Thermotolerant guard cell protoplasts of tree tobacco do not require exogenous hormones to survive in culture and are blocked from reentering the cell cycle at the G1-to-S transition

When guard cell protoplasts (GCPs) of tree tobacco [Nicotiana glauca (Graham)] are cultured at 32 degrees C with an auxin (1-napthaleneacetic acid) and a cytokinin (6-benzylaminopurine), they reenter the cell cycle, dedifferentiate, and divide. GCPs cultured similarly but at 38 degrees C and with 0.1 micro M +/- -cis,trans-abscisic acid (ABA) remain differentiated. GCPs cultured at 38 degrees C without ABA dedifferentiate partially but do not divide. Cell survival after 1 week is 70% to 80% under all of these conditions. In this study, we show that GCPs cultured for 12 to 24 h at 38 degrees C accumulate heat shock protein 70 and develop a thermotolerance that, upon transfer of cells to 32 degrees C, enhances cell survival but inhibits cell cycle reentry, dedifferentiation, and division. GCPs dedifferentiating at 32 degrees C require both 1-napthaleneacetic acid and 6-benzylaminopurine to survive, but thermotolerant GCPs cultured at 38 degrees C +/- ABA do not require either hormone for survival. Pulse-labeling experiments using 5-bromo-2-deoxyuridine indicate that culture at 38 degrees C +/- ABA prevents dedifferentiation of GCPs by blocking cell cycle reentry at G1/S. Cell cycle reentry at 32 degrees C is accompanied by loss of a 41-kD polypeptide that cross-reacts with antibodies to rat (Rattus norvegicus) extracellular signal-regulated kinase 1; thermotolerant GCPs retain this polypeptide. A number of polypeptides unique to thermotolerant cells have been uncovered by Boolean analysis of two-dimensional gels and are targets for further analysis. GCPs of tree tobacco can be isolated in sufficient numbers and with the purity required to study plant cell thermotolerance and its relationship to plant cell survival, growth, dedifferentiation, and division in vitro.     

Protein Synthesis and Breakdown during Heat Shock of Cultured Pear (Pyrus communis L.) Cells

Cultured pear (Pyrus communis L. cv Passe Crassane) cells were subjected to temperatures of 39, 42, and 45[deg]C. Heat-shock protein (hsp) synthesis was greater at 30[deg]C than at temperatures above 40[deg]C and continued for up to 8 h. Both cellular uptake of radiolabeled methionine and total protein synthesis were progressively lower as the temperature was increased. Polysome levels decreased immediately when cells were placed at 39 or 42[deg]C, although at 39[deg]C the levels began to recover after 1 h. In cells from both temperatures, reassembly occurred after transfer of cells to 25[deg]C Four heat-shock-related mRNAs[mdash]hsp17, hsp70, and those of two ubiquitin genes[mdash]all showed greatest abundance at 39[deg]C and decreased at higher temperatures. Protein degradation increased with time at 42 and 45[deg]C, but at 39[deg]C it increased for the first 2 h and then decreased. In the presence of cycloheximide, which prevented hsp synthesis, protein degradation at 39[deg]C was as great as that at 45[deg]C in the absence of cycloheximide. The data suggest that hsps may have a role in protecting proteins from degradation at the permissive temperature of 39[deg]C. At temperatures high enough to inhibit hsp synthesis, protein degradation was enhanced. Although ubiquitin may play a role in specific protein degradation, it does not appear to be involved in increased protein degradation occurring above 40[deg]C.     

Exogenous Abscisic Acid Mimics Cold Acclimation for Cacti Differing in Freezing Tolerance

The responses to low temperature were determined for two species of cacti sensitive to freezing, Ferocactus viridescens and Opuntia ficus-indica, and a cold hardy species, Opuntia fragilis. Fourteen days after shifting the plants from day/night air temperatures of 30/20[deg]C to 10/0[deg]C, the chlorenchyma water content decreased only for O. fragilis. This temperature shift caused the freezing tolerance (measured by vital stain uptake) of chlorenchyma cells to be enhanced only by about 2.0[deg]C for F. viridescens and O. ficus-indica but by 14.6[deg]C for O. fragilis. Also, maintenance of high water content by injection of water into plants at 10/0[deg]C reversed the acclimation. The endogenous abscisic acid (ABA) concentration was below 0.4 pmol g-1 fresh weight at 30/20[deg]C, but after 14 d at 10/0[deg]C it increased to 84 pmol g-1 fresh weight for O. ficus-indica and to 49 pmol g-1 fresh weight for O. fragilis. Four days after plants were sprayed with 7.5 x 10-5 M ABA at 30/20[deg]C, freezing tolerance was enhanced by 0.5[deg]C for F. viridescens, 4.1[deg]C for O. ficus-indica, and 23.4[deg]C for O. fragilis. Moreover, the time course for the change in freezing tolerance over 14 d was similar for plants shifted to low temperatures as for plants treated with exogenous ABA at moderate temperatures. Decreases in plant water content and increases in ABA concentration may be important for low-temperature acclimation by cacti, especially O. fragilis, which is widely distributed in Canada and the United States.     

Changes in the levels of abscisic acid and its metabolites resulting from chilling of tomato fruits

The 6,6,6-[²H]-analogues of abscisic acid (ABA), phaseic (PA) and dihydrophaseic (DPA) acids were used in GC-MS-SIM determination of free and total alkali hydrolyzable ABA, PA and DPA in the pericarp of tomato (Lycopersicon esculentum L. cv. Pik Red) fruit. Determinations were made on breaker-stage fruit stored 1, 2, 3 or 4 weeks at 2.5°C or at 10°C, and after subsequent ripening for 1 week in darkness at 20°C. Two-fold increases in levels of ABA occurred after storage at low temperatures with a slightly but significantly greater increase in ABA level occurring with 2.5°C storage. These increases in ABA levels were not associated with the appearance of damage symptoms that occurred with storage at the chilling temperature (2.5°C). Differences in ABA metabolism were found resulting from storage at the two temperatures, 2.5 or 10°C. Significantly greater DPA levels were found after 10°C storage than after 2.5°C storage (2 weeks). Levels of ABA ester-conjugates increased with 20°C ripening only after 10°C storage while free ABA levels decreased after both storage temperature conditions. Levels of DPA conjugates also increased only after 20°C ripening following 10°C storage. A longer period of storage resulted in decreases of free DPA levels after 10°C storage but increased DPA levels were found after 2.5°C storage.Abbreviations ABA abscisic acid - PA phaseic acid - DPA dihydrophaseic acid - GC-MS-SIM gas chromatography-mass spectrometry-selected ion monitoring - HPLC high pressure liquid chromatography - fw. fresh weight author for correspondence     

In vivo rates of protein synthesis in brain,muscle, and liver of five vertebrate species

To compare cerebral protein metabolism rates in vivo, protein synthesis rates of three organs of five vertebrate species were measured after a single i.p. injection of a flooding dose of [1-¹⁴C]valine. In muscle, brain, and liver, the respective average protein synthesis rates, expressed as percent of total protein-bound valine replaced per hour, that is, percent synthesis per hour, in goldfish at 22°C body temperature, were 0.07, 0.23, and 0.57%; in the bullfrog at 20°C, 0.06, 0.18, and 0.55%; in the white Leghorn chicken at 39°C, 0.24, 0.70, and 2.17%; and in the mouse at 38°C, 0.22, 0.65, and 2.0%. In the Tokay lizard at different body temperatures, the synthesis rates were 0.04, 0.13, and 0.43% at 26°C; 0.05, 0.20, and 0.63% at 32°C; and 0.07, 0.27, and 0.81% at 38°C. The results demonstrate differences in protein synthesis rates in organs of the various species examined. The differences among the species seem to be due, to a major extent, to differences in body temperature; rates in lizard are below those in other species at temperatures tried. Protein synthesis rates in brain in all species are almost three times lower than those in liver and almost three times higher than those in muscle.     

Relationship between Proline and Abscisic Acid in the Induction of Chilling Tolerance in Maize Suspension-Cultured Cells

Both proline and abscisic acid (ABA) induce chilling tolerance in chilling-sensitive plants. However, the relationship between proline and ABA in the induction of chilling tolerance is unclear. We compared the time course of the increase in chilling tolerance induced by proline and ABA, and the time course of the uptake of both into the cultured cells of maize (Zea mays L. cv Black Mexican Sweet) at 28[deg]C. The plateau of proline-induced chilling tolerance preceded by 12 h the plateau of ABA-induced chilling tolerance. The uptake of exogenous ABA into the cells reached a plateau in 1 h, whereas the uptake of exogenous proline gradually increased throughout the 24-h culture period. Although the proline content in ABA-treated cells was 2-fold higher than in untreated cells at the end of the 24-h ABA treatment at 28[deg]C, the correlation between the endogenous free proline content and the chilling tolerance in the ABA-treated cells was insignificant. Isobutyric acid treatment, which resulted in a larger accumulation of proline in the cells than ABA treatment, did not increase chilling tolerance. The induction of chilling tolerance by proline and ABA appeared to be additive. Cycloheximide inhibited ABA-induced chilling tolerance, but it did not inhibit proline-induced chilling tolerance. Newly synthesized proteins accumulate in ABA-treated cells at 28[deg]C while the chilling tolerance is developing (Z. Xin and P.H. Li [1993] Plant Physiol 101: 277-284), but none of these proteins were observed in the proline-treated cells. Results suggest that proline and ABA induce chilling tolerance in maize cultured cells by different mechanisms.     

Estimation and Analysis of Cucumber (Cucumis sativus L.) Leaf Cellular Heat Sensitivity

Triphenyl tetrazolium chloride (TTC) reduction by cucumber (Cucumis sativus L. cv Poinsett 76 and cv Ashley) leaf discs was used as a viability assay to examine the effect of temperature pretreatment on the tissue response to acute hyperthermia. Semi-logarithmic plots of TTC reduction as a function of incubation time at different temperatures from 40 to 60[deg]C resembled the heat survival curves of animal cells. Heat inactivation rates were obtained and subjected to "quasi" Arrhenius analyses by analytical methods derived from the animal studies. The Arrhenius plots of TTC reduction rates for cv Ashley leaf discs preincubated at 25 or 37[deg]C and for cv Poinsett 76 preincubated at 37[deg]C were linear with the same activation energy (Ea) of about 80 kcal mol-1. The Arrhenius plot of cv Poinsett 76 preincubated at 25[deg]C was nonlinear with an Ea of about 80 kcal mol-1 at temperatures below 46[deg]C and an Ea of about 27.5 kcal mol-1 at temperatures above 47[deg]C. The significance of these differences is discussed in terms of the role of protein denaturation in the thermal sensitivity of cucumber disc reduction of TTC and the applicability of these methods to the analysis of plant cellular heat sensitivity.     

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.     

The Role of Potassium Channels in the Temperature Control of Stomatal Aperture

We used the patch-clamp technique to examine the effect of temperature (13-36[deg]C) on the depolarization-activated K channels (KD channels) and on the hyperpolarization-activated channels (KH channels) in the plasma membrane of Vicia faba guard-cell protoplasts. The steady-state whole-cell conductance of both K channel types increased with temperature up to 20[deg]C. However, whereas the whole-cell conductance of the KH channels increased further and saturated at 28[deg]C, that of KD channels decreased at higher temperatures. The unitary conductance of both channel types increased with temperature like the rate of diffusion in water (temperature quotient of approximately 1.5), constituting the major contribution to the conductance increase in the whole cells. The mean number of available KH channels was not affected significantly by temperature, but the mean number of available KD channels increased significantly between 13 and 20[deg]C and declined drastically above 20[deg]C. This decrease and the reduced steady-state voltage-dependent probability of opening of the KD channels above 28[deg]C (because of a shift of voltage dependence by +21 mV) account for the depression of the whole-cell KD conductance at the higher temperatures. This may be a basic mechanism by which leaves of well-watered plants keep their stomata open during heat stress to promote cooling by transpiration.     

Two Transduction Pathways Mediate Rapid Effects of Abscisic Acid in Commelina Guard Cells

Commelina guard cells can be rapidly closed by abscisic acid (ABA), and it is thought that this signal is always transduced through increases in cytosolic calcium. However, when Commelina plants were grown at 10 to 17[deg]C, most guard cells failed to exhibit any ABA-induced increase in cytosolic calcium even though all of these cells closed. At growth temperatures of 25[deg]C or above, ABA-induced closure was always associated with an increase in cytosolic calcium. This suggests that there may be two transduction routes for ABA in guard cells; only one involves increases in cytosolic calcium. Activation of either pathway on its own appears to be sufficient to cause closure. Because the rates of ABA accumulation and transport in plants grown at different temperatures are likely to be different, we synthesized and microinjected caged ABA directly into guard cells. ABA was released internally by UV photolysis and subsequently caused stomatal closure. This result suggests a possible intracellular locale for the hypothesized ABA receptor.     

Effect of increased temperatures on RNA and protein synthesis in the cells of a synchronous Candida utilis culture

The rate of incorporation of labeled precursors for RNA ([14C]uracil) and protein ([14C]DL-leucine) into the cells of the synchronous culture of Candida utilis VKMY-1668 (the optimum temperature of growth, 31--32 degrees C) was studied as a function of different temperatures (28, 31, 32, 34, 36, 38, and 41 decrees C). The yeast was grown on a simple mineral medium containing glycerol. RNA synthesis was found to be more susceptible to elevated temperature than protein synthesis: the maximum rate of incorporation was registered at 32--34 degrees C for [14C]DL-leucine and only at 32 degrees C for [14C]uracil (the rate of its incorporation at 34 degrees C decreased by 50% as compared to that at 32 degrees C). The rate of incorporation of [14C]uracil at 34 degrees C reached 100% (the rate at 32 degrees C) when yeast autolysate was added to the medium, and 75 and 70%, respectively, upon the addition of DL-methionine or Mg2+ (as compared to 50% without them).     

Influence of dietary protein levels and water temperature on growth,body composition and nutrient utilization of Cirrhinus mrigala (Hamilton, 1822) fry

The experiment was conducted to determine the protein requirement of Cirrhinus mrigala fry at three different water temperatures, 28, 30 and 32 °C, and to investigate the influence of dietary protein levels and water temperatures on weight gain, body composition, food and nutrient utilization. The 36% protein concentration in the diet yielded highest weight gain at all temperatures from 28 to 32 °C. However, daily protein intake was lower at 28 °C than at 30 and 32 °C. The diet with 36% dietary protein and 32.17% carbohydrate produced the best weight gain and gross conversion efficiency (GCE) at 30 °C. The protein-sparing effect was observed at temperatures 30 and 32 °C in diets 1 and 2, having carbohydrate levels 37.36–44.91%. Highest protein efficiency ratio (PER) was recorded at 28% dietary protein level, while it was lowest at 40% dietary protein level in all three temperatures. Lipid in the body of fishes increased at the end of the experiment in comparison to the initial body lipid. The body protein was found to be related to daily protein intake at 30 and 32 °C. Significant difference (P<0.05) was also noted between temperatures, the hepatosomatic index (HSI) and viscerosomatic index (VSI). The diet with 36% dietary protein and 32.17% carbohydrate was observed to be the best diet for C. mrigala fry at 28–32 °C.     

Deoxyglucose uptake by mouse astrocytes: Effects of temperature and retrovirus infection

Deoxyglucose uptake by FVB/N mouse astrocytes was studied before and after infecton by tsl retrovirus which causes a neurodegenerative disease in mice similar to HIV-1 encephalopathy in man. The Michaelis-Menten kinetic parameters, Km and Vmax, of 2-deoxy-D-glucose uptake by brain and cerebellar astrocytes were measured following culture at 34°C where tsl retrovirus replicates optimally, and at 37°C. Compared to astrocytes cultured at 37°C, astrocytes cultured at 34°C had increased Km and decreased deoxyglucose uptake despite increased or unchanged Vmax. Following ts1 retrovirus infection, brain astrocyte deoxyglucose uptake doubled [132%] associated with decreased Km but unchanged Vmax, whereas cerebellar astrocyte deoxyglucose uptake doubled [102%] associated with increased Vmax but unchanged Km. These observations of altered deoxyglucose uptake kinetic parameters following retrovirus infection indicate different neurochemical mechanisms for the regional variation in deoxyglucose uptake observed following retrovirus infection of the CNS in vivo.     

Disruption of Maize Kernel Growth and Development by Heat Stress (Role of Cytokinin/Abscisic Acid Balance)

Temperature stress during kernel development affects maize (Zea mays L.) grain growth and yield stability. Maize kernels (hybrid A619 x W64A) were cultured in vitro at 3 d after pollination and either maintained at 25[deg]C or transferred to 35[deg]C for 4 or 8 d, then returned to 25[deg]C until physiological maturity. Kernel fresh and dry matter accumulation was severely disrupted by the long-term heat stress (8 d at 35[deg]C) and did not recover when transferred back to 25[deg]C, resulting in abortion of 97% of the kernels. Kernels exposed to 35[deg]C for 4 d (short-term heat stress) exhibited a recovery in kernel growth and water content at about 18 d after pollination and kernel abortion was reduced to about 23%. During the cell division phase, abscisic acid (ABA) levels showed a steady decline in the control but maintained a moderate level in the heat-stressed kernels. However, later in development heat-stressed kernels had significantly higher levels of ABA than the control. Cytokinin analysis confirmed a peak in zeatin riboside and zeatin levels in control kernels at 10 to 12d after pollination. In contrast, kernels subjected to 4 d of heat stress had no detectable levels of zeatin and the zeatin riboside peak was reduced by 70% and delayed until 18 d after pollination. The long-term heat-stressed kernels showed low to nondetectable levels of either zeatin riboside or zeatin. Regression analysis of ABA level against cytokinin level during the endosperm cell division phase revealed a highly significant negative correlation in nonstressed kernels but no correlation in kernels exposed to short-term or long-term heat stress. Application of benzyladenine to heat-stressed, growth-chamber-grown plants increased thermotolerance in part by reducing kernel abortion at the tip and middle positions on the ear. These results confirm that shift in hormone balance of kernels is one mechanism by which heat stress disrupts maize kernel development. The maintenance of high levels of cytokinins in the kernels during heat stress appears to be important in increasing thermotolerance and providing yield stability of maize.     

Fatty Acid Desaturation during Chilling Acclimation Is One of the Factors Involved in Conferring Low-Temperature Tolerance to Young Tobacco Leaves

The FAD7 gene, a gene for a chloroplast [omega]-3 fatty acid desaturase, is responsible for the trienoic fatty acid (TA) formation in leaf tissues. The TA content of the leaf tissue of the 25[deg]C-grown transgenic tobacco (Nicotiana tabacum cv SR1) plants, in which the FAD7 gene from Arabidopsis thaliana was overexpressed, increased uniformly by about 10%. Fatty acid unsaturation in all major leaf polar lipid species increased in the 25[deg]C-grown FAD7 transformants but was approximately the same between the control plants and the FAD7 transformants when grown at 15[deg]C. Therefore, the overexpression of the exogenous FAD7 gene leads to the same consequence in the tobacco plants as the low-temperature-induced TA production that may be catalyzed by an endogenous, temperature-regulated chloroplast [omega]-3 fatty acid desaturase. In the 25[deg]C-grown control plants, the chilling treatment caused symptoms of leaf chlorosis and suppression of leaf growth. The 25[deg]C-grown FAD7 transgenic plants conferred alleviation of these chilling-induced symptoms. A reductions of the chilling injury similar to that of the FAD7 transformants was also observed in the 15[deg]C-preincubated control plants. These results indicate that the increased TA production during chilling acclimation is one of the prerequisites for the normal leaf development at low, nonfreezing temperatures.     

Effect of growth temperature upon heat sensitivity in Saccharomyces cerevisiae

The resistance of exponentially growing yeast cells to killing by exposure to 52°C increased markedly as the growth temperature was increased. Identical killing curves were obtained for cells suspended in growth medium or in 0.9% saline. Cells resistant to killing at 52°C were quite sensitive to killing at slightly higher temperatures. These results suggest a primary role for membrane damage in the mechanism of heat killing.     

Temperature-dependent survival of isolates ofThiobacillus ferrooxidans

Psychrotrophic and mesophilic isolates ofThiobacillus ferrooxidans were examined for their ability to survive at temperatures above the T_max, below the T_min, and at –15°C after a slow freeze. There were no thermoduric strains among those studied; the viable counts decreased by two to five orders of magnitude in 24 h, following exposure to a supermaximum temperature (2–4°C above the T_max). Strain F1, when exposed to progressively higher temperatures, predictably showed increasingly rapid rates of death. When strain S2 was exposed to 2°C, a temperature below its T_min but still above freezing, there was little change in the viable counts over the 38-day observation period. When the various strains were subjected to a slow freeze at –15°C, the cells died quite rapidly with the percentage survival among the strains varying from .0006% to .0155% after 24 h. A survival curve for strain A1 showed that the number of viable cells decreased by approximately three orders of magnitude in the first 4–6 h, and a further three orders of magnitude over the next 40 h.     

The Effect of Leaf Temperature and Photorespiratory Conditions on Export of Sugars during Steady-State Photosynthesis in Salvia splendens

Export and photosynthesis in leaves of Salvia splendens were measured concurrently during steady-state 14CO2 labeling conditions. Under ambient CO2 and O2 conditions, photosynthesis and export rates were similar at 15 and 25[deg]C, but both declined as leaf temperature was raised from 25 to 40[deg]C. Suppressing photorespiration between 15 and 40[deg]C by manipulating CO2 and O2 levels resulted in higher rates of leaf photosynthesis, total sugar synthesis, and export. There was a linear relationship between the rate of photosynthesis and the rate of export between 15 and 35[deg]C. At these temperatures, 60 to 80% of the carbon fixed was readily exported with sucrose, raffinose, and stachyose, which together constituted over 90% of phloem mobile assimilates. Above 35[deg]C, however, export during photosynthesis was inhibited both in photorespiratory conditions, which inhibited photosynthesis, and in nonphotorespiratory conditions, which did not inhibit photosynthesis. Sucrose and raffinose but not stachyose accumulated in the leaf at 40[deg]C. When leaves were preincubated at 40[deg]C and then cooled to 35[deg]C, export recovered more slowly than photosynthesis. These data are consistent with the view that impairment of export processes, rather than photosynthetic processes associated with light trapping, carbon reduction, and sucrose synthesis, accounted for the marked reduction in export between 35 and 40[deg]C. Taken together, the data indicated that temperature changes between 15 and 40[deg]C had two effects on photosynthesis and concurrent export. At all temperatures, suppressing photorespiration increased both photosynthesis and export, but above 35[deg]C, export processes were more directly inhibited independent of changes in photorespiration and photosynthesis.     

Temperature and salinity effects on growth, survival, reproduction, and potential distribution of two non-indigenous botryllid ascidians in British Columbia

Two non-indigenous botryllid ascidian species - Botryllus schlosseri (golden star tunicate) and Botrylloides violaceus (violet tunicate) - have become established in British Columbia (BC), Canada. One species, B. schlosseri, is native to Europe while the other, B. violaceus, is native to Asia. Environmental tolerances of both species are poorly understood. We examined the effects of temperature and salinity on growth, survival, and reproduction of these species in the laboratory in order to characterize their environmental tolerances and preferences. Laboratory-raised juvenile colonies were studied using a two-factorial experimental design with five levels of temperature (5, 10, 15, 20, 25 °C) and five levels of salinity (14, 20, 26, 32, 38‰). Both B. schlosseri and B. violaceus possessed broad temperature and salinity tolerances, but B. schlosseri was slightly more euryhalinal than B. violaceus. Generally, B. schlosseri survived environmental conditions of 10-25 °C and 14-38‰, exhibited positive growth at 10-25 °C and 20-38‰, and attained its largest colony sizes at 15-20 °C and 20-38‰. Botrylloides violaceus tolerated environmental conditions between 5-25 °C and 20-38‰, demonstrated positive growth at 15-25 °C and 26-38‰, and attained its largest colony sizes at 20-25 °C and 26-38‰. Results from the laboratory experiment were then used in a modeling exercise to determine the coastal areas of BC that these organisms might be likely to exist in or invade, based on near-surface temperatures and salinities. The model predicted that no areas were totally unsuitable for survival and growth of either species (based solely on temperature and salinity tolerances), with the most suitable locations being along the west coast of Vancouver Island, a region with significant shellfish aquaculture activity.