PHOTOSYNTHETIC ADAPTATION OF A BLOOM‐FORMING CYANOBACTERIUM MICROCYSTIS AERUGINOSA (CYANOPHYCEAE) TO PROLONGED UV‐B EXPOSURE1

The bloom‐forming cyanobacterium Microcystis aeruginosa Kütz 854 was cultured with 1.05 W·m^?2 UV‐B for 3 h every day, and its growth, pigments, and photosynthesis were investigated. The specific growth rates represented by chl a concentration and OD₇₅₀ were inhibited 8% and 9% by UV‐B exposure, respectively. Six days of UV‐B treatment significantly reduced cellular contents of phycocyanin and allophycocyanin by 32% and 62%, respectively, and markedly increased the carotenoid content by 27%, but had little effect on the chl a content. The initial values of optimal photosynthetic efficiency for UV‐B treated samples were, respectively, 52%, 87%, and 93% of controls on days 4, 7, and 10 of growth. The light‐saturated photosynthetic rates at day 6 were significantly lower than controls grown without UV‐B. The probability of electron transfer beyond Q_A decreased during UV‐B exposure, and this indicated that the acceptor side of PSII was one of main damage sites. The adaptation of M. aeruginosa 854 to UV‐B radiation could be observed from light‐saturated photosynthetic rates on day 13 and diurnal changes of chl fluorescence during the late growth phase. When both exposed to higher UV‐B, samples cultured under 1.05 W·m^?2 UV‐B for 9 days recovered faster than controls. It is suggested that M. aeruginosa 854 had at least three adaptive strategies to cope with the enhanced UV‐B: increasing the synthesis of carotenoids to counteract reactive oxidants caused by UV‐B exposure, degrading phycocyanin and allophycocyanin to avoid further damage to DNA and reaction centers, and enhancing the repair of UV‐B induced damage to the photosynthetic apparatus.     

UV‐B INDUCTION OF UV‐B PROTECTION IN ULVA PERTUSA (CHLOROPHYTA)1

The green macroalga Ulva pertusa Kjellman produced UV‐B absorbing compounds with a prominent absorption maximum at 294 nm in response only to UV‐B, and the amounts induced were proportional to the UV‐B doses. Under a 12:12‐h light:dark regime, the production of UV‐absorbing compounds occurred only during the exposure periods with little turnover in the dark. There was significant reduction in growth in parallel with the production of UV‐B absorbing compounds. The polychromatic action spectrum for the induction of UV‐B absorbing compounds in U. pertusa exhibits a major peak at 292 nm with a smaller peak at 311.5 nm. No significant induction was detected above 354.5 nm, and radiation below 285 nm caused significant reduction in the levels of UV‐B absorbing compounds. After UV‐B irradiation at 1.0 W·m^?2 for 9 h, the optimal photosynthetic quantum yield of the samples with UV‐B absorbing compounds slightly increased relative to the initial value, whereas that of thalli lacking the compounds declined to 30%–34% of the initial followed by subsequent recovery in dim light of up to 84%–85% of the initial value. There was a positive and significant relationship between the amount of UV‐B absorbing compounds with antioxidant activity as determined by the α,α‐diphenyl‐β‐picrylhydrazyl scavenging assay. In addition to mat‐forming characteristics and light‐driven photorepair, the existence and antioxidant capacity of UV‐B absorbing compounds may confer U. pertusa a greater selective advantage over other macroalgae, thereby enabling them to thrive in the presence of intense UV‐B radiation.     

Different physiological responses of cyanobacteria to ultraviolet‐B radiation under iron‐replete and iron‐deficient conditions: Implications for underestimating the negative effects of UV‐B radiation

Iron deficiency has been considered one of the main limiting factors of phytoplankton productivity in some aquatic systems including oceans and lakes. Concomitantly, solar ultraviolet‐B radiation has been shown to have both deleterious and positive impacts on phytoplankton productivity. However, how iron‐deficient cyanobacteria respond to UV‐B radiation has been largely overlooked in aquatic systems. In this study, physiological responses of four cyanobacterial strains (Microcystis and Synechococcus), which are widely distributed in freshwater or marine systems, were investigated under different UV‐B irradiances and iron conditions. The growth, photosynthetic pigment composition, photosynthetic activity, and nonphotochemical quenching of the different cyanobacterial strains were drastically altered by enhanced UV‐B radiation under iron‐deficient conditions, but were less affected under iron‐replete conditions. Intracellular reactive oxygen species (ROS) and iron content increased and decreased, respectively, with increased UV‐B radiation under iron‐deficient conditions for both Microcystis aeruginosa FACHB 912 and Synechococcus sp. WH8102. On the contrary, intracellular ROS and iron content of these two strains remained constant and increased, respectively, with increased UV‐B radiation under iron‐replete conditions. These results indicate that iron‐deficient cyanobacteria are more susceptible to enhanced UV‐B radiation. Therefore, UV‐B radiation probably plays an important role in influencing primary productivity in iron‐deficient aquatic systems, suggesting that its effects on the phytoplankton productivity may be underestimated in iron‐deficient regions around the world.     

Low induction of non‐photochemical quenching and high photochemical efficiency in the annual desert plant Anastatica hierochuntica

Non‐photochemical quenching (NPQ) plays a major role in photoprotection. Anastatica hierochuntica is an annual desert plant found in hot deserts. We compared A. hierochuntica to three other different species: Arabidopsis thaliana, Eutrema salsugineum and Helianthus annuus, which have different NPQ and photosynthetic capacities. Anastatica hierochuntica plants had very different induction kinetics of NPQ and, to a lesser extent, of photosystem II electron transport rate (PSII ETR), in comparison to all other plants species in the experiments. The major components of the unusual photosynthetic and photoprotective response in A. hierochuntica were: (1) Low NPQ at the beginning of the light period, at various light intensities and CO₂ concentrations. The described low NPQ cannot be explained by low leaf absorbance or by low energy distribution to PSII, but was related to the de‐epoxidation state of xanthophylls. (2) Relatively high PSII ETR at various CO₂ concentrations in correlation with low NPQ. PSII ETR responded positively to the increase of CO₂ concentrations. At low CO₂ concentrations PSII ETR was mostly O₂ dependent. At moderate and high CO₂ concentrations the high PSII ETR in A. hierochuntica was accompanied by relatively high CO₂ assimilation rates. We suggest that A. hierochuntica have an uncommon NPQ and PSII ETR response. These responses in A. hierochuntica might represent an adaptation to the short growing season of an annual desert plant.     

Aphid orientation and performance in glasshouses under different UV‐A/UV‐B radiation regimes

Visual cues leading to host selection and landing are of major importance for aphids and evidence suggests that flight activity is very dependent on ultraviolet (UV)‐A radiation in the environment. At the same time research on insect plant hosts suggest that the UV‐B component can deter some pests via changes in secondary metabolite chemistry. Here, we examine the potential of UV (UV‐A/UV‐B) radiation to control insect pests in the glasshouse environment. We first examined artificial exposure to UV‐B and the potential to trigger morphological and biochemical modifications in pepper (Capsicum annuum L., Solanaceae) with implications for the fitness of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). UV‐B caused accumulation of leaf secondary metabolites and soluble carbohydrates, and stimulated photosynthetic pigments. However, UV‐B did not impact on foliar protein content and aphid performance was unaffected. Next, we studied how altering the UV‐A/UV‐B ratio environment affected aphid orientation and spatial distribution over time, either directly or by exposing plants to supplemental UV before insect introduction. Aphids directly settled and dispersed on their host pepper plants more readily in the presence of supplemental UV‐A and UV‐B. In the control treatment with ambient glasshouse UV‐A and UV‐B, insects remained more aggregated. Furthermore, insects were less attracted to peppers pre‐exposed to supplemental UV‐A and UV‐B radiation. Our results suggest that suppression of UV‐A and UV‐B inside the protected environment reduces aphid colonization and dispersal. Furthermore, application of moderate exposure of young pepper plants to supplemental UV‐B radiation could aid in protection from the colonization by phytophagous insects.     

UV‐B effect on Quercus robur leaf litter decomposition persists over four years

The effects of elevated UV‐B (280–315 nm) radiation on the long‐term decomposition of Quercus robur leaf litter were assessed at an outdoor facility in the UK by exposing saplings to elevated UV‐B radiation (corresponding to a 30% increase above the ambient level of erythemally weighted UV‐B, equivalent to that resulting from a c. 18% reduction in ozone column) under arrays of cellulose diacetate‐filtered fluorescent UV‐B lamps that also produced UV‐A radiation (315–400 nm). Saplings were also exposed to elevated UV‐A radiation alone under arrays of polyester‐filtered fluorescent lamps and to ambient solar radiation under arrays of nonenergized lamps. After 8 months of irradiation, abscised leaves were placed into litter bags and allowed to decompose in the litter layer of a mixed deciduous woodland for 4.08 years. The dry weight loss of leaf litter from saplings irradiated with elevated UV‐B and UV‐A radiation during growth was 17% greater than that of leaf litter irradiated with elevated UV‐A radiation alone. Annual fractional weight loss of litter (k), and the estimated time taken for 95% of material to decay (3/k) were respectively increased and decreased by 27% for leaf litter exposed during growth to elevated UV‐B and UV‐A radiation, relative to that exposed to UV‐A alone. The present data corroborate those from a previous study indicating that UV‐B radiation applied during growth accelerates the subsequent decomposition of Q. robur leaf litter in soil, but indicate that this effect persists for over four years after abscission.     

Nitric oxide is involved in integration of UV‐B absorbing compounds among parts of clonal plants under a heterogeneous UV‐B environment

In nature, ultraviolet‐B (UV‐B) radiation is highly heterogeneous, both spatially and temporally. Plants exposed to UV‐B radiation produce UV‐B absorbing compounds that function as a protective filter. For clonal plants under heterogeneous UV‐B radiation conditions, integration among ramets can allow irradiated ramets to benefit un‐irradiated ramets by causing them to increase their UV‐B absorbing compounds content. In this study, we evaluated integration between pairs of clonal ramets of Glechoma longituba under heterogeneous or homogeneous UV‐B conditions. We determined the levels of UV‐B absorbing compounds, nitric oxide (NO) and hydrogen peroxide (H₂O₂) and measured the activity of phenylalanine ammonia‐lyase (PAL) in connected ramet pairs under homogeneous or heterogeneous UV‐B conditions. Under heterogeneous UV‐B conditions, the UV‐B absorbing compounds content increased in leaves of irradiated and un‐irradiated ramets, but not in the connecting stolons. The NO content increased in irradiated and un‐irradiated leaves and stolons, but the H₂O₂ content did not. Application of NO synthesis inhibitors and an NO blocker to irradiated ramets blocked the increase in UV‐B absorbing compounds and PAL activity in un‐irradiated ramets. These results suggested that NO is involved in the integration process for UV‐B absorbing compounds among ramets. Our findings suggested that a UV‐B‐induced increase in NO transmits a signal to un‐irradiated ramets via the stolon, leading to an increase in PAL activity and UV‐B absorbing compounds content. The internal translocation of signal enables members of clonal networks to function as a whole unit and to mount an efficient defensive response to localized UV‐B radiation.     

Exogenous application of IAA alleviates effects of supplemental ultraviolet‐B radiation in the medicinal plant Withania somnifera Dunal

• Supplemental (s)‐UV‐B radiation has adverse effects on the majority of plants. The present study was conducted to evaluate the effects of exogenous application of the growth hormone indole acetic acid (IAA) on various morphological, physiological and biochemical characteristics of Withania somnifera, an indigenous medicinal plant, subjected to s‐UV‐B.
• The s‐UV‐B‐treated plants received ambient + 3.6 kJm^?2·day^?1 biologically effective UV‐B, and IAA was applied at two doses (200 and 400 ppm) to s‐UV‐B‐exposed plants.
• The plant was forced to compromise its growth, development and photosynthetic patterns to survive under s‐UV‐B by increasing concentrations of secondary metabolites and antioxidants (thiol, proline, ascorbic acid, α‐tocopherol, ascorbate peroxidase, catalase, glutathione reductase, peroxidase, polyphenol oxidase, superoxide dismutase) to counteract oxidative stress. Increases in secondary metabolites were evidenced as increased activity of phenylpropanoid pathway enzymes: phenylalanine ammonia lyase, cinnamyl alcohol dehydrogenase, 4‐coumarate CoA ligase, chalcone isomerase and dihydroflavonol reductase. Application of different IAA doses reversed the detrimental effects of s‐UV‐B on W. somnifera by improving growth and photosynthesis and reducing concentrations of secondary metabolites and non‐enzymatic antioxidants. Antioxidant enzymes, however, had a synergistic effect on s‐UV‐B treatment and IAA application.
• The effects of s‐UV‐B on W. somnifera are ameliorated to varying degrees upon exogenous IAA application, and synergistic enhancement of antioxidant enzymes under s‐UV‐B+IAA treatment might be responsible for the partial recuperation of growth and plant protein content, as a UV‐B‐exposed plant is forced to allocate most of its photosynthate towards production of enzymes related to antioxidant defence.

     

UV‐A/BLUE LIGHT–INDUCED REACTIVATION OF SPORE GERMINATION IN UV‐B IRRADIATED ULVA PERTUSA (CHLOROPHYTA)1

Recent reduction in the ozone shield due to manufactured chlorofluorocarbons raised considerable interest in the ecological and physiological consequences of UV‐B radiation (λ=280–315 nm) in macroalgae. However, early life stages of macroalgae have received little attention in regard to their UV‐B sensitivity and UV‐B defensive mechanisms. Germination of UV‐B irradiated spores of the intertidal green alga Ulva pertusa Kjellman was significantly lower than in unexposed controls, and the degree of reduction correlated with the UV doses. After exposure to moderate levels of UV‐B irradiation, subsequent exposure to visible light caused differential germination in an irradiance‐ and wavelength‐dependent manner. Significantly higher germination was found at higher photon irradiances and in blue light compared with white and red light. The action spectrum for photoreactivation of germination in UV‐B irradiated U. pertusa spores shows a major peak at 435 nm with a smaller but significant peak at 385 nm. When exposed to December sunlight, the germination percentage of U. pertusa spores exposed to 1 h of solar radiation reached 100% regardless of the irradiation treatment conditions. After a 2‐h exposure to sunlight, however, there was complete inhibition of germination in PAR+UV‐A+UV‐B in contrast to 100% germination in PAR or PAR+UV‐A. In addition to mat‐forming characteristics that would act as a selective UV‐B filter for settled spores under the parental canopy, light‐driven repair of germination after UV‐B exposure could explain successful continuation of U. pertusa spore germination in intertidal settings possibly affected by intense solar UV‐B radiation.     

INTERACTIVE EFFECTS OF PAR AND UV‐B RADIATION ON PSII ELECTRON TRANSPORT IN THE MARINE ALGA DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

To better understand the interactions between PAR and UV‐B radiation in microalgae, the marine chlorophyte alga Dunaliella tertiolecta was subjected to a UV‐B flux of 4.1 W·m ^{? 2} (unweighted) with varying PAR fluxes. Rate constants for damage and repair processes during UV‐B exposure increased with PAR flux. However, recovery after UV‐B exposure increased with PAR up to 300 μmol quanta·m ^{? 2}·s ^{? 1} 1 Received 17 September 2002. Accepted 19 February 2003. , beyond which photoinhibition of PSII electron transport was found to decrease recovery rates. In the absence of PAR during the post UV‐B exposure period, no recovery was seen, indicating that perhaps the lack of light available for photosynthesis depresses repair either directly or indirectly by affecting ATP synthesis. Possible mechanisms for the observed interactions between PAR and UV‐B exposure are discussed.     

INTERACTIONS BETWEEN UV‐B EXPOSURE AND PHOSPHORUS NUTRITION. I. EFFECTS ON GROWTH,PHOSPHATE UPTAKE,AND CHLOROPHYLL FLUORESCENCE1

The interactive effects of P starvation and exposure to UV radiation on growth rates, quantum efficiency of PSII electron transport, and P‐uptake capacity of the chlorophyte microalga Dunaliella tertiolecta Butcher are presented. Ultraviolet radiation did not in itself cause marked changes in growth rate, though it did induce changes in the effective quantum yield of PSII. Depriving cells of phosphate resulted in significant changes in all parameters examined. The decline of growth rate and fluorescence parameters after P starvation was significantly faster in the presence of UV radiation. Ultraviolet radiation also stimulated the magnitude of the transient changes in chl fluorescence (nutrient‐induced fluorescence transient) exhibited by P‐starved cells after resupply of that nutrient.     

UV‐B impact on aphid performance mediated by plant quality and plant changes induced by aphids

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV‐B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV‐B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV‐B) or 4% (low UV‐B) of ambient UV‐B. Three‐week‐old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high‐UV‐B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV‐B intensities. Cabbage aphids reproduced less on plants grown under high UV‐B than on plants grown under low UV‐B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation‐dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low‐UV‐B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV‐B radiation considerably impacts plant traits and subsequently affects specialist phloem‐feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.     

MORPHO‐FUNCTIONAL PATTERNS OF PHOTOSYNTHESIS IN THE SOUTH PACIFIC KELP LESSONIA NIGRESCENS: EFFECTS OF UV RADIATION ON 14C FIXATION AND PRIMARY PHOTOCHEMICAL REACTIONS1

The morpho‐functional patterns of photosynthesis, measured as ¹⁴C‐fixation and chl fluorescence of PSII, also as affected by different doses of UV radiation in the laboratory were examined in the South Pacific kelp Lessonia nigrescens Bory of the coast of Valdivia, Chile (40°S). The results indicated the existence of longitudinal thallus profiles in physiological performance. In general, blades exhibited higher rates of carbon fixation and pigmentation as compared with stipes and holdfasts. Light‐independent ¹⁴C fixation (LICF) was high in meristematic zones of the blades (3.5 μmol ¹⁴C·g^?1 fresh weight [FW]·h^?1), representing 2%–16% (percentage ratio) of the photosynthetic ¹⁴C fixation (20 μmol ¹⁴C·g^?1 FW·h^?1). Exposures to UV radiation indicated that biologically effective UV‐B doses (BED_{photoinhibition300}) of 200–400 kJ·m^?2 (corresponding to current daily doses measured in Valdivia on cloudless summer days) inhibit photosynthetic ¹⁴C fixation of blades by 90%, while LICF was reduced by 70%. The percentage ratio of LICF to photosynthetic ¹⁴C fixation increased under UV exposure to 45%. Primary light reactions measured as maximum quantum yield (F_v/F_m) and electron transport rate (ETR) indicated a higher UV susceptibility of blades as compared with stipes and holdfasts: after a 48 h exposure to UV‐B, the decrease in the blades was close to 30%, while in the stipes and holdfasts it was <20%. The existence of translocation of labeled carbon along the blades suggests that growth at the meristem may be powered by nonphotosynthetic processes. A possible functional role of LIFC, such as during reduction of photosynthetic carbon fixation due to enhanced UV radiation, is discussed. These results in general support the idea that the UV‐related responses in Lessonia are integrated in the suite of morpho‐functional adaptations of the alga.     

Differences in growth and physiological traits of two poplars originating from different altitudes as affected by UV‐B radiation and nutrient availability

Cuttings of Populus kangdingensis and Populus cathayana originating from altitudes of 3500 and 1500 m in southwestern China, respectively, were grown for one growing season in the field under ambient or ambient plus supplemental ultraviolet‐B (UV‐B) radiation with two levels of nutrients. In both species, enhanced UV‐B radiation significantly increased UV‐B absorbing compounds and guaiacol peroxidase (GPX) activity, while no significant effects were observed in photosynthetic pigments and proline content. On the other hand, cuttings grown with high‐nutrient availability had larger leaf area, higher total biomass and GPX activity as well as higher water use efficiency (WUE) (as measured by stable carbon isotope composition, δ¹³C) when compared with low‐nutrient conditions, while UV‐B absorbing compounds and ascorbic acid (AsA) content significantly decreased. Differences in responses to enhanced UV‐B radiation and nutrient availability were observed between the two species. Nutrient‐induced increases in chlorophyll a, chlorophyll b and total chlorophyll as well as in carotenoids were greater in P. kangdingensis than in P. cathayana. In P. cathayana, enhanced UV‐B radiation significantly decreased leaf area and total biomass, while it significantly increased WUE and ascorbate peroxidase (APX). In contrast, such changes were not observed in P. kangdingensis. In addition, the effects of enhanced UV‐B radiation on leaf area, total biomass and UV‐B absorbing compounds were closely related to the nutrient status. Our results indicated that P. kangdingensis, which originates from the altitude of 3500 m and is apparently adapted to low‐nutrient and high‐UV‐B habitats, exhibits better tolerance to enhanced UV‐B radiation and greater growth under low‐nutrient availability than does P. cathayana originating from the altitude of 1500 m.     

Distinct physiological and metabolic reprogramming by highbush blueberry (Vaccinium corymbosum) cultivars revealed during long‐term UV‐B radiation

Despite the Montreal protocol and the eventual recovery of the ozone layer over Antarctica, there are still concerns about increased levels of ultraviolet‐B (UV‐B) radiation in the Southern Hemisphere. UV‐B induces physiological, biochemical and morphological stress responses in plants, which are species‐specific and different even for closely related cultivars. In woody plant species, understanding of long‐term mechanisms to cope with UV‐B‐induced stress is limited. Therefore, a greenhouse UV‐B daily course simulation was performed for 21 days with two blueberry cultivars (Legacy and Bluegold) under UV‐B_BE irradiance doses of 0, 0.07 and 0.19 W m^?2. Morphological changes, photosynthetic performance, antioxidants, lipid peroxidation and metabolic features were evaluated. We found that both cultivars behaved differently under UV‐B exposure, with Legacy being a UV‐B‐resistant cultivar. Interestingly, Legacy used a combined strategy: initially, in the first week of exposure its photoprotective compounds increased, coping with the intake of UV‐B radiation (avoidance strategy), and then, increasing its antioxidant capacity. These strategies proved to be UV‐B radiation dose dependent. The avoidance strategy is triggered early under high UV‐B radiation in Legacy. Moreover, the rapid metabolic reprogramming capacity of this cultivar, in contrast to Bluegold, seems to be the most relevant contribution to its UV‐B stress‐coping strategy.     

Light‐induced systemic signalling down‐regulates photosynthetic performance of soybean leaves with different directional effects

• When plants are exposed to a heterogeneous environment, photosynthesis of leaves is not only determined by their local condition, but also by certain signals from other parts of the same plant, termed systemic regulation. Our present study was conducted to investigate the effects of light‐dependent systemic regulation on the photosynthetic performance of soybean (Glycine max L. Merr.) under heterogeneous light conditions.
• Soybean plants were treated with heterogeneous light. Then gas exchange characteristics were measured to evaluate the photosynthetic performance of leaves. Parameters related to photosynthetic pigments, chlorophyll fluorescence, Rubisco and photosynthates were examined to study the mechanisms of light‐dependent systemic regulation on photosynthesis.
• Light‐induced systemic signalling by illuminated leaves reduced the P_n of both upper and lower non‐illuminated leaves on the same soybean plant. The decrease in g_s and increase in C_i in these non‐illuminated leaves indicated restriction of carbon assimilation, which was further verified by the decline in content and activity of Rubisco. However, the activation state of Rubisco decreased only in upper non‐illuminated leaves. Quantum efficiency of PSII (ΦPSII) and ETR also decreased only in upper non‐illuminated leaves. Moreover, the effects of light‐induced systemic signalling on carbohydrate content were also detectable only in upper non‐illuminated leaves.
• Light‐induced systemic signalling by illuminated leaves restricts carbon assimilation and down‐regulates photosynthetic performance of non‐illuminated leaves within a soybean plant. However, effects of such systemic regulation differed when regulated in upward or downward direction.

     

UV‐B impairs growth and gas exchange in grapevines grown in high altitude

We previously demonstrated that solar ultraviolet‐B (UV‐B) radiation levels in high altitude vineyards improve berry quality in Vitis vinifera cv. Malbec, but also reduce berry size and yield, possibly as a consequence of increased oxidative damage and growth reductions (lower photosynthesis). The defense mechanisms toward UV‐B signal and/or evoked damage promote production of antioxidant secondary metabolites instead of primary metabolites. Purportedly, the UV‐B effects will depend on tissues developmental stage and interplay with other environmental conditions, especially stressful situations. In this work, grapevines were exposed to high solar UV‐B (+UV‐B) and reduced (by filtering) UV‐B (?UV‐B) treatments during three consecutive seasons, and the effects of UV‐B, developmental stages and seasons on the physiology were studied, i.e. growth, tissues morphology, photosynthesis, photoprotective pigments, proline content and antioxidant capacity of leaves. The +UV‐B reduced photosynthesis and stomatal conductance, mainly through limitation in gas exchange, reducing plant's leaf area, net carbon fixation and growth. The +UV‐B augmented leaf thickness, and also the amounts of photoprotective pigments and proline, thereby increasing the antioxidant capacity of leaves. The defense mechanisms triggered by + UV‐B reduced lipid peroxidation, but they were insufficient to protect the photosynthetic pigments per leaf dry weight basis. The +UV‐B effects depend on tissues developmental stage and interplay with other environmental conditions such as total radiation and air temperatures.