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1

In vitro screening of rice genotypes for drought tolerance using polyethylene glycol

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Joshi R. , Shukla A. , Sairam R. K.

Acta Physiologiae Plantarum

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2011

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tom 33

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nr 6

EN

The aim of the present investigation was to study in vitro somatic embryogenesis and to screen calli for drought tolerance using mature embryos as explants. Mature embryos of three aromatic (Pusa Basmati 1, Pant Sugandh Dhan 17, Taraori Basmati) and one non-aromatic (Narendra 359) indica rice (Oryza sativa L.) varieties were used for developing callus on Murashige and Skoog medium supplemented with 2, 4-dichlorophenoxy acetic acid (2, 4-D) (2.0 mg l⁻¹ for Narendra 359 and 2.5 mg l⁻¹ for Pusa Basmati 1, Taraori Basmati and Pant Sugandh Dhan 17). Screening of calli was done by sub-culturing calli for 15 days on Murashige and Skoog (MS) basal medium supplemented with different concentrations of polyethylene glycol (PEG)-6000 as chemical drought inducer. Callus volume decreased and total proline content was found to be increased significantly with increase in PEG concentration. Narendra 359 showed best response in terms of callus growth at 70 g l⁻¹ of PEG. The highest percentage somatic embryogenesis among selected calli was observed in Pusa Basmati 1 and the lowest in Pant Sugandh Dhan 17. Excellent shooting and rooting (94%) was observed in MS + 0.1 mg l⁻¹ naphthalene acetic acid (NAA) and MS + 2.0 mg l⁻¹ 2, 4-D. Regenerated plants were successfully acclimatized with 98% efficiency in greenhouse and grown under pot conditions up to maturity. It was observed that PEG treated somaclones accumulated more proline, chlorophyll content and developed more tiller and height than normal somaclones. Ten random amplified polymorphic DNA (RAPD) primers were used to amplify genomic DNA of somaclones of different varieties. Level of genetic polymorphism existing among these somaclones indicates that these markers can be used in breeding program for improving varieties through in vitro techniques.

2

Differential transcript abundance of salt overly sensitive (SOS) pathway genes is a determinant of salinity stress tolerance of wheat

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Sathee L. , Sairam R. K. , Chinnusamy V. , Jha S. K.

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tom 37

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nr 08

EN

Salt overly sensitive (SOS) pathway genes, SOS1 (plasma membrane Na+/H+ antiporter), SOS2 (CBL interacting protein kinase 24), and SOS3 (calcineurin B like protein 4) are associated with active efflux of toxic sodium ions (Na+) from cytosol and thus confer salinity tolerance in glycophytic plants such as Arabidopsis. The role of SOS pathway genes SOS2 and SOS3 in salinity tolerance of wheat is rarely studied. One-month-old seedlings of three bread wheat genotypes namely, HD 2009, HD2687 and Kharchia 65 were imposed with two levels of salinity stress (100 and 200 mM NaCl) for 30 days duration. Based on the physiological parameters, genotype Kharchia 65 was highly tolerant, HD 2009 was moderately tolerant and HD 2687 was sensitive to salinity stress. Tolerant genotypes accumulated lesser amount of Na+ in root, stem and leaf tissues. Transcript abundance of SOS1, SOS2 and SOS3 genes was significantly higher in salt tolerant genotypes under long-term salinity and correlated with improved sodium exclusion, and higher potassium/sodium (K+/Na+) ratio. Expression levels of genes involved in vacuolar partitioning of Na+, NHX1 (vacuolar Na+/H+ antiporter) and VP1 (Vacuolar pyrophosphatase) were also higher in salt tolerant wheat genotypes under 200 mM NaCl stress. Partial coding sequences of SOS1, SOS2, SOS3, NHX1 and VP1 genes were cloned and sequenced from the above mentioned three wheat genotypes. The results in the present study demonstrated that SOS pathway of ion homeostasis under salinity stress is conserved across species.

3

Expression of antioxidant defense genes in mung bean (Vigna radiata L.) roots under waterlogging is associated with hypoxia tolerance

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Sairam R. K. , Dharmar K. , Lekshmy S. , Chinnusamy V.

Acta Physiologiae Plantarum

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2011

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tom 33

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nr 3

EN

This study was conducted to examine the extent of oxidative stress and the role of antioxidant enzymes on hypoxia tolerance in highly tolerant wild species Vigna luteola, and mung bean (Vigna radiata) cvs. T 44 (tolerant) and Pusa Baisakhi (susceptible). Two days of water-logging caused about 40–50% decline in superoxide radical (O₂⁻) and hydrogen peroxide (H₂O₂) contents in all the genotypes, however, further water-logging to 8 days caused significant increase in O₂⁻ and H₂O₂ contents, and the values were 80–90% of the control values. In control and revived plants O₂⁻ and H₂O₂ contents were higher in Pusa Baisakhi, while under water-logging stress T 44 and V. luteola showed greater increases in the O₂⁻ and H₂O₂ contents. Hypoxia induced increase in superoxide dismutase, ascorbate peroxidase, and glutathione reductase activities were higher in T 44 and V. luteola compared with Pusa Baisakhi; and the increases in T 44 and V. luteola continued up to 8th day of water-logging, while in case of Pusa Baisakhi, the maximum increase was observed only on the 2nd day of water-logging. Gene expression studies showed enhanced expression of cytosolic-Cu/Zn-superoxide dismutase (SOD) and cytosolic-ascorbate peroxidase (APX) in the roots of waterlogged V. luteola and T 44, while little expression was observed in control or treated plants of Pusa Baisakhi. PCR band products were cloned and sequenced, and partial cDNAs of Cu/Zn-SOD and APX, respectively, were obtained. Results suggest that increase in the activity of antioxidant enzymes is to scavenge reactive oxygen species produced both during and after relief from water-logging stress.

4

Calcium regulates Gladiolus flower senescence by influencing antioxidative enzymes activity

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Sairam R. K. , Vasanthan B. , Arora A.

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nr 5

EN

The objective of the present investigation was to study the role of calcium on antioxidative enzymes activity during the post-harvest life of Gladiolus (Gladiolus grandiflorus). Among the various calcium (Ca) treatments, 50 mmol 1⁻¹ Ca treatments caused the highest increase in the vase life of the spike, from 5.5 days in control to about 9 days. Relative water content and membrane stability index (MSI) decreased from I to V stage. However, significant increase in relative water content and MSI were observed by 50 mmol 1⁻¹ Ca as compared to control. Indices of oxidative stress such as lipid peroxidation and lipoxygenase activity increased from I to V stage, but decreased significantly in 50 mmol 1⁻¹ Ca treatment. The activities of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) decreased initially from stage I to II, followed by an increase in stage III and thereafter started to decline at stages IV and V. Ascorbate peroxidase (APX) activity increased initially from stage I to III and thereafter declined in stage IV and V in both control and treatment. However, Ca with concentration of 50 mmol 1⁻¹ increased the activities of SOD, CAT and APX at all the stages. The results revealed that spikes treated with Ca (50 mmol 1⁻¹) solution maintained higher level of antioxidant enzymes activity and also showed delayed senescence in comparison to control.

5

Salinity-induced expression of pyrrolline-5-carboxylate synthetase determine salinity tolerance in Brassica spp

100%

Chakraborty K. , Sairam R. K. , Bhattacharya R. C.

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2012

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tom 34

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nr 5

EN

The objective of the present study was to assess the role of salinity-induced expression of pyrrolline 5-carboxylate synthetase (P5CS), P5CS activity, and proline accumulation on salinity tolerance in Brassica genotypes. A pot culture experiment was conducted with four Brassica genotypes viz. CS 52, CS 54, Varuna, (B. juncea) and T 9 (B. campestris) under control and two salinity levels, i.e., 1.65, 4.50 and 6.76 dS m⁻¹. Proline contents increased with increasing levels of salinity, and the highest content were recorded at post-flowering stage in CS 52 and CS 54. Activity of P5CS recorded at flowering stage was highest at higher level of salinity, with CS 52 and CS 54 recording highest activity. Gene expression of P5CS, which regulates the synthesis of proline, was higher in CS 52 and CS 54 under salt stress than Varuna and T 9. Comparison of partial nucleotide as well as amino acid sequence showed conserved domains, and inter and intra generic relatedness of these genes. The study suggests that salinityinduced expression of P5CS, pyrrolline-phosphate synthetase activity and proline accumulation may serve as one of the mechanism of salinity stress tolerance in Brassica genotypes.