Jatropha curcas L. (Euphorbiaceae), known as physic nut, is an oil seed species suitable as feedstock for biodiesel production, among other possible industrial applications. It is also considered tolerant to water restriction and is thus suitable for cultivation in semi-arid regions. However, the lack of uniformity in fructification and seed maturation hinders the harvest and processing of fruits and seeds and the yields from both oil and seed, as well as obtaining seed lots with good physiological quality as propagule. Thus, the aim of this study was to characterise the physiological profile during the development and maturation of J. curcas seeds and to identify the best time to harvest the fruits and seeds based on morphological and physiological aspects. Fruit and seed development was monitored and the fruits were harvested at the end of the maturation phase. Then, they were visually classified in six distinct stages of maturation based on the size and colour of the exocarp, whereas the seeds were classified into 13 distinct stages based on the appearance of the fruit and colour of the tegument. The overall analysis of the parameters indicated that the best harvest time was when the fruits were brown and dry and the seeds presented maximum dry matter accumulation, lower moisture content, the highest germination and vigour, higher lipid content and stable length and width dimensions. Whereas these parameters are related to physiological maturation in J. curcas seeds. Key words: Physic nut, dry weight, germination, physiological maturity, oil content Resumo Jatropha curcas L. (Euphorbiaceae) conhecida como pinhão manso, possui sementes oleaginosas adequadas como matéria-prima para a produção de biodiesel, dentre outras aplicações industriais. É uma espécie tolerante à restrição hídrica e por isso apropriada ao cultivo em regiões semiáridas. As irregularidades na frutificação e maturação dificultam a colheita e o processamento de frutos e sementes, o rendimento em sementes e óleo, assim como a obtenção de lotes de sementes com boa qualidade fisiológica para fins de propágulo. O objetivo deste trabalho consistiu em caracterizar o perfil fisiológico durante a maturação de sementes de pinhão manso e identificar a melhor época de colheita baseandose em aspectos morfológicos e fisiológicos. O desenvolvimento dos frutos e sementes foi monitorado no campo e, ao final da safra, os frutos foram colhidos numa única etapa e classificados visualmente em seis estádios distintos de desenvolvimento e maturação, conforme coloração do exocarpo. As sementes foram classificadas em treze estádios baseando-se no aspecto do fruto e na coloração da testa. Os parâmetros analisados indicam que a melhor época de colheita é quando os frutos estão secos e com coloração marrom, e as sementes apresentaram máximo acúmulo de matéria seca, menor teor de umidade, maior germinação e vigor, maior teor de lipídeos e dimensões estabilizadas em comprimento e largura, parâmetros estes relacionados com o ponto de maturidade fisiológica para as...

Jatropha curcas is an oil-rich Euphorbiaceae seed species renowned for its apparent tolerance to environmental stresses. It is considered a promising source of renewable feedstock for biodiesel production in the Brazilian semiarid region where crop establishment requires a better understanding of the mechanisms leading to proper seed and plant behavior under water restrictive conditions. This study describes physiological and cytological profiles of J. curcas seeds imbibed in water restriction conditions by means of osmotic stress or osmoconditioning. Seeds were characterized by size, weight, moisture content and dry mass, germinability, and cell cycle activation by means of tubulin and microtubule cytoskeleton accumulation. Osmoconditioning at-0.8 MPa did not induce priming effects as it did not improve the physiological quality of the seed lots. Western blotting and immunocytochemical analysis revealed an increasing accumulation of tubulin and microtubule cytoskeleton in seeds imbibed in water for 48h onwards, culminating in the onset of mitotic configurations after germination. Only cortical microtubules were observed during seed osmoconditioning, whereas mitotic microtubules only occurred after reimbibition of osmoconditioned seeds in water and subsequent germination.

Jatropha curcas is an oilseed crop renowned for its tolerance to a diverse range of environmental stresses. In Brazil, this species is grown in semiarid regions where crop establishment requires a better understanding of the mechanisms underlying appropriate seed, seedling and plant behaviour under water restriction conditions. In this context, the objective of this study was to investigate the physiological and cytological profiles of J. curcas seeds in response to imbibition in water (control) and in polyethylene glycol solution (osmoticum). Seed germinability and reactivation of cell cycle events were assessed by means of different germination parameters and immunohistochemical detection of tubulin and microtubules, i.e. tubulin accumulation and microtubular cytoskeleton configurations in water imbibed seeds (control) and in seeds imbibed in the osmoticum. Immunohistochemical analysis revealed increasing accumulation of tubulin and appearance of microtubular cytoskeleton in seed embryo radicles imbibed in water from 48 h onwards. Mitotic microtubules were only visible in seeds imbibed in water, after radicle protrusion, as an indication of cell cycle reactivation and cell proliferation, with subsequent root development. Imbibition in osmoticum prevented accumulation of microtubules, i.e. activation of cell cycle, therefore germination could not be resumed. Osmoconditioned seeds were able to survive re-drying and could resume germination after re-imbibition in water, however, with lower germination performance, possibly due to acquisition of secondary dormancy. This study provides important insights into understanding of the physiological aspects of J. curcas seed germination in response to water restriction conditions.

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