PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-4 (4)
 

Clipboard (0)
None
Journals
Authors
more »
Year of Publication
Document Types
1.  Sympatric species of Hibbertia (Dilleniaceae) vary in dormancy break and germination requirements: implications for classifying morphophysiological dormancy in Mediterranean biomes 
Annals of Botany  2012;109(6):1111-1123.
Background and Aims
Several ecologically important plant families in Mediterranean biomes have seeds with morphophysiological dormancy (MPD) but have been poorly studied. The aim of this study was to understand the seed ecology of these species by focusing on the prominent, yet intractably dormant Australian genus Hibbertia. It was hypothesized that the slow germination in species of this genus is caused by a requirement for embryo growth inside the seed before germination, and that initiation of embryo growth is reliant upon a complex sequence of environmental cues including seasonal fluctuations in temperature and moisture, and an interplay with light and smoke. Using the results, the classification of the MPD level in species of Hibbertia is considered.
Methods
Four species of Hibbertia in winter rainfall south-western Australia were selected. These species, whilst differing in geographic distributions, are variously sympatric, and all are important understorey components of plant communities. The following aspects related to dormancy break, embryo growth and germination were investigated: temperature and moisture requirements; effects of karrikinolide, gibberellic acid and aerosol smoke; and phenology.
Key Results
Following exposure to wet/dry cycles at low or high temperatures, embryo growth and germination occurred, albeit slowly in all species at low temperatures when moisture was unlimited, corresponding to winter in south-west Australia. Photo regime influenced germination only in H. racemosa. Aerosol smoke triggered substantial germination during the 1st germination season in H. huegelii and H. hypericoides.
Conclusions
Although the study species are con-generic, sympatric and produce seeds of identical morphology, they possessed different dormancy-break and germination requirements. The physiological component of MPD was non-deep in H. racemosa but varied in the other three species where more deeply dormant seeds required >1 summer to overcome dormancy and, thus, germination was spread over time. Embryos grew during winter, but future studies need to resolve the role of cold versus warm stratification by using constant temperature regimes. To include Mediterranean species with MPD, some modifications to the current seed-dormancy classification system may need consideration: (a) wet/dry conditions for warm stratification and (b) a relatively long period for warm stratification. These outcomes have important implications for improving experimental approaches to resolve the effective use of broadcast seed for ecological restoration.
doi:10.1093/aob/mcs034
PMCID: PMC3336950  PMID: 22362661
Framework species; germination phenology; Hibbertia; karrikinolide; Mediterranean biome; morphophysiological dormancy; restoration; seeds; smoke; underdeveloped embryos
2.  Seeds of Brassicaceae weeds have an inherent or inducible response to the germination stimulant karrikinolide 
Annals of Botany  2011;108(5):933-944.
Background and Aims
Karrikinolide (KAR1) is a smoke-derived chemical that can trigger seeds to germinate. A potential application for KAR1 is for synchronizing the germination of weed seeds, thereby enhancing the efficiency of weed control efforts. Yet not all species germinate readily with KAR1, and it is not known whether seemingly non-responsive species can be induced to respond. Here a major agronomic weed family, the Brassicaceae, is used to test the hypothesis that a stimulatory response to KAR1 may be present in physiologically dormant seeds but may not be expressed under all circumstances.
Methods
Seeds of eight Brassicaceae weed species (Brassica tournefortii, Raphanus raphanistrum, Sisymbrium orientale, S. erysimoides, Rapistrum rugosum, Lepidium africanum, Heliophila pusilla and Carrichtera annua) were tested for their response to 1 µm KAR1 when freshly collected and following simulated and natural dormancy alleviation, which included wet–dry cycling, dry after-ripening, cold and warm stratification and a 2 year seed burial trial.
Key Results
Seven of the eight Brassicaceae species tested were stimulated to germinate with KAR1 when the seeds were fresh, and the remaining species became responsive to KAR1 following wet–dry cycling and dry after-ripening. Light influenced the germination response of seeds to KAR1, with the majority of species germinating better in darkness. Germination with and without KAR1 fluctuated seasonally throughout the seed burial trial.
Conclusions
KAR1 responses are more complex than simply stating whether a species is responsive or non-responsive; light and temperature conditions, dormancy state and seed lot all influence the sensitivity of seeds to KAR1, and a response to KAR1 can be induced. Three response types for generalizing KAR1 responses are proposed, namely inherent, inducible and undetected. Given that responses to KAR1 were either inherent or inducible in all 15 seed lots included in this study, the Brassicaceae may be an ideal target for future application of KAR1 in weed management.
doi:10.1093/aob/mcr198
PMCID: PMC3177676  PMID: 21821831
Brassicaceae; butenolide; germination; karrikinolide; karrikins; KAR1; physiological dormancy; seed dormancy; weeds
3.  Prior hydration of Brassica tournefortii seeds reduces the stimulatory effect of karrikinolide on germination and increases seed sensitivity to abscisic acid 
Annals of Botany  2010;105(6):1063-1070.
Background and Aims
The smoke-derived compound karrikinolide (KAR1) shows significant potential as a trigger for the synchronous germination of seeds in a variety of plant-management contexts, from weed seeds in paddocks, to native seeds when restoring degraded lands. Understanding how KAR1 interacts with seed physiology is a necessary precursor to the development of the compound as an efficient and effective management tool. This study tested the ability of KAR1 to stimulate germination of seeds of the global agronomic weed Brassica tournefortii, at different hydration states, to gain insight into how the timing of KAR1 applications in the field should be managed relative to rain events.
Methods
Seeds of B. tournefortii were brought to five different hydration states [equilibrated at 15 % relative humidity (RH), 47 % RH, 96 % RH, fully imbibed, or re-dried to 15 % RH following maximum imbibition] then exposed to 1 nm or 1 µm KAR1 for one of five durations (3 min, 1 h, 24 h, 14 d or no exposure).
Key Results
Dry seeds with no history of imbibition were the most sensitive to KAR1; sensitivity was lower in seeds that were fully imbibed or fully imbibed then re-dried. In addition, reduced sensitivity to KAR1 was associated with an increased sensitivity to exogenously applied abscisic acid (ABA).
Conclusions
Seed water content and history of imbibition were found to significantly influence whether seeds germinate in response to KAR1. To optimize the germination response of seeds, KAR1 should be applied to dry seeds, when sensitivity to ABA is minimized.
doi:10.1093/aob/mcq061
PMCID: PMC2876004  PMID: 20348089
Karrikinolide; karrikins; butenolide; smoke; germination stimulant; seed water content; abscisic acid; ABA; gibberellin; weed; Brassica tournefortii
4.  A new type of specialized morphophysiological dormancy and seed storage behaviour in Hydatellaceae, an early-divergent angiosperm family 
Annals of Botany  2010;105(6):1053-1061.
Background and Aims
Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution.
Methods
Seed germination experiments were completed on three species of south-west Australian Hydatellaceae, Trithuria austinensis, T. bibracteata and T. submersa, to test the effects of temperature, light, germination stimulant and storage. Seeds were sectioned to examine embryo growth during germination in T. austinensis and T. submersa.
Key Results
Some embryo growth and cell division in T. austinensis and T. submersa occurred prior to the emergence of an undifferentiated embryo from the seed coat (‘germination’). Embryo differentiation occurred later, following further growth and a 3- to 4-fold increase in the number of cells. The time taken to achieve 50 % of maximum germination for seeds on water agar was 50, 35 and 37 d for T. austinensis, T bibracteata and T. submersa, respectively.
Conclusions
Seeds of Hydatellaceae have a new kind of specialized morphophysiological dormancy in which neither root nor shoot differentiates until after the embryo emerges from the seed coat. Seed biology is discussed in relation to early angiosperm evolution, together with ex situ conservation of this phylogenetically significant group.
doi:10.1093/aob/mcq062
PMCID: PMC2876005  PMID: 20338953
Hydatellaceae; morphophysiological dormancy; embryo; desiccation; seed; evolution; Trithuria submersa; Trithuria austinensis; Trithuria bibracteata

Results 1-4 (4)