Dimeric nature and amino acid compositions of homogeneous canine prostatic human liver and rat liver acid phosphatase isoenzymes. Specificity and pH-dependence of the canine enzyme.

Two isoenzymes of rat liver acid phosphatase (orthophosphoric-monoester phosphohydrolase (acid optimum) EC 3.1.3.2) have been purified to homogeneity, at least one of these for the first time. Both of the rat liver isoenzymes have identical specific activities towards p-nitrophenyl phosphate. Molecular weights of the native enzymes are 92 000 for rat liver isoenzyme I and 93 000 for isoenzyme II, while the subunit molecular weights are 51 000 and 52 000 respectively. Data on substrate specificity and pH dependence are presented for the homogeneous canine prostatic enzyme, which is also isolated as a dimeric enzyme of (native) molecular weight 89 000. Carbohydrate analysis data are presented for canine prostatic acid phosphatase and it is further noted that both isoenzymes of rat liver acid phosphatase are also glycoproteins. The amino acid compositions of the two rat liver isoenzymes are presented together with those of the similar dimeric acid phosphatase of human liver and of canine prostate. Comparison of these results with published data for the amino acid composition of human prostatic acid phosphatase shows substantial similarities. However, significant differences are seen in the amino acid composition of rat liver acid phosphatase isoenzyme I as compared to a previous literature report. Most notably, 17 histidine residues are found per mol of isoenzyme I and 18 for isoenzyme II.     

FliZ induces a kinetic switch in flagellar gene expression

FliZ is an activator of class 2 flagellar gene expression in Salmonella enterica. To understand its role in flagellar assembly, we investigated how FliZ affects gene expression dynamics. We demonstrate that FliZ participates in a positive-feedback loop that induces a kinetic switch in class 2 gene expression.     

Effects of water stress on male gametophyte development in plants

 Male reproductive development in plants is highly sensitive to water deficit during meiosis in the microspore mother cells. Water deficit during this stage inhibits further development of microspores or pollen grains, causing male sterility. Female fertility, in contrast, is quite immune to stress. The injury is apparently not caused by desiccation of the reproductive tissue, but is an indirect consequence of water deficit in the vegetative organs, such as leaves. The mechanism underlying this stress response probably involves a long-distance signaling molecule, originating in the organs that undergo water loss, and affecting fertility in the reproductive tissue, which conserves its water status. Much research has been focused on the involvement of abscisic acid in this regard, but the most recent evidence tends to reject a role for this hormone in the induction of male sterility. Stress-induced arrest of male gametophyte development is preceded by disturbances in carbohydrate metabolism and distribution within anthers, and an inhibition of the key sugar-cleaving enzyme, acid invertase. Since invertase gene expression can be modulated by sugar concentration, it is possible that decreased sugar delivery to reproductive tissue upon inhibition of photosynthesis by stress is the signal that triggers metabolic lesions leading to failure of male gametophyte development. Received: 31 October 1996 / Revision accepted: 18 February 1997     

Glucose deprivation induced upregulation of phosphoenolpyruvate carboxykinase modulates virulence in Leishmania donovani

Various physiological stimuli trigger the conversion of noninfective Leishmania donovani promastigotes to the infective form. Here, we present the first evidence of the effect of glucose starvation, on virulence and survival of these parasites. Glucose starvation resulted in a decrease in metabolically active parasites and their proliferation. However, this was reversed by supplementation of gluconeogenic amino acids. Glucose starvation induced metacyclogenesis and enhanced virulence through protein kinase A regulatory subunit (LdPKAR1) mediated autophagy. Glucose starvation driven oxidative stress upregulated the antioxidant machinery, culminating in increased infectivity and greater parasitic load in primary macrophages. Interestingly, phosphoenolpyruvate carboxykinase (LdPEPCK), a gluconeogenic enzyme, exhibited the highest activity under glucose starvation to regulate growth of L. donovani by alternatively utilising amino acids. Deletion of LdPEPCK (Δpepck) decreased virulent traits and parasitic load in primary macrophages but increased autophagosome formation in the mutant parasites. Furthermore, Δpepck parasites failed to activate the Pentose Phosphate Pathway shunt, abrogating NADPH/NADP⁺ homoeostasis, conferring increased susceptibility towards oxidants following glucose starvation. In conclusion, this study showed that L. donovani undertakes metabolic rearrangements via gluconeogenesis under glucose starvation for acquiring virulence and its survival in the hostile environment.     

Elicitors,SA and MJ enhance carotenoids and tocopherol biosynthesis and expression of antioxidant related genes in Moringa oleifera Lam. leaves

Moringa oleifera Lam. leaves are rich source of carotenoids (provitamin A) and α-tocopherol (vitamin E), and there is a scope for their further enhancement, through elicitor mediation, thereby a great potential for addressing these vitamins deficiency. In the present study, we report the efficacy of foliar administration of biotic elicitors, carboxy-methyl chitosan and chitosan, and signaling molecules, methyl jasmonate (MJ) and salicylic acid (SA) for enhancement of major carotenoids and α-tocopherol. Highest α-tocopherol content of 49.7 mg/100 g FW was recorded upon foliar application of 0.1 mM SA after 24 h of treatment, which represented a 187.5 % increase in comparison to the untreated control. Similarly, a maximum of 52.6 mg/100 g FW lutein, and 21.8 mg/100 g FW β-carotene content were observed in leaves after 24 h of treatment with MJ, which represented a 54.0 and 20.3 % increase in comparison to the untreated control, respectively. Among the major genes of carotenoid biosynthetic pathway, the expression of lycopene β-cyclase (LCY-β) was maximum influenced after treatment with elicitors and signaling molecules, compared to phytoene synthase and phytoene desaturase, suggesting the LCY-β-mediated enhancement in the production of β-carotene in elicitor treated M. oleifera leaves. Enhanced production of α-tocopherol under respective elicitor treatment was further supported by 2.0–2.7 fold up-regulation of γ-tocopherol methyl transferase, compared to untreated control. This is the first report on elicitor-mediated enhanced production of tocopherol and carotenoids in foliage of economically important food plant.     

Assessment of Genetic Diversity Among Rice Genotypes with Differential Adaptations to Salinity Using Physio-morphological and Molecular Markers

Breeding for salt tolerance using traditional screening and selection methods have been limited by the complex and polygenic nature of salt tolerance trait. This study was designed to evaluate some of the premium Basmati rice varieties for salt tolerance and to characterize genetic diversity among the rice varieties with different adaptations to saline soils using microsatellite (SSR) and ISSR markers. Plants of nine rice varieties including salt tolerant, salt sensitive and traditional Basmati, were grown in hydroponics using Yoshida solution containing 0 (control, pH 5.0) and 30 mM NaCl (Electrical conductivity 4.8 d/S, pH 5.0) and assessed for salinity tolerance on 1–9 scale as per IRRI standard evaluation system using seedling growth parameters, visual salt injuries and Na-K ratio. Physio-morphological studies showed that traditional Basmati rice varieties (Basmati 370 and HBC19) were more sensitive than the salt sensitive control variety, MI-48. SSR as well as ISSR marker systems generated higher levels of polymorphism and could distinguish between all the 9 rice cultivars. A total of 299 (225 polymorphic) and 437 (430 polymorphic) bands were detected using 28 UBC ISSR primers and 100 welldistributed mapped SSR markers, respectively. ISSR and SSR marker data-sets showed moderate levels of positive correlation (Mantel test, r = 0.43). The ISSR and SSR marker data analyzed using clustering algorithms showed two distinct clusters separating the Basmati (Basmati 370, HBC19 and CSR-30) from other non-aromatic indica (IR36, Pokkali, CSR10 and MI-48) rice varieties indicating greater divergence between Basmati and non-aromatic indica rice genotypes. Marker analysis showed a close relationship among the two traditional (Basmati 370 and HBC19) and cross-bred (CSR30) Basmati rice varieties and greater diversity between the two salt-tolerant genotypes, Pokkali and BR4-10.     

Biotic and abiotic stress down-regulate miR398 expression in Arabidopsis

MicroRNA398 targets two Cu/Zn superoxide dismutases (CSD1 and CSD2) in higher plants. Previous investigations revealed both decreased miR398 expression during high Cu²⁺ or paraquat stress and increased expression under low Cu²⁺ or high sucrose in the growth medium. Here, we show that additional abiotic stresses such as ozone and salinity also affect miR398 levels. Ozone fumigation decreased miR398 levels that were gradually restored to normal levels after relieved from the stress. Furthermore, miR398 levels decreased in Arabidopsis leaves infiltrated with avirulent strains of Pseudomonas syringae pv. tomato, Pst DC3000 (avrRpm1 or avrRpt2) but not the virulent strain Pst DC3000. To our knowledge, miR398 is the first miRNA shown to be down-regulated in response to biotic stress (P. syringae). CSD1, but not CSD2, mRNA levels were negatively correlated with miR398 levels during ozone, salinity and biotic stress, suggesting that CSD2 regulation is not strictly under miR398 control during diverse stresses. Overall, this study further establishes a link between oxidative stress and miR398 in Arabidopsis.     

Mechanism of action of aflatoxin B1 in Bacillus megaterium.

Bacillus megaterium cells from various growth phases were equally susceptible to the lethal effects of aflatoxin B1. Known surfactants (EDTA and Tween-80) accentuated the effects of aflatoxin B1. Viability and inulin uptake in aflatoxin B1-exposed cells decreased considerably. The effect was concentration dependent. A straight-line relationship observed in the death curve indicated a single target for aflatoxin B1 action in B. megaterium. Leakage of intracellular constituents in B. megaterium was also concentration dependent, and this can be related to the extent of cell membrane damage.     

Auxin: a master regulator in plant root development

The demand for increased crop productivity and the predicted challenges related to plant survival under adverse environmental conditions have renewed the interest in research in root biology. Various physiological and genetic studies have provided ample evidence in support of the role of plant growth regulators in root development. The biosynthesis and transport of auxin and its signaling play a crucial role in controlling root growth and development. The univocal role of auxin in root development has established it as a master regulator. Other plant hormones, such as cytokinins, brassinosteroids, ethylene, abscisic acid, gibberellins, jasmonic acid, polyamines and strigolactones interact either synergistically or antagonistically with auxin to trigger cascades of events leading to root morphogenesis and development. In recent years, the availability of biological resources, development of modern tools and experimental approaches have led to the advancement of knowledge in root development. Research in the areas of hormone signal perception, understanding network of events involved in hormone action and the transport of plant hormones has added a new dimension to root biology. The present review highlights some of the important conceptual developments in the interplay of auxin and other plant hormones and associated downstream events affecting root development.