Marco Antonio Oliva

Photosynthesis and activity of superoxide dismutase, peroxidase and glutathione reductase in cotton under salt stress

Abstract The effects of NaCl stress on the activity of antioxidant enzyme such as superoxide dismutase (SOD: EC 1.15.1.1), peroxidase (POD: EC 1.11.1.7), glutathione reductase (GR: EC 1.6.4.2), rate of lipid peroxidation, gas-exchange, chlorophyll content and chlorophyll fluorescence were investigated in two cotton cultivars, Guazuncho and Pora (hybrids between Gossypium hirsutum × G. arboretum × G. raimondii ) grown in nutrient solution. Plants were treated with three salt concentrations (50, 100 and 200 mol m −3 NaCl) for 21 days. The SOD activity in Pora increases with the increase in the intensity of NaCl stress, but salt treatment had no significant effect on this enzyme activity in Guazuncho. The POD and GR activities showed similar trends under salt stress, in both cotton cultivars. In Pora, there was an average increase in GR activity of about 53%, but there was no further increase at higher NaCl concentrations. In Guazuncho, no change in GR activity was observed. Net photosynthesis and stomatal conductance decreased in response to salt stress, but Pora showed a smaller reduction in photosynthesis than Guazuncho. The results indicated that stomatal aperture limited leaf photosynthetic capacity in the NaCl-treated plants of both cultivars. However, significant reduction in the leaf chlorophyll contents due to NaCl stress was observed only on Guazuncho. In both cotton cultivars, the photochemical efficiency of PSII was not affected by salt stress. These results suggest that salt-tolerant cotton varieties may have a better protection against reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes under salt stress.

Solute accumulation and distribution during shoot and leaf development in two sorghum genotypes under salt stress

Abstract Seedlings of two forage sorghum genotypes (Sorghum bicolor (L.) Moench) differing in salt tolerance were subjected to 0 and 100 mM NaCl and shoot development, leaf elongation, and organic and inorganic solutes contents in leaves were measured. Salt stress reduced both shoot development and leaf elongation and enhanced leaf senescence and injury. It also led to accumulation of toxic ions (Na+ and Cl−), organic solutes (carbohydrates, amino acids and proline), and reduction of K+ content in leaf blades. Toxic ion accumulation was higher in the basal zone of the leaf blade and occurred during the period of intense leaf growth while organic solutes accumulation, mainly proline, was higher in the apical zone and occurred when the leaves practically had reached their final size. All these changes were more conspicuous in the sensitive than in the tolerant genotype. The latter also retained more toxic ions in leaf sheath tissue than the former. It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K+ ions in the leaf blades. The accumulation of organic solutes in leaves did not appear to be related to salt tolerance. Proline accumulation appears to be a reaction to salt stress damage and not a plant response associated with salt tolerance.

CONTRIBUTION OF PROLINE AND INORGANIC SOLUTES TO OSMOTIC ADJUSTMENT IN COTTON UNDER SALT STRESS

Physiological responses to salt stress were investigated in two cotton (Gossypium hirsutum L.) cultivars (Pora and Guazuncho) grown hydroponically under various concentrations of NaCl. Dry matter partitioning, plant water relations, mineral composition and proline content were studied. Proline and inorganic solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water potential (Ψw) and osmotic potential (Ψs)decreased in response to NaCl levels. Although Ψwand Ψs decreased during salt stress, pressure potential Ψp remained between 0.5 to 0.7 MPa in control and all NaCl treatments, even under 200 mol m−3 NaCl. Increased NaCl levels resulted in a significant decrease in root, shoot and leaf growth biomass. Root / shoot ratio increased in response to salt stress. The responses of both cultivars to NaCl stress were similar. Increasing salinity levels increased plant Na+ and Cl−. Potassium level remained stable in the leaves and decreased in the roots with increasing salinity. Salinity decreased Ca2+ and Mg2+ concentrations in leaves but did not affect the root levels of these nutrients. The K/Na selectivity ratio was much greater in the saline treated plants than in the control plants. Osmotic adjustment of roots and leaves was predominantly due to Na+ and Cl− accumulation; the contribution of proline to the osmotic adjustment seemed to be less important in these cotton cultivars.

The effects of salt stress on growth, nitrate reduction and proline and glycinebetaine accumulation in Prosopis alba

Prosopis alba (algarrobo) is one of the most important salt-tolerant legumes used in the food and furniture industries. The effects of salinity on some growth and physiological parameters in algarrrobo seedlings were investigated. 17-Day-old seedlings were subjected to three salt treatments by adding NaCl to the growth medium in 50 mmol.L-1 increments every 24 h until the final concentrations of 0, 300 and 600 mmol.L-1 were reached. Only the highest NaCl concentration affected all of the considered parameters. Thus, 600 mmol.L-1 NaCl caused a significant reduction in root and shoot growth, but an increase in the root/shoot ratio. Leaf relative water content, nitrate content and nitrate reductase activity in leaves and roots were also decreased. At 300 and 600 mmol.L-1, the glycinebetaine content was significantly increased in both leaves and roots but this was not found for proline content. Total soluble carbohydrates increased only in roots. The results suggest that glycinebetaine enhancement may be important for osmotic adjustment in Prosopis alba under salinity stress.

Differential responses of superoxide dismutase in freezing resistant Solanum curtilobum and freezing sensitive Solanum tuberosum subjected to oxidative and water stress

In photosynthetic tissues superoxide dismutase (SOD) plays an important role by scavenging the superoxide radical whose production is an usual reaction in chloroplast thylakoids. To test the differential response of SOD, two Andean potato species differing in frost resistance, Solanum curtilobum (frost resistant) and Solanum tuberosum (frost sensitive), were subjected to methyl viologen-mediated oxidative stress and polyethylene glycol (PEG)-induced water stress. A significant increment (approximately two-fold) in total SOD and FeSOD activity, which occupied about 50% of the total activity, was found when leaves of S. curtilobum were exposed to water stress. In contrast, the SOD activity in leaves of S. tuberosum remained unchanged. The exposure of leaves of S. curtilobum to oxidative stress increased total SOD and FeSOD activity by 350%. High correlation between SOD activity and the F(v)/F(m )ratio under both PEG induced water stress and MV-mediated oxidative stress was observed. This suggests that SOD can protect PSII from superoxide generated by oxidative and water stress. The higher SOD activity could be an important mechanism to explain why some natives Andean potato like S. curtilobum are more resistant to abiotic stresses than S. tuberosum.

Photosynthesis and oxidative stress in the restinga plant species Eugenia uniflora L. exposed to simulated acid rain and iron ore dust deposition: Potential use in environmental risk assessment

The Brazilian sandy coastal plain named restinga is frequently subjected to particulate and gaseous emissions from iron ore factories. These gases may come into contact with atmospheric moisture and produce acid rain. The effects of the acid rain on vegetation, combined with iron excess in the soil, can lead to the disappearance of sensitive species and decrease restinga biodiversity. The effects of iron ore dust deposition and simulated acid rain on photosynthesis and on antioxidant enzymes were investigated in Eugenia uniflora, a representative shrub species of the restinga. This study aimed to determine the possible utility of this species in environmental risk assessment. After the application of iron ore dust as iron solid particulate matter (SPM(Fe)) and simulated acid rain (pH 3.1), the 18-month old plants displayed brown spots and necrosis, typical symptoms of iron toxicity and injuries caused by acid rain, respectively. The acidity of the rain intensified leaf iron accumulation, which reached phytotoxic levels, mainly in plants exposed to iron ore dust. These plants showed the lowest values for net photosynthesis, stomatal conductance, transpiration, chlorophyll a content and electron transport rate through photosystem II (PSII). Catalase and superoxide dismutase activities were decreased by simulated acid rain. Peroxidase activity and membrane injury increased following exposure to acid rain and simultaneous SPM(Fe) application. Eugenia uniflora exhibited impaired photosynthetic and antioxidative metabolism in response to combined iron and acid rain stresses. This species could become a valuable tool in environmental risk assessment in restinga areas near iron ore pelletizing factories. Non-invasive evaluations of visual injuries, photosynthesis and chlorophyll a fluorescence, as well as invasive biochemical analysis could be used as markers.

Leaf gas exchange in a clonal eucalypt plantation as related to soil moisture, leaf water potential and microclimate variables

Abstract In order to determine how environmental and physiological factors affect leaf gas exchange in a 9-year-old clonal eucalypt plantation (Eucalyptus grandis Hill ex. Maiden hybrids) in the State of Espirito Santo, Brazil, the diurnal patterns of predawn leaf water potential (Ψpd), and leaf gas exchange were monitored from November 1995 to August 1996. Soil water content (Θ) and microclimatic variables were also recorded. Most of the rainfall during the experimental period occurred from October to December 1995 and from March to April 1996, causing a significant variation in Θ and Ψpd. A high positive correlation (r2=0.92) was observed between Ψpd and Θ measured at 0.3 m depth from the soil surface. During conditions of high soil water availability, the maximum values of stomatal conductance for water vapor (gs) and net photosynthetic rate (A) were over 0.4 mol m–2 s–2 and l5 µmol m–2 s–1, respectively. The results showed that Ψpd and leaf gas exchange of the examined trees were susceptible to changes in the water content of the upper soil layers, where the major concentration of active roots occur. Multiple linear regression analysis indicated that photosynthetic active radiation (Q), vapor pressure deficit (VPD), atmospheric CO2 molar fraction (Ca), and Ψpd were the most important factors controlling gs whereas Q and VPD were the main microclimatic variables controlling A.

Flúor em chuva simulada: sintomatologia e efeitos sobre a estrutura foliar e o crescimento de plantas arbóreas

Fluoride in simulated rain: symptomatology and effects on leaf structure and growth of wood plants). The objectives of this study was to characterize the effects of fluoride on seedlings and young plants of native woody species from Parque Estadual do Rio Doce (MG) and on the leaf blade structure of the most sensitive of the studied tree species. This work was carried out to gain information on diagnosing criteria for bioindication and to throw some light on the mechanisms of plant resistance and tolerance in order to assist in the revegetation programs of highly affected areas. The employed species were Gallesia gorazema Moq. (Phytolac- caceae), Genipa americana L. (Rubiaceae), Joannesia princeps Vell. (Euphorbiaceae), Peltophorum dubium (Spreng.) Taub. (Legu- minosae, Caesalpinioideae) and Spondias dulcis Forst. f. (Anarcadiaceae). Seedlings and young plants of those species were submitted to rain with dissolved fluoride (30 mg.L -1 ), during 20 min daily, for 10 consecutive days. Apical and marginal necrosis occurred in the leaf blades of all species just after the first simulated rain. Two days after treatment, S. dulcis, in the young plant stage, showed to be the most sensitive species by exhibiting large necrotic areas, while G. americana was the most resistant species. At the young plant stage, the species that accumulated more fluoride were also the most sensitive ones; such a relation was not observed in plants at the seedling stage. The pollutant at the level employed caused drastic alterations in the leaf blade of S. dulcis and also damaged all of its anatomical structure. The high susceptibility of S. dulcis to fluoride suggests that this species possess potential features to be employed as a bioindicator. However, for a better characterization of the responses of S. dulcis to fluoride and its usage in biomonitoring programs, more studies are required. RESUMO - (Fluor em chuva simulada: sintomatologia e efeitos sobre a estrutura foliar e o crescimento de plantas arboreas). Os objetivos deste trabalho foram: caracterizar os efeitos do fluor em especies arboreas nativas, nos estadios de plântula e muda; identificar injurias provocadas pelo fluor na estrutura da lâmina foliar da especie mais sensivel; fornecer subsidios para selecao de caracteristicas a serem utilizadas na bioindicacao; e contribuir com informacoes sobre a resistencia ou tolerância das plantas, visando ao reflorestamento de areas impactadas pela chuva com fluor. As especies analisadas foram Gallesia gorazema Moq. (Phytolaccaceae), Genipa americana L. (Rubiaceae), Joannesia princeps Vell. (Euphorbiaceae), Peltophorum dubium (Spreng.) Taub. (Leguminosae, Caesalpinioideae) e Spondias dulcis Forst. f. (Anacardiaceae). Plântulas e mudas dessas especies, provenientes do Parque Estadual do Rio Doce (MG), foram submetidas a 20 min diarios de chuva com fluor (30 mg.L -1 ), por 10 dias consecutivos. Necroses apicais e marginais foram observadas em todas as especies analisadas, logo apos a primeira chuva simulada. S. dulcis, no estadio de muda, foi a especie mais sensivel ao fluor, pois apresentou extensas necroses com apenas dois dias de tratamento, enquanto que G. americana foi a especie mais resistente. Nas mudas, as especies que acumularam mais fluor foram tambem as que apresentaram maior sensibilidade a esse poluente; essa relacao nao foi verificada nas plântulas. A concentracao de fluor utilizada promoveu alteracoes drasticas na lâmina foliar de S. dulcis com extensas areas necrosadas, danificando toda a sua estrutura anatomica. A sensibilidade ao fluor observada em S. dulcis indica que essa especie apresenta potencial para ser usada como bioindicadora. Entretanto, estudos detalhados serao necessarios para a melhor caracterizacao das respostas de S. dulcis ao fluor visando a sua utilizacao em programas de biomonitoramento ambiental.

Iron excess affects rice photosynthesis through stomatal and non-stomatal limitations

Iron toxicity is the most important stressor of rice in many lowland environments worldwide. Rice cultivars differ widely in their ability to tolerate excess iron. A physiological evaluation of iron toxicity in rice was performed using non-invasive photosynthesis, photorespiration and chlorophyll a fluorescence imaging measurements and chlorophyll content determination by SPAD. Four rice cultivars (BR IRGA 409; BR IRGA 412; BRA 041171 and BRA 041152) from the Brazilian breeding programs were used. Fe(2+) was supplied in the nutrient solution as Fe-EDTA (0.019, 4, 7 and 9 mM). Increases in shoot iron content due to Fe(2+) treatments led to changes in most of the non-invasive physiological variables assessed. The reduction in rice photosynthesis can be attributed to stomatal limitations at moderate Fe(2+) doses (4mM) and both stomatal and non-stomatal limitations at higher doses. Photorespiration was an important sink for electrons in rice cultivars under iron excess. A decreased chlorophyll content and limited photochemical ability to cope with light excess were characteristic of the more sensitive and iron accumulator cultivars (BRA 041171 and BRA 041152). Chlorophyll fluorescence imaging revealed a spatial heterogeneity of photosynthesis under excessive iron concentrations. The results showed the usefulness of non-invasive physiological measurements to assess differences among cultivars. The contributions toward understanding the rice photosynthetic response to toxic levels of iron in the nutrient solution are also discussed.

Cadmium-induced oxidative stress and antioxidative enzyme response in water hyacinth and salvinia

The reactive oxygen species generation, lipid peroxidation and antioxidative enzyme response of water hyacinth and salvinia to Cd were evaluated. Cadmium was absorbed/accumulated mainly in the roots, but significant amounts also translocated to the leaves. No Cd effect on dry weight was detected, although toxicity symptoms were visible. Superoxide and H2O2 concentrations increased, in addition to lipid peroxidation in both species, especially in the leaves of salvinia. In general, antioxidative enzyme activities were reduced in both species following Cd treatment, especially in salvinia. Glutathione peroxidase (GPX, EC 1.11.1.9) activity decreased in water hyacinth but increased in salvinia. Glutathione S-transferase (GST, EC 2.5.1.18) activity increased in the leaves but decreased in the roots of both species. So, Cd induced ROS generation/accumulation, but the antioxidative enzymes were not able to combat the Cd-induced oxidative injury in these two species. Nevertheless, water hyacinth consistently showed a higher tolerance to Cd than salvinia.