Senescence Phase Research Articles

Glucosinolate Profiles Change During the Life Cycle and Mycorrhizal Colonization in a Cd/Zn Hyperaccumulator Thlaspi praecox (Brassicaceae)

Thlaspi praecox Wulfen (Brassicaceae) is a perennial Cd/Zn hyperaccumulating plant species that forms functional arbuscular mycorrhizal (AM) symbiosis. Glucosinolates (GS) were studied in different organs of field-collected T. praecox at differing plant developmental stages. Additionally, AM colonization was recorded. Total GS concentrations and profiles of nine individual GS varied during the plant life cycle. Novel individual GS that were related to specific developmental phases, mainly to flowering and seed production, were identified. The highest total GS and sinalbin concentrations in rosette leaves were found in the vegetative phase, possibly contributing to protection of young, palatable leaves. The lowest were found in roots during the flowering and the seeding phases. Increased total GS concentrations in roots and enhanced aliphatic GS, especially glucobrassicanapin, in the senescence phase may protect roots from herbivory during winter and early spring. The presence of glucotropaeolin and the absence of glucobrassicanapin in the flowering phase coincided with peak AM colonization. This is the first report on GS profiles in an AM and metal-hyperaccumulating plant.

Growth pattern of Bidens cernua L.: relationships between relative growth rate and its physiological and morphological components

Seedlings of Bidens cernua L. emerged when mean air temperature was 17.0±1.3 °C. The highest net photosynthetic rate (P N), 13.8±0.8 µmol(CO2) m-2 s-1, was monitored during the vegetative period (May-August), decreasing on an average by 50 % during flowering (August-September) and during fruiting (September-November) phases. The senescence phase (October-November) was characterised by 79, 58, and 18 % decrease of P N, chlorophyll content, and leaf area (LA), respectively, from the maximum values. The time span from seedling emergence to the end of fruiting phase was 202 d. The total plant biomass was 1.58±0.05 g of which 81 % was aboveground plant portion. The total dry mass relative growth rate averaged over the assimilation period was 0.0804±0.0002 kg kg-1 d-1, and it was correlated to both the net assimilation rate (NAR) and the leaf area ratio (LAR).

In situ detection of programmed cell death in Nicotiana tabacum leaves during senescence

Leaf senescence is a highly regulated developmental process, during which cell constituents are dismantled in an ordered progression. The final death phase of senescence is a type of programmed cell death (PCD). We showed DNA fragmentation characteristic for PCD by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay not only in senescing leaves but also in young, still developing tobacco leaves.

Effects of phytoplankton physiology on export flux

Estimates of phytoplankton sticking efficiency (α) were made in the laboratory within a 1500 l annular flume meso- cosm over the initiation, maintenance and senescence phases of a bloom of the diatom Thalassiosira pseudonana. The spatially weighted mean turbulence kinetic energy dissipation rate in the annular flume was comparable to values found at the ocean's sur- face on a calm day. The α of T. pseudonana varied as a result of physiological state, and ranged from 0 ± 0.08 during the bloom ini- tiation to 0.26 and 0.73 ± 0.16, respectively, during bloom mainte- nance and senescence phases. During the periods of high α, physiological changes included (1) diminished phytoplankton photosynthetic quantum efficiency, (2) an increase in super-oxide dismutase protein expression, reflecting oxidative stress, and (3) the induction of a biochemical cascade initiating autocatalytic pro- grammed cell death. Additionally, during the period of high physi- ological stress on the diatoms, there was an increase in the pres- ence of transparent exopolymer particles and bacteria. Applying a variable α to a 1-dimensional export flux model shows that carbon export can be increased by at least 2-fold compared to simulations assuming a typically modeled value of α = 1 (100% sticking effi- ciency). The model using a physiologically dependent α had a low initial sticking efficiency that allowed a significant increase in the critical concentration of algal cells. Such an increase in the number of cells during bloom initiation followed by an increase in α during the maintenance and senescence phases resulted in enhanced export fluxes during the latter, 'stickier', stages of the bloom.

Characterization of telomere maintenance and chromosomal integrity in human fibroblasts and keratinocytes

In spite of the significant progress in cancer biology and modern radiation biology in the last decades, it is still an open question how exactly different human cell types respond to ionizing radiation. The majority of studies have been done on two types of human cells: skin fibroblasts and peripheral blood lymphocytes. The main reason for this is the relatively easy access to these cells in individuals. Other cell types, such as normal epithelial cells, have been used on a much smaller scale and consequently there is relatively little data on how normal epithelial cells respond to ionizing radiation in comparison with fibroblasts. The study of epithelial cells is highly relevant for the elucidation of radiation-induced carcinogenesis as the majority of human solid cancers will develop from epithelial cells. The work presented here is the characterization of karyotypes and telomere loss in non-irradiated fibroblast and keratinocyte populations from the same donor during the different stages of proliferation in vitro and results for the response of fibroblasts to five doses of γ-radiation spanning the range 10-2000 mGy with respect to cell proliferation and kinetics of γH2AX foci. An increase in the incidence of telomere loss with doublings in vitro was noted; however, it followed different kinetics in the two cell types. An increase in clonal and de novo chromosomal aberrations was observed in both fibroblasts and keratinocytes as proliferation progressed into senescent phases. Clonal emergence from the second senescent plateau characterized by progressive instability of the genome and different kinetics of telomere maintenance, was observed in keratinocytes. Fibroblasts and keratinocytes showed different kinetics of γH2AX foci, with apparent higher initial induction in fibroblasts, but faster disappearance of the induced foci. The radiosensitivity and the transmission of radiation-induced damage could largely differ according to the cell type status at irradiation (fibroblasts/ keratinocytes, young/ senescent) and their role in the long-term occurrence of radiation-induced tumours needs to be characterized.

Generation and Characterization of Novel Monoclonal Antibodies Against Murine and Human TARSH Proteins

TARSH/Abi3bp was originally isolated as a novel target of NESH-SH3 by a two-hybrid yeast system. We have already identified murine TARSH (mTARSH) as a cellular senescence-related gene because of its robust induction in the early phase of mouse embryonic fibroblast cellular senescence. We have also revealed that the expression of this gene was dramatically reduced in human lung cancer cell lines and primary lung tumor, while it was predominantly expressed in normal conditions. This evidence suggests that TARSH is involved in both stress-induced senescence and prevention of cancer development; however, little is known about its molecular mechanisms. To reveal the further physiological function of this molecule, we established rat anti-TARSH monoclonal antibodies (MAb). Recombinant His-tagged partial mouse TARSH protein was expressed in Escherichia coli, affinity purified and used as an antigen to immunize rats. Hybridomas were screened by enzyme-linked immunosorbent assay, and we generated six stable hybridoma cell lines that produced antibody against murine TARSH protein, including three clones that represented cross-reactivity with human TARSH. We determined their isotypes and further examined capabilities or limitations in immunoblotting, immunoprecipitation, and immunofluorescence microscopy, realizing the most suitable antibody for each application. These MAbs should therefore be very useful tools for the study of TARSH expression and for following biological function in cellular senescence and tumor suppression.

Human Bone Marrow-Derived Mesenchymal Stem Cells Do Not Undergo Transformation after Long-Term In Vitro Culture and Do Not Exhibit Telomere Maintenance Mechanisms.

Mesenchymal sem cells (MSCs) are multipotent progenitors with the ability to differentiate along multiple cell lineages and are today considered a useful tool for cell therapy and tissue engineering approaches. Concerns that adult human MSCs may undergo malignant transformation have been recently raised. In fact, human adipose tissue-derived MSCs have been shown to spontaneously transform after long-term in vitro culture. Aim of this study was to investigate the susceptibility to transformation of human bone marrow (BM)-derived MSCs at different time points of in vitro culture. MSCs were isolated from BM of 10 healthy donors and propagated continuously in vitro until reaching a senescence phase or passage (P) 25. MSCs in the senescence phase were closely monitored for 8–12 weeks, to look for the appearance of a crisis phase. MSCs were characterized by morphology, differentiation capacity and immunophenotype at different time-points in culture. The genetic characterization of MSCs was investigated through array comparative genomic hybridization (array-CGH), classical cytogenetics and subtelomeric FISH analysis both before and after prolonged in vitro culture. MSCs were tested for the expression of telomerase activity (TA), hTERT transcripts and alternative mechanisms of telomere lengthening (ALT) at different time-points in culture. MSCs from 5 donors were also analyzed for telomere length at P3 and P15. p53 gene status was also analyzed in MSCs from donors #1 and #2 that rapidly reached senescence in culture. A huge variability between donors was noted in terms of proliferative capacity and in vitro life-span of MSCs. All MSCs maintained the typical spindle-shaped morphology, phenotype and ability to differentiate into osteoblasts and adipocytes throughout the culture period. All MSCs displayed a progressive decrease in the proliferative capacity until reaching senescence, not followed by any further growth. Array-CGH, karyotype and subtelomeric FISH analyses demonstrated that MSCs expanded in vitro did not show chromosomal rearrangements, also after long term culture. TA was not evidenced in the samples tested, including a post-senescence culture. hTERT transcripts (full-length and the additional splice variants a−, b−, a−b−) were found not to be expressed in any of the examined cultures. Telomeres shortened during the culture period. ALT were not evidenced in the MSCs tested, as indicated by the lack of ALT-associated promyelocytic leukemia bodies. Direct DNA sequencing of exons 2–11 in pre-senescence cultures from donors #1 and #2 did not evidence the presence of mutation in the p53 gene. Human BM-derived MSCs do not display an aptitude for spontaneous transformation and can be safely expanded in vitro without any sign of immortalization or development of chromosomal abnormalities. Our results provide support to the concept that the biological properties of human BM-derived MSCs after ex vivo expansion remain suitable for use in cell-therapy approaches; however, it is strongly recommended that phenotype, functional and genetic characteristics of MSCs after in vitro culture and before in vivo infusion are tested, to further guarantee safety for the patient.

Human Bone Marrow–Derived Mesenchymal Stem Cells Do Not Undergo Transformation after Long-termIn vitroCulture and Do Not Exhibit Telomere Maintenance Mechanisms

Significant improvement in the understanding of mesenchymal stem cell (MSC) biology has opened the way to their clinical use. However, concerns regarding the possibility that MSCs undergo malignant transformation have been raised. We investigated the susceptibility to transformation of human bone marrow (BM)-derived MSCs at different in vitro culture time points. MSCs were isolated from BM of 10 healthy donors and propagated in vitro until reaching either senescence or passage (P) 25. MSCs in the senescence phase were closely monitored for 8 to 12 weeks before interrupting the cultures. The genetic characterization of MSCs was investigated through array-comparative genomic hybridization (array-CGH), conventional karyotyping, and subtelomeric fluorescent in situ hybridization analysis both before and after prolonged culture. MSCs were tested for the expression of telomerase activity, human telomerase reverse transcriptase (hTERT) transcripts, and alternative lengthening of telomere (ALT) mechanism at different passages. A huge variability in terms of proliferative capacity and MSCs life span was noted between donors. In eight of 10 donors, MSCs displayed a progressive decrease in proliferative capacity until reaching senescence. In the remaining two MSC samples, the cultures were interrupted at P25 to pursue data analysis. Array-CGH and cytogenetic analyses showed that MSCs expanded in vitro did not show chromosomal abnormalities. Telomerase activity and hTERT transcripts were not expressed in any of the examined cultures and telomeres shortened during the culture period. ALT was not evidenced in the MSCs tested. BM-derived MSCs can be safely expanded in vitro and are not susceptible to malignant transformation, thus rendering these cells suitable for cell therapy approaches.

Assessment of status and biomass of Swertia angustifolia : a high value Himalayan medicinal plant

Studies on population assessment and biomass variation in selected populations of Swertia angustifolia were undertaken in west Himalaya. Low population density across the surveyed populations indicates poor availability of the species in study area. Species showed random distribution and higher frequency of occurrence in most of the population, which is the indicator of better potential of the species in these sites. Density was positively correlated with biomass. The biomass showed peak value in senescence phase and thus has positive consequences of harvesting for the survival of the species. Key words: Endangered, conservation, Himalaya, Swertia angustifolia, medicinal plant.

Accumulation of Bioactive Compounds during Growth and Development of Mango Ginger (Curcuma amada Roxb.) Rhizomes

Accumulation of bioactive compounds and storage components during developmental stages of mango ginger ( Curcuma amada Roxb.) rhizome was investigated from 60 to 240 days, as a function of physiological maturity. Four distinct developmental phases were defined, namely, vegetative phase (up to 60 days from planting), initiation and development phase (60-150 days), maturation phase (150-180 days), and senescence phase (180 days). Difurocumenonol, a bioactive terpenoid compound and phenolics were identified as biomarkers, to determine the optimum physiological maturity to harvest mango ginger rhizome. Accumulation of phenolics was observed in newly initiated rhizomes (after 60 days from planting). The phenolic content was high in mango ginger pulp compared to its juice. Newly initiated rhizome contained no difurocumenonol, and it was observed after 120 days after planting. Peak accumulation of phenolics, difurocumenonol, and total protein were noticed in 180 day old rhizome. Accordingly, the abundance of these components on 180 days was set as an optimum maturity standard for harvest of mango ginger rhizome, compared with a conventional harvest period that ranges from 200 to 240 days.

The immune system in extreme longevity

Recent observations indicate that immunosenescence is not accompanied by an unavoidable and progressive deterioration of the immune function, but is rather the result of a remodeling where some functions are reduced, others remain unchanged or even increased. In addition, it appears that the ancestral/innate compartment of the immune system is relatively preserved during aging in comparison to the more recent and sophisticated adaptive compartment that exhibit more profound modifications. The T-cell branch displays an age-dependent decline of the absolute number of total T-cells (CD3+), involving both CD4+ and CD8+ subsets, accompanied by an increase of NK cells with well-preserved cytotoxic function and by a reduction of B-cells. One of the main characteristics of the immune system during aging is a progressive, age-dependent decline of the virgin T-cells (CD95−), which is particularly profound at the level of the CD8+ subpopulation of the oldest old subjects. The progressive exhaustion of this important T-cell subpopulation dedicated primarily to the defense against new antigenic challenges (viral, neoplastic, bacterial ones), could be a consequence of both the thymic involution and the lifelong chronic antigenic stimulation. The immune function of the elderly, is therefore weakened by the exhaustion of CD95− virgin cells that are replaced by large clonal expansions of CD28− T-cells. The origin of CD28− cells has not been completely clarified yet, but it is assumed that they represent cells in the phase of replicative senescence characterized by shortening telomers and reduced proliferative capacity. A major characteristic of the immune system during aging is the up-regulation of the inflammatory responses which appears to be detrimental for longevity. In this regard, we have recently observed a progressive age-dependent increase of type 1(IL-2, IFN-γ, TNF-α) and type 2 (IL-4, IL-6, IL-10) positive CD8+ T-cells; in particular, type 1 cytokine-positive cells significantly increased, with age, in all CD8+ subsets particularly among effector/cytotoxic and memory cells. A major force able to drive a chronic pro-inflammatory state during aging may be represented by persistent viral infections by EBV and CMV. Therefore, we have determined the frequency and the absolute number of viral antigen-specific CD8+ T-cells in subjects older than 85 years, who were serologically positive for CMV or EBV. In the majority of these subjects we detected the presence of T lymphocytes positive for epitopes of CMV or EBV. In all subjects the absolute number of CMV-positive CD8+ cells outnumbered that of EBV-positive ones. In addition, the majority of CMV+ T cells were included within the CD28− subpopulation, while EBV+ T cells belonged mainly to the CD28+ subset. These data indicate that the chronic antigenic stimulation induced by persistent viral infections during aging bring about important modifications among CD8+ subsets, which are particularly evident in the presence of CMV persistence. The age-dependent expansions of CD8+CD28− T-cells, mostly positive for pro-inflammatory cytokines and including the majority of CMV-epitope-specific cells, underlines the importance of chronic antigenic stimulation in the pathogenesis of the main immunological alterations of aging and may favour the appearance of several pathologies (arteriosclerosis, dementia, osteoporosis, cancer) all of which share an inflammatory pathogenesis.

Neosis - A Parasexual Somatic Reduction Division in Cancer

KEYWORDS Origin and growth of cancers; polyploid giant cells; Raju cells; DNA damage ABSTRACT We have recently reported a novel type of cell division involved in the origin and growth of cancers. Termed neosis, as opposed to mitosis and meiosis, this type of cell division occurs only in senescent polyploid giant cells and not in normal diploid cells. Up to ~10% of tumor cells in vitro and in vivo, are polyploid giant cells and so far there is no explanation for their role in cancer. These resemble senescent cells, which are thought to play a tumor suppressor role. We have shown that such cells have the potential to undergo neosis, a parasexual, somatic reduction division characterized by karyokinesis via nuclear budding, followed by asymmetric cytokinesis, (often) giving rise to aneuploid daughter cells termed Raju cells, which are the progenitors of tumor cells. These Tumor Initiating Raju Cells (TIRCs) are unique in that they transiently display stem cell properties, have inherited genomic instability, differentiate into tumor cells and have extended, but, limited mitotic life span (*MLS). At the end of their extended MLS (EMLS), the tumor cells repeat the cycle of senescence, neosis and production of Tumor Rejuvenating Raju Cells (TRRCs), which repeat the same cycle of events several times through the life of tumor in a progressively non-synchronous fashion. When tumor cells are subjected to chemotherapy or radiotherapy, they undergo premature senescence; but, some cells escape senescence via S/T-neosis and yield TRRCs, whose mitotic progenies may be resistant to genotoxins. Although neosis-like events have appeared in the literature sporadically for more than a century under different names, they were neglected since the significance of such events was not known till now. The data on neosis questions the basic tenets of the current concepts of cancer, i.e., (1) Cancer arises via mitosis, (2) Cancer cells are immortal and (3) Cancer cell continuity is due to the unlimited asymmetric mitotic potential of mutant stem cells or Cancer Stem Cells (CSCs). Neosis paradigm supports the concept that (1) Cancer arises via neosis, (2) cancer cells are not immortal, but undergo repeated senescent phases and that (3) tumor cell lineage continuity is due to escape from senescent phase via neosis, since tumor cells carry mutant or epimutant genes in the senescent checkpoint pathway. Thus, genesis and regenesis of Raju cells via repetitive neotic divisions is responsible for the origin and continuous growth of different tumor types. This concept accommodates epigenetic expression of telomerase, meiotic genes, multidrug resistance genes and stem cell-specific genes in tumor cells and also explains the role of senescent cells found in tumor tissues. Thus, neosis appears to involve global epigenetic modulation (EM), in order to fine-tune the chromatin with DNA damage important for producing reproductively viable genomes from the non-viable polyploid genome, before being discarded by post-neotic death of neosis mother cells (NMCs).

Kinetin regulates plant growth and biochemical changes during maturation and senescence of leaves, flowers, and pods of Cajanus cajan L.

Aspects of plant growth such as height, branch number, leaf number, leaf area, pod area, 100-seed mass, etc., were correlated with biochemical changes such as contents of chlorophyll (Chl), proteins, DNA, and RNA, and protease activity during development and senescent phases in leaves, flowers, and pods of Cajanus cajan L. cv. UPAS-120 after treatments with kinetin (Kn). A significant increase was noticed in branch number, leaf number, leaf area, and seed mass while other growth processes registered a small increase after Kn application. Effectiveness of 5 µM Kn was also noticed in minimizing the loss of Chls, proteins, and nucleic acids as well as reducing the protease activity during maturity and senescence. Chl a/b ratio maintained a high value up to 30-d followed by a decline in leaves while flowers registered much lower ratio at 20-d-age. Pods were unique in having relatively lower ratio of Chl a/b in comparison to leaves.

Analysis of time-series MODIS 250 m vegetation index data for crop classification in the U.S. Central Great Plains

The global environmental change research community requires improved and up-to-date land use/land cover (LULC) datasets at regional to global scales to support a variety of science and policy applications. Considerable strides have been made to improve large-area LULC datasets, but little emphasis has been placed on thematically detailed crop mapping, despite the considerable influence of management activities in the cropland sector on various environmental processes and the economy. Time-series MODIS 250 m Vegetation Index (VI) datasets hold considerable promise for large-area crop mapping in an agriculturally intensive region such as the U.S. Central Great Plains, given their global coverage, intermediate spatial resolution, high temporal resolution (16-day composite period), and cost-free status. However, the specific spectral–temporal information contained in these data has yet to be thoroughly explored and their applicability for large-area crop-related LULC classification is relatively unknown. The objective of this research was to investigate the general applicability of the time-series MODIS 250 m Enhanced Vegetation Index (EVI) and Normalized Difference Vegetation Index (NDVI) datasets for crop-related LULC classification in this region. A combination of graphical and statistical analyses were performed on a 12-month time-series of MODIS EVI and NDVI data from more than 2000 cropped field sites across the U.S. state of Kansas. Both MODIS VI datasets were found to have sufficient spatial, spectral, and temporal resolutions to detect unique multi-temporal signatures for each of the region's major crop types (alfalfa, corn, sorghum, soybeans, and winter wheat) and management practices (double crop, fallow, and irrigation). Each crop's multi-temporal VI signature was consistent with its general phenological characteristics and most crop classes were spectrally separable at some point during the growing season. Regional intra-class VI signature variations were found for some crops across Kansas that reflected the state's climate and planting time differences. The multi-temporal EVI and NDVI data tracked similar seasonal responses for all crops and were highly correlated across the growing season. However, differences between EVI and NDVI responses were most pronounced during the senescence phase of the growing season.

Ethylene control of seed coat development in low and high sterile semidwarf indica rice cultivars

Although basally positioned inferior spikelets of rice panicles emerge late from the flag leaf enclosure (boot), they mature early which precludes adequate grain filling. It is assumed that extended exposure to ethylene inside the boot restricts assimilate partitioning to the endosperm in basal spikelets by affecting the functions of seed coat. In the present study, ethylene concentration inside the boot was measured in two high yielding rice cultivars differing in percentage of spikelet sterility. To manipulate the concentration/action of ethylene, silver nitrate, aminoethoxyvinyl glycine and 2-chloroethylphosphonic acid were injected into the boot. The effect of these chemicals on the concentration of photosynthetic pigments, lipid peroxidation and peroxidase activity of the seed coat and lemma and palea were measured to monitor development. Ethylene reduced development during the juvenile phase but accelerated degradation of the photosynthetic tissues of the spikelets in the senescent phase. Boot ethylene correlated positively with number of barren spikelets in the panicle and negatively with concentration of photosynthetic pigments of the seed coat of inferior spikelets. The concentration of ethylene was higher in the high sterile cultivar Mahalaxmi than that of the low sterile Mahanadi. Inhibition of ethylene action or synthesis improved grain filling. The chemicals were most effective on the inferior spikelets. It was concluded that ethylene retarded seed coat development during the prestorage phase and reduced grain filling of basal spikelets.

Roles for redox regulation in leaf senescence of pea plants grown on different sources of nitrogen nutrition.

Leaf senescence and associated changes in redox components were monitored in commercial pea (Pisum sativum L. cv. Phoenix) plants grown under different nitrogen regimes for 12 weeks until both nodules and leaves had fully senesced. One group of plants was inoculated with Rhizobium leguminosarum and grown with nutrient solution without nitrogen. A second group was not inoculated and these were grown on complete nutrient solution containing nitrogen. Leaf senescence was evident at 11 weeks in both sets of plants as determined by decreases in leaf chlorophyll and protein. However, a marked decrease in photosynthesis was observed in nodulated plants at 9 weeks. Losses in the leaf ascorbate pool preceded leaf senescence, but leaf glutathione decreased only during the senescence phase. Large decreases in dehydroascorbate reductase and catalase activities were observed after 9 weeks, but the activities of other antioxidant enzymes remained high even at 11 weeks. The extent of lipid peroxidation, the number of protein carbonyl groups and the level of H(2)O(2) in the leaves of both nitrate-fed and nodulated plants were highest at the later stages of senescence. At 12 weeks, the leaves of nodulated plants had more protein carbonyl groups and greater lipid peroxidation than the nitrate-fed controls. These results demonstrate that the leaves of nodulated plants undergo an earlier inhibition of photosynthesis and suffer enhanced oxidation during the senescence phase than those from nitrate-fed plants.

Apoptosis and Necrosis in Senescent Human Fibroblasts

To study the role of cell death in the aging process, cell death during spontaneous cellular senescence in vitro was examined with normal human fibroblasts. A small subset of the senescent cells showed aberrant morphology such as remarkable nuclear fragmentation or multiple micronuclei, and such cells often showed positive reactions with antibody to phosphorylated pRb. Cells showing caspase activation and binding of Annexin V, which indicate apoptotic change, increased in the senescent phase in flow cytometry analysis. Propidium iodide-positive cells, however, also increased with passaging. The results suggest that both apoptosis and necrosis are involved in cell death of senescent human fibroblasts.

Application of SEBAL approach and MODIS time-series to map vegetation water use patterns in the data scarce Krishna river basin of India

Evapotranspiration (ET) from irrigated land is one of the most useful indicators to explain whether the water is used as "intended". In this study, the Surface Energy Balance Algorithm for Land (SEBAL) was used to compute actual ET from a Landsat7 image of December 29, 2000 for diverse land use in the Krishna Basin in India. SEBAL ETa varies between 0 to 4.7 mm per day over the image and was quantified for identified land use classes. Seasonal/annual comparison of ETa from different land uses requires time series images, processed by SEBAL. In this study, the Landsat-derived snapshot SEBAL ETa result was interpreted using the cropping calendar and time series analysis of MODIS imagery. The wastewater irrigated area in the basin has the highest ETa in the image, partly due to its advanced growth stage compared to groundwater-irrigated rice. Shrub and forests in the senescence phase have similar ETa to vegetable/cash crops, and ETa from grasslands is a low 0.8 mm per day after the end of the monsoon. The results indicate that wastewater irrigation of fodder and rice is sufficient to meet crop water demand but there appears to be deficit irrigation of rice using groundwater.

Offshore distribution patterns of the cyanobacterium Trichodesmium erythraeum ehrenberg and associated phyto- and bacterioplankton in the southern Atlantic coast (Paraná, Brazil)

Studies were carried out on Thrichodesmium erythraeum occurring on the inner shelf in the state of Paraná, Brazil. Temperature, salinity, rainfall, wind velocity, total bacteria, bacterial biomass, chlorophyll-a, phytoplankton, Anabaena sp., Merismopedia sp. and T. erythraeum densities were measured in surface water. Centric and pennate diatoms, Anabaena sp. and Merismopedia sp. were most abundant at 15 m isobath, while dinoflagellate abundance was relatively constant among stations. Similarly, total bacterial densities were relatively homogeneous throughout the sampling area, suggesting that blooms of T. erythraeum were not yet in the senescent phase. Results showed that T. erythraeum was capable of surviving in relatively inhospitable environmental conditions, due to its ability to fix nitrogen and to photosynthesis at high light intensities.

Damage of PS II during senescence of Spirodela polyrrhiza explants under long-day conditions and its prevention by 6-benzyladenine

The chlorophyll a (Chl a) fluorescence technique was applied to investigate damage of PS II during senescence of excised half-fronds in Spirodela polyrrhiza P143. The green explants showed a typical Chl a fluorescence transient, OJIP. After cultivation of explants under long-day conditions for 8 days, all the J, I, and P steps disappeared, but a clear K band, an indication of senescence, was observed. JIP-test showed that at this time point, the photosynthetic performance index (PI) dropped to zero and the active reaction center (RC) per leaf cross-section (RC/CS) declined to 18%. As the oxygen-evolving complex (OEC) and the chlorophyll content all remained above 42%, it is proposed that the decline in RC contributes more to the appearance of the K band. Supplementation of 6-benzyladenine (6-BA) into the medium at the beginning of cultivation caused dramatic increase in PI, OEC, RC/CS, and chlorophyll content, and at any time before the 8th day reversed the senescence process of the explants. When 6-BA was added after 8 days of cultivation, the PI did not increase anymore, RC/CS and OEC were maintained at 22% and above 40%, respectively, and chlorophyll content decreased continuously further. These data support a view that the decline in RC is crucial for initiation of the irreversible senescence phase of explants cultivated under long-day conditions.