The effect of salinity on aspects of the early development of the kelp species Undaria pinnatifida and Saccorhiza polyschides

It is likely that the introduction of the brown macroalga Undaria pinnatfida from the Pacific into the North Atlantic will impact competitively on the native species Saccorhiza polyschides; both are large kelps occupying the same subtidal zone with very similar life histories. The present study examines their tolerance to changes in salinity, under laboratory conditions, in order to provide a better understanding of their respective competitiveness in an estuarine environment. Experiments were carried out over a full range of salinity values, from 35 to 0, with respect to zoospore settlement and attachment, germination, post-germination progression to form gametophytes, gametophyte sex ratio, sporophyte production and blade length. Undaria zoospores settled and attached over the salinity range from 35 to 14 and germinated between 35 and 3.5. Post-germination progression occurred over the range from 35 to 14 whilst only small differences in the male/female ratio were recorded. Sporophyte blade production and development occurred over the range from 35 to 17.5 and peak production and longest blade length was recorded at 21. Saccorhiza zoospores settled and attached at and above 24.5 and germinated between 35 and 21. Sporophyte production and blade development occurred over the range from 35 to 24.5. In general, Undaria was shown to be much more tolerant of reductions in salinity compared to Saccorhiza and is more likely to penetrate further into estuarine environments.

PpGRAS12 acts as a positive regulator of meristem formation in Physcomitrium patens

Key message This study focused on the key regulatory function of Physcomitrium patens GRAS12 gene underlying an increasing plant complexity, an important step in plant terrestrialization and the evolutionary history of life. Abstract The miR171‐GRAS module has been identified as a key player in meristem maintenance in angiosperms. PpGRAS12 is a member of the GRAS family and a validated target for miR171 in Physcomitrium (Physcomitrella) patens. Here we show a regulatory function of miR171 at the gametophytic vegetative growth stage and targeted deletion of the PpGRAS12 gene adversely affects sporophyte production since fewer sporophytes were produced in ΔPpGRAS12 knockout lines compared to wild type moss. Furthermore, highly specific and distinct growth arrests were observed in inducible PpGRAS12 overexpression lines at the protonema stage. Prominent phenotypic aberrations including the formation of multiple apical meristems at the gametophytic vegetative stage in response to elevated PpGRAS12 transcript levels were discovered via scanning electron microscopy. The production of multiple buds in the PpGRAS12 overexpression lines similar to ΔPpCLV1a/1b disruption mutants is accompanied by an upregulation of PpCLE and downregulation of PpCLV1, PpAPB, PpNOG1, PpDEK1, PpRPK2 suggesting that PpGRAS12 acts upstream of these genes and negatively regulates the proposed pathway to specify simplex meristem formation. As CLV signaling pathway components are not present in the chlorophytic or charophytic algae and arose with the earliest land plants, we identified a key regulatory function of PpGRAS12 underlying an increasing plant complexity, an important step in plant terrestrialization and the evolutionary history of life.

A Small Number of Gametophytes with Gametangia and Stunted Sporophytes of Antrophyum obovatum Baker (Pteridaceae): The Suppression of Functional Sporophyte Production by Prezygotic and Postzygotic Sterility

Ferns have conspicuous sporophytes as the dominant phase in their life cycle; however, the gametophytes are completely separated from the sporophytes and supply their own nutrition, unlike in bryophytes and seed plants. Among the gametophytes, some maintain their populations in the gametophyte phase without progressing to sporophyte production and are known as independent gametophytes. Independent gametophytes of Antrophyum obovatum Baker were recently reported in one population on Jeju Island, Korea. In the present study, we surveyed more places to find new independent gametophyte populations of A. obovatum using the rbcL gene sequence-based DNA barcoding technique. We identified two new sites inhabited by independent gametophytes. Archegonia and juvenile sporophytes were independently observed in each location under slightly different environmental conditions. Consequently, in the case of this species, functional sporophyte production is likely suppressed by prezygotic and postzygotic sterility, depending on microenvironmental factors.

Episodic but ample sporophyte production in the moss Drepanocladus turgescens (Bryophyta: Amblystegiaceae) in SE Sweden

In the Baltic area, the long-lived dioicous wetland moss Drepanocladus turgescens (T.Jensen) Broth. produces sporophytes rarely and at irregular intervals. Based on surveys of sporophyte occurrences at 13 sites in two regions in northern Gotland (Sweden) during three to five years, we ask: (1) Is sporophyte formation associated with precipitation and a precipitation index that considers the dry periods during July-August of the preceding year, when gametangia are formed and fertilization occurs? (2) Does the estimated spore output suffice for the species’ long-term persistence of the (Northern) European population species? In one of the study regions, where D. turgescens occurs in depressions, sporophyte formation was associated with the two precipitation parameters. In the other study region, with relatively higher precipitation and exposed occurrences on a slightly sloping bedrock with very little accumulated soil, no such association existed. We suggest that this lack of weather effects results from that the exposed rock habitat requires longer continuously wet periods than the depression habitat to allow for gametangia initiation and development, and fertilisation. Average spore production for six spore capsules, from three Gotland localities was 181,000. Based on the sporophyte counts during the survey years, we estimated the total reproductive output as 411.5 million spores in 2013, and 42.5 million in 2015, in the two respective study regions. Taken together with data on haplotype patterns and considering observations on recent colonisations, we argue that such a relatively low and episodic regional spore production is sufficient to maintain global populations of long-lived species, even if these occur in specialized and geographically restricted habitats.

Low reproductive success of hay-scented fern (Dennstaedtia punctilobula) regardless of inbreeding level or time since disturbance

Self-fertilization can facilitate the colonization of new habitats because it allows a single individual to found a population. Here we investigated the relationship between mating systems and colonization in hay-scented fern (Dennstaedtia punctilobula (Michx.) T.Moore). Throughout eastern North America, this species has been called a “native invasive” for its tendency to dominate forest understories disturbed by logging, inhibiting tree regeneration. Thus, it is important to understand the mechanisms of its spread. We hypothesized that if populations were founded through selfing, then populations disturbed more recently would retain higher selfing ability; this pattern would demonstrate an important link between mating systems and colonization. For four populations logged at different times in the past, we compared the sporophyte production of gametophytes at different levels of inbreeding (intragametophytic selfing, intergametophytic selfing, and outcrossing) using laboratory crosses. Across all treatments, only 9.8% of gametophytes formed sporophytes (N = 400 gametophytes). Neither inbreeding level nor time since disturbance affected sporophyte production. Selfing ability did not differ across populations logged at different times; there was no interaction between inbreeding level and time since disturbance. The low reproductive success of D. punctilobula, regardless of inbreeding level or time since disturbance, suggests that population establishment and expansion via sexual reproduction may be relatively rare in this clonal species.