Kathryn J. Steadman

Maturation temperature and rainfall influence seed dormancy characteristics of annual ryegrass (Lolium rigidum)

The role of temperature and rainfall during seed development in modulating subsequent seed dormancy status was studied for Lolium rigidum Gaud. (annual ryegrass). Climatic parameters relating to geographic origin were compared with annual ryegrass seed dormancy characteristics for seeds collected from 12 sites across the southern Western Australian cropping region. Seed germination was tested soon after collection and periodically during subsequent after-ripening. Temperature in the year of seed development and long-term rainfall patterns showed correlations with aspects of seed dormancy, particularly the proportion of seeds remaining dormant following 5 months of after-ripening. Consequently, for one population the temperature (warm/cool) and water supply (adequate/reduced) during seed development were manipulated to investigate the role of maternal environment in the quantity and dormancy characteristics of seeds produced. Seeds from plants grown at warm temperatures were fewer in number, weighed less, and were less dormant than those from plants grown at cool temperature. Seeds that developed under both cool temperature and reduced moisture conditions lost dormancy faster than seeds from well-watered plants. Seed maturation environment, particularly temperature, can have a significant effect on annual ryegrass seed numbers and seed dormancy characteristics.

Dormancy release in Lolium rigidum seeds is a function of thermal after-ripening time and seed water content

Dormancy release in seeds of Lolium rigidum Gaud. (annual ryegrass) was investigated in relation to temperature and seed water content. Freshly matured seeds were collected from cropping fields at Wongan Hills and Merredin, Western Australia. Seeds from Wongan Hills were equilibrated to water contents between 6 and 18% dry weight and after-ripened at constant temperatures between 9 and 50°C for up to 23 weeks. Wongan Hills and Merredin seeds at water contents between 7 and 17% were also after-ripened in full sun or shade conditions. Dormancy was tested at regular intervals during after-ripening by germinating seeds on agar at 12-h alternating 15°C (dark) and 25°C (light) periods.Rate of dormancy release for Wongan Hills seeds was a positive linear function of after-ripening temperature above a base temperature (Tb) of 5.4°C. A thermal after-ripening time model for dormancy loss accounting for seed moisture in the range 6-18% was developed using germination data for Wongan Hills seeds after-ripened at constant temperatures. The model accurately predicted dormancy release for Wongan Hills seeds after-ripened under naturally fluctuating temperatures. Seeds from Merredin responded similarly but had lower dormancy at collection and a faster rate of dormancy release in seeds below 9% water content.

Seed Persistence in the Field May Be Predicted by Laboratory-Controlled Aging

Abstract Weed management is complicated by the presence of soil seed banks. The complexity of soil–seed interactions means that seed persistence in the field is often difficult to measure, let alone predict. Field trials, although accurate in their context, are time-consuming and expensive to conduct for individual species. Some ex situ techniques for estimating seed life expectancy have been proposed, but these fail to simulate the environmental complexity of the field. Also, it has been questioned whether techniques such as the controlled aging test (CAT) are useful indicators of field persistence. This study aimed to test the validity of the standard CAT (seed aging at 45 C and 60% relative humidity) in use at the Royal Botanic Gardens, Kew, U.K., for predicting field seed-persistence. Comparison of seed persistence and CAT data for 27 northwest European species suggested a significant positive correlation of 0.31. Subsequently, 13 species of emerging and common weeds of Queensland were assessed for their seed longevity using the CAT. The seed longevity data of these species in the CAT were linked with field seed-persistence data according to three broad seed-persistence categories: < 1 yr, 1 to 3 yr, and > 3 yr. We discuss the scope for using the CAT as a tool for rapid assignment of species to these categories. There is a need for further studies that compare predictions of seed persistence based on the CAT with seed persistence in the field for a larger range of species and environments.

Dormancy release in Australian fire ephemeral seeds during burial increases germination response to smoke water or heat

Fire ephemerals are short-lived plants that primarily germinate after fire. Fresh and laboratory-stored seeds are difficult to germinate ex situ, even in response to fire-related cues such as heat and smoke. Seeds of eight Australian fire ephemeral species were buried in unburnt and recently burnt sites of natural bushland during autumn. Seeds were exhumed after 6 and 12 months and incubated in water and smoke water, either with or without a heat treatment at 70 degrees C for 1 h. Generally, germination did not increase after 6 months of burial, but after 12 months of burial germination was enhanced in seven of the eight species. Actinotus leucocephalus produced higher germination following 12 months of burial without any further treatment, and smoke water and heat further improved germination. The four Gyrostemonaceae species, Codonocarpus cotinifolius, Gyrostemon racemiger, Gyrostemon ramulosus and Tersonia cyathiflora, only germinated in the presence of smoke water, and their germination was enhanced by burial. Burial improved germination in response to a heat treatment in Grevillea scapigera and Alyogyne huegelii seeds, but did not enhance Alyogyne hakeifolia germination. During concurrent dry laboratory storage of seeds at 15 degrees C, only Actinotus leucocephalus produced increased germination in response to smoke water and heat over time. In summary, soil burial can alter the dormancy status of a number of Australian fire ephemeral seeds, rendering them more responsive to germination cues such as smoke water and heat. The requirement for a period of burial before seeds become responsive to smoke and/or heat would ensure that seeds persist in the soil until a subsequent fire, when there is an increase in nutrients available for growth and reduced competition from other plants.

Soil warming increases plant species richness but decreases germination from the alpine soil seed bank

Global warming is occurring more rapidly above the treeline than at lower elevations and alpine areas are predicted to experience above average warming in the future. Temperature is a primary factor in stimulating seed germination and regulating changes in seed dormancy status. Thus, plant regeneration from seed will be crucial to the persistence, migration and post disturbance recruitment of alpine plants in future climates. Here, we present the first assessment of the impact of soil warming on germination from the persistent alpine soil seed bank. Contrary to expectations, soil warming lead to reduced overall germination from the soil seed bank. However, germination response to soil temperature was species specific such that total species richness actually increased by nine with soil warming. We further explored the system by assessing the prevalence of seed dormancy and germination response to soil disturbance, the frequency of which is predicted to increase under climate change. Seeds of a significant proportion of species demonstrated physiological dormancy mechanisms and germination of several species appeared to be intrinsically linked to soil disturbance. In addition, we found no evidence of subalpine species and little evidence of exotic weed species in the soil, suggesting that the soil seed bank will not facilitate their invasion of the alpine zone. In conclusion, changes in recruitment via the alpine soil seed bank can be expected under climate change, as a result of altered dormancy alleviation and germination cues. Furthermore, the alpine soil seed bank, and the species richness therein, has the potential to help maintain local species diversity, support species range shift and moderate species dominance. Implications for alpine management and areas for further study are also discussed.

Native and β-cyclodextrin-enclosed curcumin: entrapment within liposomes and their in vitro cytotoxicity in lung and colon cancer.

With a view to improving the solubility and delivery characteristics of poorly water-soluble drugs, we prepared β-cyclodextrin-curcumin (βCD-C) inclusion complexes (hydrophilic curcumin) and entrapped both native curcumin (hydrophobic) and the complexes separately into liposomes; these were then assessed for in vitro cytotoxicity in lung and colon cancer cell lines. Optimization of curcumin entrapment within βCD was achieved, with the resultant βCD-C complexes prepared by methanol reflux. Inclusion complexes were confirmed using UV spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction. The water solubility of βCD-C complexes improved markedly (c.f. native curcumin) and successful entrapment of complexes into liposomes, prepared using a thin-film hydration approach, was also achieved. All the liposomal formulations were characterized for curcumin and βCD-C complex entrapment efficiency, particle size, polydispersity and stability at 2–8°C. Curcumin, βCD-C complex and their optimized liposomal formulations were evaluated for anticancer activity in lung (A-459) and colon (SW-620) cancer cell lines. All curcumin-containing formulations tested were effective in inhibiting cell proliferation, as determined via an MTT assay. The median effective dose (EC50) for all curcumin formulations was found to be in the low µM range for both lung and colon cancer cell lines tested. Our results confirm that βCD inclusion complexes of poorly water soluble drugs, such as curcumin can be entrapped within biocompatible vesicles such as liposomes, and this does not preclude their anticancer activity.

Pre- and Post-harvest Influences on Seed Dormancy Status of an Australian Goodeniaceae species, Goodenia fascicularis

BACKGROUND AND AIMS The period during which seeds develop on the parent plant has been found to affect many seed characteristics, including dormancy, through interactions with the environment. Goodenia fascicularis (Goodeniaceae) seeds were used to investigate whether seeds of an Australian native forb, harvested from different environments and produced at different stages of the reproductive period, differ in dormancy status. METHODS During the reproductive phase, plants were grown ex situ in warm (39/21 degrees C) or cool (26/13 degrees C) conditions, with adequate or limited water availability. The physiological dormancy of resulting seeds was measured in terms of the germination response to warm stratification (34/20 degrees C, 100 % RH, darkness). KEY RESULTS Plants in the cool environment were tall and had high above-ground biomass, yet yielded fewer seeds over a shorter, later harvest period when compared with plants in the warm environment. Seeds from the cool environment also had higher viability and greater mass, despite a significant proportion (7 % from the cool-wet environment) containing no obvious embryo. In the warm environment, the reproductive phase was accelerated and plants produced more seeds despite being shorter and having lower above-ground biomass than those in the cool environment. Ten weeks of warm stratification alleviated physiological dormancy in seeds from all treatments resulting in 80-100 % germination. Seeds that developed at warm temperatures were less dormant (i.e. germination percentages were higher) than seeds from the cool environment. Water availability had less effect on plant and seed traits than air temperature, although plants with reduced soil moisture were shorter, had lower biomass and produced fewer, less dormant seeds than plants watered regularly. CONCLUSIONS Goodenia fascicularis seeds are likely to exhibit physiological dormancy regardless of the maternal environment. However, seeds collected from warm, dry environments are likely to be more responsive to warm stratification than seeds from cooler, wetter environments.

Late-season non-selective herbicide application reduces Lolium rigidum seed numbers, seed viability, and seedling fitness

Experiments were conducted to investigate the effect of Lolium rigidum (annual ryegrass) seed developmental stage and application rate of glyphosate and SpraySeed (paraquat 135 g/L + diquat 115 g/L) on the number, germinability, and fitness of seeds produced. Glyphosate (450 g/L) was most effective when applied at a rate of 0.5-1 L/ha during heading and anthesis, reducing the number of filled seeds produced compared with unsprayed plants. Application post-anthesis, when seeds were at the milk to soft dough stage, was less effective. SpraySeed was most effective when applied post-anthesis, during the milk and early dough stages of seed development at a rate of 0.5-1 L/ha, resulting in the production of few viable seeds. Although some filled seeds were produced, most of the seeds were dead. Application during anthesis or once the seeds reached soft dough stage was less effective. For both herbicides, those seeds that were capable of germinating were smaller and had slower radicle and coleoptile growth, resulting in slower early seedling growth and reduced biomass production within the first month of growth. Additionally, glyphosate application reduced the proportion of seeds exhibiting dormancy. The anticipated reduction in seed competitive ability and altered emergence timing resulting from late-season herbicide application, even when application timing is not optimal, could be exploited to reduce the likelihood of successful L. rigidum establishment in the following season.

Green and blue light photoreceptors are involved in maintenance of dormancy in imbibed annual ryegrass (Lolium rigidum) seeds

Light plays an important role in two separate processes within the seeds of Lolium rigidum (annual ryegrass). Dormant seeds of L. rigidum remain dormant when imbibed in the light, but once seeds have lost dormancy through dark-stratification, light stimulates their germination. This study characterizes the light qualities and quantities which are effective in maintenance of dormancy. Dormant seeds were stratified under narrow- and broad-waveband light to identify the potential photoreceptors involved in dormancy maintenance, and to determine whether dark-induced dormancy loss is reversible by light. Blue and green light both mediated dormancy maintenance in a far-red-independent manner. Red light resulted in dormancy maintenance only when far-red wavelengths were excluded, suggesting a redundant function of phytochrome. At low fluence rates, white light was more effective than monochromatic light, suggesting the action of multiple photoreceptors in dormancy maintenance. By contrast, nondormant seeds did not germinate unless provided with red light. These results indicate that seed dormancy maintenance is potentially mediated through the actions of blue and green light photoreceptors. Seed dormancy could thus be added to the growing list of plant responses that may be mediated by green light in a cryptochrome-independent manner.

Molecular structure of fagopyritol A1 (O-α-d-galactopyranosyl-(1→3)-d-chiro-inositol) by NMR

The molecular structure of fagopyritol A1, a novel galactopyranosyl cyclitol from buckwheat seeds, was determined to be O-alpha-D-galactopyranosyl-(1 --> 3)-D-chiro-inositol by 1H and 13C NMR. Fagopyritol A1 is a positional isomer of fagopyritol B1 (O-alpha-D-galactopyranosyl-(1 --> 2)-D-chiro-inositol), representing a different series of fagopyritol oligomers. Trimethylsilyl derivatives of both compounds have similar mass spectra, but each may be identified by different abundance ratios of fragments with m/z 305/318 and 318/319.