Interaction between sugar and abscisic acid signalling during early seedling development in Arabidopsis

Sugars regulate important processes and affect the expression of many genes in plants. Characterization of Arabidopsis (Arabidopsis thaliana) mutants with altered sugar sensitivity revealed the function of abscisic acid (ABA) signalling in sugar responses. However, the exact interaction between sugar signalling and ABA is obscure. Therefore ABA deficient plants with constitutive ABI4 expression (aba2-1/35S::ABI4) were generated. Enhanced ABI4 expression did not rescue the glucose insensitive (gin) phenotype of aba2 seedlings indicating that other ABA regulated factors are essential as well. Interestingly, both glucose and ABA treatment of Arabidopsis seeds trigger a post-germination seedling developmental arrest. The glucose-arrested seedlings had a drought tolerant phenotype and showed glucose-induced expression of ABSCISIC ACID INSENSITIVE3 (ABI3), ABI5 and LATE EMBRYOGENESIS ABUNDANT (LEA) genes reminiscent of ABA signalling during early seedling development. ABI3 is a key regulator of the ABA-induced arrest and it is shown here that ABI3 functions in glucose signalling as well. Multiple abi3 alleles have a glucose insensitive (gin) phenotype comparable to that of other known gin mutants. Importantly, glucose-regulated gene expression is disturbed in the abi3 background. Moreover, abi3 was insensitive to sugars during germination and showed sugar insensitive (sis) and sucrose uncoupled (sun) phenotypes. Mutant analysis further identified the ABA response pathway genes ENHANCED RESPONSE TO ABA1 (ERA1) and ABI2 as intermediates in glucose signalling. Hence, three previously unidentified sugar signalling genes have been identified, showing that ABA and glucose signalling overlap to a larger extend than originally thought. Bas J. W. Dekkers and Jolanda A. M. J. Schuurmans contributed equally to this paper.     

Shoot regeneration and the relationship between organogenic capacity and endogenous hormonal contents in pumpkin

To induce multiple shoots from pumpkin (Cucurbita moschata Duch.), cotyledon explants excised from various ages of seedlings after in vitro germination were cultured on MS augmented with different concentrations of BA (0, 0.5, 1.0 or 2.0 mg l⁻¹). The highest frequency of shoot regeneration (63.7%) was observed from seven-day-old cotyledon explants cultured on MS containing 0.5 mg l⁻¹ BA. The frequency and duration of shoot formation showed close correlation with the donor seedling age. By contrast, BA supply was necessary to promote shoot formation but no differences were observed in relation to different concentrations. Multiple shoots elongated on MS supplemented with 0.1 mg l⁻¹ BA and 5–7 shoots per regenerated explant were recovered. Elongated shoots were rooted on MS, which was easier than that on 2/3MS, 1/2MS, or MS supplemented with 0.1 mg l⁻¹ NAA. The rooted shoots were then transferred to greenhouse where they grew and flowered normally. Quantitative analysis of endogenous auxin (IAA) and cytokinins (iPA and ZR) in initial cotyledon explants of different aged seedlings showed that the regeneration ability of cotyledon explants varied dependently on their endogenous iPA contents. This study therefore deduces that the various organogenic capabilities of cotyledon explants from pumpkin are the result of their endogenous hormonal contents.     

A comparative analysis of seed and cone characteristics and seed-dispersal strategies of three pines in the subsection Sabinianae

The seed-dispersal systems of Coulter pine (Pinus coulteri), gray pine (P. sabiniana), and Torrey pine (P. torreyana), all of the subsection Sabinianae, are not well understood. These pines occur in arid and semi-arid foothills and mountains of California that are subjected to frequent fires. Cone and seed traits of these three California pines are compared to those of four species of pines (sugar pine, P. lambertiana; Jeffrey pine, P. jeffreyi; ponderosa pine, P. ponderosa; and lodgepole pine, P. contorta) that occur in more mesic environments in the nearby Sierra Nevada mountains. The cones of the Sabinianae pines are large with thick, dense scales, and the scales of gray and Coulter pines are armed with sharp, recurved spines. The seeds of all three species are large, and those of gray and Torrey pines are nearly wingless. In contrast, the Sierra Nevada pines have small to medium-sized seeds with large wings that are initially dispersed by the wind. Heavy wing loading of the Sabinianae pine seeds causes them to fall rapidly, and they are not dispersed far by wind. However, animals remove the fallen seeds rapidly, and rodents and jays scatter hoarded many seeds in the soil. This caching activity results in seedling establishment. The unusual morphology of the cones and seeds of the Sabinianae pines is interpreted as a combination of traits that attract animal dispersers, thwart the foraging activities of seed predators, and promote the survival of seeds in an environment subject to frequent fires.     

Seedling recruitment of Succisella inflexa in fen meadows: Importance of seed and microsite availability

Abstract. The effects of different forms of land use on germination and establishment of the rare fen species Succisella inflexa were investigated in seed introduction experiments in a mown and an abandoned fen meadow in SE Germany. Treatments included abandonment, mowing in fall and mowing with creation of gaps in the moss and litter layer. Floating capacity of seeds was tested in order to estimate potential dispersal by water. On the mown meadow, gaps had a slightly positive effect on germination rates, while greatly increasing seedling survival until the next spring. At the abandoned site, litter inhibited germination, whereas mosses had a negative effect on germination and a positive effect on survival rates during the first year after germination. Both germination and seedling establishment were negatively affected by the presence of slug herbivores. On the abandoned site, no seedlings at all survived until the next spring. Even though seeds of Succisella inflexa were capable to float for several weeks and to germinate thereafter, the situation at the field sites indicates that longdistance dispersal is highly unlikely. Our results showed that not only direct effects of abandonment, such as accumulation of litter, may have led to poor germination and poor seedling establishment of the species. Additionally, indirect consequences of changes in land use, such as higher seedling herbivory by slugs and successional vegetation changes due to abandonment, were important in determining habitat quality and availability of microsites for seedling recruitment. Furthermore, early mowing imposed seed limitation on plant populations.     

小麦种质贮藏过程中生活力丧失特性及田间出苗率表现

通过对贮藏2～20年的378份中期库小麦种质进行生活力测定(每一贮藏年份测定种质份数为10～30),结果表明贮藏年限为2～12年的种质平均发芽率都高于83％,而贮藏年限为15年的种质平均发芽率已降至20％,这表明小麦种质在中期库贮藏过程中,生活力丧失存在着骤降特性。同时对同一品种分别来自中期库低活力和长期库高活力种质进行田间出苗率和农艺性状调查,发现中期库种质的室内发芽率与田间出苗率相关极显,其相关显性高于长期库种质,且不论是来自中期库低活力种质还是长期库高活力种质,总体上田间出苗率都比室内发芽率低20％以上,在子一代种子的农艺性状上两之间无显差异。     

Effects of Sward Height, Gap Size, and Slug Grazing on Emergence and Establishment of Trollius europaeus (Globeflower)

Abstract To determine the effects of sward height and gap size on the emergence and subsequent development of Trollius europaeus, seeds were introduced into artificially created gaps in mown and unmown wet meadow grassland in Ayr, Scotland. Emergence and establishment of nondormant seed (previously leached in running tap water and soaked in gibberellic acid) placed in a range of circular gaps (25 mm, 50 mm with and without root barrier, 100 and 200 mm diameter) were monitored over 305 days. Trollius demonstrated high field emergence (mean, 46% of viable seed sown) in this experiment. Emergence was not significantly affected by either sward height or gap size, although emergence was greater in mown swards. The critical factor determining subsequent survival of seedlings was slug predation rather than sward height or gap size. However, losses due to slug predation were significantly greater in unmown swards, resulting in more seedlings in mown swards. One hundred eleven days after sowing (September) seedling numbers had declined substantially in both unmown and mown swards, and by day 305 (April) seedlings were extinct in both sward types. The implications of the research for the restoration and management of T. europaeus are discussed.     

Factors affecting seedling recruitment in an invasive grass (Pennisetum setaceum) and a native grass (Heteropogon contortus) in the Hawaiian Islands

In the Hawaiian Islands, native Heteropogon contortus (pili grass) is being replaced by alien grasses, one of which is Pennisetum setaceum (fountain grass). Both grasses depend on seeds for population growth. To help understand factors promoting the spread of the alien and decline of the native, we investigated the effects of physical disturbance, nutrient addition, and seed supplementation on seedling recruitment in experimental field plots. In the first year, our field site experienced an unusual drought, and seedling recruitment was greater for H. contortus than for P. setaceum under all treatments. Disturbance increased recruitment of H. contortus seedlings during some sampling periods. Recruitment was not significantly increased by seed additions for either species despite our finding of only 49 and 4 seeds m^–2 in the seed bank for H. contortus and P. setaceum, respectively. In the first year, most P. setaceum seedlings died between monthly surveys. We resurveyed our field plots in a second, wetter year and found the pattern was reversed: recruitment of P. setaceum seedlings was greater than H. contortus seedlings in most treatments. Greenhouse comparisons of seedling survival under three drought regimes (water every 5,7 and 10 days) revealed that H. contortus seedlings tolerate drought better than P. setaceum seedlings. Seedling recruitment for these species in the leeward Hawaiian Islands appears to be primarily dependent on water availability, with the alien having the advantage in wetter years. Once seedlings of the long-lived alien become established, the alien seems capable of maintaining its dominance over H. contortus, even during periods of drought.     

Competition effects on wiregrass (Aristida beyrichana) growth and survival

We investigated neighboring plant effects (competition and facilitation)on wiregrass establishment in two frequently encountered restoration situationsof former longleaf pine-wiregrass habitats in the Southeastern United States:longleaf pine plantations and previously cultivated fields. In the plantationexperiment, we specifically examined canopy removal, neighboring wiregrassdensity, and aboveground and belowground effects on establishment and growth ofwiregrass seedlings at two different ages (3 weeks and 6 months) with 3competitive exclusion treatments (aboveground exclusion, belowground exclusion,or no exclusion). Competition treatment effects were age-dependent forsurvivorship and growth. Survival of 6 month old seedlings was unaffected bycompetition treatment; whereas, three week old seedling survival was greatestwhere roots were excluded. Seedling size increased with root exclusion for 6month seedlings, but not for 3 week old seedlings in plots lacking neighboringwiregrass. Where wiregrass was present, both 3 week and 6 month old seedlingsincreased growth with root exclusion. Furthermore, where neighboring wiregrassplants were absent, increasing canopy density resulted in decreased seedlingsize, but did not affect survivorship. In old fields, fertilizer treatments andweeding effects were also assessed using 3 week and 6 month old seedlings.Fertilizer application did not benefit seedling survival or growth and reducedsurvivorship of 3 week old seedlings. Seedlings were smaller where neighboringold field, weedy vegetation was present regardless of wiregrass seedling age;whereas, survival was dependent on seedling age at time of planting. Six monthold seedling survivorship remained high regardless of weeding treatment. It isstill unclear whether fertilizer application is beneficial to the successfulestablishment of wiregrass.     

铜尾矿对5种豆科植物种子萌发和幼苗生长影响的初步研究

通过水培实验和土培实验,研究了铜陵铜尾矿对5种豆科植物种子萌发和幼苗生长的影响。结果表明,五种豆科植物种子在尾矿浸提液中均能萌发,但萌发率比对照组低,而且浸提液对种子萌发产生一定的阻滞作用,酸化尾矿浸提液对种子萌发初期的吸胀吸水有促进作用。尾矿与土壤5种不同改良方式的基质试验也发现铜尾矿对种子萌发着阻滞作用,其中大豆、赤豆、赤小豆在70d内未发现死苗现象。