Juliane Peters

Short-term changes in free radical scavengers and chloroplast pigments in Pinus canariensis needles as affected by mild drought stress

Summary Potted Pinus canariensis seedlings were subjected to mild drought by withholding irrigation for one week. This treatment induced a reduction in maximum stomatal conductance (50 mmol m −2 s −1 ) compared to irrigated controls (130 mmol m −2 s −1 ). Needle water potentials of non-irrigated trees were maintained at control level (-0.44 MPa). Such a mild drought is a potential oxidative stressor due to the production of active oxygen species (AOS) in illuminated chloroplasts which lack CO 2 due to stomatal closure. Photoprotective pigments (e.g. the xanthophyll cycle) may avoid this situation through light energy dissipation, and antioxidants such as ascorbic acid, tocopherols, and glutathione, may detoxify AOS. Concentrations of ascorbate, glutathione, chlorophyll, and the xanthophyll cycle carotenoids were minimal in the evening (under low light) compared to light-saturated conditions. α-Carotene was highest in the evening. These short-term changes were not affected by drought. The xanthophyll cycle pool tended to be more de-epoxidized in strongly illuminated needles of non-irrigated trees at the beginning of the experiment, but this effect was transient. The glutathione pool was more oxidized in needles of non-irrigated trees (up to 20 percnt; of total vs. 10 percnt; at control) after the xanthophyll changes took place, whereas the redox state of ascorbate remained stable.

Photostress, photoprotection, and water soluble antioxidants in the canopies of five Canarian laurel forest tree species during a diurnal course in the field

Minimal relative water contents of more than 85% indicated that dehydration was not a stress factor. Stomatal conductances decreased from 150 to 200 mmol H 2 O m –2 s –1 in the morning to about 50 mmol H 2 O m –2 s –1 during the day in all species, but this did not limit CO 2 uptake. De-epoxidation of xanthophylls only occurred in sun leaves of I. canariensis (to more than 50%) and M. faya (more than 60%). Decreases in Fv/Fm were only found in sun leaves of P. indica (from ca. 0.80 in the morning to a minimum of 0.70) and, as a trend, also in L. azorica (from ca. 0.75 to ca. 0.65). I. perado showed neither of those responses. P. indica and L. azorica exhibited the highest photosynthesis rates of about 10 µmol CO2 m –2 s –1 compared to 8 in the other species. The photoprotection strategy of P. indica and L. azorica admitted slow recovery from photoinhibition, did not activate protective energy dissipation through xanthophylls, and allowed highest production under these typical conditions.

Influence of canopy position, needle age and season on the foliar gas exchange of Pinus canariensis

We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability.

Element contents and stress-physiological characterization of Pinus canariensis needles in Mediterranean type field stands in Tenerife

Abstract Contents of Ca, Mg, K, Na, S, Cl, P, N, pigments, ascorbic acid, glutathione, and tocopherol together with chlorophyll fluorescence were measured in needles of Pinus canariensis trees growing at four field stands at 4 different altitudes at the south-eastern slope of the Teide in Tenerife. S contents reflected impacts of SO 2 at lower altitudes. Via Na and Cl contents the influence from the sea was assessed up to 1000 m. Above 1000 m we found higher levels of ascorbic acid, less chlorophyll, higher carotenoid/chlorophyll-ratios, and lower α/β-carotene ratios. This pattern suits in a picture of elevated oxidative stress these trees are responding to. Decreases in Fv/Fm-ratios of chlorophyll fluorescence below 0.80 reflecting damages in the photosynthetic apparatus were only found at one site at 1500 m, where altitude stress was probably amplified by drought stress.

Structure and ultrastructure of Pinus canariensis needles.

Summary The present study using light, transmission and scanning electron microscopy contains information about the structure of the needles of Pinus canariensis , an endemic pine of the Canary Islands. As a three-needled species, they have a triangular shape in transverse section being the abaxial side hemispherical. The deeply sunken stomata and the waxes covering the epidermal cells as well as the epistomatal chamber, constitute a good adaptation to the loss of water. The mechanical tissue below the epidermis contributes to a higher drought resistance and to maintain the shape of the long needles as a skeletic tissue. The ultrastructure of mesophyll cells, transfusion tissues as well as endoderrnis and resin ducts is also described. The results of this study should be used as reference data for further investigations of physiological, biochemical and ultrastructural responses of this species to environmental variations due to pollutants and different altitudinal and exposure situations.

Different surface characteristics of primary and secondary needles of Pinus canariensis

Summary Surface characteristics of primary and secondary needles of Pinus canariensis were investigated using scanning electron micro-scopy and gas chromatography to study structure and composition of epicuticular wax, cuticle micromorphology and the structure of stomata. Tubular waxes could be observed on the whole needle surface of the glaucous primary needles whereas on secondary needles they were restricted to the lower surface of young needles. Recrystallization resulted in comparable wax tubes and, addition-ally, plate like structures recrystallized from primary needle wax. Isolated cuticles of primary needles were tender and showed a simple stomata complex with six subsidiary cells whereas the cuticles of secondary needles were massive and revealed 9–12 subsidiary cells. In contrast to the cuplike epistomatal chamber of the primary needles that of the secondary needles was larger and often irregularly formed. Main constituents of the cuticular wax were ω-hydroxy-n-alkanoic acids, 10-nonacosanol and n-alkanoic acids with no differences in the qualitative composition between primary and secondary needles but with some differences in the quantitative pattern. The possible role of the investigated cuticular features in adaptive strategies of the needles to avoid light and water stress is discussed.

Effect of Extreme Temperature on Quantum Yield of Fluorescence and Membrane Leakage of the Canarian Endemic Pine (Pinus canariensis)

The effect of extreme temperature on the quantum yield of fluorescence and membrane leakage of Pinus canariensis growing in 5 stands at different altitudes and orientation in Tenerife (Canary Islands, Spain) was determined. Needles were collected from the field and transferred to the laboratory where they were kept in a closed chamber with water-saturated air overnight. Then they were exposed for 30 minutes in plastic bags in a water bath at temperature treatments with steps of 2K between 56 °C and -24 °C and the effect was determined immediately and 24 hours after the treatment by chlorophyll fluorescence and electrolyte leakage. Needles presented incipient damage at temperatures ranging from -5 to -10 °C depending on the altitude and orientation of the stand. The results were more evident when the measurements were done 24 hours after the cold treatment and values were consistent with the electrolyte leakage results. Different resistance to high temperature depending on the altitude and orientation was also found, varying the temperature for incipient damage from 42 to 44 °C detected with the fluorescence parameters but not with the leakage of electrolytes which was not found until 50 °C. The amplitude of thermal limits for photosynthetic efficiency alteration in needles of P. canariensis was relatively narrow and similar to that of evergreen Canarian laurel forest trees

Gas Exchange of Irrigated and Non-Irrigated Pinus canariensis Seedlings Growing Outdoors in La Laguna, Canary Islands, Spain

Chlorophyll fluorescence, gas exchange, water potential and relative water content were measured in the needles of five year old seedlings of Pinus canariensis in order to know their response to mild water stress. Two trial plots of ten plants per plot, of similar age and characteristics were irrigated daily until the experiment was undertaken, then one of the plots was left without watering while the other one was irrigated as before. After a week of treatment, the water potential at midday did not change in any of the irrigated or non-irrigated plants maintaining around -0 .4 MPa, and the relative water content changed from 93% in irrigated to 84% in non-irrigated seedlings. The stomatal conductance decreased 60% in non irrigated plants and as a result CO2 assimilation decreased by 50% and transpiration was reduced at a higher proportion (70% ), indicating a good control against water loss, before any change in water status in the needles could be observed suggesting an isohydric water economy in this plant