Multifaceted roles of silicon in mitigating environmental stresses in plants.

Food security relies on plant productivity and plant's resilience to climate change driven environmental stresses. Plants employ diverse adaptive mechanisms of stress-signalling pathways, antioxidant defense, osmotic adjustment, nutrient homeostasis and phytohormones. Over the last few decades, silicon has emerged as a beneficial element for enhancing plant growth productivity. Silicon ameliorates biotic and abiotic stress conditions by regulating the physiological, biochemical and molecular responses. Si-uptake and transport are facilitated by specialized Si-transporters (Lsi1, Lsi2, Lsi3, and Lsi6) and, the differential root anatomy has been shown to reflect in the varying Si-uptake in monocot and dicot plants. Silicon mediates a number of plant processes including osmotic, ionic stress responses, metabolic processes, stomatal physiology, phytohormones, nutrients and source-sink relationship. Further studies on the transcriptional and post-transcriptional regulation of the Si transporter genes are required for better uptake and transport in spatial mode and under different stress conditions. In this article, we present an account of the availability, uptake, Si transporters and, the role of Silicon to alleviate environmental stress and improve plant productivity.

Artocarpus: a review of its traditional uses, phytochemistry and pharmacology.

The genus Artocarpus (Moraceae) comprises about 50 species of evergreen and deciduous trees. Economically, the genus is of appreciable importance as a source of edible fruit, yield fairly good timber and is widely used in folk medicines. The aim of the present review is to present comprehensive information of the chemical constituents, biological and pharmacological research on Artocarpus which will be presented and critically evaluated. The close connection between traditional and modern sources for ethnopharmacological uses of Artocarpus species, especially for treatment against inflammation, malarial fever, diarrhoea, diabetes and tapeworm infection. Artocarpus species are rich in phenolic compounds including flavonoids, stilbenoids, arylbenzofurons and Jacalin, a lectin. The extracts and metabolites of Artocarpus particularly those from leaves, bark, stem and fruit possess several useful bioactive compounds and recently additional data are available on exploitation of these compounds in the various biological activities including antibacterial, antitubercular, antiviral, antifungal, antiplatelet, antiarthritic, tyrosinase inhibitory and cytotoxicity. Several pharmacological studies of the natural products from Artocarpus have conclusively established their mode of action in treatment of various diseases and other health benefits. Jacalin, a lectin present in seeds of this plant has a wide range of activities. Strong interdisciplinary programmes that incorporate conventional and new technologies will be critical for the future development of Artocarpus as a promising source of medicinal products. In the present review, attempts on the important findings have been made on identification; synthesis and bioactivity of metabolites present in Artocarpus which have been highlighted along with the current trends in research on Artocarpus.

Evaluation of antioxidant capacity and phenol content in jackfruit (Artocarpus heterophyllus Lam.) fruit pulp.

The antioxidant capacity of jackfruit (Artocarpus heterophyllus Lam. Fam. Moracae) fruit pulp (JFP) obtained from Western Ghats India was determined by evaluating the scavenging activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing power assays and N, N-dimethyl-p-phenylendiamine (DMPD) radical cation decolorization assay. JFP was analyzed for total phenolic content (TPC) and total flavonoids content (TFC). The ethanol and water are the best solvents for the extracting phenols and flavonoids from the JFP. The antioxidant activities of JFP extracts were correlated with the total phenolic and flavonoids content. The results indicated that the jackfruit pulp is one natural source of antioxidant compounds.

Analysis of the limitations of hepatitis B surface antigen expression in soybean cell suspension cultures.

Soybean cell suspension cultures were transformed using Agrobacterium tumefaciens harboring pHBS/pHER constructs to express hepatitis B surface antigen (HBsAg). The transformed colonies were selected and analyzed for the expression of HBsAg by PCR, reverse transcription (RT) PCR, Western blot and ELISA analysis. The maximum expression of 700 ng/g F.W. was noted in pHER transformed cells. The highest expressing colonies were used to initiate the cell suspension cultures and the expression of HBsAg was estimated periodically. The expression levels were reduced drastically in cell suspension cultures compared to the colonies maintained on semi-solid medium. Various parameters were studied to maximize the cell growth and to retain the expression levels. The supplementation of culture medium with a protease inhibitor, leupeptin hemisulfate could restore up to 50% of HBsAg expression in cell suspension cultures. This is the first report to investigate the possible cause and solution to the loss of recombinant protein expression levels in plant cell suspension cultures.

Production of hepatitis B surface antigen in recombinant plant systems: an update.

There is a growing interest to develop oral vaccines for infectious diseases, as it is the most convenient and effective way to attain mucosal immunity. Hepatitis B continues to be a major infectious disease in many developing countries despite the availability of recombinant vaccine. On a global scenario, Hepatitis B Virus infection is probably the single most prevalent cause of persistent viraemia in humans. There are about 350 million chronic carriers of HBV, which is about 5% of the total world population. It is estimated that 75-100 million of them will die of liver cirrhosis and/or hepatocellular carcinoma. Progress in plant genetic engineering has enabled the transfer of useful genes for desirable traits. The recent trend is to use this technique to exploit plants as biofactories for the production of therapeutic proteins including vaccines. Rapid progress has been made in this area to develop plant-based vaccines for hepatitis B. This review describes the expression, characterization, and immunogenicity studies of hepatitis B vaccines produced in recombinant plant systems and their implications for developing a plant-based vaccine.

Secretion of hepatitis B surface antigen in transformed tobacco cell suspension cultures.

Six different expression cassettes of hepatitis B surface antigen (HBsAg) were used to transform tobacco cell suspension cultures. The transgenic nature of the cells was confirmed by PCR. The secreted HBsAg was assayed by ELISA and analyzed by Western blotting. A maximum of 31 microg antigen/l was obtained in the spent medium from the transformed cells. The use of an ethylene-forming enzyme promoter and incorporation of C-terminal endoplasmic-reticulum-retention signal enhanced the secretion of HBsAg. Salicylic or jasmonic acid at 10 microM: increased secretion of HBsAg by six fold.

Expression of hepatitis B surface antigen in transgenic banana plants.

Embryogenic cells of bananan cv. Rasthali (AAB) have been transformed with the 's' gene of hepatitis B surface antigen (HBsAg) using Agrobacterium mediated transformation. Four different expression cassettes (pHBS, pHER, pEFEHBS and pEFEHER) were utilized to optimize the expression of HBsAg in banana. The transgenic nature of the plants and expression of the antigen was confirmed by PCR, Southern hybridization and reverse transcription (RT)-PCR. The expression levels of the antigen in the plants grown under in vitro conditions as well as the green house hardened plants were estimated by ELISA for all the four constructs. Maximum expression level of 38 ng/g F.W. of leaves was noted in plants transformed with pEFEHBS grown under in vitro conditions, whereas pHER transformed plants grown in the green house showed the maximum expression level of 19.92 ng/g F.W. of leaves. Higher monoclonal antibody binding of 67.87% of the antigen was observed when it was expressed with a C-terminal ER retention signal. The buoyant density in CsCl of HBsAg derived from transgenic banana leaves was determined and found to be 1.146 g/ml. HBsAg obtained from transgenic banana plants is similar to human serum derived one in buoyant density properties. The transgenic plants were grown up to maturity in the green house and the expression of HBsAg in the fruits was confirmed by RT-PCR. These transgenic plants were multiplied under in vitro using floral apex cultures. Attempts were also made to enhance the expression of HBsAg in the leaves of transgenic banana plants by wounding and/or treatment with plant growth regulators. This is the first report on the expression of HBsAg in transgenic banana fruits.

Expression of hepatitis B surface antigen in tobacco cell suspension cultures.

Hepatitis B virus ' s ' gene coding for surface antigen was cloned into plant transformation vectors pHER100 and pHBs100 with and without endoplasmic reticulum retention signal, respectively. Transformed tobacco cell lines were analyzed for the integration of the transgene by PCR and Southern blot hybridization. Expression levels as determined by ELISA showed maximum expression levels of 2 microg HBsAg gm(-1) fresh weight and 10 ng mL(-1) of spent medium in pHER100 transformed cells. Western blot analysis confirmed the presence of 24 kDa band specific to HBsAg in the transformed cells. HBsAg was expressed both as intracellular and secreted forms in pHER100 transformed cells. The buoyant density in CsCl of HBsAg derived from pHBs100 transformed tobacco cells was determined and found to be 1.095 g mL(-1). HBsAg obtained from transformed tobacco cells is similar to the human serum derived one in buoyant density properties. This is the first report on the secretion of HBsAg particles by plant cells into the cell culture medium.

MSI-99, a magainin analogue, imparts enhanced disease resistance in transgenic tobacco and banana.

Magainin is one of the earliest reported antimicrobial peptides isolated from skin secretions of the African clawed frog Xenopus laevis. A synthetic substitution analogue of magainin, MSI-99, is employed in this study to impart disease resistance in transgenic tobacco ( Nicotiana tabacumL.) and banana [( Musaspp. cv. Rasthali (AAB)]. This peptide inhibited the growth and spore germination of Fusarium oxysporumf.sp. cubenseat 16 micro g/ml. MSI-99 has been subcloned into plant expression vectors pMSI164 and pMSI168, targeting the peptide into the cytoplasm and extracellular spaces, respectively. Tobacco plants transformed with pMSI168 showed enhanced resistance against Sclerotinia sclerotiorum, Alternaria alternataand Botrytis cinerea. Transgenic banana pants were obtained for both pMSI164 and pMSI168 transformations and showed resistance to F. oxysporumf.sp. cubenseand Mycosphaerella musicola. The transgenic nature of the transformants and expression of this peptide was confirmed through polymerase chain reaction (PCR) and reverse transcription (RT)-PCR. The results suggest that MSI-99 can be useful in imparting enhanced disease resistance in transgenic plants.

Study of trace element correlations with drought tolerance in different sorghum genotypes using energy-dispersive X-ray fluorescence technique.

Drought-tolerant and drought-susceptible genotypes of sorghum (Sorghum bicolor L. Monech) were analyzed by the energy-dispersive X-ray fluorescence (EDXRF) technique to study the correlation of trace elements with drought-tolerance capacities. Samples prepared from mature seeds, young seedlings, and old plants were analyzed using a 109Cd radioisotope source and a Si(Li) semiconductor detector of resolution 170 eV for 5.9-keV MnKalpha X-rays. Elements such as K, Fe, Cu, Zn, Rb and Sr and Y were found to be present in varying concentrations in different samples. The trace element profile studied in the seeds of 11 genotypes and in seedlings (young and old) of 4 sorghum genotypes showed considerable variation. The genotype Arfa Gadamak (AG) showed a distinct presence of a high level of Zn in its young seedling. It was observed that in most of the genotypes (seeds), K and Fe concentrations were more in the tolerant genotype as compared to the susceptible type. The concentration of Fe decreased with maturity in the tolerant group and it increased with maturity in the susceptible group.

Determination of antidiabetic activity in Allium cepa (onion) tissue cultures.

Seedling, seedling parts and callus cultures of onion were tested for their antidiabetic activity by feeding the tissue-extracts to diabetic rats. The results indicated much higher antidiabetic activity in callus cultures as compared to natural bulbs of onion. These results may be of pharmaceutical significance since the callus can be used as an alternative source for the isolation of antidiabetic compounds.

In Vitro Production Of L-dopa In Tissue Cultures Of Banana.

Shoot and callus cultures of banana ( Musa sp.) were analyzed for the accumulation of L-DOPA. Treatment of cultures with L-tyrosine and L-phenylalanine yielded higher levels of DOPA compared to those in control cultures without any treatment. Among the two amino acids, phenylalanine induced higher accumulation of DOPA. The study suggests that banana may become an useful system for the production of DOPA.

Propagation of banana through encapsulated shoot tips.

Plants were regenerated from encapsulated shoot tips of banana. Shoot tips (ca 4 mm) isolated from multiple shoot cultures of banana cv. Basrai were encapsulated in 3% sodium alginate containing different gel matrices. The encapsulated shoot tips regenerated in vitro on different substrates. Use of White's medium resulted in 100% conversion of encapsulated shoot tips into plantlets. The plantlets were successfully established in soil.

Sandalwood plantlets from 'Synthetic seeds'.

Somatic embryos of sandalwood (Santalum album) were encapsulated in an alginate matrix to prepare 'Synthetic seeds'. Encapsulated single embryos germinated to form plants with roots and shoots. Embryogenic cell suspensions encapsulated and stored at 4°C for 45 days produced embryos when recultured as suspensions.

Propagation of Morus indica L. (Mulberry) by encapsulated shoot buds.

Axillary buds of mulberry (Morus indica L) were encapsulated in alginate and agar to produce individual beads. The beads could be stored at 4°C for 45 days without loss of viability. Amongst the encapsulating agents tested, sodium alginate was found to be a better matrix. Encapsulated buds regenerated complete plantlets on an appropriate medium. This technique would provide an easy and novel propagation system for the elite as well as difficult-to-root species of mulberry.

Regeneration of plants from the culture of leaves and axillary buds in mulberry (Morus indica L.).

Stem segments, axillary buds and leaves excised from established shoot cultures of Morus indica were soaked in MS liquid medium containing benzyladenine (0.5, 1, 2 mg/1) and were cultured subsequently on semi solid medium of the same composition. Numerous shoot buds differentiated from leaf and axillary buds but stem segments were unresponsive. The shoot buds on isolation and culture developed into plantlets. Callus tissues which developed at the base of the leaf explant upon subculture also differentiated numerous shoot buds.

Plant Regeneration in Protoplast Cultures of Tylophora indica.

Protoplasts isolated from callus tissue derived from freshly cultured stem segments of Tylophora indica (Asclepiadaceae) rapidly divided and resulted in callus. Subsequent embryoid/ shoot bud differentiation in callus was observed on MS medium supplemented with auxins and cytokinins. The embryoids/shoot buds on transfer to appropriate basal medium without growth substances grew into plantlets. Protoplasts isolated from callus tissue maintained for over five years showed divisions and subsequent callus formation but failed to regenerate plants.

In vitro haploid plantlet induction in Physalis ixocarpa brot. through microspore embryogenesis.

Anthers of Physalis ixocarpa Brot. exised from 2-3 mm long flower buds were treated for 2 d at 3°C, and were cultured on the basal medium of NN (1969), supplemented with plant hormones. They formed embryoids from microspores within 6 weeks. Upon transfer to a regeneration medium, embryoids grew into functional plants with the haploid number of chromosomes (n=12).

Protoplast culture of several members of the genus Physalis.

High yields of protoplasts were obtained by enzymic treatment of mesophyll from five different species of the genus Physalis. Subsequent divisions and colony formation were achieved in all the species. However, numerous combinations of phytohormones failed to induce regeneration of shoots from callus tissue developed from protoplasts.