One-step method to prepare starch-based superabsorbent polymer for slow release of fertilizer

Here we report the use of a one-step process of reactive melt mixing to prepare starch-based superabsorbent polymers (SBSAPs) for the slow release of urea as a fertilizer. A modified twin-rotor mixer, with improved sealing to establish an oxygen-free environment, was used to study the chemical and physical reactions during the melt-processing through monitoring the temperature and torque. The effects of the initiator (ceric ammonium nitrate, or CAN), crosslinker (N,N′-methylene-bisacrylamide, or N,N′-MBA) and saponification agent (NaOH) under different reaction conditions (time, temperature, and shear intensity) were systematically studied. Also investigated was the effect of starch with different amylose content. Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) confirmed that using this simple technique, SBSAPs were successfully prepared from either high-amylopectin starch (waxy corn starch) or high-amylose starch (Gelose 50) grafted with AM and crosslinked by N,N′-MBA. Gel strength was evaluated by rheometry, which revealed a significant increase in storage modulus (G′) obtained in the crosslinked high-amylose SBSAP gels. Also, scanning electron microscopy (SEM) images showed a more sophisticated structural network with a smaller pore size in the crosslinked high-amylose gels. Urea as a fertilizer was embedded in the SBSAP gel network, and this network controlled the urea release in water. The release rate of urea depended on the gel strength, gel microstructure and water absorption capacity (WAC) of SAP, which was affected by the reaction conditions and degree of saponification

Influence of crosslinker amount on the microstructure and properties of starch-based superabsorbent polymers by one-step preparation at high starch concentration

This work concerns how crosslinker amount (N, N′-methylene-bisacrylamide) affects the microstructural, absorbent and rheological features of one-step prepared starch-based superabsorbent polymers at a high starch concentration (0.27:1 w/w starch-water). The increased crosslinker amount evidently altered the microstructure and the absorbent and rheological features. Then, the variations in starch-based superabsorbent polymer properties were discussed from a microstructure viewpoint. Particularly, the higher crosslinker quantity rose the crosslinking density and the ratio (GR) of grafted anhydroglucose unit on starch backbone (from 27% to 52%), but short the average polyacrylamide (PAM) chain length (LPAM). These structural features suppressed the chain stretch within starch-based superabsorbent polymer fractal gels (confirmed by smaller Rg value) and promoted the formation of smaller chain networks, thus weakening the water absorption to the starch-based superabsorbent polymer chain networks. Also, the increased GR and reduced LPAM, with lowered chain extension and elevated crosslinking density, probably decreased the flexibility and mobility of chain segments in starch-based superabsorbent polymer gel matrixes. This caused the enhanced robustness and storage modulus of the gels with reduced chain energy dissipation ability

Photosynthetic and physiological responses of mangroves under an environmental deterioration

Mangroves are important marine coastal ecosystems in the Pearl River Estuary in China. However, they are degraded by heavy metal pollution. Although heavy metal levels in the Pearl River Estuary have been investigated, physiological and photosynthetic responses related to mangrove health remain unclear. In this study, three typical mangrove species, namely Kandelia candel L., Aegiceras corniculatum L. and Sonneratia apetala L., were selected from six normal sites of mangrove reserves and from six deteriorated sites along the river way to investigate the variation in physiological and photosynthetic responses. The photosynthetic and transpiration rates and the enzyme activities associated with mangrove metabolic activity were significantly lower in the deteriorated sites than in the normal sites. The K+/Na+ ratio of mangroves in the normal sites was higher than that in the deteriorated sites. H2O2 contents were also higher in the deteriorated sites than in the normal sites. Cluster analysis indicated that species determined the responses of mangroves to the deteriorated environment. Principal component analysis revealed that hexose phosphate isomerase and H2O2 were representative parameters that could be used for rapid health assessment. The transpiration rate and glyceraldehyde-3-phosphate dehydrogenase were biomarkers that could be considered to distinguish mangroves with different responses to deteriorated environments. This study helps ensure the sustainable development of marine coastal ecosystems in the Pearl River Estuary

Overexpression of SeNHX1 improves both salt tolerance and disease resistance in tobacco

Recently, we found NHX1, the gene encoding a Na(+)/H(+) exchanger, participated in plant disease defense. Although NHX1 has been confirmed to be involved in plant salt tolerance, whether the NHX1 transgenic plants exhibit both salt tolerance and disease resistance has not been investigated. The T1 progenies of Nicotiana tabacum L. lines expressing SeNHX1 (from Salicornia europaea) were generated for the present study. Compared with PBI-type control plants, SeNHX1 transgenic tobaccos exhibited more biomass, longer root length, and higher K(+)/Na(+) ratio at post germination or seedling stage under NaCl treatment, indicating enhanced salt tolerance. The vacuolar H(+) efflux in SeNHX1 transgenic tobacco was increased after treatment of NaCl with different concentration. Meanwhile, the SeNHX1 transgenic tobaccos showed smaller wilted spot area, less H(2)O(2) accumulation in leaves after infection of Phytophthora parasitica var. nicotianae. Further investigation demonstrated a larger NAD(P)(H) pool in SeNHX1 transgenic tobacco. These evidences revealed that overexpression of SeNHX1 intensified the compartmentation of Na(+) into vacuole under salt stress and improved the ability of eliminating ROS after pathogen attack, which then enhanced salt tolerance and disease resistance simultaneously in tobacco. Our findings indicate NHX1 has potential value in creating crops with both improved salt tolerance and disease resistance

Overexpression of SeNHX1 improves both salt tolerance and disease resistance in tobacco

Recently, we found NHX1, the gene encoding a Na+/H+ exchanger, participated in plant disease defense. Although NHX1 has been confirmed to be involved in plant salt tolerance, whether the NHX1 transgenic plants exhibit both salt tolerance and disease resistance has not been investigated. The T1 progenies of Nicotiana tabacum L. lines expressing SeNHX1 (from Salicornia europaea) were generated for the present study. Compared with PBI-type control plants, SeNHX1 transgenic tobaccos exhibited more biomass, longer root length, and higher K+/Na+ ratio at post germination or seedling stage under NaCl treatment, indicating enhanced salt tolerance. The vacuolar H+ efflux in SeNHX1 transgenic tobacco was increased after treatment of NaCl with different concentration. Meanwhile, the SeNHX1 transgenic tobaccos showed smaller wilted spot area, less H2O2 accumulation in leaves after infection of Phytophthora parasitica var. nicotianae. Further investigation demonstrated a larger NAD(P)(H) pool in SeNHX1 transgenic tobacco. These evidences revealed that overexpression of SeNHX1 intensified the compartmentation of Na+ into vacuole under salt stress and improved the ability of eliminating ROS after pathogen attack, which then enhanced salt tolerance and disease resistance simultaneously in tobacco. Our findings indicate NHX1 has potential value in creating crops with both improved salt tolerance and disease resistance

Après le doute, l'espoir ? Table ronde organisée à l'occasion du 45e anniversaire de la RPC

Béja Jean-Philippe, Zunxin Bao, Kangkang Zhang, Ruoshui Wang, Xianyang Zhang, X. M. Après le doute, l'espoir ? Table ronde organisée à l'occasion du 45e anniversaire de la RPC. In: Perspectives chinoises, n°25, 1994. pp. 6-11

Virus-induced gene silencing reveals control of reactive oxygen species accumulation and salt tolerance in tomato by γ-aminobutyric acid metabolic pathway

gamma-Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases (SlGADs), GABAtransaminases (SlGABA-Ts) and succinic semialdehyde dehydrogenase (SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs (GABA biosynthetic genes) and SlGABA-Ts (GABA catabolic genes) led to increased accumulation of reactive oxygen species (ROS) as well as salt sensitivity under 200mm NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA-Ts-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to -hydroxybutyrate as reported previously in Arabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and -hydroxybutyrate and subsequent ROS accumulation under salt stress. -Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress, but the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. In the present study, based on loss-of-function studies, our findings revealed the functional involvement of GABA shunt in the salt tolerance of tomato and the putative roles for GABA-related metabolites (such as succinate and -hydroxybutyrate) in these processes. These results open exciting perspectives for further investigations of GABA shunt and associated metabolic pathways to the stress adaptation of plants, pointing to these pathways as potential targets for engineering of plant stress tolerance. To our knowledge, this work represents one of the most thorough studies demonstrating the roles of GABA metabolic pathway in defense against environmental stress

Virus-induced gene silencing reveals control of reactive oxygen species accumulation and salt tolerance in tomato by gamma-aminobutyric acid metabolic pathway

gamma-Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases (SlGADs), GABAtransaminases (SlGABA-Ts) and succinic semialdehyde dehydrogenase (SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs (GABA biosynthetic genes) and SlGABA-Ts (GABA catabolic genes) led to increased accumulation of reactive oxygen species (ROS) as well as salt sensitivity under 200mm NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA-Ts-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to -hydroxybutyrate as reported previously in Arabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and -hydroxybutyrate and subsequent ROS accumulation under salt stress. -Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress, but the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. In the present study, based on loss-of-function studies, our findings revealed the functional involvement of GABA shunt in the salt tolerance of tomato and the putative roles for GABA-related metabolites (such as succinate and -hydroxybutyrate) in these processes. These results open exciting perspectives for further investigations of GABA shunt and associated metabolic pathways to the stress adaptation of plants, pointing to these pathways as potential targets for engineering of plant stress tolerance. To our knowledge, this work represents one of the most thorough studies demonstrating the roles of GABA metabolic pathway in defense against environmental stress