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Les épinoches à 3 épines (Gasterosteus aculeatus), pêchées dans différentes régions de Camargue, ont été étudiées et soumises à différentes salinités. La pression osmotique du sang de poissons gardés en eau douce (FW : 5 ppm), en eau saumâtre (BW : 15 ppm) et en eau de mer (SW : 30ppm) était différente (147, 457 et 911 mOsmkg-1, respectivement). Cependant, les résultats de consommation d’oxygène montrent des valeurs similaires pour les poissons capturés dans la l’étang du Marteau (SW), le canal du Versadou (FW) et l’étang mésohalin (eau saumâtre) du Vaccarès (BW). Ainsi, ces épinoches peuvent rapidement s'acclimater à différentes salinités et se déplacer librement entre ces différents habitats avec des dépenses énergétiques limitées. Pour les épinoches du Vaccarès, le taux de consommation d'O2 diminue immédiatement après le transfert en FW jusqu'à 1 heure après transfert. L'activité branchiale Na+/ K+-ATPase (NKA) des épinoches collectées dans l’étang du Marteau et directement transférées en FW a révélé une augmentation significative 24h et 48h après le transfert (28% et 40%, respectivement). Cependant, l'activité NKA des branchies est réduite de manière significative de 36%, 24h suivant le transfert en SW.La morphologie corporelle des épinoches a également été étudiée mais des variations morphologiques limitées ont pu être observées. Le nombre moyen de plaques latérales est de 4,45 ± 0,31. Cependant, une différence morphologique significative est observée pour les branchiospines.Le marquage NKA a révélé des ionocytes avec différentes morphologies. Ces cellules sont également deux fois plus nombreuses chez les poissons FW que chez les poissons SW. Deux types d'ionocytes ont été identifiés chez les poissons FW: les cellules avec un dôme apical et les ionocytes avec une structure en nid d'abeille. Ces cellules sont bien des ionocytes du fait de leurs structures internes (présence de nombreuses mitochondries et d’un système tubulo-vésiculaire dense avec une membrane basale profondément invaginée). Chez les poissons acclimatés en SW, seuls des ionocytes avec une grande crypte apicale ont été observés le long des filaments branchiaux à la base des lamelles branchiales. Aucun ionocyte n'a pu être observé le long des lamelles branchiales. L'expression relative de l'ARNm de NKA α1 est apparue plus élevée dans les branchies des poissons acclimatés en SW que chez les poissons en BW. L’expression de la NKA α1b est significativement surexprimée dans les branchies des poissons SW par rapport aux poissons BW et FW. Cependant, pour la NKAα1a, les expressions relatives dans les branchies ne sont pas différentes selon la salinité. Pour l'expression du CFTR et de la V-ATPase, nous n'avons trouvé aucune différence significative. Par contre, NKCC1 est significativement plus élevé chez les épinoches acclimatées en SW.Les analyses histologiques du rein et le marquage de la NKA au niveau des tubules proximaux du rein n'ont révélé aucune différence pour les poissons en FW et en SW. Pour l'intestin, un fort marquage a été observé le long des membranes basolatérales des entérocytes. Cependant, là encore, nous n'avons observé aucune différence due aux conditions de salinité. Ces résultats suggèrent un haut niveau de plasticité pour ces organes.Globalement, ces résultats indiquent que les épinoches de Camargue sont homogènes au niveau morphologique et physiologique et possèdent de fortes capacités euryhalines. Cependant, des différences ont été identifiées au niveau des branchiospines entre les poissons capturés dans les habitats FW et les habitats BW/SW, probablement en raison de régimes alimentaires différents. Par conséquent, ces populations peuvent ne pas se mélanger même si les différents environnements aquatiques de Camargue sont interconnectés. / Threespined sticklebacks (Gasterosteus aculeatus) fished from different areas of the Camargue were studied and challenged to various salinity conditions. Blood osmotic pressures for fish kept in FW (5‰), BW (15‰) and SW (30‰) were different (147, 457 and 911 mOsm kg-1, respectively). However, oxygen consumption results revealed similar values for fish collected from the seawater Marteau lagoon (SW), the freshwater Versadou canal (FW) and the mesohaline/brackish water Vaccarès lagoon (BW). Therefore, sticklebacks of the Camargue can rapidly acclimate to different salinity conditions and move freely among these different habitats with limited energy expenditure. For sticklebacks from the Vaccarès lagoon, a significant reduction in O2 consumption rate occurred immediately after transfer to FW and up to 1h after transfer. The branchial Na+/K+-ATPase (NKA) activity of sticklebacks collected from the SW Marteau lagoon directly transferred from SW to FW, revealed a significant increase 24 h and 48 h after transfer (28% and 40%, respectively). However, gill NKA activity was significantly decreased by 36% within 24 h following immediate transfer to SW.Body morphology of sticklebacks was also studied but limited morphological variations could be observed for fish collected from different habitats. The average lateral plate number is 4.45±0.31. However, a significant morphological difference is observed for gill rakers.NKA labeling on histological sections revealed different ionocyte morphologies. In the gills of FW sticklebacks, ionocytes were observed along the gill filaments as well as the gill lamellae. Ionocytes were only identified along the gill filaments for SW fish. For SW fish, the ionocytes were round in shape and slightly smaller than the ionocytes of the FW fish. The ionocytes of the FW fish along the gill filaments were elongated but ionocytes along the gill lamellae were flattened and wider. Ionocytes were also twice more numerous for FW fish compared to SW fish.Also, two types of ionocyte were identified in FW fish: cells with an apical dome shape and ionocytes with a honeycomb-like structure. All these cell types were confirmed as ionocytes due to their internal structures filled with numerous mitochondria and a dense tubulo-vesicular system, with deeply invaginated basal membrane. In SW-acclimated fish, only ionocytes with a large apical crypt were observed along the gill filaments at the base of the gill lamellae. No ionocytes could be observed along the gill lamellae.Relative NKA α1 mRNA expression was higher in the gills of SW acclimated fish compared to BW fish and NKA α1b was significantly overexpressed in the gills of SW acclimated fish compared to the FW and BW fish. However, for NKAα1a, mRNA relative gene expressions in the gills are not different due to salinity. Whereas, for CFTR and V-ATPase expression, we did not find any significant difference. On the other hand, NKCC1 was significantly higher in SW acclimated sticklebacks.For sticklebacks kept in FW and for those acclimated to SW, analyses of histological sections from the kidney and NKA immunolabeling of the kidney proximal tubules revealed no difference. For the intestine, a strong immunofluorescence was observed along the basolateral membranes of the enterocytes for both the anterior and posterior intestine of FW and SW-acclimated sticklebacks but, again, we did not observe any difference due to salinity conditions. These results suggest a high level of plasticity for these organs.Altogether, these results indicate that sticklebacks of the Camargue area are morphologically and physiologically homogenous and have strong euryhaline capacities. Some differences were identified however for the gill rakers between fish collected from the FW and mesohaline / euryhaline habitats most probably due to different feeding regimes. Therefore, these fish populations may not mix even if the different Camargue aquatic environments are interconnected.

The cost of new cultivar development is high due to long juvenile periods and large tree size in tree fruit breeding programs. For apples, sour cherries, and saskatoon berries, grafting seedling scions onto the tips of branches of mature plants was hypothesized to shorten the juvenile period and reduce land use under the Canadian prairie conditions. For apples, a tip grafting system (tip grafting onto mature crabapple rootstocks) was compared with the traditional grafting system (grafting onto young Ottawa 3 rootstocks). Apple scions of Golden Delicious, McIntosh, and SK Prairie Sun which exhibit a range of inherent cold hardiness, were grafted in the spring of 2001. Over a two year period, winter survival of the scions was improved by 37% by the tip grafting system as compared to the traditional grafting system making it not feasible for evaluation of cold hardiness of scions. Vegetative growth of scions approximated the rootstocks on which the scions were grafted. Winter survival was highly correlated with shoot growth cessation (r = +0.83) and terminal bud stage (r = +0.85) observed around the time of first frost. Juvenile seedlings of saskatoon berry and sour cherry hybrids were tip grafted onto mature plants of their own species in the spring of 2000. After two growing seasons, the tip grafting system in sour cherries had reduced flowering by 69.7%, shoot length by 84%, and shoot diameter by 76% compared with the juvenile seedlings on their own roots (scion donors). Tip grafting saskatoon berry seedlings increased flowering by 68%, shoot length by 257%, and shoot diameter by 42% compared with scion donors. For sour cherries, the tip grafting system reduced winter dieback by 99.6%, hastened terminal bud development and leaf drop compared with the scion donors. Tip grafting of saskatoon berry seedlings had little effect on terminal bud development and cold hardiness of scions perhaps due to the cold hardy character of this species. For apples and sour cherries, the tip grafting system tested in this study enhanced cold hardiness of scions when combined with the appropriated rootstocks and may be useful for maintaining germplasm that otherwise would not be hardy in northern locations.

The cost of new cultivar development is high due to long juvenile periods and large tree size in tree fruit breeding programs. For apples, sour cherries, and saskatoon berries, grafting seedling scions onto the tips of branches of mature plants was hypothesized to shorten the juvenile period and reduce land use under the Canadian prairie conditions. For apples, a tip grafting system (tip grafting onto mature crabapple rootstocks) was compared with the traditional grafting system (grafting onto young Ottawa 3 rootstocks). Apple scions of Golden Delicious, McIntosh, and SK Prairie Sun which exhibit a range of inherent cold hardiness, were grafted in the spring of 2001. Over a two year period, winter survival of the scions was improved by 37% by the tip grafting system as compared to the traditional grafting system making it not feasible for evaluation of cold hardiness of scions. Vegetative growth of scions approximated the rootstocks on which the scions were grafted. Winter survival was highly correlated with shoot growth cessation (r = +0.83) and terminal bud stage (r = +0.85) observed around the time of first frost. Juvenile seedlings of saskatoon berry and sour cherry hybrids were tip grafted onto mature plants of their own species in the spring of 2000. After two growing seasons, the tip grafting system in sour cherries had reduced flowering by 69.7%, shoot length by 84%, and shoot diameter by 76% compared with the juvenile seedlings on their own roots (scion donors). Tip grafting saskatoon berry seedlings increased flowering by 68%, shoot length by 257%, and shoot diameter by 42% compared with scion donors. For sour cherries, the tip grafting system reduced winter dieback by 99.6%, hastened terminal bud development and leaf drop compared with the scion donors. Tip grafting of saskatoon berry seedlings had little effect on terminal bud development and cold hardiness of scions perhaps due to the cold hardy character of this species. For apples and sour cherries, the tip grafting system tested in this study enhanced cold hardiness of scions when combined with the appropriated rootstocks and may be useful for maintaining germplasm that otherwise would not be hardy in northern locations.

Frost assays carried out on winter barley (Hordeum vulgare cv Igri) showed that a single (10ml I) application of liquid seaweed extract (LSE) marginally increased the frost resistance of non-acclimated (NA) plants by 2.3% compared to NA controls and cold-acclimated (CA) plants by 2.1% compared to CA controls. Three applications of LSE increased the frost resistance of NA plants by 16% compared to NA controls and CA plants by 7.5% compared to CA controls. These observations were durable in a small scale field trial where LSE increased plant dry weights (control 0.55, single LSE, 0.611 and multiple LSE 0.621 log dry weight), but rain following LSE application reduced LSE mediated frost resistance. Glasshouse growth trials illustrated that LSE enhanced tiller production (control 2.8, one LSE 3.8 and three LSE 4.5 tillers) and dry weight gain, but where precipitation followed LSE application, up to 3 days post application, the LSE mediated effect was not sustained. Protein analysis demonstrated that cold-acclimation and LSE treatments increased the total soluble protein content of winter barley. A single application of LSE increased the soluble protein content of NA plants by 36.7% and three applications of LSE to NA plants increased protein concentration by 86.5%. There was not a significant increase in the soluble protein concentration of LSE treated CA plants. There was a significant increase in the number of high molecular weight proteins and the up-regulation of a 118kDa and a 57kDa protein when plants were treated with LSE. However precipitation following LSE application adversely affected LSE mediated protein expression. A tentative immunological identification of the up-regulated proteins suggested that the 118kDa protein is a dehydrin. There was a 2 fold decrease in plant water potential of NA plants treated with three applications of LSE compared to controls and a similar decrease in plant water potential was observed in cold-acclimated plants. The duration of LSE mediated decline in water potential lasted for 6 days, post LSE application. However there was no significant reduction in the percentage water content of cold-acclimated and LSE treated plants. Differential scanning calorimetry demonstrated that both cold-acclimated and LSE treated plants had significantly less frozen water in their crown tissue compared to non-acclimated controls. Further thermal analysis (infrared thermography and thermocouple data) showed that both cold-acclimation and LSE treatments reduced the speed of water removal from plant cells to the extracellular ice (NA 4.06, NA3LSE 13.4, CA 15.7 and CA3LSE 19.31 minutes). It is hypothesised that both CA and LSE treatments are modifying plant water status, so that water becomes more structured at the physico-chemical level, and thus alters the osmotic behaviour of cellular water. This higher level of water structuring reduces frost damage by conserving the cellular water environment and thus reducing protein denaturation and membrane damage.

Although it has long been recognized that physiological acclimation of photosynthesis and respiration can occur in plants exposed to changing environmental conditions (e.g. light, temperature or stress), the extent of acclimation in different tissues (i.e. pre-existing and new foliage) however, has not received much attention until recently. Furthermore, few studies have investigated the extent of photosynthetic and respiratory acclimation under natural conditions, where air temperatures vary diurnally and seasonally. In this study, the effects of variations in temperature on respiratory CO2 loss and photosynthetic carbon assimilation were examined under both controlled and natural environments. The purpose of the investigations described in this thesis was to identify the effects acclimation would have on two key metabolic processes in plants exposed to temperature change, with emphasis also placed on the role of nutrition (nitrogen) and respiratory enzymatic characteristics on the potential for acclimation in two contrasting tree species, Pinus radiata and Populus deltoides. Controlled-environment studies (Chapter 2 and 3) established that rates of foliar respiration are sensitive to short-term changes in temperature (increasing exponentially with temperature) but in the longer-term (days to weeks), foliar respiration acclimates to temperature change. As a result, rates of dark respiration measured at any given temperature are higher in cold-acclimated and lower in warm-acclimated plants than would be predicted from an instantaneous response. Acclimation in new foliage (formed under the new temperature environment) was found to result in respiratory homeostasis (i.e. constant rates of foliar respiration following long-term changes in temperature, when respiration is measured at the prevailing growth temperature). Available evidence suggests that substantial adjustments in foliar respiration tend to be developmentally dependent. This may in part explain why respiratory homeostasis was only observed in new but not in pre-existing tissues. Step changes in temperature (cold and warm transfers) resulted in significant changes in photosynthetic capacity. However, in stark contrast to the findings of respiration, there was little evidence for photosynthetic acclimation to temperature change. The results obtained from field studies (Chapter 4) show that in the long-term over a full year, dark respiration rates in both tree species were insensitive to temperature but photosynthesis retained its sensitivity, increasing with increasing temperature. Respiration in both species showed a significant downregulation during spring and summer and increases in respiratory capacity were observed in autumn and winter. Thermal acclimation of respiration was associated with a change in the concentration of soluble sugars. Hence, acclimation of dark respiration under a naturally changing environment is characterized by changes in the temperature sensitivity and apparent capacity of the respiratory apparatus. The results from controlled and natural-environment studies were used to drive a leaflevel model (which accounted for dark respiratory acclimation) with the aim of forecasting the overall impact of responses of photosynthesis and respiration in the long term (Chapter 5). Modellers utilise the temperature responses of photosynthesis and respiration to parameterize carbon exchange models but often ignore acclimation and use only instantaneous responses to drive such models. The studies here have shown that this can result in erroneous estimates of carbon exchange as strong respiratory acclimation occurs over longer periods of temperature change. For example, it was found here that the failure to factor for dark respiratory acclimation resulted in the underestimation of carbon losses by foliar respiration during cooler months and an overestimation during warmer months - such discrepancies are likely to have an important impact on determinations of the carbon economy of forests and ecosystems. The overall results substantiate the conclusion that understanding the effect of variations in temperature on rates of carbon loss by plant respiration is a prerequisite for predicting estimates of atmospheric CO2 release in a changing global environment. It has been shown here that within a moderate range of temperatures, rate of carbon uptake by photosynthesis exceeds the rate of carbon loss by plant respiration in response to warming as a result of strong respiratory acclimation to temperature change. This has strong implications for models which fail to account for acclimation of respiration. At present, respiration is assumed to increase with increasing temperatures. This erroneous assumption supports conclusions linking warming to the reinforcement of the greenhouse effect.

Abstract Branches of adult Scots pine (Pinus sylvestris L.) trees were sampled from boreal dry pine forests to study needle longevity, its variation and its relation to other shoot characteristics. The stands studied were located along transects from two smelters and one city, e.g. along gradients of pollution impact. Constant needle age structures were assumed and static life-tables generated. Mean needle longevity was calculated as the sum of the proportions of living needle fascicles on the successive annual shoots. It fully incorporated the information of the static life-tables and was preferred to median or maximum ages because of its significantly lower variation. The first half of the shedding span, the duration of the period when the needle survival gradually dropped from 90 to 50 %, proved to validly reflect the changes in the needle age structure. Needle longevity decreased 15-40 % towards the pollution sources along the transects studied. Near the smelters, needle longevity decreased with the increasing needle Fe, or Fe, Ni and Cu concentration that represented the main constituents of the airborne particle emissions. Near the city, needle longevity decreased with the increasing needle N and P concentrations, annual needle mass and needle mass packing and decreasing needle area packing. In the urban forests, needle Mg, P and K concentrations decreased linearly with the decreasing needle survival from the second to the fourth needle age class. Concentrations in the living needles of the fourth age class stayed over 80 % of the average for all the age classes, though needle survival dropped below 50 %. A decreasing needle Mn concentration was detected towards all the emission sources. Leaching, especially from the soil, as a possible cause was discussed. Needle longevity had the lowest variation among the shoot characteristics, which increases its value as a tool in ecological monitoring. Low plasticity in needle longevity could be an acclimation to the ambient environmental conditions and length of the growing season and to maximise the carbon gain per time. Needle longevity decreased and annual needle mass and leaf mass per area increased upwards in the crowns of mature Scots pines, reflecting the acclimation to irradiance.

Photoacclimation is a process by which photosynthetic capacity is regulated in response to environmental adjustments in terms of light regime. Photoacclimation is essential in determining the photosynthetic capacity to optimize light use and to avoid potentially damaging effects. Previous work in our laboratory has identified a gene, gpt2 (At1g61800) that is essential for plants to acclimate to an increase in growth irradiance. Furthermore, we observed that the accession Columbia-0 (Col-0) is unable to respond to increases in light. Therefore, a Quantitative Trait Locus (QTL) mapping analysis was performed in Landsberg erecta (Ler)/Columbia (Col) recombinant inbred line population to identify novel genes responsible for this variation to acclimation. In order to investigate the photoacclimation in Arabidopsis thaliana, photosynthetic capacity was measured in plants of the accession Wassileskija (WS) and in plants lacking expression of the gene At1g61800 (WS-gpt2) during acclimation from high to low light. Plants were grown for 6 weeks under high light (400 μmol.m-2.s-1) and half of them were transferred to low light (100 μmol.m-2.s-1) after six weeks. Gas exchange measurements were performed in order to measure the maximum capacity for photosynthesis. Acclimation to a decrease in light resulted in a decrease in the photosynthetic capacity in WS and WS-gpt2 plants. This shows that under lower or limiting light, photosynthesis was slowed down. Chlorophyll fluorescence analysis was carried out to measure changes in the quantum efficiency of PSII (ΦPSII) and non-photochemical quenching (NPQ) during acclimation. ΦPSII decreased in both WS and WS-gpt2 plants showing that under low light, PSII is more saturated. However, it was found that there was no significant changes in NPQ level for both WS and WS-gpt2. To estimate the total chlorophyll and chl a/b ratio, a chlorophyll composition analysis was performed. There was no significant changes in the total chlorophyll for both WS and WS-gpt2. However, the chlorophyll a/b ratio was seen to be decreased in low light plants representing an increase in light harvesting complexes relative to reaction centre core. Plants of WS and WS-gpt2 were also grown under natural variable light in an unheated greenhouse in Manchester, UK. This experiment was carried out to study the photosynthetic acclimation of plants under fluctuating light condition. A preliminary work on gene expression of gpt2 was conducted by doing reverse transcriptase PCR (RT-PCR). It shows that the gene expression of gpt2 decreased following transfer to low light plants in WS. Microarray analysis was also performed to investigate the role of GPT2 (if any) and to identify any potential gene that is important in high to low light acclimation.