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Ditylenchus dipsaci is a plant-parasitic nematode with a great economic impact on bulbous crops, including garlic (Allium sativum L.), and is distributed worldwide, particularly in the Mediterranean region. Traditionally, garlic was a rainfed crop in Spain, but irrigated areas have increased during the last few decades. However, the expected climatic conditions, with longer and more intense droughts, will make it necessary to reduce the water supply to garlic crops. This poses the urgent need to select garlic cultivars more tolerant to water scarcity and that are also more resistant to plant pathogenic organisms. The aim of this work was to analyze the influence of water stress on the host response of garlic plants to D. dipsaci. The specific objectives were to evaluate the level of nematode infestation in plants from four garlic genotypes treated with a reduced irrigation regime and compare them with those of control plants not subjected to water stress. The observed results were correlated with changes in the bulb and root development, as well as in the physiological parameters (total chlorophyll concentration and proline accumulation). The effects were different depending on whether the plants were subjected to water stress before or after nematode inoculation, as well as whether the water stress was continuous or discontinuous. Garlic inter-cultivar variability also affected the obtained results.

Pelagia noctiluca is the most successful and well-studied jellyfish in the Mediterranean Sea. This species tolerates a wide range of water temperatures and succeeds in low to medium food regimes, but factors driving its distribution and population dynamics remain poorly understood. Here we applied a multiscale analytical approach using survey data and a physical−biochemical coupled model to assess how environmental factors affect the 3-dimensional distribution and seasonal abundance of P. noctiluca early life stages. The surveys took place after the spring bloom, when warm water favors fecundity and growth, but food shortage limits the reproductive investment and early survival. We found that most early life stages of P. noctiluca remained above the shallow thermocline and upper mixed layer where temperature is warm. Their spatial distribution was positively correlated with surface chlorophyll concentration, and over 90% of the variation in interannual abundance was explained by basin-scale productivity in June. Warmer water during winter and spring seasons coupled with protracted spring blooms increase the population of P. noctiluca, and this explains the trend of increasing outbreaks observed in the western Mediterranean Sea over the past decades.

Pelagia noctiluca is the most successful and well-studied jellyfish in the Mediterranean Sea. This species tolerates a wide range of water temperatures and succeeds in low to medium food regimes, but factors driving its distribution and population dynamics remain poorly understood. Here we applied a multiscale analytical approach using survey data and a physical-biochemical coupled model to assess how environmental factors affect the 3-dimensional distribution and seasonal abundance of P. noctiluca early life stages. The surveys took place after the spring bloom, when warm water favors fecundity and growth, but food shortage limits the reproductive investment and early survival. We found that most early life stages of P. noctiluca remained above the shallow thermocline and upper mixed layer where temperature is warm. Their spatial distribution was positively correlated with surface chlorophyll concentration, and over 90% of the variation in interannual abundance was explained by basin-scale productivity in June. Warmer water during winter and spring seasons coupled with protracted spring blooms increase the population of P. noctiluca, and this explains the trend of increasing outbreaks observed in the western Mediterranean Sea over the past decades.

Pelagia noctiluca is the most successful and well-studied jellyfish in the Mediterranean Sea. This species tolerates a wide range of water temperatures and succeeds in low to medium food regimes, but factors driving its distribution and population dynamics remain poorly understood. Here we applied a multiscale analytical approach using survey data and a physical−biochemical coupled model to assess how environmental factors affect the 3-dimensional distribution and seasonal abundance of P. noctiluca early life stages. The surveys took place after the spring bloom, when warm water favors fecundity and growth, but food shortage limits the reproductive investment and early survival. We found that most early life stages of P. noctiluca remained above the shallow thermocline and upper mixed layer where temperature is warm. Their spatial distribution was positively correlated with surface chlorophyll concentration, and over 90% of the variation in interannual abundance was explained by basin-scale productivity in June. Warmer water during winter and spring seasons coupled with protracted spring blooms increase the population of P. noctiluca, and this explains the trend of increasing outbreaks observed in the western Mediterranean Sea over the past decades.

The long-term goal is to investigate the dynamics of coastal areas dominated by buoyancy input and wind forcing, influenced by complex topography and interacting with the deep ocean and to improve the understanding of coastal marine environmental evolution, with particular emphasis on eddy dynamics. The general objective of COCES-II is to investigate the coastal dynamics off the coast of Senegal, a region strongly dominated by coastal upwelling. Specific goals are: 1. to construct unbiased statistics of near surface circulation; 2. to describe the upwelling circulation features; 3. to simulate the coastal circulation with a numerical model and 4. to train local Senegalese oceanographers (capacity building). COCES-II is the continuation of the COCES project. It aims to consolidate the longer term cooperation between US, European and Senegalese scientists to study the North Atlantic off the west African coast. Surface drifters are deployed off the coast of Senegal on a continuous monthly basis for at least a year, with an intensification period in winter/spring to better sample the upwelling circulation features. The drifter data are analyzed in conjunction with ancillary in-situ data (ship-based CTD and ADCP) and satellite images of sea surface temperature (SST), chlorophyll concentration (Chl) and sea level height (SSH). Numerical model simulations are performed with ROMS and are compared to the observations.

The hyper-arid Atacama Desert is one of the most extreme environments for life and only few species have evolved to survive its aridness. One such species is the tree Prosopis tamarugo Phil. Because Tamarugo completely depends on groundwater, it is being threatened by the high water demand from the Chilean mining industry and the human consumption. In this paper, we identified the most important biophysical variables to assess the water status of Tamarugo trees and tested the potential of WorldView2 satellite images to retrieve these variables. We propose green canopy fraction (GCF) and green drip line leaf area index (DLLAIgreen) as best variables and a value of 0.25 GCF as a critical threshold for Tamarugo survival. Using the WorldView2 spectral bands and an object-based image analysis, we showed that the NDVI and the Red-edge Chlorophyll Index (CIRed-edge) have good potential to retrieve GCF and DLLAIgreen. The NDVI performed best for DLLAIgreen (RMSE = 0.4) while the CIRed-edge was best for GCF (RMSE = 0.1). However, both indices were affected by Tamarugo leaf movements (leaves avoid facing direct solar radiation at the hottest time of the day). Thus, monitoring systems based on these indices should consider the time of the day and the season of the year at which the satellite images are acquired.

Brassica napus is grown as an edible oil (canola) and an industrial oil (HEAR). Its fatty acid profile and chlorophyll concentration affect the quality. It is important to develop accurate and efficient methods to evaluate these traits. The first objective of this study was to improve the single nucleotide polymorphism (SNP) and sequence characterized amplified region (SCAR) molecular markers for erucic acid genotypes in the Bn-FAE1.1 and Bn-FAE1.2 genes in the A and C genomes in Brassica napus originally developed by Rahman et al. (2008). When put into practice, the error rate was unacceptably high. With the modifications that were made to the protocols, the overall accuracy remained relatively consistent indicating that further improvements are still required. The second objective was to develop a near infrared reflectance (NIR) based calibration equation for chlorophyll concentration in whole Brassica napus seeds. In this case, an equation was successfully created.

The lichen Usnea longissima was used to examine how distance from forest edge and edge contrast influence growth of pendulous lichens. Thalli of two sizes (12 and 27 cm) were transplanted to the lower canopy of old Picea abies forest at 5, 25 and 100 m distance from cutovers. Sites represented three levels of edge contrast: high (clear-cut), intermediate (3 m tall saplings) and low (6-7 m tall young forest). Lichen growth was assessed as annual length and weight gain. Growth rates of intact thalli were size-dependent, with both growth variables being higher in long than in short thalli. Distance and edge contrast had significant effects on weight gain in long thalli but not in short ones. Weight gain in long thalli was twice as high near the edge (23%) compared to the forest interior (12%). The highest weight gain (31%) occurred at intermediate contrast edges with lower growth at both low (18%) and high contrast edges (20%). Chlorophyll a concentration was highest near the edge and positively correlated with weight gain, so growth was apparently stimulated by both increased photosynthetic capacity and higher light availability near the edge. The lower part of the canopy in forest edges apparently have favourable growth conditions for U. longissima with growth being influenced by vegetation on adjoining cutovers. Therefore growth responses can not explain the previously observed decline of pendulous lichens following edge creation. Our results suggest that vegetation buffers can improve conditions for pendulous lichens near forest edges.

Accurate assessment of the specific influence of calcium carbonate and iron (Fe) oxides in soil on Fe deficiency symptoms in plants has so far been made difficult by the covariance between their contents in many soils populations. In order to overcome this problem, we designed a completely randomized block experiment in which grapevine (cv. 161–49C) was pot-grown in substrates consisting of Fe oxide-coated sand (FOCS), calcium carbonate sand (CCS) and quartz sand for 100 days (five FOCS proportions, five CCS proportions, four replicates); in this way, covariance between the FOCS and CCS proportions was suppressed. An analysis of variance revealed the absence of interactions between FOCS and CCS in relation for any of the growth-related parameters studied (leaf size, increase in shoot length, internode length, and aerial biomass) and leaf chlorophyll concentration as measured via SPAD. Some growth-related parameters were found to be negatively correlated with the proportion of CCS, and leaf size to be positively correlated with the proportion of FOCS. Also, SPAD was more markedly influenced by the proportion of FOCS (positive correlation) than it was by CCS (negative correlation). Overall, these results indicate that the relative severity of the main symptoms of Fe deficiency, growth depression and leaf chlorosis, may differ from one case to another in response to the relative contents in carbonate and Fe oxides of soil. Also, they suggest the need to develop and calibrate soil tests capable of predicting the various Fe deficiency symptoms.

Empirical band-ratio algorithms and artificial neural network techniques to retrieve sea surface chlorophyll concentrations were evaluated in the Bohai Sea of China by using an extensive field observation data set. Bohai Sea represents an example of optically complex case II waters with high concentrations of colored dissolved organic matter (CDOM). The data set includes coincident measurements of radiometric quantities and chlorophyll a concentration (Chl), which were taken on 8 cruises between 2003 and 2005. The data covers a range of variability in Chl in surface waters from 0.3 to 6.5 mg m -3. The comparison results showed that these empirical algorithms developed for case I and case II waters can not be applied directly to the Bohai Sea of China, because of significant biases. For example, the mean normalized bias (MNB) for OC4V4 product was 1.85 and the root mean square (RMS) error is 2.26.

Empirical band-ratio algorithms and artificial neural network techniques to retrieve sea surface chlorophyll concentrations were evaluated in the Bohai Sea of China by using an extensive field observation data set. Bohai Sea represents an example of optically complex case II waters with high concentrations of colored dissolved organic matter (CDOM). The data set includes coincident measurements of radiometric quantities and chlorophyll a concentration (Chl), which were taken on 8 cruises between 2003 and 2005. The data covers a range of variability in Chl in surface waters from 0.3 to 6.5 mg m -3. The comparison results showed that these empirical algorithms developed for case I and case II waters can not be applied directly to the Bohai Sea of China, because of significant biases. For example, the mean normalized bias (MNB) for OC4V4 product was 1.85 and the root mean square (RMS) error is 2.26.

Empirical band-ratio algorithms and artificial neural network techniques to retrieve sea surface chlorophyll concentrations were evaluated in the Bohai Sea of China by using an extensive field observation data set. Bohai Sea represents an example of optically complex case II waters with high concentrations of colored dissolved organic matter (CDOM). The data set includes coincident measurements of radiometric quantities and chlorophyll a concentration (Chl), which were taken on 8 cruises between 2003 and 2005. The data covers a range of variability in Chl in surface waters from 0.3 to 6.5 mg m -3. The comparison results showed that these empirical algorithms developed for case I and case II waters can not be applied directly to the Bohai Sea of China, because of significant biases. For example, the mean normalized bias (MNB) for OC4V4 product was 1.85 and the root mean square (RMS) error is 2.26.

Our long-term goal is to improve predictivity of physical, biogeochemical and optical properties of Eastern Caribbean waters under the influence of mesoscale eddies and their interaction with regional features (i.e. massive riverine discharge). Expected outcomes from this research include the capacity to infer susbsurface properties and processes as well as their temporal and spatial evolution utilizing remotely acquired surface observations. This program will contribute to the development of infrastructure for marine research and education at the University of Puerto Rico. A particular expectation is the recruitment and training of graduate students who will focus their graduate research in current scientific issues attuned with the above expressed goals.

The foraging behaviour of animals depends on the distribution, abundance and predictability of their food resources. In the marine environment, top predators such as seabirds are known to concentrate their foraging effort in specific oceanic features where productivity is elevated or prey concentrated. When marine productivity is low and prey distribution unpredictable, such as in tropical waters, selection should favour the evolution of flexible foraging strategies. By using GPS, Argos transmitters and activity recorders, we studied the foraging strategy of red-footed boobies (RFBs) Sula sula breeding on Europa Island in the Mozambique Channel, to examine the way a central place forager searches for prey in tropical waters. RFBs only foraged during the day-time and never sat on the water at night; thus, they consequently had a limited maximum foraging range of 148 km. Primary production within this range was low overall (average 0.165 mg chlorophyll m(-3)), with a high spatial and temporal heterogeneity due to the presence of strong geostrophic currents and surface mixing by storms. RFBs appear to adjust their foraging strategy to cope with this situation. Individual birds do not return to the same oceanic sites from one trip to the next, but generally head in the direction of zones where productivity is enhanced. Active foraging, i.e. periods when birds spent time on the sea surface or dived, occurred at the most distant part of the foraging trip. Despite their limited foraging range and the low productivity of surrounding waters, red-footed boobies are able to track zones of prey availability located in areas of enhanced primary production. Searching is probably favoured by the presence of sub-surface predators that chase prey to the surface. The foraging strategy of this tropical sulid appears to differ extensively from that of temperate or polar seabirds whose prey distribution and availability are more predictable.

A possibility of using physiological parameters for differentiating resistant and susceptible plants was investigated. Intensity of transpiration diffusive resistance and chlorophyll concentrations were measured. The experiments were carried out in the greenhouse. Seeds were collected from an area continually treated with atrazine over a period often years (locality Veliki Crljeni) and from treatment-free fields (locality Belgrade). A referent resistant population was obtained from Great Britain. Atrazine was applied (2,4 and 8 kg/ha) when plants were in a 2-4 leaf growth stage. Parameters were measured on the 7th and 15th post-treatment days. The results showed no significant change in the physiological parameters of the treated referent plants. On the other hand, treated plants from the localities of Veliki Crljeni and Belgrade showed a significant decrease in the intensity of transpiration and chlorophyll concentration, and increase in diffusive resistance, compared to untreated plants. Comparing the parameters analyzed, statistically significant differences were found between the domestic populations and the resistant referent population. Based on the variations found in plant responses to atrazine treatments (intensity of transpiration and diffusive resistance) in the populations investigated, we believe that assessment of these physiological parameters alone cannot provide sufficiently reliable data for differentiating between resistant and susceptible plants., U radu je ispitivana mogućnost korišćenja fizioloških parametara kao osnove za razdvajanje rezistentnih od osetljivih populacija Chenopodium album L. na atrazin. Praćeni su intenzitet transpiracije, otpor prema difuziji i relativni sadržaj ukupnog hlorofila. Semena su prikupljena sa površine na kojoj je atrazin korišćen 10 godina (lokalitet Veliki Crljeni) i sa površine na kojoj nikad nisu primenjivani herbicidi (lokalitet Beograd). Referentna rezistentna populacija dobijena je iz laboratorije iz Velike Britanije. Biljke su gajene u kontrolisanim uslovima i tretirane atrazinom (2, 4 i 8 kg/ha) u fazi 2-4 lista. Promene ispitivanih parametara su merene 7. i 15. dana od primene atrazina. Dobijeni rezultati su pokazali da kod referentne rezistentne populacije tretirane herbicidom nema značajnih promena na nivou posmatranih parametara. Međutim, kod populacija sa lokaliteta V.Crljeni i Beograd došlo je do značajnog smanjenja intenziteta transpiracije i relativnog sadržaja hlorofila, i do povećanja otpora prema difuziji. Statistička obrada podataka je pokazala da se na osnovu svih parametara može izvršiti razdvajanje osetljivih i rezistentih populacija Ch. album prema atrazinu, s tim što se relativni sadržaj ukupnog hlorofila u poređenju sa druga dva parametra pokazao kao pouzdaniji parametar. Prirodna dnevna dinamika fizioloških procesa i njihova zavisnost od velikog broja činilaca (sadržaja 07 i CO, u vazduhu, vlažnosti vazduha, otvorenosti stoma i sl.) umanjuju pouzdanost intenziteta transpiracije i otpor prema difuziji kao parametara.

The foraging behaviour of animals depends on the distribution, abundance and predictability of their food resources. In the marine environment, top predators such as seabirds are known to concentrate their foraging effort in specific oceanic features where productivity is elevated or prey concentrated. When marine productivity is low and prey distribution unpredictable, such as in tropical waters, selection should favour the evolution of flexible foraging strategies. By using GPS, Argos transmitters and activity recorders, we studied the foraging strategy of red-footed boobies (RFBs) Sula sula breeding on Europa Island in the Mozambique Channel, to examine the way a central place forager searches for prey in tropical waters. RFBs only foraged during the day-time and never sat on the water at night; thus, they consequently had a limited maximum foraging range of 148 km. Primary production within this range was low overall (average 0.165 mg chlorophyll m(-3)), with a high spatial and temporal heterogeneity due to the presence of strong geostrophic currents and surface mixing by storms. RFBs appear to adjust their foraging strategy to cope with this situation. Individual birds do not return to the same oceanic sites from one trip to the next, but generally head in the direction of zones where productivity is enhanced. Active foraging, i.e. periods when birds spent time on the sea surface or dived, occurred at the most distant part of the foraging trip. Despite their limited foraging range and the low productivity of surrounding waters, red-footed boobies are able to track zones of prey availability located in areas of enhanced primary production. Searching is probably favoured by the presence of sub-surface predators that chase prey to the surface. The foraging strategy of this tropical sulid appears to differ extensively from that of temperate or polar seabirds whose prey distribution and availability are more predictable.

The foraging behaviour of animals depends on the distribution, abundance and predictability of their food resources. In the marine environment, top predators such as seabirds are known to concentrate their foraging effort in specific oceanic features where productivity is elevated or prey concentrated. When marine productivity is low and prey distribution unpredictable, such as in tropical waters, selection should favour the evolution of flexible foraging strategies. By using GPS, Argos transmitters and activity recorders, we studied the foraging strategy of red-footed boobies (RFBs) Sula sula breeding on Europa Island in the Mozambique Channel, to examine the way a central place forager searches for prey in tropical waters. RFBs only foraged during the day-time and never sat on the water at night; thus, they consequently had a limited maximum foraging range of 148 km. Primary production within this range was low overall (average 0.165 mg chlorophyll m(-3)), with a high spatial and temporal heterogeneity due to the presence of strong geostrophic currents and surface mixing by storms. RFBs appear to adjust their foraging strategy to cope with this situation. Individual birds do not return to the same oceanic sites from one trip to the next, but generally head in the direction of zones where productivity is enhanced. Active foraging, i.e. periods when birds spent time on the sea surface or dived, occurred at the most distant part of the foraging trip. Despite their limited foraging range and the low productivity of surrounding waters, red-footed boobies are able to track zones of prey availability located in areas of enhanced primary production. Searching is probably favoured by the presence of sub-surface predators that chase prey to the surface. The foraging strategy of this tropical sulid appears to differ extensively from that of temperate or polar seabirds whose prey distribution and availability are more predictable.

A possibility of using physiological parameters for differentiating resistant and susceptible plants was investigated. Intensity of transpiration diffusive resistance and chlorophyll concentrations were measured. The experiments were carried out in the greenhouse. Seeds were collected from an area continually treated with atrazine over a period often years (locality Veliki Crljeni) and from treatment-free fields (locality Belgrade). A referent resistant population was obtained from Great Britain. Atrazine was applied (2,4 and 8 kg/ha) when plants were in a 2-4 leaf growth stage. Parameters were measured on the 7th and 15th post-treatment days. The results showed no significant change in the physiological parameters of the treated referent plants. On the other hand, treated plants from the localities of Veliki Crljeni and Belgrade showed a significant decrease in the intensity of transpiration and chlorophyll concentration, and increase in diffusive resistance, compared to untreated plants. Comparing the parameters analyzed, statistically significant differences were found between the domestic populations and the resistant referent population. Based on the variations found in plant responses to atrazine treatments (intensity of transpiration and diffusive resistance) in the populations investigated, we believe that assessment of these physiological parameters alone cannot provide sufficiently reliable data for differentiating between resistant and susceptible plants., U radu je ispitivana mogućnost korišćenja fizioloških parametara kao osnove za razdvajanje rezistentnih od osetljivih populacija Chenopodium album L. na atrazin. Praćeni su intenzitet transpiracije, otpor prema difuziji i relativni sadržaj ukupnog hlorofila. Semena su prikupljena sa površine na kojoj je atrazin korišćen 10 godina (lokalitet Veliki Crljeni) i sa površine na kojoj nikad nisu primenjivani herbicidi (lokalitet Beograd). Referentna rezistentna populacija dobijena je iz laboratorije iz Velike Britanije. Biljke su gajene u kontrolisanim uslovima i tretirane atrazinom (2, 4 i 8 kg/ha) u fazi 2-4 lista. Promene ispitivanih parametara su merene 7. i 15. dana od primene atrazina. Dobijeni rezultati su pokazali da kod referentne rezistentne populacije tretirane herbicidom nema značajnih promena na nivou posmatranih parametara. Međutim, kod populacija sa lokaliteta V.Crljeni i Beograd došlo je do značajnog smanjenja intenziteta transpiracije i relativnog sadržaja hlorofila, i do povećanja otpora prema difuziji. Statistička obrada podataka je pokazala da se na osnovu svih parametara može izvršiti razdvajanje osetljivih i rezistentih populacija Ch. album prema atrazinu, s tim što se relativni sadržaj ukupnog hlorofila u poređenju sa druga dva parametra pokazao kao pouzdaniji parametar. Prirodna dnevna dinamika fizioloških procesa i njihova zavisnost od velikog broja činilaca (sadržaja 07 i CO, u vazduhu, vlažnosti vazduha, otvorenosti stoma i sl.) umanjuju pouzdanost intenziteta transpiracije i otpor prema difuziji kao parametara.

Zea mays L. cv. amylacea, a plant tolerant of B and salinity, was used to determine the involvement of aquaporin functionality in the interactive effects of B and salinity. Also, growth, chlorophyll concentration, and water relations were studied. While growth and chlorophyll concentration did not show noticeable changes under saline conditions, the decrease in leaf water potential and osmotic potential, together with the marked decrease of stomatal conductance and root hydraulic conductance, showed that the plants were adjusted osmotically. However, no effect of B was observed. The very weak response of the Lpc of salt-stressed roots to Hg suggested that water channels were greatly reduced in number or, if present, were non-functional. The evidence that substantial B movement can occur through diffusion and channel-mediated transport is compelling, and could account for B uptake under conditions of adequate or greater B supply. Therefore, the reduction in the functionality of aquaporins for NaCl-treated plants could be related to the reduction of B concentrations in roots and leaves in B + NaCl-treated plants, in comparison with plants treated only with B.

The short-term variability of intertidal microphytobenthic biomass was characterized by analysing a 30-day time series encompassing two spring-neap tide cycles. Chlorophyll-a concentration was measured every day at the beginning and at the end of every diurnal exposure periods. Microalgal biomass exhibited predictible net increases during diurnal exposures due to a positive production-loss balance. In addition, our data series shows that after an environmental disturbance, even though biomass decreased strongly, it converged quickly back to its initial steady-state oscillation pattern. This study supports some fundamental properties of the dynamics of microphytobenthic biomass, as previously predicted in our mathematical model of primary production.

The short-term variability of intertidal microphytobenthic biomass was characterized by analysing a 30-day time series encompassing two spring-neap tide cycles. Chlorophyll-a concentration was measured every day at the beginning and at the end of every diurnal exposure periods. Microalgal biomass exhibited predictible net increases during diurnal exposures due to a positive production-loss balance. In addition, our data series shows that after an environmental disturbance, even though biomass decreased strongly, it converged quickly back to its initial steady-state oscillation pattern. This study supports some fundamental properties of the dynamics of microphytobenthic biomass, as previously predicted in our mathematical model of primary production.

The short-term variability of intertidal microphytobenthic biomass was characterized by analysing a 30-day time series encompassing two spring-neap tide cycles. Chlorophyll-a concentration was measured every day at the beginning and at the end of every diurnal exposure periods. Microalgal biomass exhibited predictible net increases during diurnal exposures due to a positive production-loss balance. In addition, our data series shows that after an environmental disturbance, even though biomass decreased strongly, it converged quickly back to its initial steady-state oscillation pattern. This study supports some fundamental properties of the dynamics of microphytobenthic biomass, as previously predicted in our mathematical model of primary production.

The influence of NaCl on senescence-related parameters (protein and chlorophyll concentrations, membrane permeability and chlorophyll fluorescence) was investigated in young and old leaves of five rice cultivars differing in salt resistance. NaCl hastened the naturally-occurring senescence of rice leaves which normally appears during leaf ontogeny: it decreased chlorophyll and protein concentrations and increased membrane permeability and malondialdehyde synthesis. Such an acceleration of deteriorative processes affected all leaves in sail-sensitive cultivars while it was more marked in oldest than in youngest leaves of sail-resistant genotypes. NaCl-induced senescence also involved specific modifications, such as an increase in basal non-variable chlorophyll fluorescence (F-0) recorded in all cultivars or a transient increase in soluble protein concentration recorded in salt-resistant genotypes only. Alteration of membrane permeability appeared as one of the first symptoms of senescence in rice leaves and allowed discrimination among cultivars after only 7 d of stress. In contrast, F-v/F-m ratio (variable fluorescence/maximal fluorescence) was the same for all cultivars during the first 18 d of stress and thus could not be used for identifying salt-resistant rice exposed to normal light conditions. Relationships between parameters involved in leaf senescence are discussed in relation to salinity resistance of rice cultivars. (C) 1996 Annals of Botany Company.

Intrathaliine and intracellular chlorophyll concentrations together with thallus structure were studied in 12 spccies of the Iichen family Urnbilicariaceae in arder to explore pigment limitations for light absorption and for maximum rates of net photosynthesis (A",aJ. Species from high light environments tended to have relatively low chlorophyll concentrations and vice versa. ChlorophyIl concentration 011 a surface area basis of all species studied was sufficient to absorb 80-99 % of the incident light, which led us to be1ieve that chlorophyIl concentration was not a limiting factor for Amax ' Amax of Umbilicariaceac was smaller than Amax of leaves of vascular plants, both on a dry weight and on a surface area basis. These differences slightly dccreased but did not disappcar whcn refcrred to the chlorophy11 concentration of the photosynthetic tissues, but refcrencc units had a confounding effect in the comparisons. Differences in Amax on a dry weight basis between Umbilicariaccae and vascular plants disappeared when comparisons were made-with the whole plant and not simply with the leaf. We found a significant, inverse rclationship between amount of alga and chlorophyIl concentration within the algal ce11s in the lichens studied. This was interpreted as a mechanism to avoid pigrnent self-shading within the algal layer, distributing more efficiently the photosynthetic pigments over a given surface area, and is the first indication of such a mechanism in lichens. It is suggested that thallus structure and physiology have a larger influence on the observed low Amax of the lichens studied than chlorophy11 content