Avaliação do metabolismo oxidativo em Pitcairnia encholirioides L. B. Sm. (Bromeliaceae) in vitro e ex vitro e sob desidratação

Abstract

Bromeliaceae is essentially a neotropical family, whose representatives are widely used for landscaping. One major source of supply for the consumer market is the extraction, which coupled with the destruction of the natural environment, has led to irreparable losses in biodiversity of the family, especially in the Atlantic Forest, where about 40% of bromeliad species are under some category of threat. Pitcairnia encholirioides L. B. Sm. is a critically endangered species. In 2004, a unique population of this species was found, with about 900 individuals in a very degraded rocky outcrop, subject to fire and trampling by animals, located in Santa Maria Madalena, RJ. The use of micropropagation can guarantee high multiplication rates, providing necessary material for the consumer market, effectively obviating the extraction of plants in their places of origin. In addition, installation and in vitro conservation of germplasm banks have special importance, ensuring the survival of rare species and/or endemic and providing micropropagated plants for reintroduction initiatives. Following the procedures of in vitro multiplication and rooting, the final stage of micropropagation is the ex vitro acclimatization, a critical period for the plants due to water loss, which causes water stress and, consequently, oxidative stress, which can cause metabolic problems and high losses. In this study, Pitcairnia encholirioides was grown for 150 days in vitro in a culture medium supplemented with two growth regulators (GA3 or NAA), and two concentrations of sucrose (15 or 30 g L-1) in two types of sealing of test tubes (hermetic seal with lids and PVC film and seal with lids that allowed gas exchange), totaling eight treatments, after which the plants were transferred to ex vitro conditions in a greenhouse, staying for more than 180 days. Two of these treatments were selected for analysis of dehydration when their plants were subjected to 30, 42 or 54 days without irrigation, apart from control irrigated periodically, being subsequently rehydrated for 90 days. After periods of in vitro cultivation and maintenance of the plants in the greenhouse, they were analyzed for proline content, total protein, activities of antioxidant metabolism enzymes SOD, CAT, POD and PPO, besides the content of photosynthetic pigments. Apart from these parameters, after dehydration and rehydration, levels of carbohydrates were also assessed. In general, the in vitro culture in medium containing the lowest concentration of sucrose and hermetically sealed tubes proved to be harmful, which was evidenced by lower levels of proline, increased 4 activity of antioxidant enzymes and lower accumulation of photosynthetic pigments. After the acclimatization period, no differences were found between treatments for most parameters, or data varied so as to not allow a generalization about the residual effects of sucrose, the type of cover and of the growth regulators used in the in vitro cultivation. During the period in which the plants were subjected to water stress, higher accumulation of proline and total soluble proteins occurred, and also increased levels of photosynthetic pigments in tissues from plants grown in vitro in medium containing 30 g L-1 sucrose and GA3. There was also, in general, sharper decrease in enzyme activity in medium with the lowest concentration of sucrose and NAA, as well as fluctuations in pigment. Relations between pigments suffered slight reduction in both treatments, and total soluble carbohydrates, sucrose, reducing sugars and starch increased with increasing stress. After rehydration, all plants showed high resilience, presenting for all analyzes values very similar to those of control plants not subjected to dehydration. The results indicate that the in vitro culture in medium supplemented with 30 g L-1 sucrose and tubes that allow gas exchange are the most appropriate. Moreover, the concentration of sucrose added to the culture medium also influences the development of plants after acclimatization, with best results found in plants grown in media supplemented with higher amount of this carbohydrate. It is believed that plants grown under these conditions would have higher capacity of resistance to transplanting and could survive for prolonged periods of water stress, which are often subjected in the natural environment.