Stomatal Cavity Research Articles

Morpho-anatomical studies of family lamiaceae species of district Lahore, Punjab: a revision to flora of Pakistan

BackgroundThis study was aimed to determine the taxonomic position and delimitation of fifteen Lamiaceae taxa using leaf epidermal morpho-anatomical features in Lahore. A main objective of the study was also the revision and upgradation of Lamiaceae taxa in the flora of Pakistan, as no details of studied species are found in the flora of Pakistan.MethodsThe examination of significant anatomical parameters, such as epidermal cell shape and size, stomatal types, guard and subsidiary cells shape and size, stomatal cavity size, trichome size and shape, oil droplets, crystals, and secretory cavity characteristics were studied using light microscopic (LM) and scanning electron microscopic (SEM) techniques. Among all the studied Lamiaceae species, these anatomical features varied significantly. Principal component analysis and correlation were done to distinguish the species’ similarities.ResultsMost species had pentagonal and hexagonal epidermal cells with straight anticlinal wall thickness. On the adaxial surface, paracytic stomata were found in Ocimum basilicum L. and Rosmarinus officinalis L. Diacytic stomata was observed in Ajuga reptans L. and anisocytic stomata in Galeopsis tetrahit L. In the abaxial surface, trichomes were present in five species, i.e., Mentha suaveolens Ehrh. A. reptans, Thymus vulgaris L., M. haplocalyx, and Salvia splendens Ewat. In S. splendens, peltate and glandular trichomes were seen whereas, in other species, trichomes were long, unbranched glandular and had tapering ends. In adaxial side trichomes were present only in M. suaveolens, A. reptans, S. bazyntina, O. basciculum, S. splendens, S. officinalis, S. rosemarinus. In other species, trichomes were absent on the adaxial surface. In abaxial view, M. suaveolens had the largest length of trichomes, and O. basciculum had the smallest. S. splendens L. had the largest trichome width, while T. vulgaris had the smallest.ConclusionHence, according to these findings, morpho-anatomical traits are useful for identifying Lamiaceae taxa. Also, there is a need of upgradation and addition of studied taxa in flora of Pakistan comprehensively.

VPD modifies CO2 fertilization effect on tomato plants via abscisic acid and jasmonic acid signaling pathways

Atmospheric CO2 concentration is elevated globally, which has “CO2 fertilization effects” and potentially improves plant photosynthesis, yield, and productivity. Despite the beneficial effect of CO2 fertilization being modulated by vapor pressure deficit (VPD), the underlying mechanism is highly uncertain. In the present study, the potential roles of hormones in determining CO2 fertilization effects under contrasting high and low VPD conditions were investigated by integrated physiological and transcriptomic analyses. Beneficial CO2 fertilization effects were offset under high VPD conditions and were constrained by plant water stress and photosynthetic CO2 utilization. High VPD induced a large passive water driving force, which disrupted the water balance and consequently caused plant water deficit. Leaf water potential, turgor pressure, and hydraulic conductance declined under high VPD stress. The physiological evidence combined with transcriptomic analyses demonstrated that abscisic acid (ABA) and jasmonic acid (JA) potentially acted as drought-signaling molecules in response to high VPD stress. Increased foliar ABA and JA content triggered stomatal closure to prevent excessive water loss under high VPD stress, which simultaneously increased the diffusion resistance for CO2 uptake from atmosphere to leaf intercellular space. High VPD also significantly increased mesophyll resistance for CO2 transport from stomatal cavity to fixation site inside chloroplast. The chloroplast “sink” CO2 availability was constrained by stomatal and mesophyll resistance under high VPD stress, despite the atmospheric “source” CO2 concentration being elevated. Thus, ABA- and JA-mediated drought-resistant mechanisms potentially modified the beneficial effect of CO2 fertilization on photosynthesis, plant growth, and yield productivity. This study provides valuable information for improving the utilization efficiency of CO2 fertilization and a better understanding of the physiological processes.

ROLE OF THERMODYNAMIC PROCESSES IN PLANT LEAF GAS EXCHANGE SYSTEM FOR ASSIMILATION OF CO2 EMISSIONS FROM THE AMBIENT AIR

When temperature in the leaf gas exchange system changes, the thermodynamic parameters describing the condition of moist air also change. A temperature change of 1 oC in plant leaf tissues leads to a change in partial water vapour pressure of 144 Pa in the gas exchange cavities. Then a temperature decrease of 1 oC in a plant leaf produces 0.897 g of condensate, from 1 m3 of air in leaf ventilation cavities on the surface. When the temperature of plant leaves in the leaf ventilation system changes, the total water vapor state on the inner surface of the leaves changes, and the water vapor state in the stomatal cavities changes. The thickness of the formed condensate film on the plant leaf canal wall surfaces depends on the canal diameter and temperature change. The paper presents information about the mechanism of water formation and thermodynamic processes in the plant leaf gas exchange system participating in the process of assimilation. The formation and change of the internal surfaces of the stomatal cavities of the water film sheet allow the participation of chemical processes in the assimilation of CO2 emissions from the environment.

Stomatal cavity modulates the gas exchange of Sorghum bicolor (L.) Moench. grown under different water levels.

This work aimed to evaluate the effects of lower water levels on leaf intercellular spaces and to assess their relations with the gas exchange, anatomy, and growth of Sorghum bicolor. Experiments were conducted in a greenhouse, in which plants were subjected to three water conditions (ten replicates, n = 30): well-irrigated, decreased irrigation, and limited irrigation. Lower water levels had no significant effect on the growth of S. bicolor but increased the biomass of the roots. Moreover, the number of leaves, leaf area, and leaf size as well as the chlorophyll content were not affected by lower water levels, and no significant changes were detected for whole plant photosynthesis, transpiration, or stomatal conductance. The water content of the plants and the water potential remained unchanged. However, compared with other treatments, the decreased irrigation decreased water loss and increased the water retention. Lower water levels increased the intercellular CO2 percentage, mesophyll area, and proportion of stomatal cavities and promoted minor changes in leaf tissue and stomatal traits. The increased stomatal cavities provided higher CO2 uptake and prevented excessive water loss. Thus, modifications to the intercellular spaces promoted conditions to avoid excessive water loss while concurrently improving CO2 uptake, which are important traits for drought-tolerant plants.

Immobilized atmospheric particulate matter on leaves of 96 urban plant species.

Plants provide many ecosystem services in urban environments, including improving ambient air quality. Leaves of plants permit the deposition of particulate matter (PM) and, depending on their leaf traits, PM may be immobilized within the epicuticular wax (EW) layer, on trichomes, on hyphae of fungi, or inside stomatal cavities. In this study, leaves of 96 perennial urban plant species consisting of 45 deciduous broadleaf/needle-like trees, 32 deciduous broadleaf shrubs, 12 evergreen needle/scale-like trees, 5 evergreen broadleaf trees, and 2 climber species were investigated in June and September 2016 to determine the effectiveness of distinct leaf surfaces in PM immobilization after leaf washing treatment. The leaf surfaces were washed vigorously using a vortex shaker. The magnetizable component of accumulated and immobilized PM on the leaf surfaces was estimated using saturation isothermal remanent magnetization (SIRM) of the unwashed and washed leaves, respectively. In June, the washed leaf SIRM of deciduous (broadleaf/needle-like) tree and shrub species (n = 77) ranged between 0.1 and 13.9 μA. In September, the washed leaf SIRM of all investigated plant species (n = 96) ranged between 1.2 and 35.0 μA. Outcomes of this study indicate that leaves of Buddleja davidii, Viburnum lantana, and Sorbus intermedia showed the highest washed leaf SIRM and thus were the most effective in immobilizing PM on their leaf surfaces while leaves of Populus alba, Robinia pseudoacacia, and Abies fraseri with lowest washed leaf SIRM were the least effective. On average, more than half (i.e., 60%) of the magnetic signal still remained after vigorous washing but a large variation exists between species (9-96%). The leaf SIRM of washed leaves of deciduous broadleaf tree and shrub species was significantly higher compared to leaves of evergreen needle/scale-like species. Evidently, the magnetic signal of unwashed leaves was higher than washed ones and higher in September than in June. Leaf traits significantly influenced the magnetic signal of both washed and unwashed leaves: leaves with a high trichome density or high leaf wettability showed a higher unwashed and washed leaf SIRM compared to leaves with no trichomes or low leaf wettability. The effect of epicuticular wax structure types on leaf SIRM was indicated to be only marginally significant. Moreover, also the immobilized fraction of PM was significantly affected by trichome density and leaf wettability, thus substantiating that plant species with high trichome density and/or leaf wettability not only accumulate more PM but are also less prone to PM re-suspension than other species. In general, the results also indicate that leaf SIRM of unwashed leaves can be a good indicator to determine the effectiveness of a plant species in PM immobilization. Plant species effective in immobilizing PM on their leaf surfaces may likely improve ambient air quality when planted in urban environments. However, it is vital that leaves of these plant species (i.e., with high PM immobilization abilities) are carefully recycled as they may be polluted.

A comprehensive stress indicator for evaluating plant water status in almond trees

This study evaluated a comprehensive plant water stress indicator that integrates the leaf temperature and the environmental conditions that can provide feedback on the plant response to irrigation scheduling. This quantity—Comprehensive Stress Indicator (CSI)—is based on the reformulation of the leaf energy balance equation. Specifically, CSI is the ratio of the temperature difference between a dry leaf (i.e., a leaf with a broken stem) and a live leaf (on the same tree) [i.e., Tdry-Tleaf] and the difference between the vapor pressure inside the stomatal cavity at saturation and the vapor pressure of the air at ambient temperature [i.e., es(TL)-e(TA)]. The required measurements to compute CSI include dry leaf temperature, live leaf temperature, relative humidity, and air temperature at the tree being monitored. In this study, all measurements were obtained using a sensor suite called the leaf monitor. Leaf monitors were connected to a wireless mesh network to communicate the data to a website. The leaf monitor included two thermal infrared sensors, one for the dry leaf and one for the live leaf, both of which were housed in the same unit with almost identical environmental conditions due to a diffusing hemispherical dome that enclosed these sensors. The CSI is a dynamic indicator with a value for every data sample collected. For a single indicator representing each day, the CSI was evaluated in two ways. First, the CSI was integrated with respect to time from 10 A.M. to 6 P.M. to obtain the Integrated Comprehensive Stress Indicator (ICSI). Second, the CSI was averaged from 1 P.M. to 3 P.M. to obtain the Average Comprehensive Stress Indicator (ACSI). Both ICSI and ACSI were compared to other stress indicators, including the existing Crop Water Stress Index (CWSI) and Integrated Degrees Above Non-Stressed (IDANS). Results show that ICSI and ACSI are satisfactorily correlated with midday stem water potential (SWP). The ICSI and ACSI indicators may be more convenient than other stress indicators because they require measurements only at the tree being monitored.

Di-1-p-menthene reduces grape leaf and bunch transpiration

Background and Aims Di-1-p-menthene, a film-forming antitranspirant, is reported to impede transpiration by acting as a physical barrier to water vapour loss from plant tissues. We tested this assumption on grapevine leaves across a range of temperature as well as on the bunch rachis and berries at several developmental stages. Methods and Results Gas exchange of Shiraz leaves was monitored at 20, 25, 30 and 35°C under controlled conditions after treatment with 1 and 2% di-1-p-menthene. Transpiration, photosynthesis and stomatal conductance were reduced at each temperature, but instantaneous water use efficiency (CO2 fixation relative to water loss) was improved only at 25 and 30°C. There was no further reduction in water use or improved water use efficiency with the application of a 2% over 1% emulsion. The antitranspirant was most effective when applied to the underside of the leaves, forming a physical barrier over the stomatal cavity without reduction in stomatal aperture. Di-1-p-menthene also curtailed bunch water loss in Merlot by lowering transpiration of both the rachis and berries at the fruitset, peppercorn, pea size and veraison stages, and at 20 and 25°Brix. Increasing the concentration of the antitranspirant from 1% to 2 or 3% added some benefit; however, this was dependent on the developmental stage. Both leaf and berry temperature was elevated by the spray application. Di-1-p-menthene did not interfere with flowering or promote fruit abortion when applied prior to capfall. Conclusion Di-1-p-menthene maintains berry turgidity through effects on both the canopy and the bunches themselves. Significance of the Study The antitranspirant, di-1-p-menthene, may provide protection against desiccation under field conditions and this will have implications for yield and berry composition.

Absorption of foliar-applied Zn in sunflower (Helianthus annuus): importance of the cuticle, stomata and trichomes.

The pathways whereby foliar-applied nutrients move across the leaf surface remain unclear. The aim of the present study was to examine the pathways by which foliar-applied Zn moves across the sunflower (Helianthus annuus) leaf surface, considering the potential importance of the cuticle, stomata and trichomes. Using synchrotron-based X-ray florescence microscopy and nanoscale secondary ion mass spectrometry (NanoSIMS), the absorption of foliar-applied ZnSO4 and nano-ZnO were studied in sunflower. The speciation of Zn was also examined using synchrotron-based X-ray absorption spectroscopy. Non-glandular trichomes (NGTs) were particularly important for foliar Zn absorption, with Zn preferentially accumulating within trichomes in ≤15 min. The cuticle was also found to have a role, with Zn appearing to move across the cuticle before accumulating in the walls of the epidermal cells. After 6 h, the total Zn that accumulated in the NGTs was approx. 1.9 times higher than in the cuticular tissues. No marked accumulation of Zn was found within the stomatal cavity, probably indicating a limited contribution of the stomatal pathway. Once absorbed, the Zn accumulated in the walls of the epidermal and the vascular cells, and trichome bases of both leaf sides, with the bundle sheath extensions that connected to the trichomes seemingly facilitating this translocation. Finally, the absorption of nano-ZnO was substantially lower than for ZnSO4, with Zn probably moving across the leaf surface as soluble Zn rather than nanoparticles. In sunflower, both the trichomes and cuticle appear to be important for foliar Zn absorption.

Natural genetic variation in stomatal response can help to increase acclimation of plants to dried environments

In the current century, global warming is becoming an alarming issue causing an increase in the area of barren lands. Arid and semi-arid regions are characterised with shortage of water in both under- and above-ground environments. Plants with high water use efficiency should be considered for cultivation in those regions. Water loss is needed for cooling plant and absorbing minerals, however, excessive water loss can result in wilting. Plants control the water loss through adjusting the volume of stomatal guard cells and fine tuning the movements of stomata. Fine tune-functioning of stomata can help the plants to cope with drought conditions. Vapour pressure difference (VPD) between stomatal cavity and surrounding environment determines the water status of the leaf. In the short term, stomata respond in a regular way to VPD. However, when plants are exposed for a long term to conditions triggering stomatal opening (such as low VPD, prolonged lighting duration and air pollutants), the behaviour of the stomata in response to drought stress changes and the stomata are incapable of suitable response to closing stimuli (stomatal malfunctioning). Finding the reasons for occurrence of stomatal malfunctioning can help us to improve plant acclimation to dried environments. Exploring genetic variation in stomatal response among naturally occurring populations is the first step to figure out the mechanism controlling stomatal movements in different environments.

Role of the outer stomatal ledges in the mechanics of guard cell movements

The modelling showed that outer ledges prevent wide opening of the stomatal pore and its lifting above leaf epidermis. This stomatal mechanics is combined with xeromorphic features of leaf epidermis. Methods of light, scanning, and transmission electron microscopy were used to study the stomata of the leaf epidermis in evergreen Acokanthera oblongifolia (Apocynaceae), A. oppositifolia (Apocynaceae), Carissa spectabilis (Apocynaceae), Exbucklandia populnea (Hamamelidaceae), and Trochodendron aralioides (Trochodendraceae). The stomata of their leaf epidermis are located on subsidiary cells, have large outer ledges, and lack inner ledges. To elucidate the role of the ledges, we applied dynamic modelling using the finite-element method. The application of dynamic modelling has shown that outer ledges prevent wide opening of the stomatal pore and their rising above the surface of leaf epidermis. The results of the modelling are supported by the observed deformations in the guard cells of the real stomata. This stomatal mechanics is combined with such stomatal xeromorphic features as thick cuticle, stomatal cavities, and waxy plugs (in A. oblongifolia). All studied species show similar leaf anatomy. It has much in common with the leaf anatomy of species connected in their origin with subhumid Tertiary laurophyllous forests.

PARTIÇÃO DA EVAPOTRANSPIRAÇÃO PARA UMA CULTURA DE MILHO

Crop transpiration is directly related to its production. Plant transpiration varies along the crop cycle and in most part of this cycle is the dominant component in evapotranspiration. There are several well-established techniques to estimate these components individually. Currently, the eddy covariance technique is widely used for measurements of evapotranspiration. However, this technique is unable to identify the flow of water between the surface and the atmosphere has its origin by evaporation from soil or plant transpiration. A new methodology based on the efficiency of water use by the plant is being used successfully. This technique determines how much water is transpired to each carbon molecule attached to the plant. This efficiency ratio is obtained by the difference of external and internal concentration on stomatal cavity of CO2 and H2O. In practice, external concentration of carbon and water is obtained from the infra-red gas analyzers used to obtain data in eddy covariance technique. In this work, the evapotranspiration for a maize crop in southern Brazil is partitioned and compared to the surface model AGRO-IBIS. Results show that the maximum development of the plant transpiration is approximately 70% of evapotranspiration.

Large lipid droplets in leaf epidermis of angiosperms

Methods of light, scanning and transmission electron microscopy were used to study the lower epidermis of the leaves in evergreen Acokanthera oblongifolia (Apocynaceae), Exbucklandia populnea (Hamamelidaceae), Ternstroemia gymnanthera (Theaceae), and Viburnum suspensum (Caprifoliaceae). All these species show similar leaf anatomy. Our results together with those of earlier studies show that large lipid droplets (LDs) can regularly be found in leaf epidermis of some flowering plants. Their diameter varies in studied species from 3 to 11μm. Large lipid droplets are typical for cells of stomatal complexes and can have irregular shape. They also occur in some ordinary cells. The formation of large LDs is accompanied by the presence of thick cuticle covering ordinary and subsidiary cells, prominent cuticular outer ledges and rims on stomata, waxy plugs in the outer stomatal cavities (in A. oblongifolia), and abundant plastoglobules in plastids. All these indicate that intensive lipid synthesis occurs in leaf epidermis. The stomatal complexes are the place with the highest occurrence of the largest LDs. They are formed in subsidiary cells, which lie beneath the stomata. In these cells plastids and mitochondria are always present. The former contain lipid inclusions. We demonstrated that breakdown of LDs takes place in dying leaves of V. suspensum. This might indicate mobilization of lipids from the globules into the LDs. Based on these new data we suggest that the LDs found in cells of stomatal complexes play important role in maintaining normal function of stomata.

Particulate matter deposited on leaf of five evergreen species in Beijing, China: Source identification and size distribution

Airborne particulate matter (PM) has become a serious problem, and urban plants can play important roles in reducing PM concentrations in the air. The morphology, size, and elemental composition of PM on tree leaves (five evergreen species) from Beijing, China, were obtained, together with number density of PM size fraction, by using scanning electron microscopy (SEM) and energy dispersive X-rays (EDX). The rinse and weigh method was used to characterize PM in three size categories (0.2–2.5 μm, 2.5–10 μm, and 10–100 μm). The results showed that PM up to 2 μm can get into the stomatal cavity, and the most furrowed areas of the leaf surfaces were sites of maximum PM deposition. The leaf-deposited PM mainly comprised C, O, Si, and Fe. The number of particles per leaf per cm2 was 1.95 × 107, and 96% of the particles were less than 2.5 μm. The mass concentration was 148.44 μg/cm2, and PM2.5 comprised only 2.09% by weight while PM larger than 10 μm comprised 79%. Juniperus formosana was most effective at mitigating airborne PM on the leaf scale. Pinus bungeana accumulated the most PM on the tree scale. The results showed that urban plants can play important roles in mitigating urban airborne PM.

Morphology and phylogenetics of Stomatisora, including Stomatisora psychotriicola sp. nov.

The morphology of the type specimen of Stomatisora geophilicola, the only species of the genus Stomatisora (Pucciniales) recognised till now, was restudied. Thin-walled probasidia (teliospores) develop exclusively in substomatal chambers, and mature metabasidia emerge through the stomata and develop suprastomatally. Uredinia are erumpent through the upper epidermis. A new species, S. psychotriicola, parasitizing Psychotria capensis (Rubiaceae) from South Africa, is described and illustrated. Only telia have been found which also develop in stomatal cavities, and, as in the type species, have partly repetitive probasidia and suprastomatal metabasidia that easily detach from fragile stalks. The similarities of telial morphology, as well as the same host family, indicate a close relationship and a generic separation from other rust genera. Molecular data support this interpretation and a possible relationship within a phakopsoroid clade.

ASSESSMENT OF SYNERGIC REGULATORY ACTIONS OF SPRUCE BARK EXTRACT AND DEUTERIUM DEPLETED WATER ON MAIZE (Zea mays L.) CROPS

The aim of this study was to evaluate the effect of polyphenolic extract and deuterium depleted water (DDW) as bioregulators in maize ( Zea mays L.) plant cultivation. The aqueous extract obtained from spruce bark (two levels of concentration), pure DDW and DDW in combination with spruce extract were used. The test solutions were applied by spraying and the maize plant growth and alelopatic effect on the development were studied. The following specific plants parameters were monitored: growth and development of vegetative organs of the plant, photosynthesis rate, transpiration rate, sub-stomatal cavity CO 2 concentration. Photosynthetically active radiation (P.A.R.) incident on leaf surface, pigments photoassimilating content, total polyphenolic content and individual polyphenolic compounds content in maize leaves were determined. It was observed that the solutions applied triggers an intensification of metabolic processes in plants (photosynthesis, transpiration, pigments synthesis, sub- stomatal cavity CO 2 concentration) with an increase in crop production. Highest percentage of stimulation was recorded in the plant groups treated with only polyphenolic extract (130 mg/L) or in combination with DDW (96 mg/L). The supplementation of the growth medium with polyphenolic extract cause an increase in the amount of catechine and synapic acid in leaves, increasing defense capability and therefore improving plant growth and development.

Leaf photosynthesis and respiration of three bioenergy crops in relation to temperature and leaf nitrogen: how conserved are biochemical model parameters among crop species?

Given the need for parallel increases in food and energy production from crops in the context of global change, crop simulation models and data sets to feed these models with photosynthesis and respiration parameters are increasingly important. This study provides information on photosynthesis and respiration for three energy crops (sunflower, kenaf, and cynara), reviews relevant information for five other crops (wheat, barley, cotton, tobacco, and grape), and assesses how conserved photosynthesis parameters are among crops. Using large data sets and optimization techniques, the C3 leaf photosynthesis model of Farquhar, von Caemmerer, and Berry (FvCB) and an empirical night respiration model for tested energy crops accounting for effects of temperature and leaf nitrogen were parameterized. Instead of the common approach of using information on net photosynthesis response to CO2 at the stomatal cavity (An–Ci), the model was parameterized by analysing the photosynthesis response to incident light intensity (An–Iinc). Convincing evidence is provided that the maximum Rubisco carboxylation rate or the maximum electron transport rate was very similar whether derived from An–Ci or from An–Iinc data sets. Parameters characterizing Rubisco limitation, electron transport limitation, the degree to which light inhibits leaf respiration, night respiration, and the minimum leaf nitrogen required for photosynthesis were then determined. Model predictions were validated against independent sets. Only a few FvCB parameters were conserved among crop species, thus species-specific FvCB model parameters are needed for crop modelling. Therefore, information from readily available but underexplored An–Iinc data should be re-analysed, thereby expanding the potential of combining classical photosynthetic data and the biochemical model.

Two new pathogenic ascomycetes in Guignardia and Rosenscheldiella on New Zealand's pygmy mistletoes (Korthalsella: Viscaceae)

Two new pathogens, Guignardia korthalsellae and Rosenscheldiella korthalsellae, are described from New Zealand's pygmy mistletoes (Korthalsella, Viscaceae). Both form ascomata on living phylloclades with minimal disruption of the tissue. Fungal hyphae within the phylloclade are primarily intercellular. Guignardia korthalsellae disrupts a limited number of epidermal cells immediately around the erumpent ascoma, while the ascomata of Rosenscheldiella korthalsellae develop externally on small patches of stromatic tissue that form above stomatal cavities. Rosenscheldiella is applied in a purely morphological sense. LSU sequences show that R. korthalsellae as well as another New Zealand species, Rosenscheldiella brachyglottidis, are members of the Mycosphaerellaceae sensu stricto. Genetically, Rosenscheldiella, in the sense we are using it, is polyphyletic; LSU and ITS sequences place the two New Zealand species in different clades within the Mycosphaerellaceae. Rosenscheldiella is retained for these fungi until generic relationships within the family are resolved. Whether or not the type species of Rosenscheldiella, R. styracis, is also a member of the Mycosphaerellaceae is not known, but it has a similar morphology and relationship to its host as the two New Zealand species.

Leaf paraheliotropism in Styrax camporum confers increased light use efficiency and advantageous photosynthetic responses rather than photoprotection

Styrax caporum is a native shrub from the Brazilian savanna. Most of its leaves are diaheliotropic, whereas some are paraheliotropic, mainly at noon. A previous study of this species revealed higher stomatal conductance (gs) and transpiration rates (E) in para- compared to diaheliotropic leaves, and a rise in CO2 assimilation rates (A) with an increase of irradiance for paraheliotropic leaves. We hypothesized that this species exploits the paraheliotropism to enhance the light use efficiency, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. Gas exchange was measured with devices that enabled light interception on only one of the leaf surfaces and with devices that enabled light interception by both leaf surfaces. Water relations, relative reflected light intensity, leaf temperature (Tl), and leaf anatomical analyses were also performed. When both leaf surfaces were illuminated, a higher A, E, and gs were observed in para- compared to diaheliotropic leaves; however, A did not depend on gs, which did not influence CO2 accumulation in the stomatal cavity (Ci). When only the adaxial leaf surface was illuminated, a greater A was detected for para- than for diaheliotropic leaves only at 11:00h; no differences in Tl were observed between leaf types. Light curves revealed that under non-saturating light the adaxial side of paraheliotropic leaves had higher A than the abaxial side, but they showed similar values under saturating light. Although the abaxial leaf side was highly reflective, both surfaces presented the same response pattern for green light reflection, which can be explained by the compact spongy parenchyma observed in the leaves, increasing light use efficiency in terms of CO2 consumption for paraheliotropic leaves. We propose that paraheliotropism in S. camporum is not related to leaf heat avoidance or photoprotection.

NUTRIENT SUPPLY IN SOILLESS CULTURE: ON-DEMAND STRATEGIES

NUTRIENT SUPPLY IN SOILLESS CULTURE: ON-DEMAND STRATEGIES

Occurrence of Severe Outbreaks of Leaf Mold Caused by Fulvia fulva in Greenhouse Tomatoes in Chile.

Severe outbreaks of leaf mold, affecting as much as 100% of the plants, have occurred in greenhouse tomatoes (Lycopersicon esculentum Mill.) in the V Region in the central zone of Chile (32°50' to 33°10' latitude south) during the past 2 years. Symptoms consisted of yellow spherical to elongated leaf spots, first noticeable on the upper surface of older leaves, followed by leaf necrosis and defoliation. Invariably, an olive green-to-gray leaf mold developed on the under surface of the spots. No symptoms were observed on fruits and rarely occurred on petioles and stems. Isolation on acidified potato dextrose agar (APDA) consistently yielded dark green colonies of a very slow growing fungus that was identified as Fulvia fulva (Cooke) Cif. (=Cladosporium fulvum Cooke) (1). Identification was based on the presence of a dark septate mycelium, ovoid to ellipsoid conidia, usually one or two cells, pale or slightly yellow, 11 × 40 μm long, and the presence of mostly unbranched conidiophores that were broader at the tip. Conidia were produced in short chains, and a very distinctive hilum was always observed (1,3). Thin sections of leaf lesions revealed the presence of inter- and intracellular mycelia that protruded through the stomata forming a small stroma in the stomatal cavity from which the conidiophores were produced. Leaf inoculations of tomato cvs. Fortaleza and Cal-Ace with a mixture of mycelia and conidia from isolates Fv1 and Fv2 on APDA (approximately 106 propagules per ml) and with three different samples of conidia (106 conidia per ml) obtained directly from actively growing lesions resulted in the development of pale to dark yellow spots after 12 to 15 days of incubation under greenhouse conditions (temperatures ranging from 9 to 30°C). Leaf spots developed mainly on inoculated leaflets, but occasionally symptoms were obtained on other leaflets on the same leaf. Reisolations made from samples of artificially inoculated leaves always yielded F. fulvia on APDA. Therefore, it was concluded that F. fulvia was the cause of the severe outbreaks of tomato leaf mold found in central Chile. Previously, it has been reported in northern Chile (I Region approximately 2,000 km away) (2). To our knowledge, this is the first confirmed report of leaf mold on greenhouse tomato in central Chile.