacco plants was higher compared to wild-type plants. Transgenic plants (T
0 and T
1) degraded anthracene to naphthalene derivatives, while no such degradation was observed in wild-type plants. The present work has shown that
in planta expression of a fungal GST in tobacco imparted enhanced tolerance as well as higher remediation potential of anthracene compared to wild-type plants.
Copper is an essential element for proper functioning of all living organisms including plants, but it can cause toxicity at elevated concentrations. In the present study, two varieties of
Brassica ...juncea L. i.e. Pusa JK and TM 4 grown axenically were compared for Cu tolerance and accumulation ability. For further detailed biochemical studies, var. TM 4 was used because of its fast growth and better Cu accumulation in shoots. Toxic effects of Cu were manifested by a reduction in photosynthetic pigments and an increase in the levels of thiobarbituric acid reactive substances. The activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase and catalase showed an increase in a concentration and exposure time dependent manner in roots of
B. juncea exposed to copper, indicating that they play an important role in combating copper stress in this species.
A Gram-stain-negative, rod and rod-curved shaped motile bacterium designated strain S25
was obtained from benthic sediment collected near the Kubbar Island coral reefs south of Kuwait. Phenotypic ...analysis revealed that strain S25
was slightly halophilic, mesophilic and facultative anaerobic, fermenting d-glucose, d-ribose, d-mannose, d-mannitol, maltose, fructose, gentiobiose, cellobiose, melibiose, trehalose and sucrose. It was positive for oxidase and indole production and negative for arginine dihydrolase and lysine and ornithine decarboxylases. It contained C
7
/C
6
(summed feature 3), C
ω7
(summed feature 8) and C
as the major fatty acids. Strain S25
grew optimally at 30 °C and pH 8 in the presence of 3 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA sequences revealed that strain S25
is related to species of the genus
, having 99.15 % similarity to '
' AK16
, 99.08 % to
96-237
and 98.66 % to
IMCC 5001
. The DNA G+C content was 48.8 mol% and the full genome analysis for the strain S25
showed that the bacterium has a genome size of 5 158 621 bp and contains 4730 predicted protein-encoding genes. The average nucleotide identity values between the S25
genome and the genomes of its nearest matches ranged between 81.39 and 94.16 %. The strain was distinguishable from the phylogenetically related genera through differences in several phenotypic properties. On the basis of the phenotypic, phylogenetic and genetic data, strain S25
represents a novel species in the genus
, for which the name
sp. nov. is proposed. The type strain of
is S25
(=DSM 28878
=LMG 28315
).
It is three decades since the first transgenic pulse crop has been developed. Todate, genetic transformation has been reported in all the major pulse crops like
Vigna species,
Cicer arietinum,
...Cajanus cajan,
Phaseolus spp,
Lupinus spp,
Vicia spp and
Pisum sativum, but transgenic pulse crops have not yet been commercially released. Despite the crucial role played by pulse crops in tropical agriculture, transgenic pulse crops have not moved out from laboratories to large farm lands compared to their counterparts – ‘cereals’ and the closely related leguminous oil crop – ‘soybean’. The reason for lack of commercialization of transgenic pulse crops can be attributed to the difficulty in developing transgenics with reproducibility, which in turn is due to lack of competent totipotent cells for transformation, long periods required for developing transgenics and lack of coordinated research efforts by the scientific community and long term funding. With optimization of various factors which influence genetic transformation of pulse crops, it will be possible to develop transgenic plants in this important group of crop species with more precision and reproducibility. A translation of knowledge from information available in genomics and functional genomics in model legumes like
Medicago truncatula and
Lotus japonicus relating to factors which contribute to enhancing crop yield and ameliorate the negative consequences of biotic and abiotic stress factors may provide novel insights for genetic manipulation to improve the productivity of pulse crops.
Potential of plants to remove radionuclides/toxic elements from soils and solutions can be successfully applied for removal of important radionuclides such as strontium-90 (
90Sr) and cesium-137 (
...137Cs). When uptake of
137Cs and
90Sr by
Calotropis gigantea plants incubated in distilled water spiked with the radionuclides either alone or in combination was studied, it was found to have a high efficiency for the removal of
90Sr, with 90% being removed from solutions (5
×
10
3
kBq
l
−1) within 24
h of incubation. However, in case of
137Cs, about 44% could be removed from solutions (5
×
10
3
kBq
l
−1) at the end of 168
h of incubation. Accumulation of
90Sr and
137Cs was higher in roots compared to shoots. The plants could remediate both
90Sr and
137Cs when they were added together to the solution. When two months old plants were incubated in low level nuclear waste, 99% of activity disappeared at the end of 15 days. The present study suggests that
C. gigantea could be used as a potential candidate plant for phytoremediation of
90Sr and
137Cs.
Introduction of foreign genes and development of transgenic plants have become an integral part of crop improvement programmes in the last decade. However, most of the present day plant ...transformation protocols require long periods for development of transgenic plants and need skilled personnel. Development of alternate, simple and rapid transformation protocols for development of transgenic plants can overcome the constraints of
in vitro
culture, regeneration and associated problems. Pollen grains, due to their abundance and ease with which they can be handled are ideal targets for introduction of foreign genes into the germ line. However, progress in introduction of transgenes into pollen grains and their subsequent use in fertilization leading to development of transgenic plants are limited. With the recent progress made in understanding of pollen development along with reports of successful pollen-mediated transformation in important crop plants, it should be possible to extend this simple method of transformation to other crop plants. The review deals with development of pollen grains as a target for introduction of genes with special emphasis on recent developments.
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