Physiological and Biochemical Mechanisms Preventing Cd Toxicity in the New Hyperaccumulator <Emphasis Type="Italic">Abelmoschus manihot</Emphasis>

Abelmoschus manihot, an ornamental plant, was examined for phytoremediation purposes in accordance with the ability to accumulate cadmium and physiological mechanisms of cadmium tolerance. A net photosynthetic rate (A _N) glasshouse experiment for 60 days was conducted to investigate the influence of different cadmium amounts (0–100 mg kg^?1) on the growth, biomass, photosynthetic performance, reactive oxygen species (ROS) production, antioxidative enzyme activities, Cd uptake and accumulation of A. manihot. Exposure to cadmium enhanced plant growth even at 100 mg kg^?1, without showing symptoms of visible damage. The cadmium concentration of shoots (stems or leaves) and roots was more than the critical value of 100 mg kg^?1 and reached 126.17, 185.26 and 210.24 mg kg^?1, respectively. BCF values of A. manihot plants exceeded the reference value 1.0 for all the Cd treatments, and TF values were greater than 1 at 15–60 mg kg^?1 Cd treatment. The results also showed that cadmium concentrations of 60 mg kg^?1 or less induced a significant enhancement in plant net photosynthetic rate (A _N), stomatal conductance (G _s), transpiration rate (T _r), photosynthetic pigments and F _v/F _m. These parameters were slightly decreased at the higher concentration (100 mg kg^?1). The ROS production (O₂ ^?, H₂O₂) and antioxidative response including SOD, CAT and POD were significantly enhanced by increasing cadmium. These results suggest that A. manihot can be considered as a Cd-hyperaccumulator and the hormetic effects may be taken into consideration in remediation of Cd contamination soil.     

Oxidative enzymes activity during abiotic and biotic stresses in <Emphasis Type="Italic">Zea mays</Emphasis> leaves and roots exposed to Cu,methyl jasmonate and <Emphasis Type="Italic">Trigonotylus caelestialium</Emphasis>

The activities of antioxidative enzymes, i.e. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX), in the leaves and roots of Zea mays L. plants exposed to abiotic (methyl jasmonate, MJ, or/and copper, Cu) and biotic (Trigonotylus caelestialium) factors were examined. The contribution of MJ as a signal molecule in the defense mechanism against abiotic and biotic stresses was studied. All plants were cultivated hydroponically and divided into three groups: not treated by abiotic factors (control), treated by MJ only (MJ) and by MJ and Cu (MJ + Cu) and in each group half of the plants were exposed to T. caelestialium attack. The enzymatic activities of SOD, CAT, APX, and GPX in the leaves were higher in the insect-treated than non-insect-treated control plants, but lower in both MJ + Cu- or MJ- and insect-treated plants. In the roots, the enzyme activities were elevated in all insect-treated plants with the highest rise in MJ + Cu, in comparison with the MJ-treated plants. The results showed that MJ and MJ + Cu were efficient in reducing the activity of the antioxidative enzymes in the leaves under the insect influence by elevating enzyme activity in the roots.     

Photosynthetic response of <Emphasis Type="Italic">Bangia fuscopurpurea</Emphasis> (Bangiales,Rhodophyta) towards dehydration and hyposalinity

Bangia fuscopurpurea, an important farmed species in China, inhabits upper intertidal zones where it suffers periodical desiccation and salinity stress. However, the physiological response and acclimation mechanism of Bangia to abiotic stress is unknown. Here, the photosynthetic response of B. fuscopurpurea to desiccation and hyposalinity was investigated by using chlorophyll fluorescence measurement. The optimum photosynthetic efficiency of photosystem II (Fv/Fm), photochemical quenching (qP) and the non-photochemical quenching (NPQ) of B. fuscopurpurea thalli maintained at basal level when the absolute water content (AWC) was 32%. As AWC decreased from 32% to 9%, Fv/Fm dropped from 0.62 to 0.1 and NPQ increased from 0.2 to 1.2. No significant change occurred in the mean qP but great standard deviation was present as AWC was 9%. Fv/Fm, qP and NPQ of the thalli with 9% AWC fully recovered after rehydration. That B. fuscopurpurea kept high photosystem II photochemical reactions even when AWC was mere 32% enabled this species to survive extreme air drying at low tide. Fv/Fm and qP dropped while NPQ increased with 1 h of varying hyposaline treatment and they regained the basal levels after 6–24 h treatment. Nine days later, Fv/Fm, qP and NPQ levels of the thalli in 100% freshwater was equal to the control level (0.62, 0.9, 0.1, respectively). The present finding suggested that this alga has high photosynthetic capacity to survive during low tide, even during heavy rainfall. We hope this study would facilitate further investigation on the stress acclimation mechanism of B. fuscopurpurea.     

Induced responses of <Emphasis Type="Italic">Bougainvillea glabra</Emphasis> Choisy (Nyctaginaceae) against <Emphasis Type="Italic">Phenacoccus peruvianus</Emphasis> Granara de Willink (Hemiptera: Pseudococcidae) attack: preliminary results

Plants respond to herbivorous attack through a defence system that includes structural barriers, release of toxic chemicals, and attraction of natural enemies of the target pests, etc. In this study, plants of Bougainvillea glabra Choisy (Nyctaginaceae) were artificially infested with the obligate phloem-feeding insect pest Phenacoccus peruvianus Granara de Willink (Hemiptera: Pseudococcidae) and compared with control uninfested plants. Leaf samples were collected at 2, 6, 12, 24, 48, 96 and 144 h after infestation to monitor the plant response. Proline (Pro), malondialdehyde (MDA), chlorophyll (Chl_a, Chl_b, and Chl_a+b), and total carotenoid (Car) contents, as well as the activities of catalase (CAT) and phenylalanine ammonia-lyase (PAL) antioxidant enzymes, were measured at each sampling time to better understand the mechanism of plant defences. Proline content was the highest at 2 h after infestation and remained high throughout the experiment, while MDA content differed significantly only at 12 h after infestation. The value of chlorophyll was higher in the control plants, indicating that insect attack seriously compromised the photosynthetic activity of infected plants. Enzymatic activities showed significant increases, CAT of about 50% after 24 h and PAL of about 43% after 6 h. This study will be useful for understanding Bougainvillea plant defence against mealybugs and for showing that this ornamental species is able to activate enzymatic and molecular mechanisms in response to insect attack.     

Accumulation and tolerance characteristics of lead in <Emphasis Type="Italic">Althaea rosea</Emphasis> Cav. and <Emphasis Type="Italic">Malva crispa</Emphasis> L.

Two ornamental plants of Althaea rosea Cav. and Malva crispa L. were exposed to various concentrations of lead (Pb) (0, 50, 100, 200 and 500 mg·kg^?1) for 70 days to evaluate the accumulating potential and the tolerance characteristics. The results showed that both plant species grown normally under Pb stress, and A. rosea had a higher tolerance than M. crispa, while M. crispa had a higher ability in Pb accumulation than A. rosea. Besides, lower Pb concentration (50 mg·kg^?1) stimulated the shoot biomass in both plant species. Pb accumulation in plants was consistent with the increase of Pb levels, and the main accumulation sites were the roots and the older leaves. In addition, the photosynthetic pigments content and chlorophyll fluorescence parameters were influenced by Pb stress. In such case, both of the plants could improve the activities of antioxidant enzymes of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), and the contents of the total soluble sugar and soluble protein, which reached the highest value at Pb 100 mg·kg^?1, as well as the accumulation of the total thiols (T-SH) and non-protein thiols (NP-SH) to adapt to Pb stress. Thus, it provides the theoretical basis and possibility for ornamental plants of A. rosea and M. crispa in phytoremediation of Pb contaminated areas.     

UV-B radiation and temperature stress-induced alterations in metabolic events and defense mechanisms in a bloom-forming cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis>

The present investigation is aimed to understand how a bloom-forming cyanobacterium Microcystis aeruginosa adapts to changing climatic conditions. The cyanobacterium was exposed to stresses of UV-B (2 Wm^?2) radiation and temperature (45 °C) for desired time intervals. Results showed that both the stresses affect growth and photosynthetic efficiency of M. aeruginosa. More than 50% loss of survival and content of photosynthetic pigments was noted after 4 h treatment of both the above stresses. Such changes were mainly due to the generation of reactive oxygen species which cause damage to proteins, DNA, lipids, and modulation of the membrane stability. An increase in the proline accumulation was noted in the cells which probably negates the harmful effects. In addition, activity of antioxidative enzymes namely, catalase, superoxide dismutase, ascorbate peroxidase, and peroxidase was induced by 1.5–3.0-fold on 3 h of UV-B and temperature treatment indicating their possible role in protection. Interestingly, induction of photoprotective compound, mycosporine-like amino acids (MAAs) were also found under UV-B stress which might be an additional strategy of defense mechanism for the survival of the cyanobacterium. Analysis of photoprotective compound revealed shinorine as the main MAA synthesized by the cyanobacterium.     

Characterization of a field-grown transgenic pineapple clone containing the genes <Emphasis Type="Italic">chitinase</Emphasis>, <Emphasis Type="Italic">AP24</Emphasis>, and <Emphasis Type="Italic">bar</Emphasis>

We previously introduced the bar gene, along with chitinase and AP24 genes, into the pineapple genome. The present report focuses on the evaluation of the first vegetative generation of a transgenic clone containing these genes. Three materials were compared: macropropagated controls (non-transformed), micropropagated controls (non-transformed), and micropropagated transformed plants. From each group, 50% of the plants were sprayed with FINALE^® 3 mo after the experiment initiation. The characterization was performed after 1 yr of field growth. FINALE^® killed all non-transgenic plants. Plants that survived the herbicide application showed 2n?=?50 chromosomes in their roots after 1 yr in the field. Micropropagated transformed plants sprayed with FINALE^® did not show phenotype differences from micropropagated transformed plants not sprayed with the herbicide. Between the micropropagated transformed plants sprayed with FINALE^® and the micropropagated control plants, the following differences were observed: modifications in levels of cell wall-linked, free and total phenolics, and total proteins. Moreover, changes of the fruit mass without crown were also recorded. Between the micropropagated transformed plants sprayed with FINALE^® and the macropropagated control plants, levels of chlorophyll b, total chlorophyll pigments, and proteins were different. Furthermore, activities of phenylalanine ammonia-lyase, superoxide dismutase, and glutamine synthetase were dissimilar. The plant height and diameter, and the crown height were also different. Until now, we have evaluated transformed pineapple plants during hardening and field growth. Although some unexpected variations were recorded, we believe they are not relevant enough to justify rejection of transgenesis as an important tool for pineapple genetic improvement.     

Changes in photosynthetic pigments and chlorophyll-<Emphasis Type="Italic">a</Emphasis> fluorescence attributes of sweet-forage and grain sorghum cultivars under salt stress

Water shortage leads to a low quality of water, especially saline water in most parts of agricultural regions. This experiment was designed to determine the effects of saline irrigation on sorghum as a moderately salt-tolerant crop. To study salinity effects on photosynthetic pigment attributes including the chlorophyll content and chlorophyll fluorescence, an experiment was performed in a climate-controlled greenhouse at two vegetative and reproductive stages. The experimental design was factorial based on a completely randomized design with five NaCl concentrations (control, 50, 100, 150, and 200 mM), two grain and sweet-forage sorghum cultivars (Kimia and Pegah, respectively) and four replications. According to the experimental data, there were no significant differences between two grain and sweet-forage cultivars. Except for 100 and 150 mM NaCl, salinity significantly decreased the chlorophyll index and pigment contents of the leaf, while it increased the chlorophyll-a fluorescence characteristics. Although salinity reduced photosynthetic pigments and the crop yield, either grain or sweet-forage cultivars could significantly control the effect of salinity between 100 and 150 mM NaCl at both developmental stages, showing the possibility of using saline water in sorghum cultivation up to 150 mM NaCl.     

Photosynthetic adjustment after rehydration in <Emphasis Type="Italic">Annona emarginata</Emphasis>

Reports indicate that Annona emarginata is tolerant to drought and is also used as an alternative rootstock for atemoya under drought conditions. The photosynthetic process can be adjusted after rehydration, resulting on total or partial recovery. The aim of this study was to determine if A. emarginata shows adjusts in gas exchange and the chlorophyll a fluorescence pattern after rehydration. During water deficits, the gas exchange and water content in the leaf decreased. However, after 5 days of rehydration, the water content in the leaf recovered and rehydrated plants presented the water use efficiency better than irrigated plants. Further remaining gas exchange parameters were lower in relation to irrigated plants. In chlorophyll a fluorescence, the rehydrated plants showed higher dissipation of light energy as heat, maintaining high activity of photoprotection. After rehydration, A. emarginata shows a positive correlation between transpiration and CO₂ assimilation rate, which optimize the water use efficiency. Thus, A. emarginata presents adjustments in gas exchange and photochemical process, resulting on a possible long-term photosynthetic acclimation to water deficiency.     

Effects of heat stress on photosynthetic electron transport in a marine cyanobacterium <Emphasis Type="Italic">Arthrospira</Emphasis> sp.

Arthrospira (Spirulina) is widely used as human health food and animal feed. In cultures grown outdoors in open ponds, Arthrospira cells are subjected to various environmental stresses, such as high temperature. A better understanding of the effects of high temperature on photosynthesis may help optimize the productivity of Arthrospira cultures. In this study, the effects of heat stress on photosynthetic rate, chlorophyll a fluorescence transients, and photosystem (PS) II, PSI activities in a marine cyanobacterium Arthrospira sp. were examined. Arthrospira cells grown at 25 °C were treated for 30 min at 25 (control), 30, 34, 37, or 40 °C in the dark. Heat stress (30–37 °C) enhanced net photosynthetic O₂ evolution rate. Heat stress caused over-reduction PSII acceptor side, damage of donor side of PSII, decrease in the energetic connectivity of PSII units, and decrease in the performance of PSII. When the temperature changed from 25 to 37 °C, PSII activity decreased, while PSI activity increased, the enhancement of photosynthetic O₂ evolution was synchronized with the increase in PSI activity. When temperature was further increased to 40 °C, it induced a decrease in photosynthetic O₂ evolution rate and a more severe decrease in PSII activity, but an increase in PSI activity. These results suggest that PSI activity was the decisive factor determining the change of photosynthetic O₂ evolution when Arthrospira was exposed to a temperature from 25 to 37 °C, but then, PSII activity became the decisive factor adjusting the change of photosynthetic O₂ evolution when the temperature was increased to 40 °C.     

<Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract alleviates nickel toxicity by suppressing its uptake and modulating antioxidative defence in rice seedlings

Terminalia arjuna (Ta) bark contains various natural antioxidants and has been used to protect animal cells against oxidative stress. In the present study, we have examined alleviating effects of Ta bark aqueous extract against Ni toxicity in rice (Oryza sativa L.). When rice seedlings were raised for 8 days in hydroponics in Yoshida nutrient medium containing 200 μM NiSO₄, a decline in height, reduced biomass, increased Ni uptake, loss of root plasma membrane integrity, increase in the level of O₂˙^?, H₂O₂ and ˙OH, increased lipid peroxidation, decline in photosynthetic pigments, increase in the level of antioxidative enzymes superoxide dismutase, catalase and glutathione peroxidase and alterations in their isoenzyme profile patterns were observed. Transmission electron microscopy (TEM) showed damage to chloroplasts marked by disorganised enlarged starch granules and disrupted thylakoids under Ni toxicity. Exogenously adding Ta bark extract (3.2 mg ml^?1) to the growth medium considerably alleviated Ni toxicity in the seedlings by reducing Ni uptake, suppressing generation of reactive oxygen species, reducing lipid peroxidation, restoring level of photosynthesis pigments and ultrastructure of chloroplasts, and restoring levels of antioxidative enzymes. Results suggest that Ta bark extract considerably alleviates Ni toxicity in rice seedlings by preventing Ni uptake and reducing oxidative stress in the seedlings.     

Tomato Jasmonic Acid-Deficient Mutant <Emphasis Type="Italic">spr2</Emphasis> Seedling Response to Cadmium Stress

The involvement of jasmonic acid (JA) in the plant response to cadmium (Cd) stress has been addressed in some publications by application experiments or analysis of endogenous contents of JA. In this study, we comparatively investigated the response of tomato wild type (WT) and its JA-deficient mutant spr2 to Cd stress aimed at clarifying the role of JA. One-month-old potted plants were exposed to CdCl₂ at final concentrations of 5, 25, and 50 mg kg^?1 in soil, respectively, for 15 days. The root and leaf Cd contents were dramatically increased, especially in the spr2 plants, in a CdCl₂ dose-effect manner. In the Cd dose-dependent inhibitory effect on plant growth, spr2 plants were more obvious than WT plants. This was also reflected by certain physiological and biochemical metabolisms. We analyzed photosynthesis-related parameters including total chlorophyll, actual efficiency of PS2, ratio of variable to maximum chlorophyll fluorescence, and net photosynthetic rate; relative water content, soluble sugar and proline contents, and starch accumulation; oxidative stress and antioxidative defense including malondialdehyde production, electrolyte leakage, H₂O₂ levels, activities of superoxide dismutase, peroxidase, and catalase, and their isoform expression profiles. The Cd-induced changes in all these parameters supported the conclusion that endogenous JA deficiency enhanced tomato seedling sensitivity to Cd. This implies that JA positively regulates the tomato plant response to Cd stress.     

Wild relatives of wheat: <Emphasis Type="Italic">Aegilops</Emphasis>–<Emphasis Type="Italic">Triticum</Emphasis> accessions disclose differential antioxidative and physiological responses to water stress

Wild relatives of wheat are an outstanding source of resistance to both abiotic and biotic stresses. In the present study, we evaluated the activity of four antioxidant enzymes—superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)—along with photosynthetic pigments and shoot biomass in 12 Aegilops–Triticum accessions with different genomic constitutions and two tolerant and sensitive control varieties under well-watered (WW; 90% FC), moderate (MS; 50% FC) and severe (SS; 25% FC) water stress treatments. The analysis of variance for measured traits indicated highly significant effects of the water stress treatments, accessions, and their interactions. The 12 domesticated and wild relatives of wheat exhibited more variability and greater activity in the expression of antioxidative enzymes than cultivated wheats. While domesticated forms of wheat, T. aestivum (AABBDD) and T. durum (AABB) seem to have a functionally active antioxidant mechanism, other accessions with alien genomes—Ae. umbellulata (UU), Ae. crassa (MMDD), Ae. caudata (CC), Ae. cylindrica (DDCC) and T. boeoticum (A^bA^b)—respond to water stress by increasing enzymatic antioxidants as the dominant mechanism that contributes to the retention of oxidative balance in the cell. Furthermore, abovementioned accessions with alien genomes had higher photosynthetic pigment contents (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid) under water stress than well-watered conditions. Hence, these accessions could be used in future breeding programs to combine beneficial stress-adaptive characters of alien genomes into synthetic hexaploid wheat varieties in the field, even at limited water supply.     

Desiccation tolerance in <Emphasis Type="Italic">Pleurostima purpurea</Emphasis> (Velloziaceae)

Previous works suggested that Pleurostima purpurea (Velloziaceae—Barbacenioideae) shows a remarkable capacity to endure desiccation of its vegetative tissues. P. purpurea occurs in monocotyledons mats on soil islands in the Pão de Açucar (Sugar Loaf) one of the most recognizable rock outcrops of the world, in Rio de Janeiro, southeastern Brazil. Mats of P. purpurea occur in cliffs by the sea some meters above the tidal zone. Although living in rock outcrops almost devoid of any soil cover, P. purpurea seems to occur preferably on less exposed rock faces and slightly shady sites. Usually, less extreme adaptations to drought would be expected in plants with the habitat preference of P. purpurea. Relying on this observation, we argue if a combination of different strategies of dealing with low water availability can be found in P. purpurea as on other desiccation tolerant angiosperms. This study aims to examine the occurrence of desiccation tolerant behavior in P. purpurea together with the expression of drought avoidance mechanisms during dehydration progression. For this, it was analyzed the gas exchanges, leaf pigments and relative leaf water content during desiccation and rehydration of cultivated mature individuals. P. purpurea behaved like typical drought avoiders under moderated drought condition with stomatal closure occurring around a relative leaf water content up to 90%. During this process, it was observed a delay in the leaf relative water content (RWC _leaf) decrease comparing to the plant-soil relative water content (RWC _plant-soil). As soil dehydration worsened, gas exchanges restrictions progressed until a lack of activity which characterizes anabiosis. The loss of chlorophyll occurs before the end of total dehydration, characterizing the presence of poikilochlorophylly. The chlorophyll degradation follows the RWC _leaf decrease, which achieved the minimum average value of 17% without incurring in leaf abscission. The chlorophyll re-synthesis seems to start well after the full rehydration of the leaf. During all of this process, carotenoid content remained stable. These results are coherent with a combination of drought avoidance and desiccation tolerance in P. purpurea which seems to be coherent with the amplitude of water availability in the rock outcrop habitat where it occurs, suggesting that the periods of water availability are sufficiently long for the success of the costly desiccation tolerant behavior but too short to make a typical drought avoider species win the competition for exploring the rock outcrop substrate where P. purpurea occurs.     

Drought-Responsive Gene Expression in Sun and Shade Plants of <Emphasis Type="Italic">Haberlea rhodopensis</Emphasis> Under Controlled Environment

Haberlea rhodopensis is a homoiochlorophyllous desiccation-tolerant plant growing mostly in shaded rock rifts below the trees at very low light intensity. These shade plants are very sensitive to photoinhibition and do not survive desiccation at irradiance of 350 μmol m^?2 s^?1, whereas plants growing on the top of rocks exposed to full sunlight (sun plants) can survive at even higher light intensities regularly. The aim of the present study was to establish how acclimation to different light intensities influences the expression of selected drought-responsive genes and the physiological activity during desiccation of shade and sun plants under controlled culture conditions. The photosynthetic activity was higher in sun plants not only when fully hydrated but also during dehydration. Thus, the higher photosynthetic capacity, reflected in PSII but especially in PSI activity, is accompanied by a reduced susceptibility to photodamage. For most of the genes examined, drought was the main factor in regulation; in addition, some were light modulated like genes coding for putative superoxide dismutase (SOD), ascorbate peroxidase (APX) and thioredoxin (TRX), whereby the former was almost purely light regulated. Differences between sun and shade plants concerned mainly on the time course. Whereas some genes reacted already at moderate desiccation only in sun plants (genes for monodehydroascorbate reductase (MDAR), plastidic translocase (PTL) similar to OEP16 and one of the genes, newly annotated ELIP-like, specific for H. rhodopensis), especially a gene for a putative UDP-glucuronic acid decarboxylase (UDP) retained its enhanced expression longer during recovery. Thus, these genes are probably especially important for survival and recovery in sun plants.     

Phosphites attenuate <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis>-induced physiological impairments in common bean

Phosphites, marketed as foliar fertilizers and resistance activators, have been shown to be useful for the control of diseases in many profitable crops. Despite the importance of white mold, caused by Sclerotinia sclerotiorum, to reduce common bean yield, knowledge of the phosphites´ effect on disease control at the physiological level is still missing. In this study, the leaf gas exchange and chlorophyll a fluorescence parameters variable-to-maximum chlorophyll a fluorescence ratio (F_v/F_m), photochemical yield [Y(II)], yield for dissipation by down-regulation [Y(NPQ)], yield for non-regulated dissipation [Y(NO)], and electron transport rate (ETR) as well as the concentrations of photosynthetic pigments in common bean plants that were sprayed with zinc (Zn) or copper (Cu) phosphites and challenged or not with S. sclerotiorum were determined. Based on the in vitro assays, Zn and Cu phosphites inhibited fungal mycelial growth in a dose-dependent manner, but the Cu phosphite showed to be more fungitoxic. Lesion area and white mold severity were reduced by Zn and Cu phosphites, but the Zn phosphite was more effective. Fungal infection dramatically decreased the values of net carbon assimilation rate, stomatal conductance to water vapor and transpiration rate on non-sprayed plants. Increases in internal CO₂ concentration indicated that fungal-induced photosynthetic impairments were chiefly governed by biochemical limitations, but these impairments were greatly abrogated in the Zn and Cu phosphite-sprayed plants. Similarly, the photochemical dysfunctions stemmed from S. sclerotiorum infection were limited in the Zn and Cu phosphite-sprayed plants. Concentrations of chlorophyll a?+?b and carotenoids decreased on inoculated plants, but lower reductions were recorded on Zn and Cu phosphites-sprayed plants. In conclusion, the potential of Zn and Cu phosphites in attenuate the S. sclerotiorum-induced physiological impairments in common bean leaflets was demonstrated and may be an effective mean for managing this disease under field conditions.     

The aromatic cytokinin <Emphasis Type="Italic">meta-</Emphasis>topolin promotes in vitro propagation,shoot quality and micrografting in <Emphasis Type="Italic">Corylus colurna</Emphasis> L.

The role of 4.1 or 8.2 μM meta-topolin (mT) on shoot multiplication, rooting and ex vitro acclimatization of micropropagated Corylus colurna L., a promising non-suckering rootstock for hazelnut (Corylus avellana L.), was examined in comparison to N⁶-benzyladenine (BA), the most used cytokinin in tissue culture of Corylus spp. The influence of 8.2 μM mT and BA on photosynthetic pigments content and antioxidant enzymes activity, catalase (CAT) and guaiacol peroxidase (POD), in regenerated shoots, and on the preparation of the rootstock for micrografting was also evaluated. The highest shoot multiplication was recorded on medium containing 8.2 μM mT and an overall positive effect of mT on growth and quality of micropropagated shoots was found. The highest chlorophyll a content (1.236 mg g^?1 fresh weight, FW) and chlorophyll a/b ratio (2.48), and the lowest total carotenoids content (0.292 mg g^?1 FW) and CAT activity (25.8 μmol min^?1 mg^?1 protein) were detected after 8.2 μM mT application, while no significant differences were found in chlorophyll b content and POD activity between the two cytokinins. The best rhizogenesis response (98% for 4.1 μM and 100% for 8.2 μM mT) and ex vitro acclimatization competence (higher than 78%) were exhibited from shoots multiplied on mT. Furthermore, the multiplication of rootstock on mT allowed obtaining the highest (70%) response of successful micrografting. The present findings provide the first evidence of the successful applicability of mT in C. colurna tissue culture and development of micrografted plantlets.     

Selenium mitigates cadmium-induced oxidative stress in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> L.) plants by modulating chlorophyll fluorescence,osmolyte accumulation,and antioxidant system

Pot experiments were conducted to investigate the role of selenium in alleviating cadmium stress in Solanum lycopersicum seedlings. Cadmium (150 mg L^?1) treatment caused a significant reduction in growth in terms of height and biomass accumulation and affected chlorophyll pigments, gas exchange parameters, and chlorophyll fluorescence. Selenium (10 μM) application mitigated the adverse effects of cadmium on growth, chlorophyll and carotenoid contents, leaf relative water content, and other physiological attributes. Lipid peroxidation and electrolyte leakage increased because of cadmium treatment and selenium-treated plants exhibited considerable reduction because of the decreased production of hydrogen peroxide in them. Cadmium-treated plants exhibited enhanced activity of antioxidant enzymes that protected cellular structures by neutralizing reactive free radicals. Supplementation of selenium to cadmium-treated plants (Cd + Se) further enhanced the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 19.69, 31.68, 33.14, and 54.47%, respectively. Osmolytes, including proline and glycine betaine, increased with selenium application, illustrating their role in improving the osmotic stability of S. lycopersicum under cadmium stress. More importantly, selenium application significantly reduced cadmium uptake. From these results, it is clear that application of selenium alleviates the negative effects of cadmium stress in S. lycopersicum through the modifications of osmolytes and antioxidant enzymes.     

Lipid peroxidation in and photo-damage to a light-sensitive chlorescence pea mutant

Leaves of 10- to 12-day-old chlorescence lethal Pisum sativum L. mutant are similar to control plants with respect to the content of chlorophylls, carotenoids, fatty acids and α-tocopherol. Subsequent development of the mutant under high irradiation resulted in th destruction of the photosynthetic pigments, polyunsaturated fatty acids, α-tocopherol, and also in the accumulation of liposoluble fluorescent products. No increase in the level of malondialdehyde was observed. In chloroplasts isolated from mutant plants the contents of chlorophyll a and β-carotene were decreased to a greater extent than the more oxidized pigments (xanthophylls and chlorophyll b ). The data obtained are discussed with special reference to the role of lipid peroxidation in the injury of plant cells under the action of visible light and to the antioxidative mechanisms stabilizing photosynthetic membranes.     

Changes in the photosynthetic characteristics of cotton leaves infested by invasive mealybugs tended by native ant species

Herbivore injury has a direct effect on the growth and performance of host plants through photosynthetic suppression. However, changes in plant photosynthesis affected by ant tending of hemipteran sap feeders remain poorly understood. We investigated the effects of an invasive mealybug (Phenacoccus solenopsis) tended by native ants (Paratrechina longicornis) on the chlorophyll content and chlorophyll fluorescence characteristics of cotton (Gossypium hirsutum) leaves under greenhouse conditions. The results showed that the relative chlorophyll content of the infested cotton leaves significantly decreased after 10 days, and the chlorophyll contents were reduced by 26.4 and 34.9 % after 20 days in the without and with ant treatments compared to the control, respectively. In addition, the light utilization efficiency and maximum relative electron transport rate were reduced by 53.0 and 51.3 % compared to the control, respectively. However, no significant differences in these factors were found between the without and with ant treatments. The light saturation coefficient, describing the capacity of a sample to resist glare, exhibited no significant difference among treatments. The number of tending P. longicornis ants increased with P. solenopsis numbers, and the P. solenopsis numbers decreased after 20 days compared to the without ant treatment. We suggest that the tending ants may enhance the feeding ability of individual mealybugs in spite of the decreased number of mealybugs in this situation. Additionally, P. longicornis decrease the relative chlorophyll content of infested cotton leaves and may accelerate the damage caused by P. solenopsis to plants over time.