Global climate changes and biological invasions are environmental disturbances that may interact synergistically, causing loss of biodiversity. As the early stages of development are the most sensitive and easily affected by these constraints, this study investigated the effects of increased carbon dioxide (CO2) and temperature, as forecasted for 2100, on seed germination and early development of three species of invasive African grasses that have gradually replaced landscapes of the Brazilian Cerrado biome. It was observed that these parameters affected percentage and rate of germination in Urochloa brizantha, rate of germination and mean germination time in Urochloa decumbens and accelerated autotrophy acquisition in U. brizantha, U. decumbens and Megathyrsus maximus.Regarding root elongation, all species showed changes in total length, absolute and relative growth rate, but at different stages of development or time intervals, with increased temperature being more significant than increased CO2, probably due to seed reserves still being the main carbon sources at this stage. Taken together, the results indicate that the effects of CO2 and increased temperature are species specific and highlight the greatest potential of U. brizantha to germinate, and of U. decumbens for seedling establishment under these environmental changes.
We determined the length, volume, dry biomass, and density in seeds of five castor bean cultivars and verified notable physicochemical trait differences. Seeds were then subjected to different toxic aluminum (Al) concentrations to evaluate germination, relative root elongation, and the role of root apices' rhizosphere mucilage layer. Seeds' physicochemical traits were associated with Al toxicity responses, and the absence of Al in cotyledons near to the embryo was revealed by Al-hematoxylin staining, indicating that Al did not induce significant germination reduction rates between cultivars. However, in the more sensitive cultivar, Al was found around the embryo, contributing to subsequent growth inhibition. After this, to investigate the role of mucilage in Al tolerance, an assay was conducted using NH4Cl to remove root mucilage before or after exposure to different Al concentrations. Sequentially, the roots were stained with hematoxylin and a quantitative analysis of staining intensity was obtained. These results revealed the significant contribution of the mucilage layer to Al toxicity responses in castor bean seedlings. Root growth elongation under Al toxicity confirmed the role of the mucilage layer, which jointly indicated the differential Al tolerance between cultivars and an efficient Al-exclusion mechanism in the tolerant cultivar.
iNDUCeD reSPONSe AGAiNST HerBivOrY iN PLANTS: Plants respond to herbivores and pathogens attack with increased emission of volatile organic compounds. These molecules act as indirect defences when attracting natural enemies of herbivores and thus benefit the plant. it remains controversial whether undamaged plants identify chemicals released by closely located, damaged plants and respond to them by increasing their defensive barriers against an imminent attack. Although the Talking Trees Hypothesis was published 25 years ago, only recently the most sceptical scientists have been convinced. The induced response to herbivory by interplant information transfer has been found in two plant-herbivore systems. However, the universality of the phenomenon and its ecological and evolutionary relevance remain unclear. The integration of Molecular Biology, Biochemistry, Physiology, and ecology begin to shed light on the mechanisms of the signal transfer. This integrative approach has developed new and more sensitive tools for identification of complex volatile mixtures and for understanding the process of biosynthesis, emission, transportation and reception of signals.Key Words: induced resistance, induced defense, insect-plant interaction, interplant air signalling, interplant communication, talking trees. respostas contra herbivoria induzidas pela transferência de informação entre plantas: Plantas respondem ao ataque de herbívoros e patógenos com liberação de compostos orgânicos voláteis. essas moléculas funcionam como defesas indiretas quando atraem inimigos naturais dos herbívoros e assim beneficiam a planta emissora. Uma questão controversa é se plantas vizinhas não-atacadas captam esses voláteis e respondem aumentando suas barreiras defensivas contra um ataque iminente. Apesar do seu forte apelo popular e da Talking Trees Hypothesis estar completando 25 anos, só recentemente os mais céticos estão sendo convencidos. Temse aceitado que respostas induzidas pela transferência de informação entre plantas ocorrem em pelo menos dois sistemas plantaherbívoro. No entanto, o grau de generalização do fenômeno e a dimensão da sua importância ecológica e evolutiva permanecem desconhecidos. Uma recente abordagem multidisciplinar, integrando Biologia Molecular, Bioquímica e Fisiologia à ecologia, acena com novas e mais poderosas ferramentas metodológicas para esclarecer os processos de biossíntese, emissão, transporte e recepção dos sinais pelas plantas. essa abordagem tem fornecido o suporte mecanicista adicional às evidências ecológicas da defesa induzida da planta, manifestada e mensurada mediante respostas ecofisiológicas e comportamentais dos insetos herbívoros.
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