Hugo Alves Pinheiro

Photochemical responses and oxidative stress in two clones of Coffea canephora under water deficit conditions

Abstract The effects of water deficit on photochemical parameters and activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as, cellular damages were investigated in two clones of Coffea canephora differing in drought tolerance. After 6 days without irrigation, predawn leaf water potential fell to −3.0 MPa that was accompanied by the suppression of net photosynthesis in both clones. The variable to maximum chlorophyll fluorescence ratio remained unchanged regardless of the imposed treatments. Both clones showed a similar decline (about 25%) in the photochemical quenching coefficient, but only the drought-sensitive clone exhibited an enhancement (31%) of thermal deactivation under water deficit conditions. The quantum yield of electron transport decreased similarly in both genotypes. Under drought conditions, activities of SOD, CAT and APX increased to a greater extent in the drought-tolerant clone than in the drought-sensitive one. This seemed to be matched with higher protection against oxidative stress, as judged from the lower levels of lipid peroxidation and electrolyte leakage in the drought-tolerant clone. Thus, the ability to increase the antioxidant system activity in order to limit cellular damages might be an important attribute linked to the drought tolerance in C. canephora.

Drought tolerance of two field-grown clones of Coffea canephora

We compared tolerance to soil drought of two field-grown clones of Coffea canephora (clone 46, drought-sensitive; and clone 120, drought-tolerant). Under irrigation, there were no marked differences between the clones in water relation parameters, gas exchange and total leaf area. Under rainfed conditions, clone 46 showed osmotic adjustment and increased tissue rigidity. These adjustments, however, were incapable of preventing substantial decreases in xylem pressure potential. By contrast, clone 120 did not exhibit osmotic adjustment, but was able to increase tissue elasticity and to maintain xylem pressure potentials to a greater extent than clone 46 (despite having twice the total leaf area of this clone). Stomatal conductance was lowered by drought in clone 120 but not in clone 46. Carbon assimilation per unit leaf area in both clones remained unaffected under stress. Long-term water use efficiency (WUE), as estimated through carbon isotope discrimination, was consistently greater in clone 120 than in clone 46. Because of these traits, clone 120 was better able to postpone dehydration and to maintain whole-tree photosynthesis. It is proposed that these features should decisively contribute to buffer its productivity in drought-prone areas.

Ecofisiologia de plantas jovens de mogno-africano submetidas a deficit hídrico e reidratação

O objetivo deste trabalho foi avaliar a capacidade de plantas jovens de mogno-africano (Khaya ivorensis) em recuperar seu status hidrico e trocas gasosas apos periodo de deficit hidrico. Plantas com aproximadamente 315 dias, irrigadas (controle) e nao irrigadas, foram avaliadas aos 14 dias da suspensao da irrigacao e apos um, tres e sete dias da retomada da irrigacao (reidratacao). No dia 14, o potencial hidrico foliar de antemanha (Ψam) das plantas estressadas foi reduzido a -2,66 MPa. Com a restricao hidrica, foram observadas reducoes significativas no conteudo relativo de agua na antemanha (reducao de 32%), na taxa de assimilacao liquida de CO2 (90%), na condutância estomatica (95%), na transpiracao (93%) e na razao entre concentracao intercelular e ambiental de CO2 (37%). Durante a reidratacao, o status hidrico das plantas estressadas foi restabelecido apos tres dias. As trocas gasosas tambem se restabeleceram, mas de forma mais lenta que o status hidrico. Sob deficit hidrico, a concentracao de prolina aumentou e a de carboidratos soluveis totais diminuiu. Plantas jovens de mogno-africano sao tolerantes ao deficit hidrico moderado.

Exogenous glycine betaine modulates ascorbate peroxidase and catalase activities and prevent lipid peroxidation in mild water-stressed Carapa guianensis plants

The hypothesis that application of exogenous glycine betaine (GBEX) may attenuate the effects of mild water deficit in leaf gas exchange and lipid peroxidation in Carapa guianensis was examined. For this reason, 110-d old plants were sprayed with 0, 25, and 50 mM GBEX and then subjected to two watering regimes. In the first, irrigation was continuously performed to maintain the soil near to field capacity (watered plants). In the second, irrigation was withheld and water deficit resulted from progressive evapotranspiration (water-stressed plants). Treatment comparisons were assessed when predawn leaflet water potential (Ψpd) of stressed plants reached −1.28 ± 0.34 MPa. Regardless of the watering regime, significant (P<0.05) increases in foliar glycine betaine (GBLeaf) concentration were observed in response to increasing GBEX; however, such increases were more expressive in stressed plants. The net photosynthetic rate, stomatal conductance to water vapor, and intercellular to ambient CO2 concentration ratio were significantly lower in water-stressed plants independently of GBEX concentration sprayed on leaves. The application of 25 and 50 mM GBEX caused significant (P<0.05) increases in ascorbate peroxidase (APX) activity in stressed plants, while significant (P<0.05) increases in catalase activity was observed just in the stressed plants treated with 50 mM GBEX. Malondialdehyde concentrations did not differ between watered and stressed plants regardless of GBEX concentration. In conclusion, C. guianensis was able to incorporate GBEX through their leaves and the resulting increases in GBLeaf attenuated lipid peroxidation in stressed plants through positive modulation of APX and CAT activities.

Activity of alternative oxidase and plant uncoupling mitochondrial protein in potato tubers stored at low temperature or submitted to artificial aging

Potato tubers (Solanum tuberosum L. cv. Binje) were stored at 18 and 4oC in order to verify changes in mitochondrial metabolism, especially in the activities of the alternative oxidase (AOX) and plant uncoupling mitochondria protein (PUMP). Tubers were also sliced and submitted to artificial aging. The oxygen consumption rate (OCR), respiratory control (RC) and ADP/O ratio for mitochondria obtained after storage at 18oC were not altered, regardless of the time of storage. Considerable increment in OCR, for both respiratory states 3 and 4, was observed after storing the tubers for five and ten days at 4oC; and it was accomplished by reductions in RC and ADP/O. The AOX activity was evident after five days at 4oC, and it was enhanced after ten days of storage at that temperature. No significant changes in PUMP activities were observed after one day at 18oC or at 4oC, neither after artificial aging. However, increased swelling of potato mitochondria was observed in the presence of valinomycin and linoleic acid when the tubers were kept at 4oC for five and ten days. Besides the changes in AOX and PUMP activities, slight alterations in ascorbate peroxidase (APX) and catalase (CAT) activities were observed after storing the tubers at 4oC for 5 days. The activities of these enzymes were higher after storage at 4oC for 10 days. The results suggest the combined effect of low temperature and time of exposure in promoting AOX activity, probably as a protective mechanism against cell damage in response to mitochondrial oxidative stress.

Aspectos fisiológicos da germinação e da qualidade de plântulas de Schizolobium amazonicum em resposta à escarificação das sementes em lixa e água quente

Seeds of Schizolobium amazonicum present physical dormancy which can be broken through different scarification methods. In this work, the effects of sandpaper and hot water seed scarification on physiological aspects related to seed germination and seedling quality were evaluated. Seeds of S. amazonicum were scarified by (i) immersion in water at 100°C/2 min and (ii) by scrubbing seeds on sandpaper. Non-scarified seeds were used as control. The following variables were evaluated: tissue viability (by using tetrazolium test), germination rate, speed germination index (SGI), seed imbibition rate, endosperm depletion, and seedling emergence rate, uniformity and biomass accumulation. Seeds from both treatments were equally dyed by tetrazolium. Seeds scarified on sandpaper showed higher germination rate, higher SGI, faster seed imbibition and endosperm depletion than those scarified in water at 100°C/2 min. Seeds scarified on sandpaper presented higher seedling emergence rate and emergence index, and their seedlings were more uniform and with greater biomass than those obtained after scarification in water at 100°C/2 min. Therefore, scarification of parica seeds on sandpaper is more efficient in promoting germination and production of uniform seedlings.

Chloroplastidic pigments, gas exchange, and carbohydrates changes during Carapa guianensis leaflet expansion

Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (PN), and the lowest stomatal conductance (gs) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on PN were more expressive until day 20. Intercellular to ambient CO2 concentration ratio (Ci/Ca) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in PN. Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting PN in this species.

Seed quality evaluation by Tetrazolium staining of Parkia multijuga Benth.

The purpose of this study was to develop a staining pattern through tetrazolium test to evaluate seed viability of Parkia multijuga Benth (fava-arara-tucupi). The seeds were scarified, soaked into water and distilled for 48 hours for tegument removal and then immersed in a 0.05%; 0.1%; and 0.3% tetrazolium solution for 6; 18 and 24 hours at 35°C, in the dark. The evaluation was performed on the basis of stain intensity and aspect of the tissues. Based on color patterns, the seed images were classified in eight viability classes. Those results were compared with the germination test in a laboratory. The treatment in concentration of 0.1% for 6 hours was considered adequate for the specie, considering the adequate staining and time for analysis.