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Rice is a crop that presents sensitivity to cold, especially in the germination phase, which leads to high economic losses. Alternative management forms are essential to increase tolerance to low temperatures, and seed priming represents a promising tool. The objective of this study was to investigate the priming effect of the aqueous extract of carrot roots on rice seeds to increase tolerance to low temperatures during germination. Seeds from cultivars BRS Querência (cold-susceptible) and Brilhante (cold-tolerant) were soaked for 24 h in concentrations of 0, 25, 50, and 100% carrot extract, sown on germitest paper and conditioned in BOD for 21 days at 15 °C. As a control, the seeds soaked in water were also germinated at 25 °C. They were evaluated for germination, first germination count, and germination speed index to calculate the stress indices: tolerance index, susceptibility index, and harmonic mean. They were also evaluated for the length and dry mass of shoot and root. The results showed that the rice seeds conditioning in carrot extract effectively reduces the damage caused by cold, significantly increasing the germination speed and the percentage of final germination and the growth evaluations, more expressive at 100% concentration. The stress indexes are efficient in estimating the tolerance of the cultivars and the effect of the different conditions in low-temperature conditions, highlighting the superiority of the Brilhante cultivar. [ABSTRACT FROM AUTHOR]

The leaf anatomy, photosynthetic system parameters and accumulation of carbohydrates were determined at different times for Bipolaris oryzae pathogenesis in two rice cultivars (BRS Querência and Inov CL), grown in an environment with 400 ppm or 700 ppm of atmospheric CO2. The results demonstrated that the plants exposed to 700 ppm underwent changes in anatomical characteristics (reduction in parenchyma thickness and size of bulliform cells), photosynthetic parameters (increased carbon assimilation rate, leaf intercellular CO2 concentration and water use efficiency, and reduction of stomatal conductance to water vapor, transpiration rate and carboxylation efficiency), and carbohydrate accumulation (increased concentration of soluble sugars and starch), when compared to plants at 400 ppm. Therefore, the changes in morphological traits of the leaf and the accumulation of carbohydrates, which were stimulated in the rice plants by increased CO2 concentration (700 ppm), were associated with less severe brown spot, caused by B. oryzae. [ABSTRACT FROM AUTHOR]

Abiotic stresses caused by excessive cold, iron, and salt are among the main growth and yield-limiting factors of rice. Among the metabolic processes, photosynthesis stands out for being closely related to crop yields, causing a yield decline by reduced photosynthetic capacity in plants under abiotic stresses. The purpose of this study was to evaluate the differential expression of chloroplast genes involved in photosynthesis by RNA sequencing (RNA-seq) and quantify gas exchanges in leaves of rice plants exposed to cold, iron, and salt stress for 24 h. Of all genes expressed in each stress, cold had the highest number of differentially expressed genes (DEGs) related to light and chloroplast reactions, with 535 mostly down-regulated genes. Salt and iron stress was associated with 309 and 115 genes, respectively, involved in light reactions and chloroplast. The three stresses had transcripts with GOs related to light reactions, all with more than ten different GO terms. With regard to chloroplast, cold and salt stress had 12 terms of GO, and iron stress has 9 terms of GO. For gas exchange, only the parameter net assimilation rate differed significantly between stresses, with the lowest mean under cold stress. The results showed that cold stress affects photosynthesis most drastically, both at the molecular and the physiological level, and despite decreases in the net assimilation rate, changes under iron and salt stress were minor, which may be related to the tolerance of cultivar BRS Querência. [ABSTRACT FROM AUTHOR]

Sesbania virgata (Leguminosae) is tolerant of long periods of soil inundation. However, its morphological adaptations to anoxia and its response to possible damage from oxidative stress are still unknown. Here, we provide new information that helps to explain the ability of S. virgata plants to grow in flooded environments. Plants containing six expanded leaves were placed in masonry tanks and were subjected to the following conditions: control (well watered), soil waterlogging (water to the setup level of 1 cm above the soil surface-roots and parts of the stems flooded), and complete submergence (whole plant flooded). Plants exposed to flooding (soil waterlogging and complete submergence) significantly increased their production of hydrogen peroxide (HO), indicating the extent of oxidative injury posed by stress conditions. We demonstrate that plants exposed to flooding develop an efficient scavenger of ROS (generated during stress) in the roots through the coordinated action of nonenzymatic ascorbic acid (Asc) and dehydroascorbate (DHA) as well as the enzymatic antioxidants superoxide dismutase (SOD), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) that are present in the tissues. Moreover, we observed the development of morpho-anatomical structures such as adventitious roots, lenticels, and cracks in the stem of plants under soil waterlogging. The secondary root of plants under soil waterlogging showed a thinner cortex and larger number of elements of small diameter vessels. Numerous aerenchymas were observed in the newly formed in the adventitious roots. We conclude that these antioxidative responses and morpho-anatomical adaptations in the roots are part of a suite of adaptations that allow S. virgata plants to survive long periods of flooding, notably under waterlogged conditions. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effects of different iron concentrations on growth characteristics, antioxidant enzyme activities, nutrient absorption, and anatomical changes in sweet potato ( Ipomoea batatas L.). To accomplish this, seedlings from apical branches of plants that had already been established in the greenhouse were rooted in a hydroponic sponge and then transplanted into a hydroponic system intermittently for 2 weeks and irrigated with nutrient solutions containing iron (ferric-EDTA) at concentrations of 0.45, 0.9, 4.5, and 9.0 mmol L. Height, leaf area, and total biomass were significantly reduced at iron concentrations of 4.5 and 9.0 mmol L. The iron concentrations in the established leaves and those that developed after the solution supplementation increased significantly. The amounts of other nutrients were also affected, with manganese showing the most significant decrease. The activities of the antioxidant enzymes, superoxide dismutase, and ascorbate peroxidase increased in plants grown in the 9.0 mmol L iron solution. At this concentration, however, the stomatal densities were reduced on the abaxial surfaces of the leaves, although the stomatal diameters increased. The ultrastructures of the radical cells showed mitochondrial impairment at high iron concentrations; however, the chloroplast structures remained unaffected. [ABSTRACT FROM AUTHOR]