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There is a very effective cross-talk between signals triggered by reactive oxygen species and hormonal responses in plants, activating proteins/enzymes likely to be involved in stress tolerance. Abscisic acid (ABA) is known as a stress hormone that takes part in the integration of signals. This work aimed to characterize the biochemical response and ultrastructural changes induced by cadmium (Cd) in the Micro-Tom (MT) sitiens ABA-deficient mutant (sit) and its wild-type (MT) counterpart. MT and sit plants were grown over a 96-h period in the presence of Cd (0, 10, and 100 μM CdCl). The overall results indicated increases in lipid peroxidation, hydrogen peroxide content and in the activities of the key antioxidant enzymes such as catalase, glutathione reductase, and ascorbate peroxidase in both genotypes. On the other hand, no alteration was observed in chlorophyll content, while the activity of another antioxidant enzyme, superoxide dismutase, remained constant or even decreased in the presence of Cd. Roots and shoots of the sit mutant and MT were analyzed by light and transmission electron microscopy in order to characterize the structural changes caused by the exposure to this metal. Cd caused a decrease in intercellular spaces in shoots and a decrease in cell size in roots of both genotypes. In leaves, Cd affected organelle shape and internal organization of the thylakoid membranes, whereas noticeable increase in the number of mitochondria and vacuoles in MT and sit roots were observed. These results add new information that should help unravel the relative importance of ABA in regulating the cell responses to stressful conditions induced by Cd apart from providing the first characterization of this mutant to oxidative stress.

Vinasse is a highly colored effluent with a high pollutant potential when disposed in the environment. Assays for decolorization of vinasse were performed, selecting the fungus Pleurotus sajor-caju CCB 020. The discoloration was cocominant with the increase of the activities of laccase, manganese-peroxidase and peroxidases. P. sajor-caju demonstrated a rise in biomass production (1.06 g 100 ml -1 ), and the enzyme activities such as laccase (varying from 400 to 450 IU l -1 ) reached between the 9th and 10th day of growth and for MnP at the 12th day of cultivation (varying from 60 to 100 IU l -1 ). It was concluded that the system P. sajor-caju/vinasse can be utilized as a bioprocess for color removal and degradation of complex vinasse compounds. It was observed an improvement in the characteristics and detoxification allowing its utilization as reused water, laccase and manganese-peroxidase enzymes production and for fungal biomass production with a high nutritional value.

Exposure to nickel (Ni) at high concentrations can lead to production of reactive oxygen species (ROS) resulting in oxidative damage at the cellular level. We investigated the antioxidative responses of Nicotiana tabacum cv BY-2 cell suspension to Ni stress (0.075 and 0.75 mM NiCl 2 ) over a 72 h period with special attention to potential alterations in isoenzymes of superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR). Two main SOD isoenzymes were observed, a Mn-SOD (band I) and a Fe-SOD (band II), as well as one CAT isoenzyme and four GR isoenzymes. Activity staining analysis revealed that CAT activity plays a major role in the early response to Niinduced oxidative stress, particularly when the Ni concentration used was low, whilst a specific GR isoenzyme appears to respond to the Ni-induced oxidative stress when a much higher Ni concentration was used to induce the stress for the same period of treatment. These results illustrate the importance and advantages of determining individual isoenzyme activities.

Plant cell cultures are a suitable model system for investigation of the physiological mechanisms of tolerance to environmental stress. We have determined the effects of Cd (0.1 and 0.2 mM CdCl 2 ) and Ni (0.075 and 0.75 mM NiCl 2 ) on Nicotiana tabacum L. cv. Bright Yellow (TBY-2) cell suspension cultures over a 72-h period. Inhibition of growth, loss of cell viability and lipid peroxidation occurred, in general, only when the TBY-2 cells were grown at 0.2 mM CdCl 2 and at 0.75 mM NiCl 2 . At 0.1 mM CdCl 2 , a significant increase in growth was determined at the end of the experiment. Increases in the activities of all of the four enzymatic antioxidant defence systems tested, were induced by the two concentrations of Cd and Ni, but at different times during the period of metal exposure. Overall, the cellular antioxidant responses to Cd and Ni were similar and were apparently sufficient to avoid oxidative stress at the lower concentrations of Cd and Ni. The activities of glutathione reductase and glutathione S-transferase increased early but transiently, whereas the activities of catalase and guaiacol peroxidase increased in the latter half of the experimental period. Therefore it is likely that the metabolism of reduced glutathione was enhanced during the initial onset of the stress, while catalase and guaiacol-type peroxidase appeared to play a more important role in the antioxidant response once the stress became severe.

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RESUMOLaranjeiras Pêra enxertadas em 11 cultivares ou híbridos de tangerineiras foram plantadas em 1988 em Itirapina (SP), num Latossolo Vermelho-Amarelo textura arenosa, no espaçamento 4,25m x 7,5m e conduzidas sem irrigação sob clima Cwa. Tristeza e declínio são endêmicos na região. As tangerineiras África do Sul , Xienkhouanga , Empress , Cleópatra , Wildt , 117.477 e Sul da África , sem diferirem entre si, induziram, em ordem decrescente, as maiores produções de frutos às laranjeiras Pêra , no total das quatro primeiras colheitas do experimento. Num total de nove colheitas, as cultivares Xienkhouanga, África do Sul, 117.477, Cleópatra, Empress, Wildt e Szinkon x Tizon, sem diferirem entre si, proporcionaram, em ordem decrescente, as maiores produções de frutos às laranjeiras Pêra . Os porta-enxertos não determinaram diferenças significativas nas características comerciais dos frutos, porém a Cleópatra induziu maturação mais precoce que os demais porta-enxertos. Apenas a Szwinkon x Szinkon-tizon proporcionou a formação de plantas nanicas, com altura inferior a 2,5m. Os dados médios de produção de frutos e de sólidos solúveis, concernentes a três anos consecutivos de colheita, revelaram que as laranjeiras Pêra enxertadas nas tangerineiras Xienkhouanga e 117.477, sem diferir das plantas enxertadas nas cultivares África do Sul, Cleópatra, Empress, Wildt e Szinkon x Tizon, foram significativamente mais produtivas em frutos e em sólidos solúveis que as enxertadas em Sul da África , Vermelha , Muscia e Szwinkon x Szinkontizon . Nenhuma das plantas apresentou sintomas de intolerância à tristeza, ao declínio dos citros ou anel de goma na região de enxertia, considerado sintoma de incompatibilidade entre a copa e o porta-enxerto. Termos para indexação:Citrus reshni, C. reticulata, declínio, tristeza. ABSTRACTPera sweet orange trees budded either on mandarins or mandarin-hybrids rootstocks were planted in 1988 at 4.25m x 7.5m spacing on a sandy textured Oxisol in Sao Paulo state, Brazil, under Cwa climatic conditions, and managed without irrigation. Tristeza and blight diseases are endemic in the area. Trees on Africa do Sul, Xienkhouanga, Empress, Cleopatra, Wildt and 117.477 cultivars, produced the highest cumulative yields in the first four crops and in the ninth crop. Regardless of the rootstock tested no significant variation on fruit quality was observed, but Cleopatra mandarin induced earlier maturation of fruit than the others roostocks. Only Szwinkon x Szinkon-tizon rootstocks induced dwarfed trees. Xienkhouanga , 117.477, Africa do Sul , Cleopatra , Empress , Wildt and Szinkon x Tizon induced the highest fruit and soluble solids production by tree in the 1996-1999 period. No one trees showed symptoms of tristeza, declinio/blight or bud-union-ring symptom of incompatibility.

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