Loss of viability during freeze-thaw of intact and adherent human embryonic stem cells with conventional slow-cooling protocols is predominantly due to apoptosis rather than cellular necrosis

10.1007/s11373-005-9051-9Journal of Biomedical Science133433-44

Physiological responses of seagrasses used to identify anthropogenic nutrient inputs

Fertilization experiments have established that seagrass growth in Moreton Bay can be limited by the supply of both N and P. In the present study, morphological and physiological characteristics (canopy height, shoot density, biomass, growth, tissue nutrient content, amino acid concentrations and δN ratios) of Zostera capricorni Aschers, in Moreton Bay, close to and distant from nutrient sources, were compared. Z capricorni at the four sites close to nutrient sources (sewage, septic or prawn-farm effluent, or fiver discharge), had physiological characteristics representative of high nutrient availability and at the five sites distant from nutrient sources had physiological characteristics representative of low nutrient availability. Differences in sediment nutrient concentrations (NH and PO/), seagrass morphology and growth were not related to proximity to nutrient sources. However, the nutrient content of the seagrasses and their amino acid concentrations were consistently higher at sites close to a nutrient source. The amino acids glutamine and asparagine were the most responsive to elevated nutrient availability, and δN values of seagrasses reflected the source of N rather than the nutrient load. These results demonstrate that physiological characteristics of seagrasses can be used to identify the nutrient load and source affecting marine ecosystems

Growth and physiological responses of three seagrass species to elevated sediment nutrients in Moreton Bay, Australia

Seagrasses, marine angiosperms with high rates of primary productivity, are often limited by the supply of nutrients, particularly nitrogen (N) and phosphorus (P). We investigated growth and physiological responses of three seagrass species (Halodule uninervis (Forsk.), Zostera capricorni Aschers and Cymodocea serrulata (r. Br.) Aschers) to elevated sediment N (100 X control) and/or P (10 x control) in adjacent monospecific beds over a 3 month period from spring to early summer. Each species exhibited different growth and biomass responses to both N and P additions. Halodule uninervis growth and biomass increased in response to N and N + P additions, indicative of exclusive N limitation of growth. In contrast, growth and biomass of Z. capricorni increased in response to N + P additions only, indicative of balanced N and P limitation. Cymodocea serrulata growth and biomass were not affected by any of the nutrient additions. Physiological characteristics (amino acid composition, tissue nutrient content, δ N) of all three seagrass species responded to N additions (+ N and N + P). Total amino acid content of seagrass leaves increased by 2 to 4 fold in N additions compared with controls. Concentrations of the N-rich amino acids, glutamine and asparagine, increased by 10-1000 fold in N additions, suggesting that these amino acids may be a metabolic storage for N. Tissue N content of leaves, roots and rhizomes increased and δ N of the leaves decreased in response to N additions. Although seagrass growth and biomass responses to nutrient additions were species specific, metabolic responses were similar for all species. This suggests physiological characteristics of seagrasses are useful for identifying saturating nutrient supply to an environment, but should not be used to determine whether nutrient availability is limiting the seagrass growth rate

Physiological and morphological responses of the seagrass Zostera capricorni Aschers, to light intensity

The responses of the seagrass Zostera capricorni Aschers, to changes in light intensity were examined in flowing seawater aquaria experiments. Plants were grown in six light regimes: full sunlight (100%), 50, 30, 20, 15, and 5% of full light over a 2-month period. Measurements of growth, biomass, pigments, stable isotopes and leaf anatomy were made at the end of the experiment. Plants survived under all light treatments, even below minimum light requirements of related seagrasses. However, the experimental light levels possibly do not correspond to light reaching seagrass leaves under natural conditions. Plants grown under high light conditions (50–100% light) had smaller shoots, higher biomass and productivity, less negative δ13C values, lower leaf nitrogen content, less chlorophyll and more ultraviolet light absorbing pigment than plants grown under low light conditions (<20% light). Photoadaptation by ultraviolet light absorbing pigment(s) was noted, with more variability in ultraviolet light pigments than in chlorophyll levels. Increased CO2 demand and/or increased CO2 recycling in internal gas spaces may account for the less negative δ13C values in high light treatments, indicating less isotopic discrimination in seagrass leaves in high light. A saturation response of growth rates to light intensity was observed, with less substantial growth reductions at lower light intensities than observed in other seagrass shading experiments. Nutrient limitation in high light was inferred by a growth maximum at 50% light level, increased root biomass and lower leaf nitrogen content in high light treatments. Overall, a wide range of morphological and physiological photoadaptive responses not previously reported in Zostera capricorni was observed