P. Sharmila

Potential of Aquatic Macrophytes for Removing Contaminants from the Environment

The role of both terrestrial and aquatic plants in phytoremediation of various contaminants is well established. Phytoremediation has been successfully implemented at different locations, including military sites, agricultural fields, industrial units, mine tailings, and sewage and municipal wastewater treatment plants, with efficient capacity for removing various organic and inorganic pollutants through processes such as extraction, degradation, or stabilization. Aquatic macrophytes represent a diverse group of plants with an immense potential for removal/degradation of variety of contaminants, including heavy metals, inorganic/organic pollutants, radioactive wastes, and explosives. The present review emphasizes the role of aquatic macrophytes in phytoremediation technologies with due importance to each group irrespective of being free-floating, submerged, or emergent. Realizing the exorbitant abilities of aquatic macrophytes, their suitability for wider use in phytoremediation technologies including constructed wetlands is emphasized.

Physiological and antioxidant responses of Salvinia natans exposed to chromium-rich wastewater

Salvinia natans possess capacity to accumulate high concentrations of chromium (Cr). Studies were carried out to evaluate physiological efficiency and defensive potential of plant exposed to Cr-rich wastewater. Among photochemical reactions, photosystem I (PS I) and photosystem II (PS II) activity noted an increase in plants exposed to Cr-rich wastewater. Fluorescence ratio F(v)/F(m) depicted no alteration in plants exposed to Cr. The activity of ribulose-1,5-biphosphate carboxylase-oxygenase (Rubisco) noted a decline, while transthylakoidal pH gradient (DeltapH) (correlative of photophosphorylation) showed increase in plants exposed to Cr-rich wastewater. Plants lacked the ability to produce malondialdehyde, but possessed efficient enzymic and non-enzymic antioxidant defense mechanisms that played important role in curtailing oxidative stress. The activities of antioxidant enzymes showed alleviation in plants exposed to Cr-rich wastewater. The levels of cellular antioxidants noted decline suggesting a defensive role in protection against oxidative stress caused by Cr. The present findings suggest that Salvinia possess efficient antioxidant machinery that curtails oxidative stress caused by Cr-rich wastewater and protects photosynthetic machinery from damage.

Photosynthetic performance of Salvinia natans exposed to chromium and zinc rich wastewater

Investigations were carried out to evaluate alterations in photosynthetic performance of Salvinia natans (L.) exposed to chromium (Cr) and zinc (Zn) rich wastewater. Accumulation of high levels of Cr and Zn in plants affected photosynthetic electron transport. Photosystem- (PS) II-mediated electron transport was enhanced in plants exposed to Cr rich wastewater while a decline was observed in Zn-exposed plants. Photosystem-I-mediated electron transport increased in plants exposed to Cr and Zn rich wastewater. Efficiency of photosystem II (Fv/Fm) measured by fluorescence did not show any significant change in Cr-exposed plants but a decrease was observed in Zn-exposed plants as compared to the control. The enhancement in PS I-induced cyclic electron transport in Cr and Zn exposed plants led to a build up of the transthylakoidal proton gradient (DpH) which subsequently helped in maintaining the photophosphorylation potential to meet the additional requirement of ATP under stress. The carbon assimilation potential was adversely affected as evident from the decrease in Rubisco (EC 4.1.1.39) activity. The alterations in photosynthetic electron transport affected stromal redox status and induced variations in the level of stromal components such as pyridine nucleotides in plants exposed to Cr and Zn rich wastewater. The present investigations revealed that alteration in the photosynthetic efficiency of Salvinia exposed to Cr could primarily be the result of a decline in carbon assimilation efficiency relative to light-mediated photosynthetic electron transport, though in the case of Zn-exposed plants both these factors were affected equally.

Metabolic engineering using mtlD gene enhances tolerance to water deficit and salinity in sorghum

Sorghum bicolor L. Moench cv. SPV462 was transformed with the mtlD gene encoding for mannitol-1-phosphate dehydrogenase from E. coli with an aim to enhance tolerance to water deficit and NaCl stress. Transgene (pCAM mtlD) integration and expression were successfully confirmed by PCR, Southern, RT-PCR and Western analysis. Segregation analysis based on germination of T0 seed on hygromycin-supplemented medium revealed an expected Mendelian ratio 3:1 in lines 5, 72 and 75. Retention of leaf water content was remarkably higher in transgenic leaf segments when exposed to polyethylene glycol 8000 (−2.0 MPa), as compared to the untransformed controls. Another significant finding is that the transgenics maintained a 1.7 to 2.8 fold higher shoot and root growth, respectively, under NaCl stress (200 mM) when compared to untransformed controls. These results demonstrate that engineering mannitol biosynthetic pathway into sorghum can impart enhanced tolerance to water deficit and salinity.

Heavy metal induced physiological alterations in Salvinia natans

Salvinia possess inherent capacity to accumulate high levels of various heavy metals. Accumulation of Cr, Fe, Ni, Cu, Pb and Cd ranged between 6 and 9 mg g(-1)dry wt., while accumulation of Co, Zn and Mn was ∼4 mg g(-1)dry wt. Heavy metal accumulation affected the physiological status of plants. Photosystem II activity noted to decline in Ni, Co, Cd, Pb, Zn and Cu exposed plants, while Photosystem I activity showed enhancement under heavy metal stress in comparison to control. The increase in PS I activity supported build up of transthylakoidal proton gradient (ΔpH), which subsequently helped in maintaining the photophosphorylation potential. Ribulose 1,5 dicarboxylase/oxygenase (Rubisco) activity noted a decline. Alterations in photosynthetic potential of Salvinia result primarily from changes in carbon assimilation efficiency with slight variations in primary photochemical activities and photophosphorylation potential. Studies suggest that Salvinia possess efficient photosynthetic machinery to withstand heavy metal stress.

Sugars have potential to curtail oxygenase activity of Rubisco

Sugars play a critical role in regulating overall cellular metabolism and owing to their general compatibility with various cellular events plants invariably show enhanced levels of sugars for maintaining desired osmoticum under osmotic stress. Sugars (sucrose and trehalose) and sugar-alcohols (glycerol, mannitol, inositol, and sorbitol) with the exception of sorbitol lowered oxygenase activity of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase, EC 4.1.1.39) without altering carboxylase activity under unstressed conditions. Most interestingly, these solutes including sorbitol fully curtailed NaCl-induced enhancement in oxygenase activity, even at concentrations as low as 50mM. However, none of these solutes could alleviate NaCl-suppressed carboxylase activity. In summary, our findings demonstrate that one of the most important roles of sugars and sugar-alcohols in plants exposed to salt stress is to curtail oxygenase activity of Rubisco.

An optimal protocol for in vitro regeneration, efficient rooting and stable transplantation of chickpea

A rapid, reproducible and efficient regeneration method was developed for chickpea (Cicer arietinum L.) using single cotyledon with half embryonal axis as explants. MS medium supplemented with 4 ìM TDZ, 10 ìM 2-iP and 2 ìM kinetin induced 50–100 adventitious buds/shoots after 14 days of culture and elongated on MS medium supplemented with 5 ìM 2-iP and 2 ìM kinetin. Healthy, strong and 100 % rooting was achieved by exposing cut ends of the shoots to 10 sec pulse treatment with 100 ìmoles/ml IBA followed by their transfer to liquid MS basal medium within 10–14 d. 2–3 cm long shoots were most suitable for rooting. Potting-mixture with good aeration and lesser capacity to retain water was most suitable for achieving successful establishment of chickpea plantlets. Garden soil mixed with sand (gravel) and bio-manure in the ratio of 1:1:1 is most suitable for achieving cent percent transplantation success. Cent percent of plantlets got acclimatized, survived in the pots and showed normal growth, development, flowering followed by podding and seeds setting. Harvesting of seeds was done after the pods were fully matured and dry. In this communication, we have demonstrated for the first time that shoot length, pulse treatment of cut ends of shoots with 100 ìmoles/ml IBA and aeration of potting mixture are key factors for rapid micro-propagation and successful establishment of chickpea.

Targeting prokaryotic choline oxidase into chloroplasts enhance the potential of photosynthetic machinery of plants to withstand oxidative damage

Chloroplasts from plants of transgenic lines expressing prokaryotic choline oxidase gene (the codA(ps) gene; GenBank accession number-AY589052) and wild-type of chickpea and Indian mustard were evaluated for their efficacy to withstand photoinhibitory damage, by exposing them to high light intensity ( approximately 1200micromolm(-2)s(-1) photon flux density) at 10 and 25 degrees C. Western analysis confirmed presence of choline oxidase in chloroplasts of only transgenic lines. The loss in PS II activity in chloroplasts of wild-type exposed to high light intensity was significantly higher than that in chloroplasts of transgenic chickpea as well as Indian mustard. Although, chloroplasts of both wild-type and transgenic chickpea as well as Indian mustard were more sensitive to photoinhibitory damage at 10 than at 25 degrees C, the damage recorded in chloroplasts harboring choline oxidase was significantly lower than those of wild-type. High light promotes H(2)O(2) production in chloroplasts more significantly at low temperature (10 degrees C) than at 25 degrees C. We compared low temperature accelerated photoinhibition of chloroplasts with that caused due to exogenously applied H(2)O(2). Although exogenous H(2)O(2) accelerated high light intensity induced loss in PS II activity of chloroplasts of wild-type, it caused only a little alteration in PS II activity of chloroplasts from transgenic lines of both chickpea and Indian mustard, demonstrating that the chloroplasts harboring choline oxidase are better equipped to resist photoinhibition. We hypothesize that H(2)O(2) produced by choline oxidase as a byproduct during synthesis of glycinebetaine is responsible for building stronger antioxidant system in chloroplasts of transgenic lines compared to that of wild-type.

Heavy Metal Removal Potential of Dried Salvinia Biomass

Investigations were carried out to evaluate heavy metal adsorption capacity of Salvinia. Batch experiments showed that dry plant biomass possess good potential to adsorb heavy metals such as Ni, Co, Cr, Fe, and Cd. The metal adsorption increased with increase in initial metal concentration. The data obtained fitted well with Freundlich equilibrium isotherm. Further characterization of plant biomass showed presence of both acidic and basic surface functionalities that might facilitate binding of metal ions. Fourier transform infrared (FTIR) spectra of plant biomass suggested involvement of carbonyl (C˭O), carboxyl (-COO), and hydroxyl (-OH) groups in binding heavy metals to plant biomass. The studies establish S. natans as an effective biosorbent for removing heavy metals from wastewater and further emphasize biomass utilization in wastewater treatment technologies.

Evaluating Performance of Plants Infected with Vescicular Arbuscular Mycorrhizal Fungi for Alleviating Abiotic Stresses

Mycorrhizal association increases the tolerance of plants to various nutritional and environmental stresses. The mycorrhizal plants get adapted to survive in unsuitable conditions. VA mycorrhizal plants become resistant to soil-borne pathogens. There is improved growth and survival of micropropagated plantlets upon association with VAM fungi. Different simple and modern techniques to study this aspect has been described.