Regulation of seed dormancy and germination in Arabidopsis thaliana

Seed germination is one of the most important developmental steps in the life cycle of a higher plant. Because of this, seed producing plants have evolved mechanisms, such as dormancy, that time germination based on environmental cues. The present study uses Arabidopsis thaliana as a model to address questions about seed dormancy and germination. Three different lines of investigation were followed. The first involved an investigation of how light quality regulates phytohormones in order to control germination. This identified a light-dependent mechanism that differentially regulates expression of the ALLENE OXIDE SYNTHASE and OXOPHYTODIENOATE-REDUCTASE 3 genes resulting in accumulation of cis-12-oxo-phytodienoic acid (cis-OPDA) and repression of seed germination under FR conditions. The second line of investigation involved a re- examination of the role of the ABSCISIC ACID INSENSITIVE (ABI) 5 and ABI4 transcription factors in regulating seed germination and oil mobilization respectively. The study found that abscisic acid (ABA) is able to block testa rupture in nicked seeds and this involves the ABI5, but not the ABI4, transcription factor. Furthermore, it was found that ABI4 is involved in the repression of ABA and cis-OPDA biosynthesis in a light- dependent manner, but has only a minor role in regulating oil mobilization in seeds. The third line of investigation focused on the regulation of dormancy during after-ripening and found that changes in phytohormone levels over an extended period can account for changes in dormancy state

Control of seed coat rupture by ABA-INSENSITIVE 5 in Arabidopsis thaliana

In Arabidopsis, seed germination is a biphasic process involving rupture of the seed coat followed by emergence of the radicle through the micropylar endosperm. Embryo expansion results in seed coat rupture and removal of seed coat imposed dormancy with DELLA proteins blocking embryo expansion in the absence of gibberellins. Exogenous abscisic acid (ABA) treatment does not block seed coat rupture but does block radicle emergence. We used this limited effect of exogenous ABA to further investigate the mechanism by which it blocks the onset of germination marked by seed coat rupture. We show that physical nicking of the seed coat results in exogenous ABA treatment blocking both seed coat and endosperm rupture and this block requires the transcription factors ABI3 and ABI5, but not ABI4. Furthermore, we show that the repression of expression of several EXPANSIN genes (EXPA1, EXPA2, EXPA3, EXPA9 and EXPA20) by exogenous ABA requires ABI5. We conclude that ABI5 plays an important role in the ABA-mediated repression of germination through prevention of seed coat rupture and propose that this involves EXPANSIN related control of cell wall loosening

AQUISIÇÃO DE REPERTÓRIO DISCRIMINATIVO AUDITIVO EM ESQUEMA MÚLTIPLO: EXPLORANDO PROCEDIMENTO PARA ESTUDO DA FORMAÇÃO DE CLASSES FUNCIONAIS EM RATOS

Studies on stimulus class formation usually require training of baseline discriminations that comprise multiple interrelated simple and/or conditional discriminations. The purpose of the present study was to replicate the acquisition of baseline discriminations of a previous study with rats as subjects, introducing changes in the procedure in order to make more efficient the baseline training. Six albino rats (Rattus norvegicus) were exposed to a successivesimple discrimination training procedure with auditory stimuli in long duration sessions. Two different auditory stimuli (A1 and B1) were correlated to a variable ratio schedule (VR) and two other stimuli (A2 and B2) were correlated to differential reinforcement of low rates schedule (DRL). Five out of the six rats acquired the discriminations showing two distinct patterns of response (high rates in the VR schedule and low rates in the DRL Schedule) under control of the auditory stimuli. Results suggest that the use of a multiple schedule with auditory stimuli in long duration sessions may be a fast and efficient alternative to build a baseline repertoire in studies on functional class formation with auditory stimuli and rats as subjects.Key-words: variable ratio, differential reinforcement of low rates, auditory stimulus, Rattus norvegicusEstudos sobre a formação de classes de estímulos usualmente requerem o treino de discriminações de linha de base que incluem múltiplas discriminações simples e/ou condicionais inter-relacionadas. O objetivo do presente estudo foi replicar a fase de aquisição de discriminações de linha de base de um estudo anterior com ratos como sujeitos, com mudanças de procedimento objetivando tornar mais eficiente o treino de linha de base. Seis ratos albinos (Rattus norvegicus) foram submetidos a treino de discriminações simples sucessivas, com estímulos auditivos, em sessões de longa duração. Dois estímulos auditivos (A1 e B1) foram correlacionados a esquema de razão variável (VR) e dois outros estímulos (A2 e B2) foram correlacionados a esquema de reforço diferencial de taxas baixas (DRL). Cinco dos seis ratos demonstraram aquisição das discriminações, desenvolvendo dois padrões distintos de responder (taxas altas no esquema VR e taxas baixas no esquema DRL) sob controle dos estímulos auditivos. Este trabalho sugere que o emprego de esquemas múltiplos com estímulos auditivos em sessões de longa duração pode representar uma alternativa rápida e eficaz na formação de uma linha de base necessária aos estudos de formação de classes funcionais com estímulos auditivos e com ratos como sujeitos. Palavras-chave: razão variável, reforço diferencial de taxas baixas, estímulos auditivos, Rattus novergicu

Accessible protocol for practice classroom about physical and chemical factors that affect the biomembranes integrity

The aim of the current work is to review a protocol used in practical classes to demonstrate some factors that affect biomembrane integrity. Sugar-beet fragments were utilized as the experimental model as membrane damage could be visualized by leakage of betacyanins, hydrophilic pigments accumulated in the cell vacuoles. The tests were carried out as discrete experiments utilizing physical agents and chemical products present in the student daily routine. To test the effect of temperature, sugar-beet fragments were submitted to heat, cold or both at different times of exposition. When chemical products were tested, sugar-beet fragments were exposed to organic solvents (common alcohol and acetone) or polar and amphipathic substances (disinfectant, detergent, hydrogen peroxide, and sodium hypochlorite). The obtained results were discussed in terms of the capacity of the physical and chemical factors to cause membrane damage. The review of this protocol using reagents that are present in the student daily routine were able to demonstrate clearly the effect of the different tested factors, allowing the utilization of this practical class under limited conditions

Low-temperature and circadian signals are integrated by the sigma factor SIG5

Chloroplasts are a common feature of plant cells and aspects of their metabolism, including photosynthesis, are influenced by low-temperature conditions. Chloroplasts contain a small circular genome that encodes essential components of the photosynthetic apparatus and chloroplast transcription/translation machinery. Here, we show that in Arabidopsis, a nuclear-encoded sigma factor that controls chloroplast transcription (SIGMA FACTOR5) contributes to adaptation to low-temperature conditions. This process involves the regulation of SIGMA FACTOR5 expression in response to cold by the bZIP transcription factors ELONGATED HYPOCOTYL5 and ELONGATED HYPOCOTYL5 HOMOLOG. The response of this pathway to cold is gated by the circadian clock, and it enhances photosynthetic efficiency during long-term cold and freezing exposure. We identify a process that integrates low-temperature and circadian signals, and modulates the response of chloroplasts to low-temperature conditions

Low-temperature and circadian signals are integrated by the sigma factor SIG5.

Acknowledgements: This research was funded by Biotechnology & Biological Sciences Research Council (UK) (BB/I005811/2, BB/J014400/1, BB/T003030/1, Institute Strategic Programme GEN BB/P013511/1 to A.N.D.; studentship 1518540 awarded to P.E.P.), Norwich Research Park Doctoral Training Partnership (BB/T008717/1, to R.D. and A.B.), The Leverhulme Trust (RPG-2018-216, to A.N.D.), the Bristol Centre for Agricultural Innovation (to A.N.D.), the Wolfson Foundation (to A.N.D.), NAGASE Science Technology Foundation (Japan), the Ministry of Education, Culture, Sports, Science and Technology (Japan) (Grants-in-Aid 17K07438, to K.T. and S.I.) and Tokyo Institute of Technology World Research Hub Initiative Program of Institute of Innovative Research (to K.T.). D.L.C.-R. is grateful to the Consejo Nacional de Ciencia y Tecnología (Mexico) for granting a PhD scholarship. We thank the University of Bristol Genomics Facility and Z. Song for experimental support; G. Jenkins for seed donation; S. Samwald, E. Tee, J. Sallmen and N. Holmes for help with protein analysis; C. Faulkner, T. Oyama and T. Muranaka for advice about transient expression; and M. Knight, Y. Yoshitake and M. Shimojima for technical advice. Figure 5 created with BioRender.com.Funder: Bristol Centre for Agricultural Innovation Consejo Nacional de Ciencia y Tecnología (Mexico)Funder: BBSRC (Durham) Studentship 1518540 The Leverhulme Trust RPG-2018-216Funder: NAGASE Science Technology Foundation Tokyo Institute of Technology World Research Hub InitiativeFunder: The Leverhulme Trust RPG-2018-216 Bristol Centre for Agricultural InnovationChloroplasts are a common feature of plant cells and aspects of their metabolism, including photosynthesis, are influenced by low-temperature conditions. Chloroplasts contain a small circular genome that encodes essential components of the photosynthetic apparatus and chloroplast transcription/translation machinery. Here, we show that in Arabidopsis, a nuclear-encoded sigma factor that controls chloroplast transcription (SIGMA FACTOR5) contributes to adaptation to low-temperature conditions. This process involves the regulation of SIGMA FACTOR5 expression in response to cold by the bZIP transcription factors ELONGATED HYPOCOTYL5 and ELONGATED HYPOCOTYL5 HOMOLOG. The response of this pathway to cold is gated by the circadian clock, and it enhances photosynthetic efficiency during long-term cold and freezing exposure. We identify a process that integrates low-temperature and circadian signals, and modulates the response of chloroplasts to low-temperature conditions