Pseudophoenix ekmanii (Arecaceae) seeds at suboptimal temperature show reduced imbibition rates and enhanced expression of genes related to germination inhibition.

Pseudophoenix ekmanii is a critically endangered palm species that can be found in the southeast of the Dominican Republic. The temperatures to which P. ekmanii seeds are exposed upon dispersal range from 32 to 23 °C (max and min) and can reach a low of approximately 20 °C in January. Our aim was to analyse the effect of suboptimal (20 °C) and optimal (30 °C) germination temperature on seed imbibition, moisture content, embryo growth and gene expression patterns in this tropical palm species. Seed imbibition was tracked using whole seeds, while moisture content was assessed for individual seed sections. Embryo and whole seed size were measured before and after full imbibition. For transcriptome sequencing, mRNA was extracted from embryo tissues only and the resulting reads were mapped against the Elaeis guineensis reference genome. Differentially expressed genes were identified after statistical analysis and subsequently probed for enrichment of Gene Ontology categories 'Biological process' and 'Cellular component'. Our results show that prolonged exposure to 20 °C slows whole seed and embryo imbibition and causes germination to be both delayed and inhibited. Embryonic transcriptome patterns associated with the negative regulation of germination by suboptimal temperature include up-regulation of ABA biosynthesis genes, ABA-responsive genes, as well as other genes previously related to physiological dormancy and inhibition of germination. Thus, our manuscript provides the first insights into the gene expression patterns involved in the response to suboptimal temperature during seed imbibition in a tropical palm species.

Seed enhancing treatments: comparative analysis of germination characteristics of 23 key herbaceous species used in European restoration programmes.

The response of seeds from 23 wild plant species to a range of seed enhancing treatments was studied. We tested the hypothesis that sensitivity of the 23 species to these compounds is related to their ecological niche. The three ecological niches considered were open land, open-pioneer and woodland. Hence, the germination of a species is likely adapted to different light conditions and other environmental signals related to the niche. As representatives of environmental signals, the effects of smoke-related compounds (karrikinolide, KAR1 ), nitrate and plant growth regulator (gibberellic acid, GA3 ) on germination were studied. Seeds were exposed to these additives in the imbibition medium; all described as germination cues. We also investigated the effect of light regimes and additives on germination parameters, which included final germination, germination rate and uniformity of germination. Seeds were placed to germinate under three light conditions: constant red light, constant darkness and 12 h white light photoperiod. We observed inhibition by KAR under light in some species, which may have ecological implications. The results showed that no single treatment increased the germination of all the tested species, rather a wide variation of responsiveness of the different species to the three compounds was found. Additionally, no interaction was found between responsiveness to compounds and ecological niche. However, species in the same ecological niche and dormancy class showed a similar responsiveness to light. Species that share a similar environment have similar light requirements for germination, while differences exist among species in their responsiveness to other germination cues.

A role for fruit structure in seed survival and germination of Swartzia langsdorffii Raddi beyond dispersal.

Diaspore structure has been hypothesised to play a role in seed viability and/or germination of recalcitrant seeds, especially for Swartzia langsdorffii. Thus, this work aims to (i) investigate the in situ contribution of pericarp and aril on seed viability and germination, and (ii) identify morphoanatomical traits of S. langsdorffii diaspores that allow its desiccation-sensitive seeds to remain viable. The role of the pericarp and aril in seed survival and germination was investigated by placing the whole fruit, whole seeds (arillate seed) and bare seeds (without aril) in soil in the forest understorey, assessing germination, emergence, dead, firm and predated seeds, and water content of pericarps, arils and seeds. Correlation analysis was performed between environmental variables and physiological parameters. Histochemical features of diaspores were also investigated. Pericarp water content fell after several months, while the aril maintained its water content. Seeds did not lose water even without the presence of the pericarp and aril. However, presence of the pericarp promoted seed water content, viability and germination long after dispersal. The embryo had a thickened outer periclinal cell wall. Pericarp and aril are not essential to prevent water loss in seeds, but do help to retain seed moisture, favouring viability maintenance and promoting germination during the rainy season. Morphoanatomical features of seeds are suggested as main factors that reduce water loss. Survival of these desiccation-sensitive seeds upon dispersal during the dry season appears to be facilitated by multiple diaspore features that prevent viability loss.

Seedling survival of Handroanthus impetiginosus (Mart ex DC) Mattos in a semi-arid environment through modified germination speed and post-germination desiccation tolerance.

Uniform rapid seed germination generally forms a great risk for the plant population if subsequent intermittent precipitation causes desiccation and seedling death. Handroanthus impetiginosus can be found commonly in a wide range of biomes within Brazil including those that are semi-arid. Germination and early growth was studied to understand how germinated seeds survive under these stringent conditions. Accessions were sampled from four seasonally dry biomes in Brazil. Precipitation at the start of the rainy season in the Caatinga, a semi-arid biome, is less predictable and the number of successive dry days per dry interval in the first four months of the rainy season was higher than in the other studied biomes. Plants from the Caatinga produced thicker seeds and this trait concurred with slow germination and stronger osmotic inhibition of germination across the accessions, forming a stress avoidance mechanism in the Caatinga. Post-germination desiccation tolerance was high in the Caatinga accession, could be re-induced in accessions from biomes with more regular precipitation (Cerrado and transition zone), but remained poor in the Cerradão accession; thus forming a stress tolerance mechanism. Production of adventitious roots ascertained survival of all tested individuals from all four locations, even if protruded radicles did not survive desiccation, forming an additional stress tolerance mechanism. A sequence of stress avoidance and stress tolerance mechanisms in seeds and germinated seeds was associated with precipitation patterns in different biomes. These mechanisms purportedly allow rapid seedling establishment when conditions are suitable and enable survival of the young seedling when conditions are adverse.

Seedling survival of Handroanthus impetiginosus (Mart ex DC) Mattos in a semi-arid environment through modified germination speed and post-germination desiccation tolerance / Sobrevivência de plântulas de Handroanthus impetiginosus (Mart ex DC) Mattos em ambiente semi-árido ocorre por modificação da velocidade de germinação e da tolerância à dessecação pós germinação

Abstract Uniform rapid seed germination generally forms a great risk for the plant population if subsequent intermittent precipitation causes desiccation and seedling death. Handroanthus impetiginosus can be found commonly in a wide range of biomes within Brazil including those that are semi-arid. Germination and early growth was studied to understand how germinated seeds survive under these stringent conditions. Accessions were sampled from four seasonally dry biomes in Brazil. Precipitation at the start of the rainy season in the Caatinga, a semi-arid biome, is less predictable and the number of successive dry days per dry interval in the first four months of the rainy season was higher than in the other studied biomes. Plants from the Caatinga produced thicker seeds and this trait concurred with slow germination and stronger osmotic inhibition of germination across the accessions, forming a stress avoidance mechanism in the Caatinga. Post-germination desiccation tolerance was high in the Caatinga accession, could be re-induced in accessions from biomes with more regular precipitation (Cerrado and transition zone), but remained poor in the Cerradão accession; thus forming a stress tolerance mechanism. Production of adventitious roots ascertained survival of all tested individuals from all four locations, even if protruded radicles did not survive desiccation, forming an additional stress tolerance mechanism. A sequence of stress avoidance and stress tolerance mechanisms in seeds and germinated seeds was associated with precipitation patterns in different biomes. These mechanisms purportedly allow rapid seedling establishment when conditions are suitable and enable survival of the young seedling when conditions are adverse.

Resumo A germinação rápida e uniforme geralmente pode apresentar riscos para a população de plantas caso a precipitação ocorra de maneira intermitente, provocando seca e morte das plântulas. Handroanthus impetiginosus pode ser encontrado em uma grande variedade de biomas no Brasil. A germinação e o crescimento inicial das plântulas de Handroanthus impetiginosus foram estudadas para compreender como as sementes germinadas sobrevivem nestas condições. Acessos de quatro biomas que apresentam secas sazonais foram amostrados. A precipitação, no início da estação chuvosa na Caatinga, um bioma semi-árido, é menos previsível e o número de dias secos consecutivos por intervalo de seca, nos primeiros quatro meses da estação chuvosa, foi maior do que nos outros biomas estudados. Plantas do bioma Caatinga produzem sementes mais espessas e essa característica está associada com uma germinação lenta e com a inibição osmótica maior da germinação através dos acessos, formando um mecanismo para evitar o estresse. Tolerância à dessecação em sementes germinadas foi superior no bioma Caatinga e que podem ser reinduzida em acesso com uma precipitação mais regular (Cerrado e na zona de transição), mas manteve-se baixa no acesso Cerradão, formando assim um mecanismo para evitar o estresse. Produção de raízes adventícias foi observada nos indivíduos estudados de todos os quatro biomas, mesmo quando as raízes primárias não sobreviveram à dessecação, formando um mecanismo adicional de tolerância ao estresse. Assim, foi observado estratégias para evitar o estresse e mecanismos de tolerância ao estresse em sementes e sementes germinadas associada com padrões de precipitação nos diferentes biomas estudados. Estes mecanismos podem favorecer o estabelecimento das plântulas de forma rápida quando as condições são adequadas e permitirem a sobrevivência de plântulas quando as condições são adversas.

The second step of the biphasic endosperm cap weakening that mediates tomato (Lycopersicon esculentum) seed germination is under control of ABA.

The role of abscisic acid (ABA) in the weakening of the endosperm cap prior to radicle protrusion in tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seeds was studied. The endosperm cap weakened substantially in both water and ABA during the first 38 h of imbibition. After 38 h the force required for endosperm cap puncturing was arrested at 0.35 N in ABA, whereas in water a further decrease occurred until the radicle protruded. During the first 2 d of imbibition endo-beta-mannanase activity was correlated with the decrease in required puncture force and with the appearance of ice-crystal-induced porosity in the cell walls as observed by scanning electron microscopy. Prolonged incubation in ABA resulted in the loss of endo-beta-mannanase activity and the loss of ice-crystal-induced porosity, but not in a reversion of the required puncture force. ABA also had a distinct but minor effect on the growth potential of the embryo. However, endosperm cap resistance played the limiting role in the completion of germination. It was concluded that (a) endosperm cap weakening is a biphasic process and (b) inhibition of germination by ABA is through the second step in the endosperm cap weakening process.