In this article, the authors aimed to analyze the physiological and biochemical alterations in Melanoxylon brauna seeds subjected to heat stress. For this, seed germination, electric conductivity (EC), the production of reactive oxygen species (ROS), and the activity of antioxidant enzymes were assessed. Seeds were incubated at constant temperatures of 25, 35, and 45 °C. Independent samples were first incubated at 35 and 45 °C and then transferred to 25 °C after the intervals of 24, 48, 72, and 96 h. To evaluate EC, seeds were soaked for 0, 24, 48, and 72 h, at 25, 35, and 45 °C and then transferred to Erlenmeyer flasks containing 75 mL of deionized water at 25 °C, for 24 h. ROS production and enzyme activity were assessed every 24 h in seeds soaked at the aforementioned temperatures. Germination did not occur at 45 °C. Seeds soaked at 35 °C for 72 h and then transferred to 25 °C showed higher percentages of germination and a higher germination speed. Seed soaking at 45 °C increased peroxide production, which compromised the antioxidant enzyme system due to a reduction in the activity of enzymes APX, POX, and CAT, thus ultimately also compromising the cell membrane system.

Seed germination studies provide essential information for biodiversity conservation and ecological restoration programs. This work aimed to investigate the relationship between the substrates and the mobilization of reserves during germination of Ormosia coarctata seeds under different temperatures. Samples were collected every 48 h for up to 240 h for quantification of lipids, soluble sugars, starch, and soluble proteins. The optimum temperature range for germination was 25 to 35 °C. The highest germination percentages were obtained using sand or paper roll. Carbohydrate, lipid, and protein contents decreased during germination, regardless of temperature.

The physical, physiological and biochemical changes during the development until the dispersal of rubber tree seeds were evaluated with the purpose of estimating the point at physiological maturity. A total of 30 plants were selected at different points in a commercial planting area and had their flowers marked during the anthesis and every 15 days after marking. Fruits and seeds were collected for analysis of moisture content, dry matter, diameter and length. Details of the anatomy ultra-structure of the seeds were evaluated. The seed emergence, emergency speed index, heat resistant proteins and oxidative stress enzymes were examined. It was observed that fruits reached maximum size at 120 days after anthesis and seeds at 150 days. The seeds acquired germination capacity after 150 days. At 175 days, they presented the highest percentage of dry matter and lowest moisture, in addition to a higher percentage of germination and vigor. Therefore, it was possible to conclude that the physiological maturity of the rubber tree seeds occurs at 175 days after anthesis, and coincides with its maximum physiological quality. At 175 and 180 days post-anthesis, there is a greater expression of heat resistant proteins as well as low molecular weight and greater oxidative stress enzyme activity.

Dieback is a physiological disorder that has caused losses on eucalyptus plantations. Thinking that water stress is one of the triggers for the physiological disorder and aiming at the early identification of tolerant genotypes, we evaluated plantlets of four commercial clones with divergent behavior in field conditions. The plantlets were grown in a greenhouse where the drought conditions were provided by the application of polyethylene glycol 6000 solutions at 100 and 300 g L⁻¹. After water deficit treatments, the morphological, physiological, nutritional and metabolic analyses were performed. SuzT maintained the carbon fixation and the instantaneous water use efficiency, even under water deficit, while sustaining growth. This resulted in higher leaf area and total dry mass in SuzT. Despite higher photosynthetic rate, SuzS exhibited reduced dry biomass accumulation, implying less efficient carbon use. SuzT revealed a higher level of calcium that supports cell structure and homeostasis and indicates higher capacity to manage specific resources and survival under water deficit. SuzT suffered reduction in some free amino acids; however, there was no significant variation for total amino acid content. The principal component and cluster analyses indicated that SuzMT and SuzTP genotypes behave similarly to SuzT under water deficit, while SuzS clustered in isolation. Our results support that there are common trends in water deficit responses for contrasting eucalypt genotypes. The existence of other strategies coping with water deficit resistance is not discarded and should be further evaluated.

The endosperm of coffee beans is an important structure which is composed of different reserve compounds. In the present work, we followed anatomical features during the reserve mobilization of Coffea arabica L. ‘Catuaí’ seed samples, harvested at 20 different sites, after 0, 3, 6, 12, 24, 33 and 45 days of imbibition. Seed samples were properly fixed and stored, respectively, for histochemical and enzyme activity approach. Fixed samples were cross-sectioned for detection of starch, lipids, essential oils, oleoresins, proteins, phenolic compounds, neutral polysaccharides, alkaloids, β-1,3 and β-1,4 glucans, and lignin. Overall, based on histochemical tests and enzyme activity, seed reserve mobilization was similar among the evaluated altitudes and mountainsides. During soaking, there is an intense consumption of reserve compounds, starting at the region close to the embryo. Reserve mobilization intensifies after root protrusion, from 12 days of soaking. The intensification of the reserve consumption is concomitant with an increased activity of MDH is observed at the first 12 days, whereas SOD showed higher expression after 33 days of soaking. At the 33rd day, little reserve is observed in the endosperm. At 45th day, cotyledon leaves are expanded, and the root system, constituted by the taproot and lateral roots, is well established. Key words: Coffea arabica; germination; reserve breakdown; histochemistry; seed anatomy.