RESUMO

Leaf galls induced by a still undescribed new species of Cecidomyiidae (Diptera) are frequent on leaves of Clusia arrudae Planchon & Tirana (Clusiaceae) in the rupestrian fields at 1400 m a.s.l. in Serra do Cipó, Minas Gerais, Brazil. Galls were 7.1 ± 0.7 mm in diameter, one chambered with only one larva inside. Gall tissue is green and soft. Assessments of photosynthetic capacity using chlorophyll-a fluorescence measurements revealed that photosynthetic performance of gall tissue and healthy leaf tissue were rather similar. Hence, the morphological changes due to gall development were not associated with significant changes in the photosynthetic capacity of the tissue.

Assuntos

RESUMO

Leaf galls induced by a still undescribed new species of Cecidomyiidae (Diptera) are frequent on leaves of Clusia arrudae Planchon & Tirana (Clusiaceae) in the rupestrian fields at 1400 m a.s.l. in Serra do Cipó, Minas Gerais, Brazil. Galls were 7.1 ± 0.7 mm in diameter, one chambered with only one larva inside. Gall tissue is green and soft. Assessments of photosynthetic capacity using chlorophyll-a fluorescence measurements revealed that photosynthetic performance of gall tissue and healthy leaf tissue were rather similar. Hence, the morphological changes due to gall development were not associated with significant changes in the photosynthetic capacity of the tissue.

Galhas induzidas por uma espécie nova ainda não descrita de Cecidomyiidae (Diptera) são frequentes nas folhas de Clusia arrudae Planchon & Tirana (Clusiaceae) em áreas de campos rupestres a 1400 metros de altitude na Serra do Cipó, Minas Gerais, Brasil. As galhas apresentaram um diâmetro médio de 7,1 ± 0,7 mm e uma loja com uma larva dentro. As galhas são verdes e de tecido macio. Análises da capacidade fotossintética usando medidas de fluorescência da clorofila a revelaram que o desempenho fotossintético dos tecidos da galha e sadios foi similar. Assim, as mudanças induzidas pelo desenvolvimento das galhas não foram associadas a mudanças significativas da capacidade fotossintética do tecido.

Assuntos

RESUMO

Leaf galls induced by a still undescribed new species of Cecidomyiidae (Diptera) are frequent on leaves of Clusia arrudae Planchon & Tirana (Clusiaceae) in the rupestrian fields at 1400 m a.s.l. in Serra do Cipó, Minas Gerais, Brazil. Galls were 7.1 ± 0.7 mm in diameter, one chambered with only one larva inside. Gall tissue is green and soft. Assessments of photosynthetic capacity using chlorophyll-a fluorescence measurements revealed that photosynthetic performance of gall tissue and healthy leaf tissue were rather similar. Hence, the morphological changes due to gall development were not associated with significant changes in the photosynthetic capacity of the tissue.

Galhas induzidas por uma espécie nova ainda não descrita de Cecidomyiidae (Diptera) são frequentes nas folhas de Clusia arrudae Planchon & Tirana (Clusiaceae) em áreas de campos rupestres a 1400 metros de altitude na Serra do Cipó, Minas Gerais, Brasil. As galhas apresentaram um diâmetro médio de 7,1 ± 0,7 mm e uma loja com uma larva dentro. As galhas são verdes e de tecido macio. Análises da capacidade fotossintética usando medidas de fluorescência da clorofila a revelaram que o desempenho fotossintético dos tecidos da galha e sadios foi similar. Assim, as mudanças induzidas pelo desenvolvimento das galhas não foram associadas a mudanças significativas da capacidade fotossintética do tecido.

RESUMO

Leaf galls induced by a still undescribed new species of Cecidomyiidae (Diptera) are frequent on leaves of Clusia arrudae Planchon & Tirana (Clusiaceae) in the rupestrian fields at 1400 m a.s.l. in Serra do Cipó, Minas Gerais, Brazil. Galls were 7.1 ± 0.7 mm in diameter, one chambered with only one larva inside. Gall tissue is green and soft. Assessments of photosynthetic capacity using chlorophyll-a fluorescence measurements revealed that photosynthetic performance of gall tissue and healthy leaf tissue were rather similar. Hence, the morphological changes due to gall development were not associated with significant changes in the photosynthetic capacity of the tissue.

Galhas induzidas por uma espécie nova ainda não descrita de Cecidomyiidae (Diptera) são frequentes nas folhas de Clusia arrudae Planchon & Tirana (Clusiaceae) em áreas de campos rupestres a 1400 metros de altitude na Serra do Cipó, Minas Gerais, Brasil. As galhas apresentaram um diâmetro médio de 7,1 ± 0,7 mm e uma loja com uma larva dentro. As galhas são verdes e de tecido macio. Análises da capacidade fotossintética usando medidas de fluorescência da clorofila a revelaram que o desempenho fotossintético dos tecidos da galha e sadios foi similar. Assim, as mudanças induzidas pelo desenvolvimento das galhas não foram associadas a mudanças significativas da capacidade fotossintética do tecido.

RESUMO

High irradiances, high air temperatures and low relative humidities characterize the seasonal savannas of central Brazil, locally known as cerrados. In the present study, we investigated the implications to photoprotection of diurnal adjustments in photochemical and non-photochemical processes in five cerrado woody species that differed in photosynthetic capacity and in the duration and extension of the midday depression of photosynthesis. We also evaluated the contribution of photorespiration to minimize the danger of photoinhibition and the potential carbon costs of the operation of this mechanism in response to changes in irradiance levels. Notwithstanding the large differences in diurnal patterns of photosynthesis and in stomatal conductance, four out of the five species showed a tight common linear relationship between net CO2 assimilation rates and transpiration over the large range of environmental conditions that prevailed during typical sunny days at the end of the rainy season. Large reversible decreases in photochemical efficiency were compensated by proportional increases in non-photochemical processes related to photoprotection, irrespective of the prevailing irradiance levels and degree of stomata closure. Light response curves were used to evaluate the relative contribution of photorespiratory CO2 production to electron flow in response to changes in irradiance levels. A large percentage of the electron flow was used to drive photorespiration in light-saturated leaves. In conclusion, an efficient control of photochemical and non-photochemical quenching and adjustments in the partition of electron flow between assimilative and non-assimilative processes alleviated the danger of photoinhibition. However, the results also suggest that losses in potential carbon gain because of high photorespiratory costs could impose strong limitations on leaf carbon balance of cerrado woody species.

RESUMO

Crassulacean acid metabolism (CAM) plants are dependent on the organic acids that accumulate overnight in the vacuoles as a source of CO(2) during the daylight deacidification period, when stomata are closed and high irradiances generally prevail. We performed an integrative analysis of diurnal changes in gas exchange, chlorophyll fluorescence parameters and organic acid decarboxylation to understand the adjustments in photochemical and non-photochemical processes during the different CAM phases in Clusia hilariana Schlecht., a dominant tree species in the sandy coastal plains of southeastern Brazil. A linear relationship was obtained between the quantum yields of photochemical and non-photochemical quenching, irrespective of the CAM phase and prevailing irradiance. Degradation of malic and citric acids during the midday stomatal closure period could lead to potential CO(2) fixation rates of 23 &mgr;mol m(-2) s(-1), whereas CO(2) losses, measured as CO(2) evolution, corresponded to about 3% of this value. Thus, decarboxylation of malate and citrate provided high internal CO(2) concentrations during phase III of CAM, even though the stomata were closed, allowing optimal utilization of light energy, as indicated by the non-saturating electron transport rates (ETR) in the light response curves, with highest rates of ETR occurring at midday in the diurnal curves. At the transition from phase III to IV of CAM, depletion of internal CO(2) sources and low stomatal conductances, which restricted the supply of exogenous CO(2), reduced the demand for photochemical energy to drive carbon assimilation. This was compensated by increases in thermal energy dissipation as indicated by higher rates of non-photochemical quenching, while high irradiances still prevailed. Shifts in the CAM phases and changes in protective thermal dissipation potential allowed C. hilariana to match changes in PPFD patterns for leaves of different orientations. Evidence that most of the decline in photochemical efficiency was probably related to the fast-relaxing component of non-photochemical quenching is provided by the high values of the quantum yield of photosystem II after 20 min of relaxation in darkness, and an almost complete recovery after sunset. These adjustments in photosynthetic machinery minimized the danger of photo-inhibition in C. hilariana, which is commonly found in fully exposed habitats.

RESUMO

Clusia rosea Jacq. is abundant in the moist parts of the Caribbean island of St John (US Virgin Islands, Lesser Antilles) but relatively rare along the dry south coast. Three types of seedlings were encountered, terrestrial seedlings, seedlings growing as humus-epiphytes on other trees, and seedlings growing inside the tanks of the bromeliad Aechmea lingulata (L.) Baker. Free-living trees grow from terrestrial seedlings or from epiphytic seedlings strangling and shading their host trees. Leaf-Na+ levels were always low (1-4 mequiv I-1 tissue water); trees close to the shore were not affected by salinity. In leaves of mature C. rosea trees, levels of Ca2+ , Mg2+ and K+ were about 60-90, 40-50, 45-55 mequiv I-1 tissue water, respectively. Epiphytic seedlings tended to contain lower levels of these inorganic cations than seedlings growing terrestrially or in the tanks of Ae. lingulata. Epiphytic seedlings contained significantly less nitrogen than terrestrial seedlings. In the leaves of mature trees N-levels were independent of altitude and location on the island, but shaded leaves had significantly higher N-levels than exposed leaves. Light compensation point of photosynthesis in epiphytic seedlings performing C3 -photosynthesis was 17-5 (µmol photons m-2 s-1 ), photosynthesis was saturated at about 300µmol photons m-2 s-1 showing a maximum rate of CO2 -uptake of 2-3 µmol m-2 s-1 .

RESUMO

A comparison of the performance of two epiphytes with crassulacean acid metabolism (CAM) was made during the rainy season and dry season at the Ciénega el Ostional, Chichiriviche in northern Venezuela. The epiphytic bromeliad, Tillandsia flexuosa has water-retaining tanks and leaf trichomes, and propagates mainly vegetatively to produce large populations in the shrubby island vegetation. The epiphytic orchid, Schomburgkia humboldtiana formed smaller populations, and had large succulent leaves with uniform chlorenchyma and no distinct water-storage parenchyma, unlike T. flexuosa. Both epiphytes were myrmecophilous. Leaf succulence (kg m-2 ) declined by ∼ 10% in the dry season for both plants. Both epiphytes showed reduced CO2 uptake during Phase I (dark period) and (dawn-dusk) titratable acidity (ΔH+ ) in the dry season. Water-use efficiency (WUE) was higher for S. humboldtiana (16.0 × 10-3 mol CO2 per mol H2 O compared with 5.0 × 10 -3 for T. flexuosa) although WUE remained constant during rainy and dry season for each species. Sixty to seventy per cent of the dawn dusk titratable acidity was derived internally from respiratory CO2 (recycling) for both species, and in absolute terms, recycling decreased in the dry season, in contrast to the expected progression under drought stress. Recycling is an important facet of carbon balance for both species in both rainy and dry seasons. Leaf Na+ concentration was higher than values quoted for terrestrial salt stressed CAM plants. Fructose and glucose declined in leaf bases of T. flexuosa during the dark period, but not in the more distal regions of the leaf. S. humboldtiana showed a decrease in sucrose at night, and mannitol was also an important constituent of the leaves. Xylem sap tension maxima increased from 0.38 ± 0.09 MPa (rainy season) to only 0.55 ± 0.06 MPa (dry season) for T. flexuosa, these values being much lower than those found for terrestrial shrubs and herbs at the same site, the two epiphytes use CAM in conjunction with differing morphological adaptations to maintain growth throughout the year at the Ciénega el Ostional, but it would seem that T. flexuosa has better physiological characteristics for maintenance of carbon acquisition during the dry season.

RESUMO

Seasonal effects on leaf gas exchange and water relations were compared for Avicennia germinans, a true mangrove, and Conocarpus erectus, a mangrove associate, at coastal sites in northern Venezuela. On the Ciénega el Ostional at Chichiriviche, A. germinans was most abundant around lagoons on the seaward side of the vegetation-free alluvial sand plain. C. erectus was the dominant shrub in inland communities, but the two species co-occurred on vegetation islands at the landward edge of the alluvial plain. On the vegetation islands of the Ciénega el Ostional, gas exchange in A. germinans (a species with foliar salt glands) was less severely curtailed in the dry season compared with the rainy season than was gas exchange in C. erectus (a species lacking salt glands). Average rates of photosynthesis at near-saturating light intensities and total diurnal CO2 uptake were reduced in the dry season to 69 and 61%, respectively, of their values in the rainy for A. germinans, but to 48 and 30%, respectively, of their rainy-season values for C. erectus. Similarly, stomatal conductance and transpirational water loss were more reduced in the dry season for C. erectus than for A. germinans, with the result that C. erectus showed a 3.4-fold increase in water-use efficiency in the dry season compared with the rainy season. The importance of the soil environment in determining plant gas-exchange Patterns was evidenced by large seasonal shifts in dawn xylem tension for the two species (which increased from 1.34 MPa in the rainy season to 5.50 MPa in the dry season for A. germinans, and from 0.40 to 5.78 MPa for C. erectus). These values reflected changes in the soil environment caused by inundation of the upper soil layers by fresh water in the rainy season and a progressive increase in salt concentrations (to almost twice those in sea water) by evaporation from the soil in the dry season. Large changes in xylem tension were observed for both species during individual day-night cycles, reaching a maximum of 2.36 MPa for A. germinans. For C. erectus, the magnitude of these day-night changes was greatly reduced in the dry season, consistent with its very low transpiration rates at this time of year. Leaf-cell osmotic pressures also tended to be higher in A. germinans than C. erectus (attaining a maximum of 8.3 MPa for A. germinans in the dry season), and were related to the more seaward distribution of the true mangrove on the alluvial plain. Whereas leaves of A. germinans did not show any changes in succulence, leaf succulence in C. erectus increased with leafage and was slightly higher in the dry season than the rainy season. The more succulent leaves also had higher cell-sap osmotic pressures and NaCl concentrations. The most succulent leaves of C. erectus were observed for exposed shrubs growing on the shoreline. During the dry season, these shoreline plants showed high rates of gas exchange and low values for dawn xylem tension (0.89 MPa), indicating that they had access to relatively non-saline water from the shallow water table. On individual plants, exposed shoots had more succulent leaves and higher osmotic pressure and NaCl concentrations than sheltered leaves, demonstrating the importance of foliar absorption of salt borne in sea spray for the ionic relations of C. erectus. Thus, although the distribution of C. erectus is centred on brackish-water zones, this species can apparently extend from habitats with permanent access to a shallow water table through to areas where it is seasonally exposed to low soil water potentials and high salt concentrations in the substratum.

RESUMO

The terrestrial CAM plant Bromelia humilis was examined in the salinas of the Ciénega el Ostional, on the north coast of Venezuela, in the rainy and dry seasons. Three colour forms were distinguished; yellow (in full sun), green exposed (also in sun) and green shaded (beneath woodland). Plant size decreased with increasing irradiance. An examination was made of the three phenotypes in terms of CO2 exchange (Jco2 ), dawn-dusk changes in titratable acidity (ΔH+ ) and malate and citrate levels, osmotic pressure, xylem tension, sugar and amino acids levels, nitrogen and ion concentrations and ambient temperature fluorescence. All phenotypes exhibited lowered Jco2 and ΔH+ in the dry as compared to the rainy season. Citrate, as well as malate, showed dawn-dusk fluctuations. Soluble sugars were the major source of carbon skeletons for nocturnal organic acid production. The dawn-dusk changes in osmotic pressure were negligible. Yellow plants performed poorly in contrast to shaded plants in both seasons. The former showed higher dawn-dusk changes of citrate levels and contained much less nitrogen than shaded plants. Nocturnal recycling of respiratory CO2 was more important in yellow plants and, in the dry season, reached 87%. These differences were reflected in the overall productivity, shaded plants showing increases in size whereas yellow plants utilized energy mainly for leaf replacement. Water availability and nitrogen supply appear to be the overriding factors determining higher productivity and CO2 assimilation in partially shaded plants as compared with plants in full sun.

RESUMO

The perennial halophytes, Batis maritima L., Sesuvium portulacastrum L., and Portulaca rubricaulis H.B.K. which inhabit the extreme environment on parts of the salt plain and at the edges of the vegetation islands of Ciénega el Ostional were examined to determine their strategies for growth and survival in the rainy and dry seasons. All of the three species are leaf-succulents. High leaf-sap osmotic pressures, xylem tensions and Na+ and Cl- levels indicated that S. portulacastrum and B. maritima are salt-accumulating halophytes. Succulence, leaf-sap osmolalities and Na+ and Cl- levels increased in the dry season in B. maritima by a factor of 1.5-2.0 and in S. Portulacastrum by a factor of 1.9-2.7. B. maritima also accumulated sulphate with a two-fold increase of concentrations in the dry season. In S. portulacastrum Na+ accumulation much exceeded Cl- accumulation and oxalate synthesis was found to serve charge balance. In this species the compatible solutes, proline and pinitol, were clearly detectable in both seasons; their levels increased by a factor of about 6 in the dry season. Exchange of water vapour and CO2 was measured with a portable steady-state porometer. Photosynthesis in B. maritima showed little response to the transition from the rainy to the dry season while S. portulacastrum was severely impaired in the dry season, showing pronounced midday depressions of gas exchange and about 40% inhibition of light-saturated rates of CO2 uptake. P. rubricaulis shed its leaves in the dry season. According to carbon isotope ratios (δ13 C), B. maritima (δ13 C =-26.4‰) and S. portulacastrum (δ13 C =-25.8 ‰) are C3 plants while P. rubricaulis (δ13 C =-12.3‰) performed C4 photosynthesis.

RESUMO

This paper describes the ecology of a coastal alluvial plain at Chichiriviche in northern Venezuela. The area supports a great diversity of plant communities, ranging from mangroves on the seaward edge of the plain to non-halophytic, fresh-water communities on the landward side. Small differences on topography result in a mosaic of saline and less-saline environments. Rainfall is strongly seasonal, causing superficial flooding of the alluvial plain in the rainy season and the creation of a hypersaline Substratum during the dry season. As a consequence, much of the plain is devoid or vegetation. Towards the landward side of the plain there are numerous small 'vegetation islands', fringed by halophilic succulent herbs, and made up of deciduous and semi-deciduous shrubs and trees together with non-halophytic CAM plants such as cacti and bromeliads. In subsequent papers the results of ecophysiological studies of these diverse plant species are presented.

RESUMO

In an ecophysiological field investigation of plant communities of vegetation islands of an alluvial plain in northern Venezuela the members of the Cactaceae, Pereskia guamacho, and a columnar ceroid cactus, Subpilosocereus ottonis, were studied. The alluvial plain was flooded by fresh water in the rainy season in November/December 1985 and was dry and saline in the dry season in March/April 1986. The highly succulent leaves of P. guamacho were shed in the dry season. They performed C3 photosynthesis in the wet season and did not show signs of considerable salt accumulation. P. guamacho avoids stress due to drought and salinity by leaf-shedding. The columnar stem succulent ceroids are salt-excluding plants with crassulacean acid metabolism (CAM). Rapid die back and regeneration of absorptive roots, water parenchyma and CAM, with the possibility of nocturnal stomatal closure and CO2 recycling, are traits of adaptive value under fluctuating conditions between rainy and dry seasons on the alluvial plain.

RESUMO

The relationship between the electrochemical proton gradient, Δ µH+ (-) , and citrate transport has been studied in tonoplast vesicles from Hevea brasiliensis (the rubber tree). Vesicles were generated from lyophilized samples of fresh vacuoles obtained from the latex sap. Methylamine was used to measure intravesicular pH and lipophilic ions to determine the electrical potential difference (ΔΨ) across the tonoplast. When incubated at pH 7.5 in the absence of ATP, the tonoplast vesicles showed a ΔpH of 0.6 units (interior acid) and a ΔΨ of about-100 mV (interior negative). This potential is thought to be made up of contributions from an H(+) diffusion potential, diffusion potentials from other cations and a Donnan potential arising from the presence of internal citrate. In the presence of 5 mol m(-3) MgATP the ΔpH was increased to about 1.0 unit and the ΔΨ to about-10 mV. Under these conditions the proton-motive force (Δ p Δ µH+ (-) /F) became positive and reached +50 mV. These effects were specific to MgATP (ADP and Mg(2+) having no significant effect) and were prevented by the protonophore p-trifluoromethoxycarbonylcyanidephenylhydrazone (FCCP). Citrate uptake by the vesicles was markedly stimulated by MgATP; ADP and Mg(2+) again had no effect. Nigericin greatly increased ΔpH and this was associated with a large increase in citrate accumulation. The results indicate that the vesicle membrane possesses a functional H(+)-translocating ATPase. The Δ µH+ (-) generated by this ATPase can be used to drive citrate uptake into the vesicles. The properties of the tonoplast vesicles are compared with those of the fresh latex vacuoles.