ABSTRACT Low-temperature storage is one of the most effective techniques to maintain the quality and durability of cut flowers. Both quality maintenance and durability are dependent on plant metabolism factors such as antioxidant system. The objective was to evaluate the effect of low-temperature on precooling and storage after harvest, on the metabolism of calla lily [Zantedeschia aethiopica (L.) K. Spreng] concerning the antioxidant system, levels of hydrogen peroxide (H2O2), and malondialdehyde (MDA). Therefore, different storage temperatures (4 ºC and 21 ºC) were tested as well as the effect of precooling in different periods (0 to 24 hours). It was observed that the activity of catalase (CAT) and superoxide dismutase (SOD) was increased at 4 °C, as well as inflorescence durability in the commercial standard (around 12 days). At 21 °C, the content of H2O2 and MDA was higher and the visual quality reduction in the inflorescence was accelerated. Low-temperature leads to a higher activity of the enzymes of the antioxidant system (CAT and SOD) and increases postharvest longevity for calla lily. Precooling did not influence the visual quality and longevity of calla lily. Long-term exposure periods at low temperatures, with 12 and 24 hours of precooling caused stress, evidenced higher MDA levels and higher CAT activity. SOD activity was related to low temperature and shorter precooling periods resulted in better antioxidant system activity and lower MDA levels.

RESUMO O armazenamento em baixa temperatura é uma das técnicas mais eficazes para manter a qualidade e a durabilidade das flores cortadas. Tanto a manutenção da qualidade quanto a durabilidade são dependentes de fatores do metabolismo da planta como o sistema antioxidante. O objetivo foi avaliar o efeito da baixa temperatura no pré-resfriamento e armazenamento pós-colheita, no metabolismo do copo-de-leite [Zantedeschia aethiopica (L.) K. Spreng] quanto ao sistema antioxidante, níveis de peróxido de hidrogênio (H2O2) e malondialdeído (MDA). Portanto, diferentes temperaturas de armazenamento (4 ºC e 21 ºC) foram testadas assim como o efeito do pré-resfriamento em diferentes períodos (0 a 24 horas). Foi observado que a atividade da catalase (CAT) e da superóxido dismutase (SOD) aumentou no armazenamento à 4 °C, assim como a durabilidade da inflorescência no padrão comercial (aproximadamente 12 dias). À 21 °C, o teor de H2O2 e MDA foi maior e a redução da qualidade visual na inflorescência foi acelerada. A baixa temperatura leva a uma maior atividade das enzimas do sistema antioxidante (CAT e SOD) e aumenta a longevidade pós-colheita do copo-de-leite. O pré-resfriamento não influenciou na qualidade visual e longevidade do copo-de-leite. Períodos de exposição de longa duração a baixas temperaturas, com 12 e 24 horas de pré-resfriamento causaram estresse, evidenciados por maiores níveis de MDA e maior atividade de CAT. A atividade da SOD foi relacionada à baixa temperatura e períodos mais curtos de pré-resfriamento resultaram em melhor atividade do sistema antioxidante e menores níveis de MDA.

Resumo: Com o crescimento da produção de forrageiras, a demanda por sementes de alta qualidade aumenta. O condicionamento fisiológico vem como técnica para produzir sementes de alta qualidade e tolerância à estresses. O objetivo deste trabalho foi avaliar o efeito de agentes condicionantes sobre a germinação de sementes e crescimento de plântulas de Urochloa ruziziensis em condições de estresse hídrico e salino. Foi estabelecido um experimento em delineamento inteiramente casualizado testando o efeito de seisagentes condicionantes e três condições de germinação. Foram avaliados conteúdo de água, porcentagem e velocidade de germinação, viabilidade das sementes remanescentes do teste de germinação, comprimento da plântula, atividade do sistema antioxidante e a quantidade do malonaldeído. Melhor performance foi observada em sementes condicionadas submetidas ao déficit hídrico e salino do que aquelas não condicionadas. Um aumento significante foi observado na percentagem e velocidade de germinação de sementes, bem como no tamanho de raízes e caule. O nitroprussiato de sódio tem maior potencial para uso no condicionamento fisiológico de sementes de U. ruziziensis.

Abstract: As forage production increase, high-quality seeds demand follows. Priming have been reported as a technique for improve seed quality and stress tolerance. The aim of this study was to evaluate the priming agents effect on Urochloa ruziziensis seed germination and seedling establishment under water deficit and salt stress. A completely randomized experiment assessing six priming agents and three germination conditions were established. We evaluated: seed water content; germination percentage and speed index; viability of seeds remaining from the germination test; seedling length; antioxidant enzymatic activity; and malondialdehyde quantity. Seeds primed under water deficit and salt stress showed better physiological performance than dry seeds. There was a significant increase in seed germination percentage and speed and in seedling roots and shoots length. Sodium Nitroprusside shows significant potential for use in the physiological priming of U. ruziziensis seeds.

ABSTRACT Soil water saturation requires different adaptative strategies by tree species that live under such conditions. We aimed to study the responses that ensure flooding tolerance by tree species and so provide support for recovery projects with degraded areas subject to flooding. We evaluated the ecophysiology of Cedrela fissilis under different water saturations, including anatomical traits, gas exchange parameters, antioxidant system analysis and growth. We subjected 100 day-old plants to three treatments: Control (FC) where the substrate was kept at field capacity; Flooded Roots (FR), where the substrate remained submerged but with no surface layer of water, and Flooded Stem (FS), with a water layer accumulation of around 3.0 cm over the substrate, flooding part of the stems. The plants were kept under such conditions for 90 days. Plants survived in all treatments due to a marked development of cortical intercellular spaces in flooded plants. However, photosynthesis and other gaseous exchange were limited under FR and FS treatments. In addition, the periderm thickness was reduce by flooding and there was an accumulation of starch grains in the parenchyma cells of the xylem, cortex and pith of the stem. There was also a significant lipid peroxidation on the leaves under FR and FS treatments. The superoxide dismutase activity was decreased, but the activities of the ascorbate perioxidases and catalase in the leaves were increased. We concluded that young Cedrela fissilis plants partially tolerate flooding since they developed ecophysiological changes in order to survive in this condition. Consequently, this species is a good candidate for the reforestation projects in environments where intermittent flooding occurs, such as riverside and riparian forests.