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Salvia ceratophylloides (Ard.) is an endemic and rare plant species recently rediscovered as very few individuals at two different Southern Italy sites. The study of within-plant variation is fundamental to understand the plant adaptation to the local conditions, especially in rare species, and consequently to preserve plant biodiversity. Here, we reported the variation of the morpho-ecophysiological and metabolic traits between the sessile and petiolate leaf of S. ceratophylloides plants at two different sites for understanding the adaptation strategies for surviving in these habitats. The S. ceratophylloides individuals exhibited different net photosynthetic rate, maximum quantum yield, light intensity for the saturation of the photosynthetic machinery, stomatal conductance, transpiration rate, leaf area, fractal dimension, and some volatile organic compounds (VOCs) between the different leaf types. This within-plant morpho-physiological and metabolic variation was dependent on the site. These results provide empirical evidence of sharply within-plant variation of the morpho-physiological traits and VOCs profiles in S. ceratophylloides, explaining the adaptation to the local conditions.

beta-1,3-glucans such as paramylon act as elicitors in plants, modifying the hormonal levels and the physiological responses. Plant hormones affect all phases of the plant life cycle and their responses to environmental stresses, both biotic and abiotic. The aim of this study was to investigate the effects of a root treatment with Euglena gracilis paramylon on xylem hormonal levels, photosynthetic performance and dehydration stress in tomato (Solanum lycopersicum L.). Paramylon granules were processed to obtain the linear fibrous structures capable to interact with tomato cell membrane. Modulation of hormone levels (abscisic acid, jasmonic acid and salicylic acid) and related physiological responses such as CO2 assimilation rate, stomatal and mesophyll conductance, intercellular CO2 concentration, transpiration rate, water-use efficiency, quantum yield of photosystem II and leaf water potential were investigated. The results indicate a clear dose-dependent effect of paramylon on the hormonal content of xylem sap, photosynthetic performance and dehydration tolerance. Paramylon has the capability to enhance plant defence capacity against abiotic stress, such as drought, by modulating the conductance to CO2 diffusion from air to the carboxylation sites and improving the water-use efficiency.

Callistemon citrinus and Viburnum lucidum are appreciated and widespread ornamental shrubs for their abundant flowering and/or brilliant foliage. The intrinsic tolerance to drought/salinity supports their use in urban areas and in xeriscaping. Despite adaptive responses of these ornamental species to sodium chloride (NaCl) have been extensively explored, little is known on the effects of other salt solution, yet iso-osmotic, on their growth, mineral composition and metabolism. The present research was aimed to assess responses at the biochemical, physiological and anatomical levels to iso-osmotic salt solutions of NaCl and CaCl2 to discriminate the effects of osmotic stress and ion toxicity. The two ornamental species developed different salt-tolerance mechanisms depending on the salinity sources. The growth parameters and biomass production decreased under salinization in both ornamental species, independently of the type of salt, with a detrimental effect of CaCl2 on C. citrinus. The adaptive mechanisms adopted by the two ornamental species to counteract the NaCl salinity were similar, and the decline in growth was mostly related to stomatal limitations of net CO2 assimilation rate, together with the reduction in leaf chlorophyll content (SPAD index). The stronger reduction of C. citrinus growth compared to V. lucidum, was due to an exacerbated reduction in net photosynthetic rate, driven by both stomatal and non stomatal limitations. In similar conditions, V. lucidum exhibited other additional adaptive response, such as modification in leaf functional anatomical traits, mostly related to the reduction in the stomata size allowing plants a better control of stomata opening than in C. citrinus. However, C. citrinus plants displayed an increased ability to retain higher Cl- levels in leaves than in roots under CaCl2 salinity compared to V. lucidum, thus, indicating a further attempt to counteract chloride toxicity through an increased vacuolar compartmentalization and to take advantages of them as chip osmotica.

This study aimed to evaluate the physiological and phytochemical responses of Stevia rebaudiana to arbuscular mycorrhizal fungi (AMF) inoculation (Rhizoglomus irregulare) and P fertilization (0, 25 and 50 mg P205 kg"' of substrate). At the end of the vegetative phase, AMF colonization, growth parameters (leaf specific weight, harvest index and below-ground biomass), steviol glycosides (SVglys) concentration and composition, leaf gas exchanges, photosynthetic pigments and soluble sugar content, were assessed. The inoculated plants showed increased harvest index, reduced specific leaf weight and a significant increase of total soluble sugars and total monosaccharides in their roots. Both AMF and P fertilization had meaningful effects on stevia, modifying sugar partitioning and stimulating leaf gas exchanges. AMF x P interaction positively affected SVglys concentration and composition, shifting the pathway towards the production of rebaudioside A, B and C. So, a highest rebaudioside (A+B+C) to ste-vioside ratio was observed in all inoculated plants, to indicate an increased stevia leaf quality in terms of organoleptic properties.

Drought represents one of the most relevant abiotic stress affecting growth and yield of crop plants. In order to improve the agricultural productivity within the limited water and land resources, it is mandatory to increase crop yields in presence of unfavorable environmental stresses. The use of biostimulants, often containing seaweed extracts, represents one of the options for farmers willing to alleviate abiotic stress consequences on crops. In this work, we investigated the responses of Arabidopsis plants treated with an extract from the brown alga Ascophyllum nodosum (ANE), under drought stress conditions, demonstrating that ANE positively influences Arabidopsis survival. Pre-treatment with ANE induced a partial stomatal closure, associated with changes in the expression levels of genes involved in ABA-responsive and antioxidant system pathways. The pre-activation of these pathways results in a stronger ability of ANE-treated plants to maintain a better photosynthetic performance compared to untreated plants throughout the dehydration period, combined with a higher capacity to dissipate the excess of energy as heat in the reaction centers of photosystem II. Our results suggest that drought stressed plants treated with ANE are able to maintain a strong stomatal control and relatively higher values of both water use efficiency (WUE) and mesophyll conductance during the last phase of dehydration. Simultaneously, the activation of a pre-induced antioxidant defense system, in combination with a more efficient energy dissipation mechanism, prevents irreversible damages to the photosynthetic apparatus. In conclusion, pre-treatment with ANE is effective to acclimate plants to the incoming stress, promoting an increased WUE and dehydration tolerance.

This study was undertaken to investigate how different cultivars of sweet basil (Ocimum basilicum) responded to boron (B) excess. Two purple-leafed and eight green-leafed cultivars were hydroponically grown for 20 d with 0.2 or 20 mg L–1 B in the nutrient solution. Leaf B concentration, gas exchanges, chlorophyll a fluorescence, and oxidative stress were determined at the end of the treatment along with the severity of leaf necrosis. A range of tolerance to B toxicity was found: the green cultivars were more susceptible than the purple-leafed ones characterized by a higher constitutive anthocyanin concentration. In all the genotypes B excess resulted in oxidative stress as determined by accumulation of malondialdehyde by-products (MDA), reduced photosynthesis, and the occurrence of leaf burn. A close correlation was found between leaf B accumulation and oxidative stress, as well as between oxidative stress and the severity of leaf burn. Net photosynthesis (Pn) was reduced due to both stomatal and nonstomatal limitations in the green cultivars whereas the reduction of Pn in the purple leaves was only attributable to stomatal factors. Chlorophyll a fluorescence revealed a decrease in the maximum quantum yield of PSII (Fv/Fm) and in the electron transport rate (ETR) in plants grown with B excess although less reduction was observed in the purple genotypes. The quantum yield of PSII (UPSII) decreased as a result of B toxicity only in the green cultivars. It is concluded that anthocyanins are involved in attenuation of the negative effects of B toxicity.

Forest functionality and productivity are directly related to canopy light interception and can be affected by potential damage from high irradiance. However, the mechanisms by which leaves adapt to the variable light environments along the multilayer canopy profile are still poorly known. We explored the leaf morphophysiological and metabolic responses to the natural light gradient in a pure European beech (Fagus sylvatica L.) forest at three different canopy heights (top, middle and bottom). Structural adjustment through light-dependent modifications in leaf mass per area was the reason for most of the variations in photosynthetic capacity. The different leaf morphology along the canopy influenced nitrogen (N) partitioning, water- and photosynthetic N-use efficiency, chlorophyll (Chl) fluorescence and quali-quantitative contents of photosynthetic pigments. The Chl a to Chl b ratio and the pool of xanthophyll-cycle pigments (VAZ) increased at the highest irradiance, as well as lutein and ?-carotene. The total pool of ascorbate and phenols was higher in leaves of the top and middle canopy layers when compared with the bottom layer, where the ascorbate peroxidase was relatively more activated. The non-photochemical quenching was strongly and positively related to the VAZ/(Chl a + b) ratio, while Chl a/Chl b was related to the photochemical efficiency of photosystem II. Along the multilayer canopy profile, the high energy dissipation capacity of leaves was correlated to an elevated redox potential of antioxidants. The middle layer gave the most relevant contribution to leaf area index and carboxylation capacity of the canopy. In conclusion, a complex interplay among structural, physiological and biochemical traits drives the dynamic leaf acclimation to the natural gradients of variable light environments along the tree canopy profile. The relevant differences observed in leaf traits within the canopy positions of the beech forest should be considered for improving estimation of carbon fluxes in multilayer canopy models of temperate forests.

International audience; Soil carboxydovore bacteria are the biological sink of atmospheric carbon monoxide (CO). The initial oxidation of CO is catalyzed by a CO-dehydrogenase (CODH), and the gene coxL encodes the large subunit of the enzyme. Only a few carboxydovore isolates were shown to oxidize atmospheric CO and little is known about the potential impact of global change on the ecophysiology of this functional group. The main objective of this study was to assess the impact of land-use and soil properties on coxL gene diversity and identify molecular indicators for the soil uptake of atmospheric CO. Soil samples were collected in three neighboring sites encompassing different land-use types, namely deciduous forest, larch plantation and maize field. CO uptake activity was related to total carbon and nitrogen content in soil, with the highest activity observed in deciduous forest. An extensive coxL database was assembled to optimize a PCR detection assay targeting sequences belonging to functional type I-CODH and hypothetical type II-CODH. Fully replicated coxL gene libraries unveiled a unique molecular signature in deciduous forest soil, with enrichment of type I sequences. Genetic profiles of larch and maize monocultures were not statistically different and showed higher level of coxL gene richness than deciduous forest. Soil water content and CO uptake activity explained 38% of the variation of coxL gene profiles in a canonical ordination analysis, leading to the identification of sequences belonging to the δ-Proteobacteria cluster as indicator for high affinity CO uptake activity. Enrichment of type I and δ-Proteobacteria coxL sequences in deciduous forest were confirmed by qPCR in an independent soil survey. CO uptake activity in model carboxydovore bacteria suggested that a significant fraction of detected putative high affinity CO oxidizers were active in soil. Land-use was a driving force separating coxL diversity in deciduous forest from monocultures.

Leaf anatomy, photosynthetic performance, and the role of poly(ADP-ribosyl)ation in maintaining genomic stability in winter and summer leaves of Cistus incanus L. were investigated to evaluate the strategies allowing this species to grow in a Mediterranean climate. Measurements on summer leaves (SL) were conducted at midday and on the following morning to assess the reversibility of changes induced by high temperatures and irradiances reached at midday. Winter leaves (WL) were thicker with a lower leaf density and higher intercellular spaces compared with SL, which showed reduced net photosynthesis (Pn) and a decrease in Rubisco activity. Compared with WL, SL showed a higher thermal dissipation (ΦNPQ) in compensating for the reduced Pn. This allowed minimization of ROS production (low ΦNO) and hence prevented photo-oxidative damage. In SL, poly(ADP-ribose) polymerase (PARP) activity was down-regulated, probably allowing leaves to become tolerant to high temperatures and irradiances. SL are also characterised by chloroplasts occupying larger cell volume and well exposed to intercellular spaces. This may well favour better liquid-phase CO2 diffusion towards carboxylation sites, contributing to reducing the negative influence of high leaf density and the low percentage of intercellular spaces on photosynthesis.

This study aimed to evaluate the behavior of zucchini (Cucurbita pepo L.) and cucumber (Cucumis sativus L.) under boron (B) excess. Plants were grown under greenhouse conditions in a sandy soil-peat mixture using a nutrient solution containing 0.2 (control), 10 and 20 mg L(-1) B. Visible symptoms were quantified and leaf B accumulation, gas exchanges, chlorophyll (Chl) a fluorescence, malondialdehyde by-products and antioxidants were investigated 20 days after the beginning of the treatments. Boron toxicity induced oxidative load and leaf necrotic burns coupled with the reduction of leaf growth and biomass accumulation in both species. Boron excess resulted in a decrease of Chl a/b ratio, potential (Fv/Fm) and actual (ΦPSII) PSII quantum efficiency, photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) as well. A general stimulation of the antioxidant enzymes ascorbate peroxidase, catalase and superoxide dismutase was observed, and a significant increase in the oxidized form of ascorbate and glutathione was evidenced for treated plants of both species. A difference between the two species was observed: C. pepo appeared to be more sensitive to B stress being damaged at all B concentration. C. sativus grown at 10 mg L(-1) B in nutrient solution showed some down-regulated mechanisms, i.e. increase in Chl b content and a good photochemical PSII efficiency as well as a higher amount of constitutive antioxidant molecules, that, however, are not sufficient to contrast the negative effects of B.

An integrated approach has been used to analyse the dependence of three Mediterranean species, A. unedo L., Q. ilex L., and P. latifolia L. co-occurring in a coastal dune ecosystem on two different water resources: groundwater and rainfed upper soil layers. The approach included leaf level gas exchanges, sap flow measurements and structural adaptations between 15 May and 31 July 2007. During this period it was possible to capture different species-specific response patterns to an environment characterized by a sandy soil, with a low water retention capacity, and the presence of a water table. The latter did not completely prevent the development of a drought response and, combined with previous studies in the same area, response differences between species have been partially attributed to different root distributions. Sap flow of A. unedo decreased rapidly with the decline of soil water content, while that of Q. ilex decreased only moderately. Midday leaf water potential of P. latifolia and A. unedo ranged between −2.2 and −2.7 MPa throughout the measuring period, while in Q. ilex it decreased down to −3.4 MPa at the end of the season. A. unedo was the only species that responded to drought with a decrease of its leaf area to sapwood area ratio from 23.9±1.2 (May) to 15.2±1.5 (July). While A. unedo also underwent an almost stepwise loss on hydraulic conductivity, such a loss did not occur for Q. ilex, whereas P. latifolia was able to slightly increase its hydraulic conducitivity. These differences show how different plant compartments coordinate differently between species in their responses to drought. The different responses appear to be mediated by different root distributions of the species and their relative resistances to drought are likely to depend on the duration of the periods in which water remains extractable in the upper soil layers.

Aniba rosaeodora is an Amazonian tree species that belongs to the family Lauraceae. Due to intense exploitation for extraction of essential oils (mainly linalol), A. rosaeodora is now considered an endangered species. On the other hand, there is little information about its ecophysiology which would be useful to support future forest planting programs. Hence, the effect of different light intensities on the growth and photosynthetic characteristics of young plants of A. rosaeodora was studied. Nine-month-old plants were subjected to four light treatments (T1= 10 a 250 µmol.m-2.s-1 / control; T2=500 to 800, T3=700 to 1000 and T4=1300 to 1800 µmol.m-2.s-1 / full sunlight). Allometric variables, gas exchange, contents of pigments and chlorophyll a fluorescence were analysed. As to the relative growth rates, it was found that plants of A. rosaeodora showed higher biomass accumulation when grown under intermediary irradiance conditions (T2). The best photosynthetic performance was achieved under conditions of T3. When growth was correlated with photosynthesis, it was found that plants under treatments T2 and T3 presented better responses in comparison with the lowest (T1) and highest (T4) light extremes. The highest pigment contents were obtained for plants in the shade (T1) and the lowest for those exposed to full sunlight (T4). The photochemical efficiency of photosystem II (Fv/Fm) was found that only plants in the shade treatment (T1) presented no stress from high irradiance. These findings suggest that both treatments (T1 and T4) altered the function of the A. rosaeodora plants, inhibiting photosynthesis and growth. Plants of A. rosaeodora developed photo-protection mechanisms under full sunlight. However, the species presented better photosynthetic response and biomass gain under intermediary irradiance conditions, displaying relative physiological plasticity, during the seedling phase. Essa espécie arbórea da Amazônia, Aniba rosaeodora Ducke, pertence à família das Lauraceae. Em vista da intensa e desordenada exploração, visando à extração de óleos essenciais (linalol), o pau-rosa figura na lista de espécies ameaçadas de extinção. Poucos estudos ecofisiológicos têm sido feito no sentido de subsidiar futuros programas de plantios florestais. Dessa forma, pesquisou-se o efeito de diferentes irradiâncias sobre as características fotossintéticas e de crescimento em plantas de A. rosaeodora, na fase juvenil. Plantas com nove meses foram submetidas a quatro tratamentos de luz (T1 = 10 a 250 µmol.m-2.s-1 / controle; T2 = 500 a 800, T3 = 700 a 1.000 e T4 = 1.300 a 1.800 µmol.m-2.s-1 / pleno sol). Analisaram-se variáveis alométricas, trocas gasosas, teores de pigmentos cloroplastídicos e a fluorescência da clorofila a. Quanto ao crescimento relativo, observou-se que plantas de A. rosaeodora exibiram maior acúmulo de biomassa quando crescidas sob condições intermediárias de irradiância (T2). O melhor desempenho fotossintético foi induzido por T3. Quando se correlacionou crescimento com fotossíntese, percebeu-se que as plantas submetidas aos tratamentos T2 e T3 exibiram melhores respostas em comparação com os extremos de menor (T1) e maior irradiâncias (T4). Os maiores teores de pigmentos cloroplastídicos foram obtidos nas plantas sob sombra (T1) e os menores teores encontrados naquelas expostas a pleno sol (T4). Quanto à eficiência fotoquímica do fotossistema II (Fv/Fm) observou-se que apenas as plantas do tratamento de sombra (T1) não apresentaram estresse por alta irradiância. Os resultados sugerem que ambos os tratamentos (T1 e T4) alteraram a funcionalidade das plantas de A. rosaeodora, inibindo a fotossíntese e o crescimento. A pleno sol, plantas de A. rosaeodora desenvolveram mecanismos de fotoproteção. No entanto, a espécie apresentou melhor resposta fotossintética e ganho de biomassa em condições intermediárias de irradiância, demonstrando relativa plasticidade fisiológica, durante o estádio juvenil.

Thirty-month-old 'Pêra' orange trees grafted on 'Rangpur' lemon trees grown in 100 L pots were submitted to water stress by the suspension of irrigation. CO2 assimilation (A), transpiration (E) and stomatal conductance (g s) values declined from the seventh day of stress, although the leaf water potential at 6:00 a.m. (psipd) and at 2:00 p.m. (psi2) began to decline from the fifth day of water deficiency. The CO2 intercellular concentration (Ci) of water-stressed plants increased from the seventh day, reaching a maximum concentration on the day of most severe stress. The carboxylation efficiency, as revealed by the ratio A/Ci was low on this day and did not show the same values of non-stressed plants even after ten days of rewatering. After five days of rewatering only psi pd and psi2 were similar to control plants while A, E and g s were still different. When psi2 decreases, there was a trend for increasing abscisic acid (ABA) concentration in the leaves. Similarly, stomatal conductance was found to decrease as a function of decreasing psi2. ABA accumulation and stomatal closure occurred when psi2 was lower than -1.0 MPa. Water stress in 'Pera´ orange trees increased abscisic acid content with consequent stomatal closure and decreased psi2 values. Laranjeiras 'Pêra' de dois anos e meio de idade enxertadas em limoeiros 'Cravo' foram cultivadas em vasos de 100 L com solo e submetidas ao estresse hídrico, pela suspensão da irrigação. Valores de assimilação de CO2 (A), transpiração (E) e condutância estomática (g s) começaram a declinar a partir do sétimo dia de estresse, embora o potencial da água na folha às 6 a.m. (psipd) e às 2 p.m. (psi2) começaram a declinar a partir do quinto dia de deficiência hídrica. A concentração interna de CO2 (Ci) das plantas estressadas aumentou a partir do mesmo dia, atingindo uma concentração máxima no dia de estresse mais severo. Assim, a eficiência de carboxilação dessas plantas, verificada pela relação A/Ci foi menor nesse dia, não ocorrendo recuperação dessa razão mesmo dez dias após a reidratação. Até o quinto dia após a reirrigação, somente o psipd e o psi2 se recuperaram, sendo semelhantes aos das plantas controle. Quando o potencial da água na folha diminuiu, ocorreu uma tendência de aumento da concentração de ácido abscísico (ABA) nas folhas; da mesma forma, foi possível verificar que a condutância estomática diminuiu em função do decréscimo em psi2. O acúmulo de ABA e o fechamento estomático ocorreram quando psi2 foi menor que -1.0 MPa. A deficiência hídrica em laranjeiras 'Pêra' aumentou o conteúdo de ABA, com conseqüente fechamento estomático e decréscimo em psi2.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:37Z No. of bitstreams: 1 S0006-87052002000300005.pdf: 176918 bytes, checksum: 3c6b6c53305f1a083909669bac9d6af1 (MD5) Made available in DSpace on 2013-08-22T18:49:37Z (GMT). No. of bitstreams: 1 S0006-87052002000300005.pdf: 176918 bytes, checksum: 3c6b6c53305f1a083909669bac9d6af1 (MD5) Previous issue date: 2002-12-01 Made available in DSpace on 2013-09-30T18:45:29Z (GMT). No. of bitstreams: 2 S0006-87052002000300005.pdf: 176918 bytes, checksum: 3c6b6c53305f1a083909669bac9d6af1 (MD5) S0006-87052002000300005.pdf.txt: 36669 bytes, checksum: c57c4c97f44db6894708344c02ffd6f6 (MD5) Previous issue date: 2002-12-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:04:04Z No. of bitstreams: 2 S0006-87052002000300005.pdf: 176918 bytes, checksum: 3c6b6c53305f1a083909669bac9d6af1 (MD5) S0006-87052002000300005.pdf.txt: 36669 bytes, checksum: c57c4c97f44db6894708344c02ffd6f6 (MD5) Made available in DSpace on 2014-05-20T14:04:04Z (GMT). No. of bitstreams: 2 S0006-87052002000300005.pdf: 176918 bytes, checksum: 3c6b6c53305f1a083909669bac9d6af1 (MD5) S0006-87052002000300005.pdf.txt: 36669 bytes, checksum: c57c4c97f44db6894708344c02ffd6f6 (MD5) Previous issue date: 2002-12-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) A Região do Planalto Ocidental Paulista tem se destacado como pólo produtor de borracha natural. Visando fornecer informações sobre a adaptação dos clones de seringueira [Hevea brasiliensis (Wildd. ex. Adr. de Juss) Müell. Arg.] RRIM 600, GT 1, RRIM 701, IAN 873 e PB 235, em São José do Rio Preto (SP), realizaram-se avaliações de alguns caracteres de sua biologia, pelo acompanhamento das trocas gasosas e mensuração do desenvolvimento vegetativo durante os primeiros 18 meses após o enxerto sobre Tjir 16. A altura de RRIM 600 atingiu, em média, 3,74 m e o diâmetro do caule de IAN 873 e RRIM 600, 2,50 cm. PB 235 apresentou o menor índice relativo de crescimento durante o período. No período úmido, os valores das trocas gasosas não diferiram significativamente entre os clones, com valores médios da taxa fotossintética de 9,45 mmol.m-2.s-1; para a taxa de transpiração, 3,84 mmol.m-2.s-1, e para a condutância estomática, de 0,096 mol.m-2.s-1. Diferenças entre os valores de trocas gasosas ocorreram apenas no período seco, com redução mais acentuada para PB 235. Considerando o conjunto dos caracteres analisados, o desempenho dos clones IAN 873 e RRIM 600 foi superior, e do clone PB 235, inferior. The region of São Paulo Occidental Plateau is well known for its part as a major producer of natural rubber. In order to obtain information about adaptation of rubber tree clones [Hevea brasiliensis (Wildd. ex. Adr. de Juss) Müell. Arg.] RRIM 600, RRIM 701, IAN 873, PB 235 and GT 1, in the city of São José do Rio Preto some biologic characteristics were evaluated. Analysis were performed by monitoring gas exchanges and by measuring vegetative development, during the 18 months after engraft on the Tjir 16 clonal rootstocks. The height of RRIM 600 reached a mean of 3,74 m, and the diameter of the stem of IAN 873 and RRIM 600 reached the mean of 2,50 cm. Clone PB 235 presented the lowest relative growth during the period. During the wet period, the values of the gas exchange did not show significant variation among the clones; the mean value of photosynthetic rates was 9,45 mmol.m-2.s-1; of transpiration rates was 3,84 mmol.m-2 s-1, and of stomatic conductance was 0,096 mol.m-2 s-1. Differences in values of gas exchanges were observed only during the dry period, with notably large reduction for clone PB 235. The characteristics analyzed lead to the conclusion that performances of clones IAN 873 and RRIM 600 were superior, and that of clone PB 235 were inferior. UNESP PIBIC CNPq UNESP Instituto de Biociências, Letras e Ciências Exatas Departamento de Zoologia e Botânica UNESP PIBIC UNESP Instituto de Biociências, Letras e Ciências Exatas Departamento de Zoologia e Botânica

The aim of this work is to analyze the effects of a) short-term treatments with different concentrations of O 3 (daily 6-hour fumigation with 0, 65, 175 and 300 ppb for 3-4 days); and b) a medium term treatment with O 3 (150 ppb three times a week for thirty days on the whole) and CO 2 (700 ppm) on gas exchange, chlorophyll fluorescence, and peroxidase activity in holm oak (Quercus ilex L.) leaves. The results show that net photosynthesis, transpiration, F V /F M ratio and POD activity were not influenced until an O 3 concentration of 300 ppb was reached. At this threshold, significant alterations in these physiological and biochemical parameters were found. The treatment with +CO 2 +O 3 showed an increase of net photosynthesis suggesting thus an antagonistic effect of CO 2 with regard to O 3 -induced injuries, while CO 2 alone increased photosynthesis and decreased transpiration but induced no effects on F V /F M ratio or peroxidase activity. From out data, holm oak shows a resistance to episodes of photochemical O 3 stress, that in the Mediterranean region can reach peaks of > 100 ppb. This response is likely to be due to the inorpho-anatomic structure of holm oak leaves and their sclerophyllous adaptations. This might leads holm oak to adopt a stress tolerance strategy with regard to leaf response to O 3 , the effects of which cannot be ameliorated by an increase of atmospheric CO 2 .