Respostas enzimáticas na enxertia de tomateiro

RESUMO Visando avaliar a compatibilidade de tomateiros enxertados em diferentes portaenxertos, sob ambiente protegido, foi determinada a atividade das enzimas antioxidantes, peroxidases (POXs), polifenoloxidase (PPO) e superóxido dismutase (SOD). A primeira etapa experimental consistiu na avaliação, aos seis e onze dias após a enxertia, das mudas enxertadas e não enxertadas com três combinações de enxertia (Maxifort, Multifort e autoenxertia), em três regiões de coleta no caule: a) 2 cm acima da região da enxertia; b) na região de enxertia e c) 2 cm abaixo da região da enxertia, além do tratamento adicional, constituído de mudas não enxertadas de 'Alambra' (pé franco). O delineamento experimental foi inteiramente casualizado, em esquema fatorial 3x3+1, com cinco repetições. Na segunda etapa experimental houve o transplantio das mudas para a casa de vegetação, com as combinações de enxertia 'Maxifort', 'Multifort', autoenxertia e pé franco, considerando nas parcelas as combinações da enxertia e nas subparcelas os quatro períodos de coleta 30, 60, 90 e 120 dias após o transplantio. O delineamento experimental foi em blocos ao acaso, em esquema de parcela subdividida, sendo cada parcela experimental constituída de seis plantas, com seis repetições. Os resultados da primeira etapa mostram que houve incremento na atividade das POXs e PPO durante o pegamento das enxertias com os portaenxertos 'Maxifort', 'Multifort' e também na autoenxertia. Na segunda etapa, observou-se maior incremento na atividade de SOD e POXs para o portaenxerto 'Multifort' aos 120 dias após o transplantio. As plantas enxertadas e o pé franco não apresentaram indícios de incompatibilidade, sendo o aumento da atividade enzimática atribuído ao processo de cicatrização e lignificação das mudas enxertadas, tendo mantido esse comportamento ao longo do ciclo de crescimento e desenvolvimento das plantas de tomateiro. A produção por planta não sofreu influência da enxertia

Differential responses between mature and young leaves of sunflower plants to oxidative stress caused by water deficit

The effects of water stress and rehydration on leaf gas exchange characteristics along with changes in lipid peroxidation and pirogalol peroxidase (PG-POD) were studied in mature and in young leaves of sunflower (Helianthus annuus L.), which were grown in a greenhouse. Water stress reduced photosynthesis (Pn), stomatal conductance (g s), and transpiration (E) in both young and mature leaves. However, the amplitude of the reduction was dependent on leaf age. The intercellular CO2 concentration (Ci) was increased in mature leaves but it was not altered in young leaves. Instantaneous water use efficiency (WUE) in mature stressed leaves was reduced when compared to control leaves while in young stressed leaves it was maintained to the same level as the control. After 24h of rehydration, most of the parameters related to gas exchange recovered to the same level as the unstressed plants except gs and E in mature leaves. Water stress did not activated PG-POD independently of leaf age. However, after rehydration the enzyme activity was increased in mature leaves and remained to the same as the control in young leaves. Malondialdehyde (MDA) content was increased by water stress in both mature and young leaves. The results suggest that young leaves are more susceptible to water stress in terms of gas exchange characteristics than mature leaves although both went through oxidative estresse.Os efeitos do estresse hídrico e da reidratação nas trocas gasosas juntamente com alterações na lipoperoxidação e atividade da pirogalol peroxidase (PG-POD) foram estudados em folhas adultas e jovens de plantas de girassol (Helianthus annuus L.) cultivadas em casa de vegetação. O estresse hídrico reduziu a fotossíntese (P N), a condutância estomática (g s) e a transpiração (E) nas folhas adultas e jovens. No entanto, a amplitude da redução foi dependente da idade da folha. A concentração intercelular de CO2 (Ci) aumentou nas folhas adultas, mas não apresentou alteração nas folhas jovens sob condições de estresse hídrico. A eficiência instantânea do uso da água (WUE) nas folhas adultas e estressadas foi reduzida em comparação com o controle, enquanto que, nas folhas jovens e estressadas, não foi alterada. Após 24h de reidratação, as folhas apresentaram valores semelhantes aos dos controles em todos os parâmetros relacionados com as trocas gasosas, exceto gs e E nas folhas adultas. O estresse hídrico não ativou a PG-POD, independente da idade da folha, e após a reidratação a atividade da PG-POD foi aumentada apenas nas folhas adultas. O estresse hídrico aumentou o teor de malondialdeído (MDA) nas folhas adultas e jovens. Os resultados sugerem que as folhas jovens são mais susceptívies ao déficit hídrico em termos de trocas gasosas que as folhas adultas, embora ambas tenham sido expostas ao estresse oxidativo

ETHEPHON AND CALCIUM CHLORIDE, A COMBINATION THAT IMPROVES SKIN COLOR OF ‘RUBI’ TABLE GRAPE

ABSTRACT ‘Rubi’ table grape has wide acceptance of the consumer market due to its affordable price and attractive color as a function of the accumulation of anthocyanins. However, environmental conditions do not always favor the suitable accumulation of these pigments, resulting in commercial devaluation and nutritional depreciation of fruits. Thus, the present study aimed to investigate the effect of application of different ethephon concentrations, associated or not with CaCl2 application, on the skin color and quality of ‘Rubi’ grape berries. First, specific traits of berries treated with 0, 200, 400, 600, 800 mg L-1 ethephon associated with 1.5% CaCl2 solution were evaluated and pH, titratable acidity (TA), soluble solids (SS), berry firmness, total and reducing soluble sugars, and anthocyanin and flavonol levels were analyzed. This first stage of evaluation revealed no changes in total sugar levels, firmness, SS, TA, SS/TA ratio, and flavonol levels, while changes were detected regarding reducing sugar and anthocyanin levels. Thus, in the second stage, the following variables were evaluated: SS, TA, reducing sugar levels, anthocyanin levels, phenylalanine ammonia lyase (PAL) and glutathione S-transferase (GST) activity of ‘Rubi’ grape berries treated with 0, 200, 400, 600, 800 mg L-1 ethephon, associated or not with 1.5% CaCl2 solution. The results of the present study indicate that ethephon associated with CaCl2 can contribute to improve the post-harvest quality of ‘Rubi’ grape, since this association increased the accumulation of anthocyanins due to the higher activity of PAL and GST, related to biosynthesis and storage of antocyanins, respectively, and increased the levels of reducing sugars (at low ethephon concentrations), not changing other quality aspects. Therefore, a single ethephon application from 200 mg L-1 associated with the application of 1.5% CaCl2 at the final ripening stage, when bunches present from 30 to 50% skin color coverage, was sufficient to produce satisfactory results regarding skin color improvement of ‘Rubi’ grape berries

Nitric oxide reduces oxidative damage induced by water stress in sunflower plants

Drought is one of the main environmental constraints that can reduce plant yield. Nitric oxide (NO) is a signal molecule involved in plant responses to several environmental stresses. The objective of this study was to investigate the cytoprotective effect of a single foliar application of 0, 1, 10 or 100 µM of the NO donor sodium nitroprusside (SNP) in sunflower plants under water stress. Water stressed plants treated with 1μM SNP showed an increase in the relative water content compared with 0 μM SNP. Drought reduced the shoot dry weight but SNP applications did not result in alleviation of drought effects. Neither drought nor water stress plus SNP applications altered the content of photosynthetic pigments. Stomatal conductance was reduced by drought and this reduction was accompanied by a significant reduction in intercellular CO2 concentration and photosynthesis. Treatment with SNP did not reverse the effect of drought on the gas exchange characteristics. Drought increased the level of malondialdehyde (MDA) and proline and reduced pirogalol peroxidase (PG-POD) activity, but did not affect the activity of superoxide dismutase (SOD). When the water stressed plants were treated with 10 μM SNP, the activity of PG-POD and the content of proline were increased and the level of MDA was decreased. The results show that the adverse effects of water stress on sunflower plants are dependent on the external NO concentration. The action of NO may be explained by its ability to increase the levels of antioxidant compounds and the activity of ROS-scavenging enzymes.Universidade Estadual Paulista, Faculty of Sciences Department of Biological SciencesUniversidade Estadual Paulista Faculty of Agricultural Sciences Department of Plant ProtectionUniversidade Estadual Paulista, Faculty of Sciences Department of Biological SciencesUniversidade Estadual Paulista Faculty of Agricultural Sciences Department of Plant Protectio