भारत कल और आज

भारत कल और आ

Single-molecule photochemical reactions of Auger-ionized quantum dots

Photoinduced electron transfer in donor-acceptor systems composed of quantum dots (QDs) and electron donors or acceptors is a subject of considerable recent research interest due to the potential applications of such systems in both solar energy harvesting and degradation of organic pollutants. Herein, we employed single-molecule imaging and spectroscopy techniques for the detection of photochemical reactions between 1,4-diaminobutane (DAB) and CdSe/ZnS single QDs. We investigated the reactions by analyzing photoluminescence (PL) intensity and lifetime of QDs at ensemble and single-molecule levels. While DAB was applied to single QDs tethered on a cover slip or QDs dispersed in a solution, PL intensity of QD continuously decreased with a concomitant increase in the PL lifetime. Interestingly, these changes in the PL properties of QD were predominant under high-intensity photoactivation. We hypothesize that the above changes in the PL properties surface due to the transfer of an electron from DAB to Auger-ionized QD followed by elimination of a proton from DAB and the formation of a QD-DAB adduct. Thus, a continuous decrease in the PL intensity of QDs under high-intensity photoactivation is attributed to continuous photochemical reactions of DAB with single QDs and the formation of QD-(DAB)n adducts. We believe that detection and analysis of such photochemical reactions of single QDs with amines will be of considerable broad interest due to the significant impact of photoinduced electron transfer reactions in energy management and environmental remediation

Multiple evolutionary trajectories have led to the emergence of races in <em>Fusarium oxysporum</em> f. sp. <em>lycopersici</em>

Race 1 isolates of Fusarium oxysporum f. sp. lycopersici (FOL) are characterized by the presence of AVR1 in their genomes. The product of this gene, Avr1, triggers resistance in tomato cultivars carrying resistance gene I. In FOL race 2 and race 3 isolates, AVR1 is absent, and hence they are virulent on tomato cultivars carrying I. In this study, we analyzed an approximately 100-kb genomic fragment containing the AVR1 locus of FOL race 1 isolate 004 (FOL004) and compared it to the sequenced genome of FOL race 2 isolate 4287 (FOL4287). A genomic fragment of 31 kb containing AVR1 was found to be missing in FOL4287. Further analysis suggests that race 2 evolved from race 1 by deletion of this 31-kb fragment due to a recombination event between two transposable elements bordering the fragment. A worldwide collection of 71 FOL isolates representing races 1, 2, and 3, all known vegetative compatibility groups (VCGs), and five continents was subjected to PCR analysis of the AVR1 locus, including the two bordering transposable elements. Based on phylogenetic analysis using the EF1-α gene, five evolutionary lineages for FOL that correlate well with VCGs were identified. More importantly, we show that FOL races evolved in a stepwise manner within each VCG by the loss of function of avirulence genes in a number of alternative ways. IMPORTANCE Plant-pathogenic microorganisms frequently mutate to overcome disease resistance genes that have been introduced in crops. For the fungus Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt in tomato, we have identified the nature of the mutations that have led to the overcoming of the I and I-2 resistance genes in all five known clonal lineages, which include a newly discovered lineage. Five different deletion events, at least several of which are caused by recombination between transposable elements, have led to loss of AVR1 and overcoming of I. Two new events affecting AVR2 that led to overcoming of I-2 have been identified. We propose a reconstruction of the evolution of races in FOL, in which the same mutations in AVR2 and AVR3 have occurred in different lineages and the FOL pathogenicity chromosome has been transferred to new lineages several times

Pterobryopsis kegeliana (Müll. Hal.) M. Fleisch. and P. scabriuscula (Mitt.) M. Fleisch. - new to the moss flora of the Eastern Ghats

Pterobryopsis kegeliana (Müll. Hal.) M. Fleisch., so far known from Pachmarhi and the Western Ghats in India, and P. scabriuscula (Mitt.) M. Fleisch., known from the Western Ghats, Sri Lanka and Thailand (?), are recorded for the first time in the Eastern Ghats. A perusal of literature revealed that Meteorium scabriusculum Mitt., the holotype of P. scabriuscula, collected by Law from Concan, presumed to be a place in Thailand by Noguchi refers to only the present-day Konkan region in Peninsular India. Hence, the distribution of P. scabriuscula is amended here. Detailed descriptions with figures and photographic plates are provided

The moss genus Regmatodon Brid. (Regmatodontaceae) - new to the Eastern Ghats

Regmatodon orthostegius Mont. was earlier reported from Central India, the Himalaya, Northeast India and the Western Ghats in India. However, while collecting bryophytes from the Eastern Ghats, the authors came across a moss which was later identified as Regmatodon orthostegius which is a new distributional record for this genus as well. A detailed description with figure and photographic plates is provided

The moss genus Aulacopilum (Erpodiaceae, Bryophyta) new to the Eastern Ghats in Peninsular India

Aulacopilum beccarii, earlier known from the Western Ghats for India is added here to the moss flora of the Eastern Ghats. This record is just the second for Asia and India as well, and on the other hand, the genus is new to the Eastern Ghats. A brief description with figures and a photographic plate are provided

Genus Symphysodontella M. Fleisch. (Pterobryaceae: Bryophyta) - new to the moss flora of the Eastern Ghats

Surveys carried out in the Kolli Hills of Eastern Ghats resulted in the discovery of 2 species of Symphysodontella M. Fleisch. namely S. cylindracea (Mont.) M. Fleisch. and S. involuta (Thwaites &amp; Mitt.) M. Fleisch. of which the former is new to the moss flora of India whereas the latter is new to the moss flora of Eastern Ghats. Detailed descriptions with figures substantiated by photo plates and a key to distinguish the two species are provided. Incidentally, genus Symphysodontella is new to the moss flora of Eastern Ghats