Carlos Alberto Martinez

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.

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.

Gas exchange and chlorophyll fluorescence in four citrus rootstocks under aluminium stress

Summary A greenhouse experiment using nutritive solution was carried out to determine the effect of aluminium (AI) on several photosynthesis-related characteristics in Citrus limonia (‘Cravo’), Citrus volkameriana (‘Volkamer’), Citrus reshni (‘Cleopatra’), and Citrus sunki (‘Sunki’) seedlings. The effects of five AI concentrations (0, 50, 100, 200, and 400 μmol L -1 ) in the solution were determined. The lemon seedlings had the highest net photosynthesis in the absence of AI. The net photosynthesis decreased in the presence of AI in all the rootstocks, and the ‘Cravo’ lemon seedling was the most affected, with a decrease of 85% at the highest AI concentration evaluated. Stomatal conductance of water vapor (g s ) was not significantly affected in the lemon seedlings, but it was increased by the AI in the tangerine seedlings. The internal concentration of CO 2 (C i ) increased significantly in all the rootstocks with the increase in the AI concentration, but this increase did not result in higher net photosynthesis values. The greatest water use efficiency (WUE) in the absence of AI, was observed in the lemon seedlings. The WUE decreased in all rootstocks with the increase in the AI concentration in the nutritive solution, due to the decrease in the net photosynthesis and increase in the transpiration rate. One of the probable reasons for the reduction in the net photosynthesis was the structural damage to the thylakoids, which affected the photosynthetic transport of electrons, as indicated by the reduction of the ratio between variable fluorescence and initial fluorescence (F v /F 0 ).

In vitro salt tolerance and proline accumulation in Andean potato (Solanum spp.) differing in frost resistance

Abstract Four species of potato ( Solanum andigena, Solanum curtilobum, Solanum juzepczukii and Solanum tuberosum L.) differing in frost resistance were subjected to various levels of salinity conditions (NaCl). Salt resistance was measured by survival, growth and proline content of the stressed plantlets. Each Solanum species studied responded differently to salt stress. Growth of S. andigena and S. tuberosum was inhibited by given range levels of NaCl. However, the frost resistant genotypes S. juzepczuckii and S. curtilobum showed high salt tolerance (up to 200 mol/m 3 NaCl). The salt tolerance was positively related to leaf proline content. There was a close relationship ( r 2 = 0.95) between the growth and survival of plantlets with proline content. Results suggest that proline accumulation could be used as a biochemical marker for increased salt tolerance in potato.

Photosynthesis and Water Use Efficiency in Twenty Tropical Tree Species of Differing Succession Status in a Brazilian Reforestation

Leaf gas exchange characteristics were measured in twenty woody species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) in a Brazilian rain-reforestation ecosystem. Photon-saturated photosynthetic rate, calculated per either a leaf area (PNA) or a dry mass (PNM) basis, differed among species. PNA and PNM were highest in PS and lowest in LS. Variation among species was 3-fold (from 7 to 23 μmol m−2 s−1) for PNA, and 5-fold (from 50 to 275 μmol kg−2 s−1) for PNM. The highest PNA (23 μmol m−2 s−1) and PNM (275 μmol kg−2 s−1) values were recorded in PS Croton urucurana, while the lowest PNA (7 μmol m−2 s−1) and PNM (50 μmol kg−2 s−1) values were recorded in LS Aspidosperma cylindrocarpon. A considerable overlap was recorded between PS and LS in values of stomatal conductance (gs), transpiration rate (E), and leaf mass to area ratio (ALM). However, C. urucurana also showed highest gs and E. PNM was highly correlated with ALM in both PS and LS (r=−0.75 and −0.90, respectively). The high values of instantaneous transpiration efficiency (ITE) and intrinsic water use efficiency (WUEi) were also observed in the PS when compared with the LS.

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.

Responses of Legume Versus Nonlegume Tropical Tree Seedlings to Elevated CO2 Concentration

We investigated responses of growth, leaf gas exchange, carbon-isotope discrimination, and whole-plant water-use efficiency (WP) to elevated CO2 concentration ([CO2]) in seedlings of five leguminous and five nonleguminous tropical tree species. Plants were grown at CO2 partial pressures of 40 and 70 Pa. As a group, legumes did not differ from nonlegumes in growth response to elevated [CO2]. The mean ratio of final plant dry mass at elevated to ambient [CO2] (ME/MA) was 1.32 and 1.24 for legumes and nonlegumes, respectively. However, there was large variation in ME/MA among legume species (0.92–2.35), whereas nonlegumes varied much less (1.21–1.29). Variation among legume species in ME/MA was closely correlated with their capacity for nodule formation, as expressed by nodule mass ratio, the dry mass of nodules for a given plant dry mass. WP increased markedly in response to elevated [CO2] in all species. The ratio of intercellular to ambient CO2 partial pressures during photosynthesis remained approximately constant at ambient and elevated [CO2], as did carbon isotope discrimination, suggesting that WP should increase proportionally for a given increase in atmospheric [CO2]. These results suggest that tree legumes with a strong capacity for nodule formation could have a competitive advantage in tropical forests as atmospheric [CO2] rises and that the water-use efficiency of tropical tree species will increase under elevated [CO2].

An efficient and rapid DNA minipreparation procedure suitable for PCR/SSR and RAPD analyses in tropical forest tree species

ABSTRACT An efficient and rapid DNA minipreparation modified method for frozen samples was developed for five tropical tree species: Copaifera langsdorffii, Hymenaea courbaril, Eugenia uniflora, Tabebuia roseo alba and Cariniana estrellensis. This procedure that dispenses the use of liquid nitrogen, phenol and the addition of proteinase K, is an adaptation of the CTAB-based DNA extraction method. The modifications included the use of PVP to eliminate the polyphenols, only one chloroform-isoamyl alcohol step and the addition of RNase immediately after extraction with chloroform. The yields of the DNA samples ranged from 25.7 to 42.1 µg from 100 mg leaf tissue. The DNA samples extracted by this method were successfully used for PCR (SSR and RAPD) analyses in these five and other twelve tropical tree species. Key words: Copaifera langsdorffii, Hymenaea courbaril, Eugenia uniflora, Tabebuia roseo alba, Cariniana estrellensis , DNA extraction * Author for correspondence: anaalzate@rge.fmrp.usp.br