Abundance and seasonal distribution of Penaeus monodon postlarvae in the Sundarbans mangrove,Bangladesh

We record the decline of Penaeus monodon postlarvae (PL) in five rivers of the world's largest mangrove ecosystem, the Sundarbans, from 1992 to 1999. Shrimp aquaculture in the coastal belt of Bangladesh is dependent on the collection of P. monodon PL from the coastal rivers, and horizontal expansion of shrimp farming has resulted in a severe decline of this wild resource in the Sundarbans. Abundance of P. monodon PL was significantly (P<0.05) reduced in 1999 compared to the previous two-year studies (1992 and 1995) in the rivers. About 12–551 postlarvae of other shrimps, 5–152 finfish postlarvae and 26–1636 other macro-zooplankters are wasted during the collection of a single P. monodon PL. Water temperature and salinity of the river systems are correlated with P. monodon PL abundance. Besides P. monodon PL, inshore fishery of Hilsa ilisha, catfishes and Scylla serrata are also overexploited. The management practices and conservation of fishery resources of Sundarbans are reviewed in the context of its world heritage status.     

Ring width and vessel features of the mangrove Excoecaria agallocha L. depend on salinity in the Sundarbans,Bangladesh

The Bangladesh Sundarbans is the largest continuous mangrove in the world that providing crucial environmental services, particularly related to coastal protection and livelihoods of millions of people. However, anthropogenic disturbances, diseases infestation and environmental changes including sea level rise (SLR) and fresh-water flux into the delta are threatening the Sundarbans and other mangrove ecosystems worldwide. Protection of mangrove ecosystems requires knowledge on factors that mainly drive growth and vitality of tree species to evaluate which consequences can be expected from, mainly hydrology-related, environmental changes. In this study, we assessed the nature and periodicity of tree rings in Excoecaria agallocha, a wide spread mangrove species in the Bangladesh Sundarbans. We also analysed the influence of climatic factors, such as precipitation, temperature and vapor pressure deficit (VPD), and river discharge, as a proxy of salinity on ring width (RW) and vessel features, such as mean vessel area (MVA) and mean vessel density (MVD). E. agallocha forms distinct tree-ring boundary that characterized by a narrow (2–4 cells wide) band of radially flattened fibres. The RW as well as the MVA and MVD are crossdatable. The RW is mainly driven by salinity which is influenced by freshwater inputs through precipitation during monsoon along with river discharge January to April. The MVA and MVD responded to similar seasons and months as RW, but mostly with opposite signs in MVD. The results suggest that fresh water inputs through precipitation and river discharge positively influence the radial growth of E. agallocha in the Sundarbans. The RW and vessel features can be used as proxies to explore the growth dynamics of this species, especially in relation to global environmental changes.     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.     

Distribution,Abundance and Life Cycles of Oligochaeta from the Marine Hygropsammal with Special Reference to the Phallodrilinae (Tubificidae)

Tubificid and enchytraeid oligochaetes are common members of the interstitial fauna of sandy beaches. Their abundance dynamics, life cycles and distribution patterns were investigated at two beaches on the western Baltic Sea and at a North Sea beach (Isle of Sylt). Populations of 115,000 ind./m² were found at protected Baltic beaches. Reproduction of the tubificids, Phallodrilus monospermathecus and Spiridion insigne takes place within a well defined breeding period once a year. The market horizontal and vertical distribution patterns of various tubificid and enchytraeid species are elucidated by preference reactions to several physiographic parameters, such as oxygen and water content of the sediment, and salinity.     

Chemotaxis of Fungal Zoospores,with Special Reference to Aphanomyces cochlioides

Zoospores of phytopathogenic fungi accumulate at the potential infection sites of host roots by chemotaxis. The aggregated spores then adhere, encyst, germinate, and finally penetrate into the root tissues to initiate infection. Some of the host-specific attractants have already been identified. The host-specific attractants also induce cell differentiation of certain zoospores under laboratory conditions. This indicates that a signal released from the roots of the host plant guides the pest propagules for orientation and prepares them for establishing a host-pathogen relationship by necessary physiological changes. Some non-host plant secondary metabolites were found to markedly regulate behavior and viability of zoospores, suggesting that non-host compounds may also play a role in protecting the non-host plants from the attack of zoosporic fungi. We hypothesized that zoospores perceive the host signal(s) by specific G-protein-coupled receptors and translate it into responses by way of the phosphoinositide-Ca²⁺ signaling cascade. The details of the signal transduction mechanism in fungal zoospores are yet to be discovered. In this report, we review the signaling and communications between phytopathogenic fungal zoospores and host and non-host plants with special reference to Aphanomyces cochlioides.     

The Tridimensional Morphology of Rice Embryo Development with Special Reference to the Scutellum and the Coleoptile

Using scanning electron microscopy and semi-thin plastic sections, the pattern of development of the rice ( Oryza sativa L. ) embryo from 2 days after pollination (DAP) to maturity was followed. ( 1 ) At 2 DAP, the young embryo was observed to consist of an embryo proper, a hypoblast and a suspensor. The trum-pet-shaped hypoblast was a transitional region situated between the suspensor and the embryo proper. To label the hypoblast as suspensor is incorrect. During this time, dorsiventrality was established, but a radicle was not yet differentiated. Therefore it is still referred to as a proembryo. (2) 3 ~ 5 DAP, the embryo underwent definite morphological and anatomical changes. In the young embryo at 3 DAP the scutellum and colcoptile appeared simultaneously directly from the proembryo. The coleoptile did not originate from the scutellmn. During these foremost 3 days, the coleoptile primordium underwent a special kind of morphological change and formed a young coleeptile having the shape of an inverted hollow cone. This process revealed the true mechanism of c61eeptile formation. Anatomical observation indicated that the embryo at 3 DAP began to differentiate procambium, ground meristem and root cap. At 4 DAP a dome-like growth cone and protoderm of radicle appeared. Then the shoot-root axis became established. At 5 DAP the plumule, hypocotyl and radicle were formed. (3) It was shown that the embryo of rice actually has two cotyledons: the scutellum (a part of the embryonic envelope) and the coleeptile (The scutellum being the lateral cotyledon, a part of outside cotyledon, and the coleoptile the apical cotyledon--the coleoptile may be considered to be a modified form of a cotyledon). This kind of structural arrangemem can be referred to as dimorphic cotyledon.     

Measurements of some Groups of Microbial Populations with Special Reference to Denitrification in Water and Sediments of Fish Farming Ponds under Mono- and Polyculture Systems

The spatial and seasonal distribution of some groups of bacteria as well as the rates of denitrification (natural and potential) have been investigated in water and sediments of four fish farming ponds under monoculture, traditional and polyculture systems in India. Marked differences in the monthly means of bacteria were found to exist in these fish ponds depending upon their trophic statuses. The seasonal changes of bacteria are discussed in relation to the variation of environmental factors.     

Correlation of Size of Dye Particle and Density of Substrate, with Special Reference to Mucin Staining

Phase contrast observations indicate that most mucins, and the perilacunar capsules of cartilage matrix, are of low refractive index and hence probably of low density. Mast cell granules and cell nuclei are somewhat more dense, but are rather variable. Cytoplasmic chromidial substance, nucleoli and the interstitial matrix of cartilage are of high density. The selectivity of alcian blue, dialysed iron, mucicarmine, mucihaematein and aldehyde fuchsin depends partly on these dyes being of large particle size (as shown by dialysis experiments); they are able to penetrate into and stain basophilic structures of low density (high “permeability” or “porosity”) but not into denser structures. Best's carmine also consists of large particles, and probably stains only those mucins which are of low density and which contain some strongly basic (acidophilic) groups.     

Biodiversity Characterization in Nubra Valley, Ladakh with Special Reference to Plant Resource Conservation and Bioprospecting

Trans-Himalayan mountains, owing to harsh climatic conditions and a short growing season support low vegetation cover (<20%), yet it is known to harbour a unique assemblage of flora and fauna which have not been systematically inventoried and documented so far. This paper deals with spatial and non-spatial information on landscape units, vegetation characteristics and plant species diversity of Nubra Valley in Ladakh, India. Based on digital – visual (on screen) interpretation of remote sensing data coupled with knowledge-based classification we delineated 19 cover classes (11 vegetation types and 8 non-vegetation categories). The vascular plants (angiosperms and gymnosperms) were systematically collected using stratified random sampling of different landscape/vegetation to characterize plant communities and assess the distribution patterns of species. The study reveals that nearly 78–80% of plant species in Nubra are restricted to the valley bottoms. In all, 414 species of vascular plants were recorded from the study area. These belongs to 56 families and 202 genera. Of these, 102 species were reported to be used in traditional system of medicine by Amchis over 80 species are largely associated with cultivated fields and human habitation. As many as 49 species were cultivated which include several varieties of crop plants especially those of barley and buckwheat. Aspects of bioprospecting and conservation of valuable species have been discussed.     

Optimal Reproductive Strategy of Plants, with Special Reference to the Modes of Reproductive Resource Allocation

Abstract A growth model for reproductive energy allocation pattern and schedule is proposed. Assumptions are as follows: (1) the assimilation rate for an individual is given by a logistic curve of vegetative dry weight; (2) size variability is expressed by the parameter W of the logistic curve (asymptotic value of vegetative dry weight); (3) a plant controls allocation of the assimilate to vegetative and reproductive structures so as to maximize the reproductive energy investment at the end of the growth period. The models were analyzed in comparison with field and experimental observations and gave reasonable explanations for the reproductive allocation pattern of individuals which reflects ecological preferences and life history characteristics, such as environmental conditions of habitats (stable or changing), length of life span (annual, biennial or perennial) and growth form (erectophile or planophile). Decreasing RA (reproductive allocation) with individual size and delayed switchover time from vegetative to reproductive growth were found in plants which occur in stable environments and have a more or less fixed growth period; in those which occur in changing environments where growth period depends on individual size, RAs that remain constant or increase with variations in individual size and early switchover time were detected. Most perennials conform to the former case, but annuals and biennials conform to the latter case. Under extremely overcrowded conditions, planophiles, which are much more subject to crowding effect than erectophiles, tend to have increasing RA with increasing size, while erectophiles tend to have almost constant RA irrespective of size. These trends are discussed in the light of the life history characteristics and ecological distribution of plant species studied.     

Distribution of Catecholamines in the Ventral Mesencephalon of Human Brain, with Special Reference to Parkinson's Disease

Abstract: The high levels of dopamine (DA) detected in the ventral tegmental area (VTA), as well as in the substantia nigra (SN) of human brain, suggest the presence of DA cells in these areas. This favors the possible existence of a mesocortico-limbic system besides the mesostriatal pathway. In Parkinson's disease both DA systems seem to be deficient.     

Cytochemical Nature and Fine Structure of the Gregarine Zeylanocystis burti Dissanaike, with Special Reference to Microfilaments, Microtubules and Movement

SYNOPSIS. The mature trophozoite of the acephaline gregarine Zeylanocystis burti Dissanaike, parasitic in the seminal vesicles of the Sri Lankan earthworm Pheretima peguana Rosa, was studied by cytochemical methods and by electron microscopy. Some observations were also made on gametocysts and oocysts. The trophozoite has a peculiar saucer shape, unlike other monocystid gregarines, and has marginal papillae with cytoplasmic hairs. Its fine structure conforms broadly to that of other gregarines, but differs with respect to its fibrillar organization and in some details of cytoplasmic organelle structure. The pellicle is composed of 2 parallel unit membranes elevated into a number of stumpy epicytary folds, more or less evenly distributed on both surfaces of the gregarine. Some of these are associated with adjacent accessory cells and may have a nutritive role. Bundles of fine microfilaments (5–6 nm) were detected both in the ectoplasm and deep in the endoplasm; these are possibly the main contractile elements (“myonemes”) involved in movement. Microtubules are larger (22–24 nm) and are found predominantly in papillae and cytoplasmic hairs, but extend also in small bundles beneath the pellicle—they appear to be more skeletal in nature. The significance of these findings is discussed in the light of recent work on the roles of microfilaments and microtubules in nonmuscle cells. Mitochondria are located superficially and have a complex organization. The endoplasmic reticulum is poorly developed, but ribosomes are abundant. Golgi lamellae-like membranes and vesicles akin to lysosomes were observed. Typical paraglycogen granules were found together with blobs of lipid and glycogen. The nucleus had a wrinkled envelope, a homogeneous matrix, and a spherical nucleolus. A variety of staining reactions and cytochemical tests were carried out. The distribution of lipids, polysaccharides, nucleic acids, calcium, and melanin were studied. Succinate dehydrogenase was detected in mitochondria, thiamine pyrophosphatase in Golgi bodies, and acid phosphatase in lysosomes. Golgi structures were found to be chemically very complex. Gametocysts and oocysts were associated with extraneous cells which probably contribute to the formation of their walls. The gametocyst wall is thin and consists of 2 membranes of the unit type. The oocyst wall is thicker and composed of 2 chemically different layers. Telolysosomes were seen in the disorganized residual cytoplasm within gametocysts.