Arsenic-induced straighthead: An impending threat to sustainable rice production in South and South-East Asia!

Straighthead is a physiological disorder of rice (Oryza sativa L.) that results in sterile florets with distorted lemma and palea, and the panicles or heads may not form at all in extreme cases. Heads remain upright at maturity, hence the name 'straighthead'. The diseased panicles may not emerge from the flag leaf sheath when the disease is severe. Straighthead disease in rice results in poorly developed panicles and significant yield loss. Although other soil physicochemical factors involved, arsenic contamination in soil has also been reported to be closely associated with straighthead of rice. Monosodium methanearsonate has been a popular herbicide in cotton production in the USA, which has shown to cause injuries in rice that are similar to straighthead. Since toxicity of inorganic arsenic (iAs) is higher than other forms of arsenic, it may produce a more severe straighthead disorder in rice. The use of iAs-rich groundwater for irrigation, and the increase of iAs concentrations in agricultural soil in arsenic epidemic South and South-East Asia may cause a high incidence of straighthead in rice, resulting in a threat to sustainable rice production in this region. © 2011 Springer Science+Business Media, LLC

Phytotoxicity of arsenate and salinity on early seedling growth of rice (oryza sativa l.): A threat to sustainable rice cultivation in South and South-East Asia

Arsenic (As) contamination is an important environmental consequence in some parts of salinity-affected South (S) and South-East (SE) Asia. In this study, we investigated the individual and combined phytotoxicity of arsenic (As) [arsenate; As(V)] and salinity (NaCl) on early seedling growth (ESG) of saline-tolerant and non-tolerant rice varieties. Germination percentage (GP), germination speed (GS) and vigor index (VI) of both saline-tolerant and non-tolerant rice varieties decreased significantly (p[0.01) with increasing As(V) and NaCl concentrations. The highest GP(91%) was observed for saline non-tolerant BRRI dhan28 and BRRI dhan49, while the lowest (62%) was for salinetolerant BRRI dhan47. The ESG parameters, such as weights and relative lengths of plumule and radicle, also decreased significantly (p\0.01) with increasing As(V) and NaCl concentrations. Relative radicle length was more affected than plumule length by As(V) and NaCl. Although VI of saline-tolerant and non-tolerant rice seedlings showed significant variation (p\0.05), weights and lengths of plumule and radicle of different rice varieties did not show significant variation for As(V) and NaCl treatments. Results reveal that the combined phytotoxicity of As(V) and NaCl on rice seed germination and ESG are greater than their individual toxicities, and some saline-tolerant rice varieties are more resistant to the combined phytotoxicity of As(V) and NaCl than the saline non-tolerant varieties. © Springer Science+Business Media, LLC 2012

Arsenic uptake by aquatic macrophyte Spirodela polyrhiza L.: Interactions with phosphate and iron

The uptake of arsenate (As(V)) and dimethylarsinic acid (DMAA) by aquatic macrophyte Spirodela polyrhiza L. was investigated to determine the influence of arsenic interaction with PO43- and Fe ions. Plants were grown hydroponically on standard Murashige and Skoog (MS) culture solutions. Arsenic concentrations in Fe-oxide (Fe-plaque) on plant surfaces were determined by citrate-bicarbonate-ethylenediaminetetraacetic acid (CBE) technique. S. polyrhiza L. accumulated 51-fold arsenic from arsenate solution compared to that from DMAA solution with initial concentrations of 4.0 and 0.02 μM of arsenic and phosphate, respectively. The arsenate uptake was negatively (p 0.05) with iron accumulation. The results suggest that adsorption of arsenate on Fe-plaque of the surface of S. polyrhiza L. contributes to the arsenic uptake significantly. Thus, arsenate uptake in S. polyrhiza L. occurred through the phosphate uptake pathway and by physico-chemical adsorption on Fe-plaques of plant surfaces as well. The S. polyrhiza L. uses different mechanisms for DMAA uptake. © 2008 Elsevier B.V. All rights reserved

Influence of EDTA and chemical species on arsenic accumulation in Spirodela polyrhiza L. (duckweed)

The influence of ethylenediaminetetraacetic acid (EDTA) and chemical species on arsenic accumulation in aquatic floating macrophyte Spirodela polyrhiza L. (duckweed) was investigated. The uptake of inorganic arsenic species (arsenate; As(V) and arsenite; As(III)) into the plant tissue and their adsorption on iron plaque of plant surfaces were significantly (p0.05) by EDTA addition to the culture media while its concentration in CBE-extract decreased significantly (p<0.05). The As(inorganic)/Fe ratios in plant were higher than those of CBE-extract which indicate the increased uptake of these arsenic species into the plant relative to the iron. The lower As(organic)/Fe ratios in plant and on CBE-extract suggest the reduction of accumulation of these arsenic species relative to the iron. © 2007 Elsevier Inc. All rights reserved

Potential of proteins and their expression level in marine phytoplankton (Prymnesium parvum) as biomarker of N, P and Fe conditions in aquatic systems

Nitrogen (N), phosphorus (P) and Iron (Fe) are im-portant nutrients for phytoplankton, and are key limiting nutrients in many marine systems. In the present study, growth and protein expression of ma-rine phytoplankton Prymnesium parvum under dif-ferent nitrate, phosphate and iron conditions were investigated in order to evaluate whether proteins and their expression level can be used as biomarker of N, P, and Fe conditions in aquatic systems. The growth of P. parvum increased with the increase of nitrate, phosphate and iron concentrations in the culture medium. Protein expression levels also differed significantly (p < 0.001) for different nitrate, phosphate and iron conditions in the culture medium. The expression level of an 83 kDa protein at 0 and 5 µM nitrate treatments differed significantly (p < 0.001) from those at 20, 30, 50 and 100 µM nitrate treatments, indicating the expression levels of this protein as a biomarker of N status in the culture me-dium. A 121 kDa protein was up-regulated at phos-phate stress conditions ([P] = 1.0 µM), while this pro-tein was not expressed at phosphate replete conditions ([P] = 5 µM). Therefore, the expression of 121 kDa protein in P. parvum is indicative of phosphate replete condition in aquatic systems. The expression level of a 42 kDa was significantly higher (p < 0.01) at Fe-stress condition ([Fe] = 0.01 µM) than Fe-replete conditions ([Fe] = 0.1 µM). In addition, a new protein of 103 kDa was only expressed under Fe-deplete condition ([Fe] = 0.01 µM). Therefore, the 42 and 103 kDa proteins can be used as a biomarker of Fe-limitation condition of aquatic systems. However, further studies (two dimensional gel electrophoresis and mass spectrometry) are needed to identify and characterize these proteins in P. parvum

Influence of phosphate and iron ions in selective uptake of arsenic species by water fern (Salvinia natans L.)

In the present study, the effect of phosphate ion and iron hydroxides (Fe-plaques) on the selective uptake of arsenic species by water fern (Salvinia natans L.) was investigated. The plants were grown for 5 days in aqueous Murashige and Skoog (MS) culture media modified in arsenic and phosphate concentrations. Arsenic accumulations in S. natans L. increased with the increase of arsenate and DMAA concentrations in the culture solutions. Compared to the control treatment, S. natans L. accumulated significantly higher amount of arsenic from phosphate-deficient solutions, when the source was arsenate. However, arsenic uptake was not affected significantly by phosphate, when the source was dimethylarsinic acid (DMAA). From solutions containing 100 μM of phosphate and 4.0 μM of either arsenate or DMAA, the S. natans L. accumulated 0.14 ± 0.02 and 0.02 ± 0.00 μmol (g dry weight)-1 of arsenic, respectively. In contrast, plants accumulated 0.24 ± 0.06 and 0.03 ± 0.00 μmol (g dry weight)-1 of arsenic from solutions containing 4.0 μM of either arsenate and DMAA in phosphate deficient conditions, respectively. Thus, it is reasonable to state that increasing phosphate concentration in culture solutions decreased the arsenic uptake into the water fern significantly, when the source was arsenate. Moreover, arsenic and phosphate content in plant tissue correlated significantly (r = -0.66; p 0.05). Similarly, significant correlation was observed between arsenic and iron content in plant tissues (r = 0.66; p < 0.05), when initial source was arsenate while the correlation was not significant (r = 0.23; p < 0.05), when initial source was DMAA. The results indicate the adsorption of arsenate on Fe-plaques of aquatic plant surfaces. Furthermore, the study demonstrates that the DMAA uptake mechanisms into the water fern are deferent from those of arsenate. © 2008 Elsevier B.V. All rights reserved

Straighthead disease of rice (Oryza sativa L.) induced by arsenic toxicity

Straighthead disease is a physiological disorder of rice (Oryza sativa L.) characterized by sterility of the florates/spikelets leading to reduced grain yield. Though the exact cause of straighthead is unknown, a glass house experiment was conducted to investigate the effect of inorganic arsenic on straighthead disease in rice (Oryza sativa L.). BRRI dhan 29, a popular Bangladeshi rice strain, was grown in soils spiked with arsenic (prepared from sodium arsenate, Na2HAsO4·7H2O) at the rate of 10, 20, 30, 40, 50, 60, 70, 80 and 90 mg of As kg-1 and one control treatment was also run to compare the results. Although there may be some other soil physico-chemical factors involved, arsenic concentration was found to be closely associated with straighthead of rice. With the increase of soil arsenic concentration, the severity of straighthead increased significantly. Up to the 50 mg of As kg-1 soil treatments, the severity of straighthead incidences were not prevalent. Straighthead resulted in sterile florets with distorted lemma and palea, reduced plant height, tillering, panicle length and grain yield. Straighthead caused approximately 17-100% sterile florates/spikelets formation and about 16-100% loss of grain yield. Straighthead also causes the reduction of panicle formation and panicle length significantly (p < 0.01). In the present study, panicle formation was found to be reduced by 21-95% by straighthead. © 2007 Elsevier B.V. All rights reserved

Arsenic accumulation in duckweed (Spirodela polyrhiza L.): A good option for phytoremediation

Some unavoidable drawbacks of traditional technologies have made phytoremediation a promising alternative for removal of arsenic from contaminated soil and water. In the present study, the potential of an aquatic macrophyte Spirodela polyrhiza L. for phytofiltration of arsenic, and the mechanism of the arsenic uptake were investigated. The S. polyrhiza L. were grown in three test concentrations of arsenate and dimethylarsinic acid (DMAA) (i.e. 1.0, 2.0 and 4.0 μM) with 0 (control), 100 or 500 μM of phosphate. One control treatment was also set for each test concentrations of arsenic. The PO43 - concentration in control treatment was 0.02 μM. When S. polyrhiza L. was cultivated hydroponically for 6 d in culture solution containing 0.02 μM phosphate and 4.0 μM arsenate or DMAA, the arsenic uptake was 0.353 ± 0.003 μmol g-1 and 7.65 ± 0.27 nmol g-1, respectively. Arsenic uptake into S. polyrhiza L. was negatively (p 0.05) with iron accumulation in plant tissues, which indicates that S. polyrhiza L. uses different mechanisms for DMAA uptake. © 2007 Elsevier Ltd. All rights reserved

Arsenic accumulation in rice (Oryza sativa L.) varieties of Bangladesh: A glass house study

A glass house study was conducted to investigate the accumulation of arsenic in tissues of five widely cultivated rice (Oryza sativa L.) varieties of Bangladesh namely BRRI dhan 28, BRRI dhan 29, BRRI dhan 35, BRRI dhan 36, BRRI hybrid dhan 1. Arsenic concentrations were measured in straw, husk and brown and polish rice grain to see the differential accumulation of arsenic among the rice varieties. The results showed that the concentrations of arsenic in different parts of all rice varieties increased significantly (p BRRI dhan 35 > BRRI dhan 36 > BRRI dhan 29 > BRRI hybrid dhan 1. The order of arsenic contents in tissues of rice was: straw > husk > brown rice grain > polish rice grain. © 2007 Springer Science+Business Media B.V

Efficient production of transgenic soybean (Glycine max [L] Merrill) plants mediated via whisker-supersonic (WSS) method

The present study was designed to evaluate the transformation efficiency and proof the capability of whisker supersonic (WSS) method as an alternative option for soybean (Glycine max [L] Merrill)transformation. We compared soybean transformation efficiency obtained by WSS-mediated with that of particle bombardment transformation by carrying out molecular analysis of the T0 plants in two independent experiments. For this, we used for both transformation techniques the same genotype, the same plasmid and the same selection method. To assess the efficiency of soybean genetictransformation, we evaluated the efficiency of multi gene transformation by the selection with hygromycin and the expression of green fluorescent protein [sGFP (S65T)] resulted from both techniques. Regenerable embryogenic cells were induced from immature cotyledons of soybean c.v Jack on MSD40 media within 3 weeks then proliferated on FN lite liquid media and engineered with pUHG gene construct through both WSS and particle bombardment-mediated transformation. The pUHG was constructed with pUC 19 and contain the hpt gene conferring resistance to hygromycin as a selective marker and sGFP(S65T) as a reporter gene. Fluorescence microscopy screening after the selection of hygromycin, identified the clearly expression of sGFP(S65T) in the transformed soybean embryos. Stable integration of the transgenes was confirmed by polymerase chain reaction (PCR) andSouthern blot analysis. The average transformation efficiency achieved with WSS was higher than that obtained by particle bombardment and hence it may represent an alternative method for soybeantransformation