The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.     

Temporal variations of coagulation factor VII activity in mice are influenced by lighting regime

It was recently reported that the circadian clock machinery controls plasma levels of factor (F) VII, the serine protease triggering blood coagulation. Here, by exploiting the mouse model, this study showed that variations of photoperiod (i.e., winter or summer conditions or simulated chronic jetlag conditions) have a strong impact on plasma FVII activity levels. Under conditions mimicking summer or winter photoperiods, FVII activity showed a clear 24 h rhythmicity. Interestingly, mean daily FVII activity levels were significantly reduced in mice exposed to summer photoperiods. Behavioral activity rhythms under both photoperiods were synchronized to LD cycles, and the amount of activity per 24 h was comparable. The authors also investigated the influence of chronic jetlag (CJL) on the FVII activity rhythms, which can be easily mimicked in mice through continuous abrupt shifts in the lighting schedule. The exposure of mice to simulated CJL of either consecutive westward or consecutive westward and eastward flights for 15 days did not abolish the behavioral activity rhythms but was associated with a period significantly different from 24 h. Intriguingly, both types of CJL exerted a strong influence on FVII activity rhythms, which were virtually suppressed. Moreover, the mean daily FVII activity was significantly lower in the CJL than in the winter photoperiod condition. Taken together, these findings in mice provide novel insights into the modulation of FVII activity levels, which might have implications for human pathophysiology.     

Photothermal control of the imposition of summer dormancy in Poabulbosa, a perennial grass geophyte

Poa bulbosa L., like many other Mediterranean geophytes, grows in the winter and enters a phase of summer dormancy in the spring. Summer dormancy enables these plants to survive the hot and dry summer. Long days are the main environmental factor active in the induction of summer dormancy in P . bulbosa and elevated temperatures accelerate dormancy development. P . bulbosa becomes dormant earlier than most other species that grow actively in the winter. Previous studies suggested that pre-exposure of P . bulbosa to short days and low temperatures during the autumn and early winter increased its sensitivity to photoperiodic induction in late winter, and thus enabled the early imposition of dormancy. To study this hypothesis, experiments were carried out under controlled photothermal conditions in the phytotron, under natural daylight extended with artificial lighting. The critical photoperiod for induction of summer dormancy at an optimal temperature (22/17°C day/night) was between 11 and 12 h. Photoperiods shorter than 12 h were noninductive, while 14- and 16-h days were fully inductive. A night break of 1 h of light given at the middle of the dark period of an 8-h photoperiod also resulted in full induction of dormancy. Pre-exposure to either low temperature (chilling at 5°C) or to short days of 8 h (SD) enhanced the inductive effect of subsequent 16-h long days (LD). The enhancing effect of chilling and SD increased with longer duration, i.e. fewer LDs were required to impose dormancy. However, the day-length during the low-temperature pretreatment had no effect on the level of induction at the following LD. Chilling followed by SD did not induce dormancy. The relevance of these responses to the development and survival of P . bulbosa in its natural habitat is discussed.     

Temporal Variations of Coagulation Factor VII Activity in Mice Are Influenced by Lighting Regime

It was recently reported that the circadian clock machinery controls plasma levels of factor (F) VII, the serine protease triggering blood coagulation. Here, by exploiting the mouse model, this study showed that variations of photoperiod (i.e., winter or summer conditions or simulated chronic jetlag conditions) have a strong impact on plasma FVII activity levels. Under conditions mimicking summer or winter photoperiods, FVII activity showed a clear 24 h rhythmicity. Interestingly, mean daily FVII activity levels were significantly reduced in mice exposed to summer photoperiods. Behavioral activity rhythms under both photoperiods were synchronized to LD cycles, and the amount of activity per 24 h was comparable. The authors also investigated the influence of chronic jetlag (CJL) on the FVII activity rhythms, which can be easily mimicked in mice through continuous abrupt shifts in the lighting schedule. The exposure of mice to simulated CJL of either consecutive westward or consecutive westward and eastward flights for 15 days did not abolish the behavioral activity rhythms but was associated with a period significantly different from 24 h. Intriguingly, both types of CJL exerted a strong influence on FVII activity rhythms, which were virtually suppressed. Moreover, the mean daily FVII activity was significantly lower in the CJL than in the winter photoperiod condition. Taken together, these findings in mice provide novel insights into the modulation of FVII activity levels, which might have implications for human pathophysiology.     

Refractoriness to short and long days determines the end and onset of the breeding season in subtropical goats

The objective was to determine whether refractoriness to short and long days were involved in the end and onset of the breeding season, respectively, in goats adapted to subtropical latitudes. Ovariectomized does given a subcutaneous implant constantly releasing estradiol-l7 β (OVX+E) were used in two experiments. Plasma LH concentrations were determined twice weekly. In Experiment 1, the control group remained in an open-shed pen (natural day length and ambient temperature). Two experimental groups were placed in light-proof buildings (with natural temperature variations). One group was exposed to natural simulated increasing days (winter to spring), whereas the other was exposed to a winter solstice photoperiod (10 h of light) from December 21 to April 28. In Experiment 2, the control group remained under natural day length and ambient temperature. One experimental group was exposed to natural simulated decreasing days (summer to autumn), whereas the other group was exposed to a summer solstice photoperiod (14 h of light) from June 21 to October 20. In Experiment 1, the breeding season was not prolonged in does maintained in the winter solstice day length. Mean dates of decrease in LH secretion (end of the breeding season) did not differ significantly between does exposed to natural (February 3 ± 5 d) or natural simulated photoperiod (January 26 ± 14 d) and those exposed to constant short days of winter solstice (February 4 ± 10 d). In Experiment 2, the onset of the breeding season was not delayed in does maintained in the summer solstice day length. Mean dates of increase in LH secretion (onset of the breeding season) did not differ significantly between does exposed to natural (September 7 ± 8 d) or natural simulated photoperiod (September 18 ± 10 d) and those exposed to constant long days photoperiod of summer solstice (September 24 ± 4 d). In goats adapted to a subtropical environment, we concluded that: 1) the end of breeding season was due to refractoriness to short days, and not the inhibitory effect of increasing day length; and 2) the onset of the breeding season was due to refractoriness to long days, and not a stimulatory effect of decreasing day length.     

New findings in body mass regulation in zebra finches (Taeniopygia guttata) in response to photoperiod and temperature

Small birds in temperate zones increase body mass in winter (Lehikoinen, 1987). We investigated daily and annual variation of body mass and fat reserves of locally-reared Australian zebra finches Taeniopygia guttata , by exposing them to different photoperiods, feeding periods, and temperatures.
Experiments with long and short photoperiods and long and short feeding periods, showed that long photoperiods increased body mass and fat reserves of the zebra finches, and readiness to breed, independently of the actual feeding period.
Furthermore, the zebra finches in indoor aviaries with constant temperature (22-24°C) and in outdoor aviaries with ambient temperature, both exposed to the natural daylength changes of Bielefeld, Germany (52 °N), had high dawn body mass in summer (12.9 and 12.0-12.4g, respectively) and low in winter (10.7 and 11.1 g, respectively). Thirty to sixty percent of these mass changes were related to changes in fat reserves, so that the finches had only 0.1-0.2g of metabolizable fat reserves in short photoperiods (or in winter), which increased up to 1.5g in long photoperiods (or in summer).
Indoor finches consumed more seeds in summer than in winter (3.3 vs. 2.7g/day), while outdoor finches consumed 4-5g of seeds per day throughout the year, which probably represented the limit of energy intake for a 11-13g bird (Kirkwood, 1983). Nightly mass loss, increasing from 0.7g in summer up to 2.0g in winter, was highly positively correlated with night length, not influenced by ambient temperature. Foraging before dawn and after dusk, roosting with well-filled crops, and decreasing body mass and fat reserves, seem to be adaptations of zebra finches for survival in winter. The summer fattening probably accelerates reproduction in this opportunistic breeder, by allocating more time to reproductive behaviour and more endogenous nutrients to egg-formation.     

Cold hardiness of rhododendron cultivars grown in different photoperiods and temperatures

Two rhododendron cultivars, 'Pohjola's Daughter' and 'Helsinki University', were grown at +15 and +24°C, each combined with a photoperiod of 14 h (short day, SD) or 20 h (long day, LD). After a 112-day growing season, they were subjected to a hardening regime of fortnightly decreasing temperature (+9, +5, +1 and −2°C) and a 12-h photoperiod, except that part of the plants grown in LD had LD also at +9 and +5°C. At −2°C, all plants were in darkness. Controlled freezing tests of the leaves were performed before each change in temperature. The injury was evaluated visually and by electrolyte leakage (EL) tests. The observations on the visual assessment were analysed with logit models, and the EL data with non-linear sigmoid functions. The visually scored 50% damage (VD₅₀) correlated better with the EL tests than 10 or 90% damage. Photoperiod and temperature during the growing season affected the cold hardiness of both cultivars, but they differed in their responses. 'Pohjola's Daughter' benefited from SD as well as from high temperature, while 'Helsinki University' attained better hardiness at a cool growing season temperature and was less sensitive to photoperiod.     

Photoperiod and temperature effects on gametogenesis in winter flounder Pseudopleuronectes americanus

The winter flounder is an in‐shore flatfish living in shallow waters on the east coast of North America from Labrador to Georgia. In the St Lawrence estuary, the reproductive season is May and June. Our objective was to test the effects of winter‐spring photoperiod and temperature conditions on the timing of sexual maturation in both males and females. Groups (16 animals each) of winter flounder breeders were maintained from mid‐January to mid‐May under five different experimental conditions: (1) natural photoperiod and temperature conditions; (2) natural photoperiod, 6° C; (3) 15L : 9D, natural temperature conditions; (4) 15L : 9D, 6° C; (5) accelerated photoperiod increase from winter to spring conditions, 6° C. Natural photoperiod and temperature conditions correspond to a gradual increase in light period from 8L : 16D (January) to 15L : 9D (May) and in temperature from −1° C (January to April) to 6° C (May). GSI and condition factor did not differ among the treatments ( P  > 0·05). In males, milt production occurred simultaneously in the different treatments and histological examination did not indicate any significant effect of either photoperiod or temperature on testes development. In females, seven stages of oocyte development were observed. Both the number of oocytes at the cortical alveoli stage and number of atretic oocytes increased at 6° C (warm temperature conditions). Overall, neither photoperiod nor temperature modified the reproductive period. Warm winter‐spring temperature conditions, however, may decrease egg numbers and egg quality.     

Constancy of synaptic ribbon numbers in the retina of the arctic chary,Salvelinus alpinus

Synopsis At high latitudes, such as in Iceland, the daily photoperiod varies from almost continuous darkness in winter to virtually constant light in summer. Previous studies of detailed retinal structure in vertebrates have shown significant daily and annual effects of photoperiod. We sampled arctic charr in Iceland during the summer, including fish that were both light- and dark-adapted, during both day and night. We observed retinomotor responses characteristic of light- and dark-adaptation, but found no difference in the number of synaptic ribbons in the retina. The morpho-physiological changes, appearing as retinomotor responses, are thus not expressed at the synaptic level.     

The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle,Colaphellus bowringi (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal summer and winter diapause. Its photoperiodic response highly depends on temperature. All adults entered diapause at ≤ 20 °C regardless of photoperiods. High temperatures strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting influence of short daylengths was expressed only at high temperatures (above 20 °C). This indicates that the beetle has a cryptic ability to reproduce in summer. In fact, summer and winter diapause were induced principally by relatively low temperatures in the field, whereas photoperiod had less influence on diapause induction. The critical daylength for the autumnal population was between 12 h and 13 h. By transferring from a long day to a short day or vice versa at different times after hatching, it was shown that the sensitive stage with regard to photoperiod was the larva, whereas a long day was photoperiodically more potent than a short day. The sensitive stage to temperature encompassed the larval, pupal and adult stages. This different response pattern serves to ensure that the beetle enters summer and winter diapause in time. The selections for non-diapause trait under laboratory (at 25 °C) and natural conditions (at >24 °C) showed that the beetle could lose its sensitivity to photoperiod very rapidly.     

Photoperiod and cell mediated immunity of clinically normal dogs

Abstract

Previously, the authors have reported seasonal variations in cell mediated immunity in the dog during the period July, 1977 ‐ October 1978 as measured by whole blood lectin‐induced lymphocyte transformation. Peak activity occurred in the summer, suggesting association with photoperiodicity. Here the authors report on immune response of dogs kept indoors ‐ under controlled physical environment ‐ with a natural (outdoor) photoperiod or under a 12:12 h (LD) regime, and a control group kept in outdoor kennels. Peak immune activity in 1979 occurred in the winter, in both indoor groups as well as the outdoor groups subject to natural photoperiod. Since the indoor dogs were kept at a constant temperature and humidity in clean (filtered) air, photoperiod, temperature, and particulate air contaminants probably are not associated with seasonal variations in immunity. The underlying cause for either the seasonal variations or the shift from peak activity in the summer of 1978 to winter of 1979 is unknown. Dogs under LD = 12:12 light regime had a significantly lowered immunity relative to the dogs with the natural photoperiod.     

Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to Winter Low Temperature in a Marginal Tropical Area

In marginal tropical areas, air temperature in winter usually decreases by 10℃ compared with summer at night/day. Although tropical plants are sensitive to low temperature, the mechanism underlying photosynthetic acclimation of tropical trees to winter low temperature is unclear. To address this question, the photosystem I (PSI) and photosystem II (PSII) activities, and energy distribution in PSI and PSII were examined in summer and winter in two tropical high quality timber tree species Erythrophleum guineense and Dalbergia odorifera grown in a marginal tropical area (21°54′N, 101°46′E). Our results indicated that the photosynthetic apparatus of Eguineense and Dodorifera was maintained stable in winter. The effective quantum yield of PSII decreased significantly in winter, but non photochemical quenching (NPQ) significantly increased. In winter, cyclic electron flow (CEF) was significantly stimulated in both species, which was significantly and positively correlated with NPQ. Meanwhile, the stimulation of CEF led to an increase in P700 oxidation ratio and the over reduction of PSI acceptor side was prevented. Antimycin A (a specific inhibitor of PGR5 dependent CEF) significantly aggravated PSII photoinhibition under high light in both species. These results suggested that stimulation of CEF is an important mechanism for photosynthetic acclimation to winter low temperature in a marginal tropical area in the two tropical tree species.     

Hormonal regulation of the annual pelage color cycle in the Djungarian hamster, Phodopus sungorus. I. Role of the gonads and pituitary

The Djungarian hamster exhibits an agouti pelage in the summer and a predominantly white pelage in the winter. This pelage color cycle is known to be regulated by the length of the daily photoperiod probably acting through the pineal gland, as is the seasonal cycle of reproductive function with which it is closely correlated ( Figala et al., '73; Hoffmann, ' 78b ). The possibility of a causal relationship between the decline in gonadal hormone secretion and the coat color change occurring in short photoperiod was examined. Gonadectomized and intact male and female hamsters were exposed to either long (16L:8D) or short ( 10L : 14D ) photoperiod for several months. Gonadectomy neither induced the change to the winter pelage color in long photoperiod-housed animals, nor prevented either the change to the winter pelage or the spontaneous return to summer pelage color in short photoperiod-housed animals. Chronic implants of testosterone in castrated males delayed and attenuated the short photoperiod-induced coat color change. Administration of ovine prolactin (100 micrograms/day) stimulated pigmentation in hamsters with the winter pelage, whereas administration of a alpha MSH (30 micrograms/day) was without effect. These results suggest that changes in pelage color may be regulated largely by changes in pituitary prolactin secretion and modified to some extent by changes in gonadal steroid hormone secretion.     

Influence of water temperature on demand-feeding rhythms in sea bass

Under natural environmental conditions, sea bass feeding rhythms are nocturnal in winter and diurnal during the rest of the year. Increasing water temperature from 22 to 28°C or decreasing it to 16°C had little effect on the dual feeding behaviour of sea bass. An 8:16 LD photoperiod with low temperature or 16:8 LD with high temperature also failed to change the diurnal/ nocturnal behaviour of sea bass. In conclusion, sea bass feeding rhythms did not follow passively the manipulated environmental factors simulating summer and winter conditions in the laboratory, which suggests an endogenous circannual control of the seasonal phase inversion.     

Habitat preference in the dark-eyed junco (Junco hyemalis): The role of photoperiod and dominance

Wild-caught dark-eyed juncos (Junco hyemalis), simultaneously presented with projected slides of their winter and summer habitats, demonstrated distinct preferences (in terms of time spent in front of particular slides) consistent with their season of capture and prior laboratory experience. Juncos caught in and kept on winter or summer photoperiods preferred winter and summer habitat slides respectively. A gradual increase in photoperiod up to natural summer conditions induced a switch from winter to summer habitat preference: a decrease in photoperiod induced a range of slide preferences correlated with the junco's size, a measure of the bird's dominance rank.     

Regulation of frost resistance during cold de-acclimation and re-acclimation in oilseed rape. A possible role of PSII redox state

A possible role of photosynthetic apparatus during cold de-acclimation was studied in oilseed rape ( Brassica napus var. oleifera ). Plants of spring (Star) and winter (Górczañski) cultivars were cold acclimated at + 5°C, and de-acclimated during 4 weeks at combinations of + 12 and + 20°C operating in the light or/and dark, with a 12-h photoperiod. Evidence is presented that the photosynthetic apparatus may be involved in temperature perception during de-acclimation. De-acclimation was faster under a 20/12°C (day/night) treatment than under the reverse 12/20°C (day/night). De-acclimation rate was constant when the day temperature was constant, irrespective of the night temperature both under cold day temperature regimes (12/20, 12/12°C (day/night) and warm-day treatments (20/12, 20/20°C (day/night). The fast decrease in frost resistance observed under warm-day de-acclimation was always accompanied by an acceleration of elongation growth. In the spring cultivar, elongation growth increased starting from the second week of de-acclimation, regardless of temperature conditions. Once elongation growth had commenced during de-acclimation, it continued throughout the period necessary for re-acclimation to low temperature. Re-acclimation to the initial freezing tolerance level was only possible when plant elongation was reduced. In addition re-acclimation of the photosynthetic apparatus to low temperature was impossible in fast growing plants. A possible relationship between PSII, growth rate and frost resistance during cold acclimation and de-acclimation is discussed.     

Short day length alone does not inhibit spermatogenesis in the seasonally breeding four-striped field mouse (Rhabdomys pumilio).

This study was an examination of the effect of photoperiod on spermatogenesis and the accessory glands of the four-striped field mouse (Rhabdomys pumilio), a seasonally breeding rodent that occurs through Southern Africa. Adult scrotal males were exposed to either short day length (10L:14D), long day length (14L:10D), or natural photoperiod in constant-environment rooms (25 degrees C, 41% humidity; food and water ad libitum) for 8 wk in late summer, when males in the wild were spermatogenically active, and in mid-winter, when they were inactive. In neither experiment did prolonged exposure to short day length or naturally decreasing day length inhibit spermatogenic activity, and we conclude that the normal cessation of spermatogenesis that occurs in most male four-striped field mice in winter is not stimulated by day length alone.     

Variation in the timing of the reproductive season among breeds of sheep in relation to differences in photoperiodic synchronization of an endogenous rhythm.

Photoperiod may regulate seasonal reproduction either by providing the primary driving force for the reproductive transitions or by synchronizing an endogenous reproductive rhythm. This study evaluated whether breed differences in timing of the reproductive seasons of Finnish Landrace (Finn) and Galway ewes are due to differences in photoperiodic drive of the reproductive transitions or to differences in photoperiodic synchronization of the endogenous rhythm of reproductive activity. The importance of decreasing photoperiod after the summer solstice in determining the onset and duration of the breeding season was tested by housing ewes from the summer solstice in either a simulated natural photoperiod or a fixed summer-solstice photoperiod (18 h light:6 h dark; summer-solstice hold). Onset of the breeding season within each breed did not differ between these photoperiodic treatments, but Galway ewes began and ended their breeding season earlier than Finn ewes. The duration of the breeding season was shorter in Galway ewes on summer-solstice hold than on simulated natural photoperiod; duration did not differ between photoperiodic treatments in Finn ewes. The requirement for increasing photoperiod after the winter solstice for initiation of anoestrus was tested by exposing ewes from the winter solstice to either a simulated natural photoperiod or a winter-solstice hold photoperiod (8.5 h light:15.5 h dark). Onset of anoestrus within each breed did not differ between these photoperiodic treatments, but the time of this transition differed between breeds. These observations suggest that genetic differences in timing of the breeding season in Galway and Finn ewes do not reflect differences in the extent to which photoperiod drives the reproductive transitions, because neither breed requires shortening days to enter the breeding season or lengthening days to end it at appropriate times. These findings are consistent with the hypothesis that photoperiod synchronizes an endogenous rhythm of reproductive activity in both breeds and that genetic differences in timing of the breeding season reflect differences in photoperiodic synchronization of this rhythm.     

Quantitation of gibberellins and indoleacetic acid in Begonia leaves: Relationship with environment, regeneration and flowering

Indole-3-acetic acid (IAA) was purified by high performance liquid chromatography (HPLC) and identified by gas chromatography - mass spectrometry (GC-MS) in leaf extracts of Begonia × cheimantha Everett cv. Nova. The content of IAA and of gibberellins A4, A9, A19 and A20 (GAs) previously identified in this material, were quantified by GC-MS in leaves of Begonia plants grown under different temperature and daylength conditions, using deuterated compounds as internal standards. GA1, which was also identified, was present in too low quantities for reliable quantitation. Rapid and significant decreases (within 2–4 days) occurred in the content of both IAA and GAs when the plants were transferred from conditions which are non-inductive for adventitious bud formation and flowering (24°C/long day) to inductive conditions (24°C/short day, 15°C/long day or 15°C/short day). GA4 and GA9 were affected by photoperiod only, whereas IAA, GA19 and GA20 were affected by both photoperiod and temperature. The data suggest that biosynthesis of GA9 and GA4 are blocked in short days at a step located before GA9. Conversion of GA19 to GA20 seemed to be blocked by both short days and low temperature, while an additional block located before GA19 seemed to be imposed in 15°C/short day. The results confirm earlier results and support the hypothesis that photoperiod and temperature effects in Begonia are mediated by endogenous hormones.     

The response of trout red cells to adrenaline during seasonal acclimation and changes in temperature

Adult rainbow trout were acclimated to three different temperature and photoperiod regimes: 17°C, 14 h light: 10 h dark (summer); 7° C, 14 h light: 10 h dark; and 5° C, 8 h light: 16 h dark (winter). Blood was collected from these fish after 40 days acclimation, and the response of red blood cells to in vitro adrenergic stimulation was assessed. To examine potential seasonal variations in endogenous levels of circulating catecholamines, plasma levels of adrenaline (Ad) and noradrenaline (NAd) were measured at rest and after exercise. At rest, there were no differences between groups in plasma levels of either Ad or NAd, but, after exercise, the pattern of catecholamine elevation differed. In fish acclimated to 17 and 7° C in summer, Ad and NAd increased by about the same amount (10–15 times). In fish acclimated to 5° C in winter, NAd increased about three-fold, compared to the near 50-fold increase in Ad levels. Whether this difference between groups can be attributed to seasonal influences is unclear. At both low (0·5%) and high (2%) PCO ₂, adrenergic stimulation (2 × 10^-7 M Ad) of trout red cells in vitro led to a significant reduction in MCHC (mean cell [haemoglobin]), compared to non-stimulated cells. However, only at the high PCO ₂ were pHe and red cell pHi significantly different from those in the non-stimulated cells: the latter was higher and the former lower in the stimulated cells. There were no differences in the response of red cells to adrenergic stimulation between groups of fish. Under the conditions of the present study no influence of season and/or temperature on the in vitro response of trout red cells to adrenergic stimulation was shown.