Phytochelatins are bioindicators of atmospheric metal exposure via direct foliar uptake in trees near Sudbury, Ontario, Canada.

Plants produce phytochelatins in response to copper and nickel, the primary metal pollutants emitted by the dominant smelting operation in Sudbury. Copper and nickel concentrations in soils decline sharply with distance from this facility, primarily as a result of early smelting practices. Phytochelatin concentrations in Sudbury-area trees, however, do not correlate with metal levels in soils. Rather, phytochelatin production in tree leaves is driven by metals currently released to the atmosphere through the 381 m emissions stack. Phytochelatin concentrations in the foliage of three tree species growing in situ are highest 20-30 km from the stack, correlated with maximum acid-leachable concentrations of deposited copper and nickel. Similar results observed in potted trees placed adjacent to indigenous trees confirm that aerially deposited metals are the source of current metal stress patterns. The addition of peat moss "filters" to potted soils did not alter this response, indicating that direct foliar metal uptake is responsible.

Alterations in cell pigmentation, protein expression, and photosynthetic capacity of the cyanobacterium Oscillatoria tenuis grown under low iron conditions.

To better describe the iron-limited nutrient status of aquatic photosynthetic microorganisms, we examined the effects of iron limitation on pigment content, maximum rates of photosynthetic oxygen evolution, and respiratory oxygen consumption in the filamentous cyanobacterium Oscillatoria tenuis Ag. Within the range of iron (4.2 x 10(-5)-5.1 x 10(-9) M FeCl3), growth rates were not limited by photosynthetic capacity but rather by another, as of yet undetermined, iron-requiring cellular function. We have also investigated membrane proteins that are induced when the cells are grown in low iron medium. Using membrane fractionation techniques we were able to recognize specific proteins localized in the outer membrane and periplasmic space of O. tenuis. The recovery of growth rates at low iron levels occurred in parallel with the induction of these proteins and the production of extracellular siderophores. The additional iron acquired by this high affinity transport system did not reestablish photosynthesis in O. tenuis to the iron-satiated level but did reestablish growth to iron-replete levels. Oscillatoria tenuis appears to invoke an alternate physiology to compensate for iron deficiency.

Growth at Low Temperature Mimics High-Light Acclimation in Chlorella vulgaris.

Structural and functional alterations to the photosynthetic apparatus after growth at low temperature (5[deg]C) were investigated in the green alga Chlorella vulgaris Beijer. Cells grown at 5[deg]C had a 2-fold higher ratio of chlorophyll a/b, 5-fold lower chlorophyll content, and an increased xanthophyll content compared to cells grown at 27[deg]C even though growth irradiance was kept constant at 150 [mu]mol m-2 s-1. Concomitant with the increase in the chlorophyll a/b ratio was a lower abundance of light-harvesting polypeptides in 5[deg]C-grown cells as observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and confirmed by western blotting.The differences in pigment composition were found to be alleviated within 12 h of transferring 5[deg]C-grown cells to 27[deg]C. Furthermore, exposure of 5[deg]C-grown cells to a 30-fold lower growth irradiance (5 [mu]mol m-2 s-1) resulted in pigment content and composition similar to that in cells grown at 27[deg]C and 150 [mu]mol m-2 s-1. Although both cell types exhibited similar measuring-temperature effects on CO2-saturated O2 evolution, 5[deg]C-grown cells exhibited light-saturated rates of O2 evolution that were 2.8-and 3.9-fold higher than 27[deg]C-grown cells measured at 27[deg]C and 5[deg]C, respectively. Steady-state chlorophyll a fluorescence indicated that the yield of photosystem II electron transport of 5[deg]C-grown cells was less temperature sensitive than that of 27[deg]C-grown cells. This appears to be due to an increased capacity to keep the primary, stable quinone electron acceptor of photosystem II (QA) oxidized at low temperature in 5[deg]C- compared with 27[deg]C-grown cells regardless of irradiance. We conclude that Chlorella acclimated to low temperature adjusts its photosynthetic apparatus in response to the excitation pressure on photosystem II and not to the absolute external irradiance. We suggest that the redox state of QA may act as a signal for this photosynthetic acclimation to low temperature in Chlorella.

Cloning and characterization of an Anacystis nidulans R2 superoxide dismutase gene.

The E. coli iron superoxide dismutase gene (sodB) was utilized as a heterologous probe to isolate a superoxide dismutase (sod) gene from Anacystis nidulans R2. Nucleotide sequence analysis revealed a 603 bp open reading frame with deduced amino acid sequence similar to other sod genes and to cyanobacterial superoxide dismutase amino-terminal sequences. Assuming proteolytic cleavage of the initial methionine residue, the molecular mass of the mature A. nidulans R2 sodB polypeptide is 22,000 daltons. Only a single copy of the superoxide dismutase sequence was detected in the A. nidulans R2 genome using Southern hybridization. Northern hybridization analysis indicated a single, monocistronic RNA transcript of approximately 720 bases. Primer extension mapping localized the transcription start site to 46 bases upstream from the initial methionine residue. A single orientation of a 2.1 kb PstI fragment containing the entire sod gene cloned into pUC18 was able to complement E. coli sodAsodB mutants. Complementation of the E. coli mutants was based on the ability of the cells to grow aerobically on minimal glucose medium. Growth curves of the complemented E. coli sodAsodB mutants showed that these cells exhibited levels of resistance to paraquat comparable to that of the wild-type E. coli phenotype.

Prorocentrin: An Extracellular Siderophore Produced by the Marine Dinoflagellate Prorocentrum minimum.

Prorocentrin, a putative iron transport compound, has been extracted from the filtrates of Prorocentrum minimum cultures by XAD-2 resin. Production of prorocentrin can be stimulated by culturing Prorocentrum minimum under conditions of iron deficiency. The iron(III) complex of prorocentrin has an ultraviolet-visible absorption spectrum typical of hydroxamate siderophores.