Quantitative characters of the flowering head of a garden population ofMicroseris laciniata were scored during the second, third, and fourth season of growth. Number of achenes per head, number of phyllaries per head and the average number of pappus parts per achene in single heads show significant plant to plant variation. Achenes per head and pappus parts per achene were scored in identical plants in two subsequent seasons. The number of pappus parts per achene varies freely between five and ten. This contrasts with annual species ofMicroseris in which either five or ten pappus parts are found, depending on the species. In spite of a clear plant-specific average of pappus parts, both high and low pappus part determination can be demonstrated in all specimens. The number of pappus parts depends on the position of an achene on the receptacle, marginal achenes usually having fewer pappus parts than central ones. This gradient is not closely correlated with the position of an achene on the genetic spiral. 相似文献
This study presents the carpological heterogeneity of Tragopogon pterodes, an endemic plant species from Balkan Peninsula. The goal of this paper was to determine the variability of morphological characters of achenes and assess the degree of their morphological differentiation relative to the position they occupy in the receptacle. Analysis included four different populations of T. pterodes and examination of 18 (8 qualitative and 10 quantitative) characters of achenes in total. Data analysis employed basic statistic, univariate (ANOVA, Tukey HSD) and multivariate (CDA, CA) analyses to check the level of heterocarpy in this species. The results indicate possible morphological differentiation of three groups of achenes (outer, median and inner achenes), depending of their position on the receptacle. The members of all three types were described, illustrated and compared. The variability of investigated carpological characters in this species is providing important information prior to their further taxonomic treatment. 相似文献
There are few reliable diagnostic morphological characters for species of the asteracean genus Microseris, and quantitative differences in the shapes of the achenes and the paleaceous pappus parts play a decisive role in species recognition. The genetic basis of species and strain differences in various characters has been studied previously, but little is known about quantitative characters of the achenes.
We performed a quantitative trait locus (QTL) analysis in the F2 of an interspecific cross between Microseris douglasii and M. bigelovii for achene length, achene diameter, achene shape, palea length, awn length, and achene pigmentation.
Independent inheritance of the main heritable achene characters – achene length, palea length and achene pigmentation – was revealed by the detection of distinct and specific QTLs for these characters. For palea length five QTLs with about equal phenotypic effects were mapped on four different linkage groups. Achene length and achene shape (achene length / achene diameter) were determined by two different genetic systems with one major gene and two modifiers. The detection of QTLs with a polarity of the effects opposite to that in the parental strains for achene length and achene shape reveals genetic variation for a potential increase in species differences. For the highly heritable trait, achene pigmentation, the bimodal F2 distribution suggested single-factor inheritance for absence versus presence of spots, with dominance for the spotted condition. However, only relatively weak QTL effects on that trait could be detected. Additional molecular markers (RAPDs, AFLPs) have to be tested for cosegregation with that major gene. The results are discussed in the context of different theories for the evolution of morphological characters. 相似文献
The ability of Anthemis chrysantha to form a soil seed bank (SB) was investigated in order to understand better the adaptation of this rare annual species to its arid and unpredictable natural habitat. The natural seed bank population was analyzed in five consecutive plant cohorts (2006–2010) by sampling at two different times: in May, after the germination period, and in October, after the first dispersal episodes due to the beginning winter rainfall. In addition, to determine the persistence in the soil of the two achene morphs of this species’ (white and dark achenes), an artificial SB was created where achenes were buried and exhumed successively after each season, during two years. In all the cohorts studied, seedling emergence from May samples indicated the existence of a persistent seed bank (PSB). Moreover, the dark achenes were largely responsible for the permanent fraction because, after two years of burial in the artificial SB, 85.0% of them remained apparently healthy without having germinated, versus 9.9% of white achenes. Both types of buried achenes exhibited an annual conditional dormancy/non-dormancy cycle, induced by low winter temperatures. The PSB dynamics appeared to oscillate between the minimum values at the end of the germination period in spring (up to 2000 achenes per square meter) and the maximum values of the dispersal episodes in early autumn (up to 6000 achenes per square meter), with fluctuations of achene density due to the variability in annual rainfall. Hence, the SB showed a decline due to the failure of fruiting in the 2008 cohort, caused by drought, although the low value of ca. 560 achenes per square meter was able to establish the following population. Our study highlights the importance of the PSB, which, in “bad” years, may be critical for the persistence of this species. 相似文献
Aim Mirabilis himalaica (Nyctaginaceae) is an endangered medicinal plant mainly distributed in the plateau region of northern Tibet, China. The outer surface of M. himalaica achenes is covered by a pectinaceous mucilaginous layer upon hydration. However, the role of the achene mucilage is poorly understood. In this study, we investigated the effects of mucilage on achene germination and sprout growth under abiotic stress to explain how M. himalaica survive the alpine environment.Methods We investigated the effect of mucilage on achenes germination by contrast the capacity of water absorption, dehydration and respiration of intact achene and the achene with mucilage removal. We performed abiotic stresses experiments including drought stress, salt stress, cold stress and high temperature stress, and quantified the effects of mucilage removal on achene germination rate, root and shoot lengths of seedlings.Important findings Mucilage is extremely hydrophilic, and the mass of intact achenes can be 9-fold greater than that of demucilaged achenes. The removal of the mucilaginous layer did not significantly change final germination percentages under ideal conditions, but intact achenes (i.e. with mucilage) took longer to germinate. The mucilage significantly decreased seed respiration rates by acting as a physical barrier that prevented oxygen diffusion. Germination rates, shoot and root growth of intact achenes were higher than those of demucilaged ones during exposures to cold, heat, osmotic and salt stresses. Achene mucilage presumably plays an ecologically important role in the life cycle of M. himalaica by aiding the critical achene germination and early seedling growth in the stressful habitats of the plateau region of northern Tibet. 相似文献
When analyzing sunflower (Helianthus annuus L.) remains, which are often carbonized, archaeobotanists commonly differentiate between wild and domesticated achenes and
seeds based on the measured length (L) and width (W) or the calculated index L*W. Carbonization reduces the dimensions. To
compensate for these reductions, archaeobotanists use a single correction factor proposed by Richard Yarnell (1978) for all
cases. The use of a single correction factor can bias the reconstructed dimensions as carbonization is a highly variable process.
The current study determines the relationship between carbonization and the dimensions of length and width. Measurements established
that a decrease of 2.5-22.5% in achene length and 10-29% in achene width can occur, depending on temperature, heating rate,
and variety. For seeds, temperature is of most importance, and shrinkage ranges from 0-27% for the length and from 0-20% for
the width. These ranges make the use of a single correction factor problematic. A method is developed in which reflectance
(an optical property applied in coal technology to determine coal rank) is used to measure the carbonization temperature,
and in turn the shrinkage can be calculated. Subsequently, correction factors are calculated to reconstruct the original length
and width. When applied to an assemblage of carbonized sunflower achenes, the newly developed method shows that the Yarnell
single correction factor may bias the dimensions towards classifications of “wild” or “ruderal” forms of sunflower 相似文献
Artemisia ordosica Krasch. is a dominant shrub occurring mainly on stable sand dunes in the Gobi Desert of China, in the Mongolian phytogeographic region. Achenes of A. ordosica germinate in light but poorly in dark and light is the limiting factor regulating the achene germination in sand depth. Achenes germinate in spring or autumn with an optimal temperature of 20 ℃. Achene mucilage can absorb large amounts of water and has important ecological function. Salt concentrations and sand moisture may regulate achene germination in sand. A. ordosica, A. sphaerocephala Krasch. and A. monosperma Delile. from different climates have similar responses to light, the underground location of achene, and sand moisture. Percentage of seedling emergence from different levels of sand depth is depends on the specific, temperature and intensity of light penetrating through the sand depths, as well as on sand moisture. The desert sand habitat seems to have had a dominant influence on the evolution of the germination strategies of these 3 Artemisia species. 相似文献