High Irradiance Research Articles

Phytochromes mediate germination inhibition under red, far-red, and white light in Aethionema arabicum.

The view on the role of light during seed germination stems mainly from studies with Arabidopsis (Arabidopsis thaliana), where light is required to initiate this process. In contrast, white light is a strong inhibitor of germination in other plants, exemplified by accessions of Aethionema arabicum, another member of Brassicaceae. Their seeds respond to light with gene expression changes of key regulators converse to that of Arabidopsis, resulting in opposite hormone regulation and prevention of germination. However, the photoreceptors involved in this process in A. arabicum remain unknown. Here, we screened a mutant collection of A. arabicum and identified koy-1, a mutant that lost light inhibition of germination due to a deletion in the promoter of HEME OXYGENASE 1, the gene for a key enzyme in the biosynthesis of the phytochrome chromophore. koy-1 seeds were unresponsive to red- and far-red light and hyposensitive under white light. Comparison of hormone and gene expression between wild type and koy-1 revealed that very low light fluence stimulates germination, while high irradiance of red and far-red light is inhibitory, indicating a dual role of phytochromes in light-regulated seed germination. The mutation also affects the ratio between the 2 fruit morphs of A. arabicum, suggesting that light reception via phytochromes can fine-tune several parameters of propagation in adaptation to conditions in the habitat.

The Right Light

High irradiance testing of consumer electronics is growing in popularity, but without a precise understanding of the methodology, testers run the risk of inaccurate or misleading results, says Atlas Material Testing Technology.

Exposição de três espécies de Cattleya (Orchidaceae) a pleno sol: efeito sobre sua plasticidade fisiológica e resposta a mudanças nas condições de luz

Abstract In order to establish a link between the evolutionary history and the photochemical attributes, measurements of chlorophyll (Chl) a fluorescence were made in Cattleya warneri, C. shofieldiana and C. harrisoniana exposed to high irradiance for 5, 35, and 120 min (hereafter referred to as treatments T5, T35, and T120, respectively). The following questions are addressed: (1) Is the increased energy dissipation enough to counterbalance the excess energy that drives photosynthesis at different times of high irradiance exposure? (2) Is there an influence of the incidence and duration of light radiation on Cattleya species in full sunlight, compared to Cattleya species submitted to low irradiance? Higher relative variable fluorescence at the J-step (Vj) values followed by the lower quantum yield of electron transport (ψEo) indicate the accumulation of reduced Quinone A (QA) proportionally of sunflecks exposure time in C. warneri. The higher performance index (PIABS) and plasticity index values in C. schofieldiana indicate higher efficiency in modulating the photosynthetic apparatus under sunflecks. C. harrisoniana shows the lowest plasticity index, suppression of maximum fluorescence (Fm), and no recovery of PIABS after sunflecks. This study evidences the importance of physiological plasticity in the current geographic distribution of Cattleya in response to light pulses in species derived from fragmented habitats and the maintenance of shade to species of more primitive clades.

Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness

Evening light-emitting visual displays may disrupt sleep, suppress melatonin and increase alertness. Here, we control melanopic irradiance independent of display luminance and colour, in 72 healthy males 4 h before habitual bedtime and expose each of them to one of four luminance levels (i.e., dim light, smartphone, tablet or computer screen illuminance) at a low and a high melanopic irradiance setting. Low melanopic light shortens the time to fall asleep, attenuates evening melatonin suppression, reduces morning melatonin, advances evening melatonin onset and decreases alertness compared to high melanopic light. In addition, we observe dose-dependent increases in sleep latency, reductions in melatonin concentration and delays in melatonin onset as a function of melanopic irradiance—not so for subjective alertness. We identify melanopic irradiance as an appropriate parameter to mitigate the unwanted effects of screen use at night. Our results may help the many people who sit in front of screens in the evening or at night to fall asleep faster, feel sleepier, and have a more stable melatonin phase by spectrally tuning the visual display light without compromising the visual appearance.

Alternative electron transport pathways contribute to tolerance to high light stress in lichenized algae.

The photosynthetic apparatus of lichen photobionts has been well-characterized by chlorophyll fluorescence analysis (e.g., by pulse amplitude modulation [PAM]), which provides a proxy of the activity of photosystem II (PSII) and its antenna. However, such kinetics are unable to directly characterize photosystem I (PSI) activity and the associated alternative electron pathways that may be involved in photoprotection. Instead, PSI can be probed in vivo by near-infrared absorption, measured at the same time as standard chlorophyll fluorescence (e.g., using the WALZ Dual PAM). Here, we used the Dual PAM to investigate cyclic electron flow and photoprotection in a range of mostly temperate lichens sampled from shaded to more open microhabitats. Sun species displayed lower acceptor side limitation of PSI (Y[NA]) early in illumination when compared to shade species, indicative of higher flavodiiron-mediated pseudocyclic electron flow. In response to high irradiance, some lichens accumulate melanin, and Y[NA] was lower and NAD(P)H dehydrogenase (NDH-2)-type cyclic flow was higher in melanised than pale forms. Furthermore, non-photochemical quenching (NPQ) was higher and faster relaxing in shade than sun species, while all lichens displayed high rates of photosynthetic cyclic electron flow. In conclusion, our data suggest that (1) low acceptor side limitation of PSI is important for sun-exposed lichens; (2) NPQ helps shade species tolerate brief exposure to high irradiance; and (3) cyclic electron flow is a prominent feature of lichens regardless of habitat, although NDH-2-type flow is associated with high light acclimation.

Ability of short exposures from laser and quad-wave curing lights to photo-cure bulk-fill resin-based composites

This study investigated the ability of a laser, and a 'quad-wave' LCU, to photo-cure paste and flowable bulk-fill resin-based composites (RBCs). Five LCUs and nine exposure conditions were used. The laser LCU (Monet) used for 1s and 3s, the quad-wave LCU (PinkWave) used for 3s in the Boost and 20s in the Standard modes, the the multi-peak LCU (Valo X) used for 5s in the Xtra and 20s in the Standard modes, were compared to the polywave PowerCure used in the 3s mode and for 20s in the Standard mode, and to the mono-peak SmartLite Pro used for 20s. Two paste consistency bulk-fill RBCs: Filtek One Bulk Fill Shade A2 (3M), Tetric PowerFill Shade IVA (Ivoclar Vivadent), and two flowable RBCs: Filtek Bulk Fill Flowable Shade A2 (3M), Tetric PowerFlow Shade IVA (Ivoclar Vivadent) were photo-cured in 4-mm deep x 4-mm diameter metal molds. The light received by these specimens was measured using a spectrometer (Flame-T, Ocean Insight), and the radiant exposure delivered to the top surface of the RBCs was mapped. The immediate degree of conversion (DC) at the bottom, and the 24-hour Vickers Hardness (VH) at the top and bottom of the RBCs were measured and compared. The irradiance received by the 4-mm diameter specimens ranged from 1035mW/cm2 (SmartLite Pro) to 5303mW/cm2 (Monet). The radiant exposures between 350 and 500nm delivered to the top surface of the RBCs ranged from 5.3J/cm2 (Monet in 1s) to 26.4 J/cm2 (Valo X), although the PinkWave delivered 32.1J/cm2 in 20s 350 to 900nm. All four RBCs achieved their maximum DC and VH values at the bottom when photo-cured for 20s. The Monet used for 1s and the PinkWave used for 3s on the Boost setting delivered the lowest radiant exposures between 420 and 500 nm (5.3J/cm2 and 3.5J/cm2 respectively), and they produced the lowest DC and VH values. Despite delivering a high irradiance, the short 1 or 3-s exposures delivered less energy to the RBC than 20-s exposures from LCUs that deliver>1000mW/cm2. There was an excellent linear correlation (r>0.98) between the DC and the VH at the bottom. There was a logarithmic relationship between the DC and the radiant exposure (Pearson's r=0.87-97) and between the VH and the radiant exposure (Pearson's r=0.92-0.96) delivered in the 420-500 nm range.

Genomic Analysis of Haloarchaea from Diverse Environments, including Permian Halite, Reveals Diversity of Ultraviolet Radiation Survival and DNA Photolyase Gene Variants

Ultraviolet (UV) radiation responses of extremophilic and archaeal microorganisms are of interest from evolutionary, physiological, and astrobiological perspectives. Previous studies determined that the halophilic archaeon, Halobacterium sp. NRC-1, which survives in multiple extremes, is highly tolerant of UV radiation. Here, Halobacterium sp. NRC-1 UV tolerance was compared to taxonomically diverse Haloarchaea isolated from high-elevation salt flats, surface warm and cold hypersaline lakes, and subsurface Permian halite deposits. Haloterrigena/Natrinema spp. from subsurface halite deposits were the least tolerant after exposure to photoreactivating light. This finding was attributed to deviation of amino acid residues in key positions in the DNA photolyase enzyme or to the complete absence of the photolyase gene. Several Halobacterium, Halorubrum and Salarchaeum species from surface environments exposed to high solar irradiance were found to be the most UV tolerant, and Halorubrum lacusprofundi from lake sediment was of intermediate character. These results indicate that high UV tolerance is not a uniform character trait of Haloarchaea and is likely reflective of UV exposure experienced in their environment. This is the first report correlating natural UV tolerance to photolyase gene functionality among Haloarchaea and provides insights into their survival in ancient halite deposits and potentially on the surface of Mars.

Development of an Optoelectronic Integrated Sensor for a MEMS Mirror-Based Active Structured Light System.

Micro-electro-mechanical system (MEMS) scanning micromirrors are playing an increasingly important role in active structured light systems. However, the initial phase error of the structured light generated by a scanning micromirror seriously affects the accuracy of the corresponding system. This paper reports an optoelectronic integrated sensor with high irradiance responsivity and high linearity that can be used to correct the phase error of the micromirror. The optoelectronic integrated sensor consists of a large-area photodetector (PD) and a receiving circuit, including a post amplifier, an operational amplifier, a bandgap reference, and a reference current circuit. The optoelectronic sensor chip is fabricated in a 180 nm CMOS process. Experimental results show that with a 5 V power supply, the optoelectronic sensor has an irradiance responsivity of 100 mV/(μW/cm2) and a -3 dB bandwidth of 2 kHz. The minimal detectable light power is about 19.4 nW, which satisfies the requirements of many active structured light systems. Through testing, the application of the chip effectively reduces the phase error of the micromirror to 2.5%.

The Effect of Light Availability on Photosynthetic Responses of Four Aglaonema commutatum Cultivars with Contrasting Leaf Pigment

Plants can be grouped into sun- and shade-type owing to their distinct irradiance adaptation. Aglaonema commutatum is a typical shade-tolerant perennial foliage plant native to South Asia with various leaf colorations. ‘Red’ cultivars are widely used for interior decorations and as courtyard ornamental plants, owing to their unique hue and bi-adaptation of both low and high irradiance. However, the underlying source of ‘red’ pigment-dependent irradiance bi-adaptation remains largely unknown. Therefore, four A. commutatum cultivars were comparatively evaluated in terms of pigment composition and photosynthetic rate under full light (sunlight) or 50% full light (shade) to unveil the relationship between pigmentation and irradiance bi-adaptation. Our results showed that the photosynthetic rate of sun leaves generated from light response curves was significantly correlated with anthocyanin content and chlorophyll in red cultivars, suggesting the influence of anthocyanin–light interactions on the high/low irradiance bi-adaptation of red A. commutatum. This study provides a theoretical basis for further cultivating red foliage A. commutatum cultivars under diverse light conditions.

Design and Performance Analysis of an Oil Pump Powered by Solar for a Remote Site in Nigeria

Oil companies typically abandon stripper wells with production rates below 15 barrels per day because the production and maintenance cost exceed the pumping rate. Oil spillage is the primary cause of low production rates; an example of such failure is the Oloibiri oil well in Nigeria. During the peak of operation, the flow rate was 5,100 barrels per day in 1960 and was abandoned due to the declining production rate. The Oloibiri oil site has 18 drilled wells, and only the oil well 17 can be classified as stripper well. Because Nigeria has high solar irradiance and insolation, a proper PV system sizing for a solar-powered pump that should lift oil from a depth of 3800 metres at a flow rate of 15 barrels per day is evaluated for two different running times. In that way, the solar-powered pump will be used to solve the ongoing issue of stripper oil wells by curbing oil spillage from the oil wells abandoned by these production companies and rendering a low-cost pumping system. This paper evaluates the pump performance and completes the system design. It compares the system design to the PVsyst and HOMER sizing.

Theoretical growth rate of microalgae under high/low-flashing light

Dynamic light regimes strongly impact microalgal photosynthesis efficiency. Finding the optimal way to supply light is then a tricky problem, especially when the growth rate is inhibited by overexposition to light and, at the same time, there is a lack of light in the deepest part of the culture. In this paper, we use the Han model to study the theoretical microalgal growth rate by applying periodically two different light intensities. Two approaches are considered depending on the period of the light pattern. For a large light period, we demonstrate that the average photosynthetic rate can be improved under some conditions. Moreover, we can also enhance the growth rate at steady state as given by the PI-curve. Although, these conditions change through the depth of a bioreactor. This theoretical improvement in the range of 10-15% is due to a recovery of photoinhibited cells during the high irradiance phase. We give a minimal value of the duty cycle for which the optimal irradiance is perceived by the algae culture under flashing light regime.

Emission of cyanobacterial volatile organic compounds and their roles in blooms.

Cyanobacteria are photosynthetic prokaryotes and one of dominant species in eutrophicated waters, which easily burst blooms in summer with high irradiance and temperature conditions. In response to high irradiance, high temperature, and nutrient conditions, cyanobacteria release abundant of volatile organic compounds (VOCs) by up-regulating related gene expression and oxidatively degrading β-carotene. These VOCs not only increase offensive odor in waters, but also transfer allelopathic signals to algae and aquatic plants, resulting in cyanobacteria dominating eutrophicated waters. Among these VOCs, β-cyclocitral, α-ionone, β-ionone, limonene, longifolene, and eucalyptol have been identified as the main allelopathic agents, which even directly kill algae by inducing programmed cell death (PCD). The VOCs released from cyanobacteria, especially the ruptured cells, exhibit repelling effects on the herbivores, which is beneficial to survival of the population. Cyanobacterial VOCs might transfer aggregating information among homogeneous species, so the acceptors initiate aggregation to resist the coming stresses. It can be speculated that the adverse conditions can promote VOC emission from cyanobacteria, which play important roles in cyanobacteria dominating eutrophicated waters and even bursting blooms.

STUDY OF A SOLAR ENERGY KALINA CYCLE APPLIED IN BOM JESUS DA LAPA - BAHIA

Modern population’s needs increased demands for electricity in such a way that new energy sources were explored, in search of lower environment impacts and fossil fuels dependency. Renewable energy sources for electricity production, such as solar and wind energy, have significantly attracted attention and places as the west region of Bahia state has a good potential for its application. This location is characterized by high solar irradiance of 2136 kWh/m² a year, already having 4 photovoltaic power plants in operation and 2 more in project phases. Another possible application is the solar thermal energy and Kalina Cycle presents as a good possibility for employing it, since the non-azeotropic mixture of ammonia-water as working fluid allows low temperature heat sources utilization. Based on that, this research proposed the study of a Kalina power cycle, with steady state conditions, using thermal solar energy as low temperature heat source and applied to the solar irradiance of Bom Jesus da Lapa – BA. The thermodynamic cycle was developed and simulated with Engineering Equation Solver (EES®), thermal efficiency was analyzed by varying parameters such as: heat source temperature from 90 °C to 120 °C, high pressure line from 10 to 35 bar and ammonia mass fraction from 0.35 to 0.95. The final cycle presented a superheater before the turbine and a regenerator with poor ammonia-water mixture from the separator (as hot side) and ammonia-water mixture before entering the boiler (as cold side). Results indicated maximum efficiency of ~7.4%, with high pressure side of 35 bar, heat source temperature of 120 °C, superheater heat source temperature of 200 °C and ammonia mass fraction of 0.64 kg/kg.

Euendolithic Infestation of Mussel Shells Indirectly Improves the Thermal Buffering Offered by Mussel Beds to Associated Molluscs, but One Size Does Not Fit All

Mussel beds form important intertidal matrices that provide thermal buffering to associated invertebrate communities, especially under stressful environmental conditions. Mussel shells are often colonized by photoautotrophic euendoliths, which have indirect conditional beneficial thermoregulatory effects on both solitary and aggregated mussels by increasing the albedo of the shell. We investigated whether euendolithic infestation of artificial mussel beds (Perna perna) influences the body temperatures of four associated mollusc species during simulated periods of emersion, using shell temperature obtained via non-invasive infrared thermography as a proxy. Shell temperatures of the limpet Scutellastra granularis and the chiton Acanthochitona garnoti were higher in non-infested than infested mussel beds during simulated low tides under high solar irradiance and low wind speeds. However, this was not the case for the limpet Helcion pectunculus or the top shell Oxystele antoni. Morphological differences in mollusc shape and colour could, in part, explain this contrast between species. Our results indicated that endolith-induced improvements in humidity and temperature in mussel beds could benefit associated molluscs. The beneficial thermal buffering offered by euendolithic infestation of the mussel beds was effective only if the organism was under heat stress. With global climate change, the indirect beneficial effect of euendolithic infestation for invertebrate communities associated with mussel beds may mitigate intertidal local extinction events triggered by marine heatwaves.

Mathematical model validation of floating PV parks impact on the growth of green algae using experimental chamber

ABSTRACT The demand for clean energy increases around the globe and for that purpose the need for new renewable installations increases. Floating photovoltaic power plants are being increased to accommodate the extraordinary usage of active land. These solar plants offer new investment opportunities for clean energy producers, but the rise of floating photovoltaic power plants is impacting marine ecosystems. This study aims to gauge the growth of green algae that is affected due to floating power plants by using a mathematical decay model and experimental results. A mathematical model is applied that consists of an ordinary differential equation for green algae decay estimation due to the unavailability of a light source. Additionally, an experimental chamber is constructed to create an artificial environment with an absence of high irradiance to determine the algal growth. Different sensors are installed that include temperature, humidity, and lux for data logging on each instance. The fresh green algae were kept in the experimental chamber to measure the decay rate. The result shows that the weight of fresh green algae drops from 40.9 to 37.7 g and the color transformed from green to dark brown, which shows the decrement in chlorophyll level in the period of 7 days. The mathematical model is simulated in MATLAB that validates the experimental results which show the decrement in NADPH concentration at minimum irradiance. Linear regression analysis was applied to the quantitative data obtained during the experimentation process that shows a linear relationship between a number of days and the decay of algae in the chamber. The experimental results also concluded that not only green algae were affected, but underwater oxygen levels were also reduced. Therefore, it is recommended to have a complete marine environmental analysis before the installation of a huge floating photovoltaic power plant.

Potassium Phosphite Induces Tolerance to Water Deficit Combined with High Irradiance in Soybean Plants

Changes in plant metabolism due to water deficit combined with other stresses, such as high irradiance and high temperatures, cause damage to the physiology and development of crops, which can lead to significant yield losses. The aim of this study was to determine the potential of potassium phosphite (PP) to induce tolerance to water deficit combined with high irradiance in soybean plants. The experiment was carried out in an acclimatized growth chamber. Soybean plants, upon reaching the R1 developmental stage, received the following treatments: PP application (0 L ha−1–control; 0.6 L ha−1 PP; and 1.2 L ha−1 PP), two levels of PAR irradiance (650 µmol m−2 s−1–control; and 1500 µmol m−2 s−1–high irradiance (HI)), and three water availability levels (90% of field capacity (FC), and water deficit at 40% FC and 50% FC). The treatments were maintained for 12 days. The PP increased the photosynthetic rate of plants submitted to a dosage of 1.2 L ha−1 and stresses of 50% FC + HI. PP also decreased the intensity of lipid peroxidation, and rate of electrolyte leakage, which suggests stability of cell membranes. These responses may have occurred due to the activation of the antioxidant enzymes superoxide dismutase and peroxidase. Furthermore, the application of PP increased the proline concentrations, suggesting osmotic adjustment in response to stress. These results provide the first record of PP-induced tolerance in plants under combined water and HI stresses. PP proves to be a potential alternative method to reduce the harmful effects caused by the combined stresses of water deficit and high irradiance in soybean.

Light Drives and Temperature Modulates: Variation of Phenolic Compounds Profile in Relation to Photosynthesis in Spring Barley.

Accumulation and metabolic profile of phenolic compounds (PheCs; serving as UV-screening pigments and antioxidants) as well as carbon fixation rate (An) and plant growth are sensitive to irradiance and temperature. Since these factors are naturally co-acting in the environment, it is worthy to study the combined effects of these environmental factors to assess their possible physiological consequences. We investigated how low and high irradiance in combination with different temperatures modify the metabolic profile of PheCs and expression of genes involved in the antioxidative enzyme and PheCs biosynthesis, in relation to photosynthetic activity and availability of non-structural carbohydrates (NSC) in spring barley seedlings. High irradiance positively affected An, NSC, PheCs content, and antioxidant activity (AOX). High temperature led to decreased An, NSC, and increased dark respiration, whilst low temperature was accompanied by reduction of UV-A shielding but increase of PheCs content and AOX. Besides that, irradiance and temperature caused changes in the metabolic profile of PheCs, particularly alteration in homoorientin/isovitexin derivatives ratio, possibly related to demands on AOX-based protection. Moreover, we also observed changes in the ratio of sinapoyl-/feruloyl- acylated flavonoids, the function of which is not yet known. The data also strongly suggested that the NSC content may support the PheCs production.

A carbon cycling model shows strong control of seasonality and importance of sponges on the functioning of a northern Red Sea coral reef

Coral reefs in the northern Red Sea experience strong seasonality. This affects reef carbon (C) cycling, but ecosystem-wide quantification of C fluxes in such reefs is limited. This study quantified seasonal reef community C fluxes with incubations. Resulting data were then incorporated into seasonal linear inverse models (LIM). For spring, additional sponge incubation results allowed for unique assessment of the contribution of sponges to C cycling. The coral reef ecosystem was heterotrophic throughout all seasons as gross community primary production (GPP; 136–200, range of seasonal means in mmol C m−2 d−1) was less than community respiration (R; 192–279), and balanced by import of organic carbon (52–100), 88‒92% of which being dissolved organic carbon (DOC). Hard coral GPP (74–110) and R (100–137), as well as pelagic bacteria DOC uptake (58–101) and R (42–86), were the largest C fluxes across seasons. The ecosystem was least heterotrophic in spring (highest irradiance) (GPP:R 0.81), but most heterotrophic in summer and fall with higher water temperatures (0.68 and 0.60, respectively). Adding the sponge community to the model increased community R (247 ± 8 without to 353 ± 13 with sponges (mean ± SD)). Sponges balanced this demand primarily with DOC uptake (105 ± 6, 97% by cryptic sponges). This rate is comparable to the uptake of DOC by pelagic bacteria (104 ± 5) placing the cryptic sponges among the dominant C cycling groups in the reef.

Carbon and Nitrogen Allocation between the Sink and Source Leaf Tissue in Response to the Excess Excitation Energy Conditions.

Plants are inevitably exposed to extreme climatic conditions that lead to a disturbed balance between the amount of absorbed energy and their ability to process it. Variegated leaves with photosynthetically active green leaf tissue (GL) and photosynthetically inactive white leaf tissue (WL) are an excellent model system to study source-sink interactions within the same leaf under the same microenvironmental conditions. We demonstrated that under excess excitation energy (EEE) conditions (high irradiance and lower temperature), regulated metabolic reprogramming in both leaf tissues allowed an increased consumption of reducing equivalents, as evidenced by preserved maximum efficiency of photosystem II (ФPSII) at the end of the experiment. GL of the EEE-treated plants employed two strategies: (i) the accumulation of flavonoid glycosides, especially cyanidin glycosides, as an alternative electron sink, and (ii) cell wall stiffening by cellulose, pectin, and lignin accumulation. On the other hand, WL increased the amount of free amino acids, mainly arginine, asparagine, branched-chain and aromatic amino acids, as well as kaempferol and quercetin glycosides. Thus, WL acts as an important energy escape valve that is required in order to maintain the successful performance of the GL sectors under EEE conditions. Finally, this role could be an adaptive value of variegation, as no consistent conclusions about its ecological benefits have been proposed so far.

Complex exudates in inflorescences of Vriesea species reveal evidence of lipophilic secretions by scales of bromeliads

Trichomes are a key feature of bromeliads. These structures absorb water and minerals, potentially constituting an important element in plant-environment interactions. Recent studies have shown a glandular function associated with mucilage-secreting scales in inflorescences of bromeliads. During a prospective study of secretions in bromeliad inflorescences, we observed the presence of an oily exudate in three species of Vriesea sect. Xiphion. To verify whether scales in bromeliads can produce lipophilic secretions, we investigated the secretory activity in these species to identify the source and chemical nature of the secretions which spread over the inflorescences. We used standard methods of histochemistry, light, and electron microscopy applied to samples of floral bracts in two distinct phases of development. The secretions comprised hydrophilic and lipophilic substances secreted by trichomes on the adaxial side of bracts. The exudate was heterogeneous in V. aff. bituminosa and V. fenestralis, with a lipophilic phase composed of terpenoids and lipids. Vriesea aff. bituminosa also presented alkaloids. In V. platynema var. rosea, the lipophilic content was lipids. The secretory activity was restricted to the early stages of organ development and might be characterized by a temporal disjunction between the secretion of hydrophilic and lipophilic contents. The functions of the exudate seem to include protection against herbivores but might also relate to protection against pathogens, water loss and high irradiance. The secretion of lipophilic substances by the typical peltate trichome of bromeliads was reported here for the first time.