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Published in J. Environ. Qual. 33:1369-1375 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS

Plant and Environment Interactions

Differences in the Effects of Simulated Sea Aerosol on Water Relations, Salt Content, and Leaf Ultrastructure of Rock-Rose Plants

M. J. Sánchez-Blancoa,*, P. Rodrígueza,b, E. Olmosa, M. A. Moralesa and A. Torrecillasa

a Centro de Edafología y Biología Aplicada del Segura (CSIC), P.O. Box 164, E-30100 Espinardo, Murcia, Spain
b Instituto Nacional de Ciencias Agrícolas (INCA), Gaveta Postal 1, 32700 San José de Las Lajas, La Habana, Cuba

* Corresponding author (quechu{at}cebas.csic.es).

Received for publication April 6, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
White-leaf rock-rose (Cistus albidus L.) and Montpellier rock-rose (C. monspeliensis L.) plants were sprayed 2 to 3 min per day over a 7-d period, in an unheated plastic greenhouse, with different aqueous solutions containing deionized water alone (control); an anionic surfactant (sodium dodecylbenzenesulfonate 82.5%, 50 mg L–1) (S1); a solution simulating the composition of sea aerosol (S2); and a solution simulating sea aerosol with anionic surfactant (S3). White-leaf rock-rose was more sensitive to sea aerosol, showing greater leaf damage and markedly decreased growth, and the presence of surfactant enhanced the phytotoxic effect leading to greater increases in mortality. Montpellier rock-rose did not appear to be more adversely affected when surfactant was used in combination with sea aerosol, and manifested slight or less severe symptoms than white-leaf rock-rose. There was a significant increase in leaf turgor potential in the plants treated with both sea aerosol treatments by osmotic adjustment effect. The decrease in photosynthesis level seems to be due to both stomatal and nonstomatal factors. The results of microscopical analysis of Montpellier rock-rose plants show that sea aerosol treatment caused alterations in the chloroplast structure, reducing the starch grain and swelling the thylakoid membranes. The results of this study indicated that Montpellier rock-rose was more tolerant to sea aerosol than white-leaf rock-rose, showing a lower reduction in plant growth and less leaf damage, probably because of its ability to compartmentalize the toxic ions at the intracellular level.

Abbreviations: gs, leaf stomatal conductance • Pn, photosynthetic rate • {Psi}l, leaf water potential • {Psi}os, leaf osmotic potential at full turgor • {Psi}p, leaf turgor potential


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE EFFECTS of sea aerosol and pollution by surfactants on coastal vegetation have been studied for several decades in a number of European Mediterranean regions (Gellini et al., 1983, 1987; Garrec and Sigoillot, 1992; Astorga et al., 1993; Bussotti and Grossoni, 1993). The damage is attributed to an excessive absorption of salts as a result of the action of the surfactants, since leaf chloride and sodium absorption is made easier by the presence of surfactant (Bussotti et al., 1995). These substances are absorbed through the stomata and cuticle, causing deterioration of the epistomatal wax structures and inducing alterations in the stomatal guard cell walls. In this form, the efficiency of photosynthesis and gaseous exchange processes may be affected (Bussotti et al., 1997). However, photosynthesis is affected to varying degrees within and between species (Darrall, 1989; Schönherr, 1993), since the nature of the cuticle, particularly epicuticular waxes, plays an important role in the retention of aqueous sprays (Bukovac et al., 1981; Jefree, 1986) and may differ depending on species (Turunen and Huttunen, 1990).

Previous papers have studied the anatomical and ultrastructural aspects of plants treated with simulated sea aerosol both with and without surfactant, pointing to a marked increase in the damaged stomata of treated plants as compared with the controls (Gellini et al., 1987; Wolter et al., 1988; Bussotti et al., 1995), although with differences between species and consequently various degrees of sensitivity in productivity. However, the action of salt and surfactants in plant water relations in different species has rarely been reported.

White-leaf rock-rose and Montpellier rock-rose plants are native of lands surrounding the Mediterranean Sea, mainly southwestern Europe and northern Africa. Both species are evergreen woody shrubs and their blooms are profuse and attractive. Native ornamental species of wild flora are very interesting options for use in landscaping and gardening projects, since these plant species are largely resistant to environmental stresses (Sánchez-Blanco et al., 1998, 2002). However, although both rock-rose species responded to saline stress by developing avoidance (reduction of the canopy area to regulate transpiration) and tolerance (osmotic adjustment) mechanisms, this response differed between species, with Montpellier rock-rose being more tolerant to saline irrigation water than white-leaf rock-rose (Torrecillas et al., 2003). In this sense, the response of the species to sea aerosol is related to the degree of salinity tolerance (Barbour et al., 1985; Sykes and Wilson, 1988).

The purpose of this study was to investigate the differences in growth, water relations, gas exchange, and mineral content that occur in white-leaf rock-rose and Montpellier rock-rose plants following the application of simulated sea aerosol with and without an anionic surfactant. Anatomical and ultrastructural responses were also studied to evaluate chloroplast alterations in Montpellier rock-rose. This study may provide information useful in mitigating the effects of pollution by selecting tolerant species.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Treatments
Four-month-old plants of white-leaf rock-rose and Montpellier rock-rose, obtained from seeds, were sprayed with different aqueous solutions containing an anionic surfactant (sodium dodecylbenzenesulfonate 82.5%, 50 mg L–1) (S1), a solution simulating the composition of sea aerosol (S2), and a solution with sea aerosol and anionic surfactant (S3). Another group of plants was used as control and treated with deionized water alone. The treatment consisted of spraying the leaves with a handpump until the dripping point was reached. Each treatment lasted 2 to 3 min and was repeated once per day over a 7-d period.

The experiment was conducted from August to November 1999 in an unheated plastic greenhouse in Santomera (Murcia, Spain). Plants were grown individually in 8- to 10-cm-diameter plastic containers filled with a mixture of silt loam, perlite, and clay (equal parts per volume). The soil was covered with plastic to avoid salt absorption by the root system. The design of the experiment was a completely randomized block with three replications (eight plants per replicate).

The plants were irrigated daily with an automated drip irrigation system, which provided 500 mL plant–1 of nutrient solution (0.3 g L–1 NH4NO3, 0.15 g L–1 KNO3, 0.15 g L–1 NH4PO4H, 0.06 g L–1 Ca, 0.005 g L–1 Fe, and 0.005 g L–1 Zn). The maximum and minimum average temperatures were 30 and 10°C in the greenhouse, respectively, and the relative humidity ranged between 30 and 90%. The average maximum photosynthetically active radiation (PAR) was 1250 µmol m–2 s–1.

Measurements of Growth
At the end of the application period (7 d), 48 plants per species (four per treatment and replicate) were harvested and stem, root, and leaf dry weights were recorded. Leaf area was determined using an image analysis system (Delta-T Devices, Cambridge, UK).

Ion leakage was measured as an indicator of any alteration in membrane permeability caused by the applications. Plants from each treatment were collected at the end of the experimental period and then the measurements of ion leakage were obtained in leaf discs according to Lafuente et al. (1991). Leaf segments of uniform maturity were cut in discs and washed three times with deionized water to eliminate the external residues. Discs were placed in Erlenmeyer flasks with 10 mL of 0.3 M mannitol and shaken for 24 h. Then, the conductivity of the solution was read with a Crison Instruments (Barcelona, Spain) Model 524 conductivity meter. After that, the sample was boiled for 10 min to kill the tissues and then, after cooling, the conductivity of this solution was recorded. Percentage of electrolytes originally diffused out was calculated as follows:

where C1 and C2 are the conductivities of the solution before and after killing the tissues, respectively.

Leaf damage, consisting of leaf chlorosis and necrosis, was determined at the end of the experimental period. The fresh weight of the damaged leaf tissue was recorded and expressed as a percent of the fresh weight of the control plants.

Water Status and Gas Exchange Measurements
Leaf water potential ({Psi}l), leaf osmotic potential ({Psi}s), and leaf osmotic potential at full turgor ({Psi}os) were measured, at maximum PAR level (midday) in 15 plants of each species and treatment, at the end of the experimental period using leaves of the same age. Leaf water potential was determined using a pressure chamber (Soil Moisture Equipment Co., Santa Barbara, CA) according to Scholander et al. (1965). Leaf osmotic potential ({Psi}s) was estimated using a vapor pressure osmometer (Model 5500; Wescor, Logan, UT) in excised leaves harvested at midday and immediately frozen and stored at –30°C. Before the measurements, samples were thawed and leaf sap was extracted for immediate osmotic potential determination according to Gucci et al. (1991). The leaves used for determining {Psi}os were subjected to a rehydration by dipping the petioles in distilled water overnight and then measuring, as explained previously, using a Wescor 5500 vapor pressure osmometer. Leaf turgor potential ({Psi}p) was estimated as the difference between {Psi}l and {Psi}s.

Leaf stomatal conductance (gs) and the photosynthesis rate (Pn) of attached leaves were measured using a LI-1600 steady state porometer (LI-COR, Lincoln, NE) and a LI-6200 portable closed gas-exchange photosynthesis system, respectively. All measurements were taken immediately before each harvest.

Mineral Content
Five plants per species and treatment were harvested and separated into leaves and stems, which were washed with distilled water, dried at 70°C, ground, and stored at room temperature for inorganic solute analyses. The Cl– contents were analyzed in the aqueous extracts by a chloride analyzer (Model 926; Sherwood Scientific Ltd., Cambridge, UK). The Na+ contents were determined in a digestion extract with HNO3 and HClO4 (2:1, v/v) by atomic absorption spectrometry (Model AA-6701; Shimadzu, Kyoto, Japan).

Transmission Electron Microscopy
This study was performed only in Montpellier rock-rose plants because of the high rate of mortality recorded on white-leaf rock-rose plants treated with sea aerosol with and without surfactant (S2 and S3 treatments). Thus, for conventional microscopy, samples from Montpellier rock-rose leaves were fixed for 2.5 h at 4°C in a 0.1 M Na-phosphate buffered (pH = 7.2) mixture of 2.5% glutaraldehyde and 4% paraformaldehyde (Hernández et al., 1995). Tissue was postfixed with 1% osmium tetroxide for 2 h. The samples were then dehydrated in a graded alcohol series and embedded in Spurr's resin (Spurr, 1969). Blocks were sectioned on a Leica ultracut microsystem (Hernalser Hauptstrass, Vienna, Austria). Thin sections for transmission electron microscopy (TEM) were picked up on copper grids and stained with uranyl acetate followed by lead citrate (Reynolds, 1963). The ultrastructure of the tissue was observed with a Zeiss (Oberkochen, Germany) EM10 and a Zeiss EM109.

For morphometric analysis, a minimum of 15 micrographs per treatment and tissue were studied. The morphometric parameters were measured for both treatments by image analysis (Q500MC; Leica, Wetzlar, Germany).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Growth and Plant Morphology
There were clear differences in the plant growth of both species under simulated sea aerosol conditions. The action of the combined treatment of sea aerosol plus surfactant (S3) caused visible damage in white-leaf rock-rose, provoking the death of the plants at the end of the application period. However, this situation was not observed in Montpellier rock-rose, in which similar effects in growth parameters were detected in both sea aerosol treatments (S2 and S3) (Tables 1 and 2). These effects, corresponding to reductions in the total plant biomass (13%) in S2 and S3 treatments compared with the control (Table 1), were due to the reductions in the leaf dry weight (Table 1). In this genotype, total canopy area (leaf area and leaf number) was similarly affected by both sea aerosol treatments (Table 2). White-leaf rock-rose plants of the S2 treatment showed a significant decrease in total biomass of 34% compared with control plants. In this case, leaf dry weight and canopy area were more markedly affected than in Montpellier rock-rose. The stem dry weight values were also affected (Table 1 and 2).


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  		Table 1. Root, stem, leaf, and total dry weight for white-leaf rock-rose and Montpellier rock-rose at the end of the experimental period after four different treatments.

 

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  		Table 2. Total leaf area (LA), leaf number (LN), leaf damage (LD), and ion leakage (IL) of white-leaf rock-rose and Montpellier rock-rose at the end of the experimental period after four different treatments.

 
Leaf damage, consisting of leaf chlorosis and necrosis, was observed in plants of both species in the sea aerosol treatments (Table 2). In white-leaf rock-rose this tissue damage was higher, being 84% in S2 and 100% (plants dead after 7 d from the initial treatments) in S3 with respect to the control treatment (0%). These values were around 64% in both S2 and S3 in Montpellier rock-rose (Table 2).

The rate of ion leakage was significantly higher in the sea aerosol treatments than in the control and S1 treatments (Table 2). In Montpellier rock-rose ion leakage was similar (around 60%) in plants exposed to sea aerosol treatments (with and without surfactant) (S2 and S3), and was lower than in sea-aerosol-treated plants (S2) of white-leaf rock-rose (Table 2).

Water Relations and Gas Exchange
The study of leaf water relations showed that the midday leaf water potential ({Psi}l) decreased in sea-aerosol-treated white-leaf rock-rose plants (S2) at the end of the application period (Table 3). In Montpellier rock-rose plants, on the other hand, the sea aerosol treatments (S2 and S3) produced higher values of {Psi}l than the control and S1 treatments. Leaf turgor potential ({Psi}p) showed a substantial increase in sea-aerosol-treated plants in both species, but especially in Montpellier rock-rose (Table 3), where it was similar for both treatments (S2 and S3). From the outset of the application period, the values of the leaf osmotic potential at full turgor ({Psi}os) decreased in both sea aerosol treatments with no significant differences between S2 and S3 in Montpellier rock-rose. Less pronounced changes in this parameter as a result of the sea aerosol treatment (S2) were observed in white-leaf rock-rose (Table 3).


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  		Table 3. Leaf water potential ({Psi}l), leaf turgor potential ({Psi}p), leaf osmotic potential at full turgor ({Psi}os), leaf stomatal conductance (gs), and net photosynthesis (Pn) of white-leaf rock-rose and Montpellier rock-rose at the end of the experimental period after four different treatments.

 
In both species of rock-rose, treated plants presented lower gs and Pn values than control plants at the end of the application period (Table 3). The highest reduction in gs and Pn occurred in the sea-aerosol-treated plants of both species but more markedly in Pn (Table 3). These reductions were similar in both sea aerosol treatments (with and without surfactant, S2 and S3) in Montpellier rock-rose.

Mineral Content
Chemical analysis of the treated leaves showed differences in Cl– and Na+ content in both species investigated (Table 4). In plants treated only with surfactant (S1) no differences in the content of the ions studied were seen with respect to the control. In white-leaf rock-rose plants exposed to the simulated sea aerosol (S2), the chloride content was 2.05 times greater than that observed in the control. The highest chloride contents were detected in Montpellier rock-rose in both sea aerosol treatments, 3171.91 mmol for S2 and 2820.74 mmol for S3. The sodium content was around 9.0 times greater in both rock-rose plants than in the controls.


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  		Table 4. The Na+ and Cl– concentrations in leaves of white-leaf rock-rose and Montpellier rock-rose plants after four different treatments.

 
Leaf Ultrastructure
Transmission electron microscopy (TEM) observation of Montpellier rock-rose control leaves showed well-organized chloroplasts with abundant starch grains and a structured cytoplasm (Fig. 1A and 2A) while the vacuole contents appeared to be electron-dense due to the presence of osmiophylic compounds (Fig. 1A). In plants treated only with surfactant (S1) (Fig. 1B), the ultrastucture of the organelles was not altered. However, the golgi apparatus showed an increase in vesicles (Fig. 2B). When leaves were treated only with sea aerosol (S2), the structure of some chloroplasts was altered, the starch grain was notably reduced and even disappeared, and in some of the chloroplasts, the thylakoid membranes appeared to be swollen (Fig. 2C). The vacuoles were less electron-dense in sea-aerosol-treated plants than in control leaves (Fig. 1C).



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  		Fig. 1. Mesophyll cells from leaves of Montpellier rock-rose: (A) control leaves, (B) plants treated only with surfactant, (C) plants treated only with sea aerosol, and (d) plants treated with sea aerosol plus surfactant. Scale bar = 5 µm; V, vacuole; Cl, chloroplast; S, starch grain; IS, intercellular space. The arrows indicate vacuolar content.

 


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  		Fig. 2. Details of cytoplasm from cells of Montpellier rock-rose leaves: (A) control leaves, (B) plants treated only with surfactant, (C) plants treated only with sea aerosol, and (d) plants treated with sea aerosol plus surfactant. Scale bar = 5 µm; CW, cell wall; V, vacuole; Cl, chloroplast; M, mitochondria; G, golgi; VS, vesicle.

 
In leaves treated with sea aerosol plus surfactant (S3), the vacuoles showed a greatly reduced osmiophylic content, with only small droplets attached to the tonoplast (Fig. 1D). In the cytoplasm osmiophylic droplets were also observed, some of which appeared to discharge into small vacuoles with which vesicles from the golgi apparatus were fused (Fig. 2D). The chloroplasts showed the same alterations as plants treated with only sea aerosol (S2).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
This study has revealed that simulated sea aerosol affects the physiological and morphological aspects studied in Montpellier rock-rose and white-leaf rock-rose, but not in the same manner. White-leaf rock-rose species was more sensitive to sea aerosol and presented higher leaf damage and more pronounced decreases in plant growth with respect to the control than Montpellier rock-rose (Tables 1 and 2). According to Bussotti and Grossoni (1993), the first plant organs to be affected under these conditions are the leaves. In some sensitive species, the damage can even extend to the shoot, as occurred with the white-leaf rock-rose plants. Also, ion leakage, used as a gross measurement of membrane permeability (Lafuente et al., 1991), was higher in white-leaf rock-rose plants. In this sense, the response of the species studied was related to their degree of salinity tolerance (Sykes and Wilson, 1988). Although both species are wild natives from lands surrounding the Mediterranean Sea, Montpellier rock-rose is more tolerant to saline stress (Torrecillas et al., 2003).

Mortality increased in white-leaf rock-rose when the plants were submitted to the combined treatment of sea aerosol plus surfactant. In this case, the presence of surfactant enhanced the phytotoxic effects (consisting of tissue chlorosis and necrosis and plant death). In this sense, damage caused when salts are applied in combination with anionic surfactants (Bussotti et al., 1995) has already been described in other coastal vegetation, namely Norfolk Island pine [Araucaria heterophylla (Salisb.) Franco] (Moodie et al., 1986) and Aleppo pine (Pinus halepensis Mill.) (Garrec and Sigoillot, 1992). Montpellier rock-rose, on the other hand, did not appear to be more adversely affected by the combined sea aerosol and surfactant treatment (S3). However, synthetic surfactant alone (S1) did not seem to affect plant growth in either of the species of rock-rose studied. The effect of salt sprays on growth may have significant ecological implications, since they may be positively linked to the establishment and competitive ability in coastal ecosystems (Cheplick and Demetry, 1999). The effect on growth and reproduction depends on the species, as occurred in our experiment. Leaf anatomical and morphological differences between species (higher size of white-leaf rock-rose leaves or presence of glandular hairs in Montpellier rock-rose leaves) may be related to the responses to salt exposure. It has also been suggested that differential permeabilities of cuticles and even the leaf area size (Tan and Crabtree, 1994) from different plant species may limit the rates of foliar uptake (Schönherr, 1993).

However, although white-leaf rock-rose was the more sensitive species to sea aerosols, as we have indicated, leaf tissue Na+ and Cl– contents were not correlated directly with the severity of the symptoms observed (Polizzi, 1995). This was even more evident in Montpellier rock-rose: Although presenting less severe symptoms, it also had a higher Cl– and the same Na+ content than white-leaf rock-rose. An important aspect of salt tolerance is related to the ability of a plant to compartmentalize toxic ions, such as Na+ and Cl– (Boursier and Läuchli, 1989). In this sense, Montpellier rock-rose plants showed a greater ability to compartmentalize these ions, and thus protect salt-sensitive enzymes (Leigh and Storey, 1993) and reduce the possible damage of these toxic ions on different subcellular organs. This behavior makes Montpellier rock-rose a more salt-tolerant species than white-leaf rock-rose. The fact that the response of the plants treated with surfactant did not show differences with respect to the control suggests that it was the salt absorbed that was responsible for the physiological changes in salinized plants.

The study of leaf water relations pointed to an increased turgor potential in plants treated with sea aerosol, which was more pronounced in Montpellier rock-rose (Table 3). This can be attributed to the salt absorption. Under these conditions, the tissues tend to exert greater water retention to balance the osmotic pressure (Dobson, 1991). Whatever the case, the increase in turgor did not permit the maintenance of growth in either of the species of rock-rose studied (Table 1), confirming that cell enlargement in plants exposed to salinity is not always correlated with cell turgor (Van Volkenburgh and Boyer, 1985; Sánchez-Blanco et al., 1998). The osmotic adjustment (decreased {Psi}os) which occurred in both species was probably due to the fact that the accumulation of solutes in vacuoles was consistent although, in spite of the decrease of {Psi}l detected in S2-treated white-leaf rock-rose plants, the turgor potential increased (Table 3). The relatively high leaf water potential in these treatments (–0.5 and –0.46 MPa) compared with the control and S1 treatments may result from the inhibition of gs and transpiration, as was observed in needles of Norway spruce [Picea abies (L.) H. Karst.] (Sauter and Voss, 1986).

Atmospheric concentration of pollutants may lead to stomatal opening or closure at higher concentrations (Robinson et al., 1998). In our experiment, the stomatal response to the solutions applied was not directly related to the leaf water status of the plants, since, regardless of the {Psi}l and {Psi}p values for each species, sea aerosol and surfactant alone caused reductions in gs. Nevertheless, sea aerosol treatments affected in a higher degree gs values in both species than surfactant aerosol treatments. This could due to the NaCl in contact with the guard cells, which could inhibit stomatal opening. Some studies have shown that guard cells have a greater ability to exclude Na+ than other leaf cells in halophyte species but not in nonhalophyte species, which respond to NaCl in an opposite way (Perera et al., 1994). The stomatal opening that occurs when guard cells in nonhalophytes accumulate Na+ leads to interference with the normal control of stomatal opening by signals such as light, water status, CO2, and abscisic acid (Jarvis and Mansfield, 1980; Thiel and Blatt, 1991).

Sea aerosol could affect photosynthesis levels in both species by altering stomatal conductance or by changing the metabolic capacity of mesophyll cells. In this experiment, gs was decreased by NaCl, while stomatal effects could also have been involved in reducing photosynthesis. Sauter et al. (1987) reported a decrease of about 30% in the photosynthesis rate of spruce needles exposed to pollutants.

The subcellular effects of surfactant and its combination with sea aerosol are hardly mentioned in the literature. Bussotti et al. (1995)( 1997), using anionic and nonionic surfactant, showed that the above compounds are notably toxic to cells, mainly affecting the stomatal apparatus and causing degeneration of the cytoplasm in cells of the mesophyll, particularly the chloroplast ultrastructure. In our work, we observed no significant effect on the ultrastructure of the cells of Montpellier rock-rose plants treated with the surfactant; only a significant increase of golgi apparatus was observed in treated plants. Bussotti et al. (1997) observed the intercellular spaces to be filled by an osmiophylic substance. However, we never observed this substance in the intercellular space of leaves treated with surfactant alone or in combination with seawater.

When Montpellier rock-rose plants were treated with sea aerosol, the effect observed in chloroplasts was typical of plants stressed by extreme temperatures, water stress, saline stress, and pollution (Hernández et al., 1995; Morales et al., 2001). The explanation of the substantial reduction of starch grains might be that mesophyll cells use soluble sugars to contribute to the osmotic adjustment induced by saline stress (Yeo and Flowers, 1983). The nature of the osmiophylic material in the vacuoles might be the essential oils present in rock-rose, while the significant reduction of these substances observed in plants treated with sea aerosol and sea aerosol plus surfactant might be explained by the reduced secondary metabolism during stress conditions, when cells save energy by reducing the production of metabolites such as essential oils (El-Keltawi and Croteau, 1987).


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Montpellier rock-rose plants are more tolerant to sea aerosol than white-leaf rock-rose, based on to their capacity to respond with a lower reduction in plant growth and less leaf damage. Montpellier rock-rose was also more efficient at decreasing the toxic salt content, probably because of its greater ability to compartmentalize toxic ions at the cellular level. In Montpellier rock-rose the combined action of salt and surfactant did not enhance the phytotoxic effect. Exposure to these substances (salt and surfactant) in combination does not always increase the sensitivity of plants by making leaves more penetrable to sea salt.


   ACKNOWLEDGMENTS
 
The authors are grateful to M.D. Velasco and M. Garcia for their technical assistance. This research was supported by the SENECA (PI-75/00819/FS/01) project. P. Rodríguez was a recipient of a MUTIS research fellowship from the Agencia Española de Cooperación Internacional (AECI).


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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This Issue in Journal of Environmental Quality

JEQ 2004 33: 1177-1182. [Full Text]  




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