RESUMO -(Tipos de aberturas dos grãos de pólen de espécies de Passifl ora L. (Passifl oraceae)). Estudos palinológicos revelam uma ampla variação de formas, número e tipos de aberturas nos grãos de pólen em Passifl ora. Este estudo tem como objetivo caracterizar as aberturas polínicas de onze espécies do gênero ocorrentes no Rio Grande do Sul e duas em Santa Catarina (Brasil), pertencentes a três dos quatro subgêneros atualmente reconhecidos: Astrophea, Decaloba e Passifl ora. Foram utilizadas várias técnicas de microscopia óptica de campo claro e microscopia eletrônica de varredura. Passifl ora haematostigma (Astrophea) possui grãos de pólen 6-colporados, com três endoaberturas lalongadas. Passifl ora alata, P. amethystina, P. caerulea e P. edulis (Passifl ora) apresentam pólen 6-colpados, com fusões das ectoaberturas, aos pares, na região do apocolpo. Passifl ora actinia, P. elegans e P. tenuifi la (Passifl ora) apresentam grãos de pólen com 6 a 12 colpos, também fusionados aos pares. Passifl ora misera, P. morifolia, P. suberosa e P. truncata (Decaloba) apresentam grãos de pólen 6-colporados operculados, com diferenças no tamanho das endoaberturas e largura do opérculo. Passifl ora capsularis (Decaloba) apresenta pólen 12-colporado. São discutidos os principais termos relacionados às descrições polínicas do grupo e indicados os termos mais apropriados e sinônimos. Palavras-chave: Passifl ora, tipos aperturais, pseudopérculo, opérculo, palinologia ABSTRACT -(Aperture types of pollen grains of Passifl ora L. species (Passifl oraceae)). Palynological studies reveal a wide variation in shape, number and types of apertures in Passifl ora pollen grains. This study aimed to characterize pollen grain apertures of eleven species of Passifl ora from Rio Grande do Sul state and two species from Santa Catarina state (Brazil), belonging to three of the four subgenera now recognized: Astrophea, Decaloba and Passifl ora. Several techniques of light and scanning electron microscopy were employed. Passifl ora haematostigma (Astrophea) has 6-colporate pollen grains with three lalongate endoapertures. Passifl ora alata, P. amethystina, P. caerulea and P. edulis (Passifl ora) have 6-colpate pollen grains, with fusion of ectoapertures pairs in the apocolpium. Passifl ora actinia, P. elegans and P. tenuifi la (Passifl ora) have pollen grains with 6 to 12 colpi, also fused in pairs. Passifl ora misera, P. morifolia, P. suberosa and P. truncata (Decaloba) have 6-colporate operculate pollen grains, with differences in endoaperture size and operculum width. Passifl ora capsularis (Decaloba) has 12-colporate pollen. The main palynological terms and synonyms in the literature are discussed.
Iron (Fe) is an essential element to plants, but can be harmful if accumulated to toxic concentrations. Fe toxicity can be a major nutritional disorder in rice ( Oryza sativa ) when cultivated under waterlogged conditions, as a result of excessive Fe solubilization of in the soil. However, little is known about the basis of Fe toxicity and tolerance at both physiological and molecular level. To identify mechanisms and potential candidate genes for Fe tolerance in rice, we comparatively analyzed the effects of excess Fe on two cultivars with distinct tolerance to Fe toxicity, EPAGRI 108 (tolerant) and BR-IRGA 409 (susceptible). After excess Fe treatment, BR-IRGA 409 plants showed reduced biomass and photosynthetic parameters, compared to EPAGRI 108. EPAGRI 108 plants accumulated lower amounts of Fe in both shoots and roots compared to BR-IRGA 409. We conducted transcriptomic analyses of roots from susceptible and tolerant plants under control and excess Fe conditions. We found 423 up-regulated and 92 down-regulated genes in the susceptible cultivar, and 42 up-regulated and 305 down-regulated genes in the tolerant one. We observed striking differences in root gene expression profiles following exposure to excess Fe: the two cultivars showed no genes regulated in the same way (up or down in both), and 264 genes were oppositely regulated in both cultivars. Plants from the susceptible cultivar showed down-regulation of known Fe uptake-related genes, indicating that plants are actively decreasing Fe acquisition. On the other hand, plants from the tolerant cultivar showed up-regulation of genes involved in root cell wall biosynthesis and lignification. We confirmed that the tolerant cultivar has increased lignification in the outer layers of the cortex and in the vascular bundle compared to the susceptible cultivar, suggesting that the capacity to avoid excessive Fe uptake could rely in root cell wall remodeling. Moreover, we showed that increased lignin concentrations in roots might be linked to Fe tolerance in other rice cultivars, suggesting that a similar mechanism might operate in multiple genotypes. Our results indicate that changes in root cell wall and Fe permeability might be related to Fe toxicity tolerance in rice natural variation.
Cold-tolerance in rice may be related to increased cellulose deposition in the cell wall, membrane fatty acids unsaturation and differential expression of several newly identified genes. Low temperature exposure during early vegetative stages limits rice plant's growth and development. Most genes previously related to cold tolerance in rice are from the japonica subspecies. To help clarify the mechanisms that regulate cold tolerance in young indica rice plants, comparative transcriptome analysis of 6 h cold-treated (10 °C) leaves from two genotypes, cold-tolerant (CT) and cold-sensitive (CS), was performed. Differentially expressed genes were identified: 831 and 357 sequences more expressed in the tolerant and in the sensitive genotype, respectively. The genes with higher expression in the CT genotype were used in systems biology analyses to identify protein-protein interaction (PPI) networks and nodes (proteins) that are hubs and bottlenecks in the PPI. From the genes more expressed in the tolerant plants, 60% were reported as affected by cold in previous transcriptome experiments and 27% are located within QTLs related to cold tolerance during the vegetative stage. Novel cold-responsive genes were identified. Quantitative RT-PCR confirmed the high-quality of RNAseq libraries. Several genes related to cell wall assembly or reinforcement are cold-induced or constitutively highly expressed in the tolerant genotype. Cold-tolerant plants have increased cellulose deposition under cold. Genes related to lipid metabolism are more expressed in the tolerant genotype, which has higher membrane fatty acids unsaturation, with increasing levels of linoleic acid under cold. The CT genotype seems to have higher photosynthetic efficiency and antioxidant capacity, as well as more effective ethylene, Ca and hormone signaling than the CS. These genes could be useful in future biotechnological approaches aiming to increase cold tolerance in rice.
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