Microbial ACC-Deaminase: Prospects and Applications for Inducing Salt Tolerance in Plants

Salinity is one of the most important stresses that hamper agricultural productivity in nearly every part of the world. Enhanced biosynthesis of ethylene in plants under salinity stress is well established. Higher ethylene concentration inhibits root growth and ultimately affects the overall plant growth. Overcoming this ethylene-induced root inhibition is a prerequisite for successful crop production. Recent studies have shown that ethylene level in plants is regulated by a key enzyme 1-aminocyclopropane-1-carboxylicacid (ACC)-deaminase. This enzyme is present in plant growth-promoting bacteria (PGPR) and lowers the ethylene level by metabolizing its precursor ACC into α-ketobutyrate and ammonia (NH₃). Inoculation of plants under salinity stress with PGPR having ACC-deaminase activity mitigates the inhibitory effects of salinity on root growth by lowering the ethylene concentration in the plant. This in turn results in prolific root growth, which is beneficial for the uptake of nutrients and maintenance of growth under stressful environment. The present review critically discusses the effects of salinity stress on plant growth with special reference to ethylene production and the effects of rhizobacteria containing ACC-deaminase on crop improvement under salinity stress. It also discusses how much progress has been made in producing transgenic lines of different crops over-expressing the gene encoding ACC-deaminase and how far such transformed lines can tolerate salinity stress.     

A Putative Leucine-Rich Repeat Receptor-Like Kinase of Jute Involved in Stress Response

A putative leucine-rich repeat receptor-like protein kinase (LRR-RLK) gene together with its 5′ and 3′ untranslated regions of jute (Corchorus olitorius L.) has been identified and sequenced. The gene is 3,371 bp long containing two exons and one intron. The coding sequence of the gene is 2,879 bp long encoding a peptide of 957 amino acids. The predicted protein contains several domains and motifs characteristic of a transmembrane protein kinase. It is complete with domains for an N-terminal leucine-rich repeat and a protein kinase core, an active site for serine/threonine protein kinase, an ATP binding conserved site and a transmembrane region. Expression of the gene is induced by low temperature, high salt concentration, dehydration, abscisic acid treatment, and fungal infection, suggesting the involvement of the gene in multiple stress response pathways in jute (C. olitorius L.). A possible mechanism of the role of the gene in signal transduction and environmental stress response is discussed. To date, LRR-RLK is the only jute gene which has been completely sequenced and characterized.     

Characterization of Defense Signaling Pathways of <Emphasis Type="Italic">Brassica napus</Emphasis> and <Emphasis Type="Italic">Brassica carinata</Emphasis> in Response to <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> Challenge

Canola (Brassica napus L.) is an agriculturally and economically important crop in Canada, and its growth and yield are frequently influenced by fungal pathogens. Sclerotinia sclerotiorum is among those fungal pathogens and causes stem rot disease in B. napus whereas it has been reported that Brassica carinata is moderately tolerant to S. sclerotiorum. Jasmonic acid/ethylene (JA/ET) and salicylic acid (SA) are phytohormones that are known to be involved in plant disease responses. To investigate the defense signaling cascades involved in the interaction of B. napus and B. carinata with S. sclerotiorum, we examined the expression of five orthologs of B. napus genes involved in JA/ET or SA signaling pathways using quantitative RT-PCR. Our results indicated that there are differences in the timing of JA/ET and SA signaling pathways between B. napus and B. carinata. Our results in these two Brassica species also support previous observations that necrotrophic pathogens trigger JA/ET signaling in response to infection. Finally, we observed that transgenic canola expressing 1-aminocyclopropane-1-carboxylate-deaminase producing low levels of ET was relatively more susceptible to S. sclerotiorum than its wild-type counterpart, suggesting that ET inhibits S. sclerotiorum-induced symptom development.     

Ctr1 transports silver into mammalian cells

Silver is a non-essential, toxic metal. The use of silver as an antimicrobial agent in many applications and its presence as a contaminant in foods and air can lead to accumulation in tissues. Despite its widespread use, the systems involved in the uptake of silver into mammalian cells are presently unknown. Previous studies have shown that copper uptake at the plasma membrane by copper transporter 1 (Ctr1) is inhibited by an excess of silver, suggesting that Ctr1 may function in importing silver into cells. In this study we examined directly the role of Ctr1 in the accumulation of silver in mammalian cells using over-expression experiments and mouse embryonic fibroblast cells lacking Ctr1. COS-7 cells transfected to express a human Ctr1-green fluorescent protein (hCtr1-GFP) fusion protein hyper-accumulated silver when incubated in medium supplemented with low micromolar concentrations (2.5–10 μmol/L) of AgNO₃. An hCtr1-GFPM150L,M154L variant deficient for copper transport failed to stimulate accumulation of silver. Mouse embryonic fibroblast cells lacking Ctr1 showed approximately a 50% reduction in silver content when incubated in silver-supplemented medium compared to a wild-type isogenic cell line. Collectively, these data demonstrate that Ctr1 transports both copper and silver and suggest that Ctr1 is an important transport protein in the accumulation of silver in mammalian cells.     

Strobilanthes crispus attenuates renal carcinogen, iron nitrilotriacetate (Fe-NTA)-mediated oxidative damage of lipids and DNA

This study was aimed to evaluate the effect of Strobilanthes crispus extract for possible protection against lipid peroxidation and DNA damage induced by iron nitrilotriacetate (Fe-NTA) and hydrogen peroxide (H₂O₂). Fe-NTA is a potent nephrotoxic agent and induces acute and subacute renal proximal tubular necrosis by catalyzing the decomposition of H₂O₂-derived production of hydroxyl radicals, which are known to cause lipid peroxidation and DNA damage. Incubation of postmitochondrial supernatant and/or calf thymus DNA with H₂O₂ (40 mM) in the presence of Fe-NTA (0.1 mM) induces lipid peroxidation and DNA damage to about 2.3-fold and 2.9-fold, respectively, as compared to control (P < 0.05). In lipid peroxidation protection studies, S. crispus treatment showed a dose-dependent inhibition (45–53% inhibition, P < 0.05) of Fe-NTA and H₂O₂ induced lipid peroxidation. Similarly, in DNA damage protection studies, S. crispus treatment also showed a dose-dependent inhibition (18–30% inhibition, P < 0.05) of DNA damage. In addition, the protection was closely related to the content of phenolic compounds as evident by S. crispus extract showing the value of 124.48 mg/g total phenolics expressed as gallic acid equivalent (GAE, mg/g of extract). From these studies, it is concluded that S. crispus inhibits peroxidation of membrane lipids and DNA damage induced by Fe-NTA and H₂O₂ and possesses the potential to be used to treat or prevent degenerative diseases where oxidative stress is implicated.     

Pre and post cloning characterization of a β-1,4-endoglucanase from <Emphasis Type="Italic">Bacillus</Emphasis> sp.

Consistent with its precloning characterization from the cellulolytic Bacillus sp., β-1,4-endoglucanase purified from the recombinant E. coli exhibited maximum activity at 60°C and pH 7.0. It was highly specific for CMC hydrolysis, with stability up to 70°C and over a pH range of 6.0–8.0. The K _m and V _max values for CMCase activity of the enzyme were 4.1 mg/ml and 25 μmole/ml min⁻¹, respectively. The purified enzyme was a monomer of 65 kDa, as determined by SDS-PAGE. The presence of sucrose and IPTG in fermentation media increased the endoglucanase activity of the recombinant enzyme to 5.2-folds as compared with that of the actual one.     

Distribution of the triterpenoid saponins and chemotaxonomy of the genus Clematis L. by high-performance liquid chromatography–mass spectrometry

Selected species of the genus Clematis (Ranunculaceae) have been screened for occurrence of triterpenoid saponins by qualitative HPLC-MSⁿ analysis of root and rhizome materials from 18 Clematis samples as well as the whole plant materials of Clematis puberula var. ganpiniana and Clematis terniflora. The HPLC-MSⁿ analysis allowing the detection of 17 oleanolic acid or hederagenin saponins was carried out in the negative selected ion monitoring (SIM) mode. Triterpenoid saponin profiles of these taxa were used for phylogenetic studies, and results are presented as a dendrogram. Huzhangoside B could be unambiguously identified in all analyzed Clematis taxa, as well as in the investigated Ranunculus taxa. The distribution and chemotaxonomic importance of the triterpenoid saponin profile within this genus are discussed.     

Reproductive performance of repeat breeders in dairy herds

The objectives were to characterize repeat breeding in dairy cows, including reproductive performance and risk factors. Data from 613 Holstein Friesian cows in nine dairy herds across Japan were enrolled. A repeat breeder was defined as a cow that did not become pregnant after three inseminations, despite no clinically detectable reproductive disorders. In contrast, cows that became pregnant within three inseminations were considered to have normal fertility. Of the 613 cows, 87.3% eventually became pregnant after repeated AI (maximum calving to conception interval was 435 d). Mean (±SEM) first AI conception rate, days in milk at first AI, calving to conception interval and service per conception were 38.3%, 82 ± 2 d, 125 ± 3 d, and 2.0 ± 0.1 times, respectively. Normal fertility cows (n = 479) required only 114 ± 3 d to conceive and 1.7 ± 0.1 inseminations per pregnancy, whereas repeat breeders (n = 86) required significantly more days to conceive (211 ± 10) and more inseminations per pregnancy (4.7 ± 0.2). Based on survival analysis, it took 94 d after calving for 50% of normal fertility cows to become pregnant, compared to 155 d for repeat breeders. For repeat breeders, 31.4, 50.0, and 58.1% became pregnant within 210, 300, and 435 d after calving, respectively. The risk factors for repeat breeding were parity (relative risk [RR] = 0.809; P = 0.058), resumption of postpartum ovarian cycles (RR = 1.928; P = 0.009), and days in milk at first AI (RR = 0.991; P = 0.039). In conclusion, repeat breeder dairy cows had very poor reproductive performance. Lower parity, abnormal resumption of postpartum ovarian cycles, and shorter days in milk at first AI were risk factors for repeat breeding.     

Carotenoid inhibitors reduce strigolactone production and Striga hermonthica infection in rice

The strigolactones are internal and rhizosphere signalling molecules in plants that are biosynthesised through carotenoid cleavage. They are secreted by host roots into the rhizosphere where they signal host-presence to the symbiotic arbuscular mycrorrhizal (AM) fungi and the parasitic plants of the Orobanche, Phelipanche and Striga genera. The seeds of these parasitic plants germinate after perceiving these signalling molecules. After attachment to the host root, the parasite negatively affects the host plant by withdrawing water, nutrients and assimilates through a direct connection with the host xylem. In many areas of the world these parasites are a threat to agriculture but so far very limited success has been achieved to minimize losses due to these parasitic weeds. Considering the carotenoid origin of the strigolactones, in the present study we investigated the possibilities to reduce strigolactone production in the roots of plants by blocking carotenoid biosynthesis using carotenoid inhibitors. Hereto the carotenoid inhibitors fluridone, norflurazon, clomazone and amitrole were applied to rice either through irrigation or through foliar spray. Irrigation application of all carotenoid inhibitors and spray application of amitrole significantly decreased strigolactone production, Striga hermonthica germination and Striga infection, also in concentrations too low to affect growth and development of the host plant. Hence, we demonstrate that the application of carotenoid inhibitors to plants can affect S. hermonthica germination and attachment indirectly by reducing the strigolactone concentration in the rhizosphere. This finding is useful for further studies on the relevance of the strigolactones in rhizosphere signalling. Since these inhibitors are available and accessible, they may represent an efficient technology for farmers, including poor subsistence farmers in the African continent, to control these harmful parasitic weeds.