Post‐pollination process in a partially self‐compatible distylous plant,Primula sieboldii (Primulaceae)

Pollen germination and pollen‐tube growth under natural conditions were observed in a population of a distylous species, Primula sieboldii, in which partial self‐compatibility has been demonstrated in some long‐styled genets. We observed post‐pollination processes microscopically in styles collected after self‐morph and inter‐morph hand pollination (with standardized pollen load on the stigmas) in four genets each from the following three ‘genet types’: self‐incompatible long‐styled (SI), partially self‐compatible long‐styled (SC) and self‐incompatible short‐styled morph genets. Irrespective of the genet type, pollen germination began within 24 h after pollination and tubes of pollen reached to the style base with 48–96 h after inter‐morph pollination. Although pollen tubes germinated after self‐pollination in the SC genets, the number of germinated pollen tubes was significantly lower than in the case of inter‐morph pollination. Few pollen tubes germinated after self‐pollination of the SI or short‐styled genets. In SC genets, the rate of pollen‐tube growth did not differ between self‐morph and inter‐morph pollination (～1.9 mm/day). Therefore, differences in self‐compatibility between SC and SI genets in P. sieboldii are likely to be attributable to differential pollen germination rates rather than to differential pollen‐tube growth rates.     

STAGING OF NEWT BLASTULA EMBRYOS AND FIRST APPEARANCE OF PRIMARY MESODERMAL COMPETENCE

Using the swimbladder of the crusian carp ( Carrasius auratus ) as an inductor, the first appearance of mesodermal competence in the presumptive ectoderm of the newt ( Triturus pyrrhogaster ) blastula was investigated. The time course of embryonic development before the gastrula stage was determined by counting the number of surface cells on a 0.25 mm line at the animal pole. Pregastrula embryos with 2–3, 4–5, 6–7 and 7–8 cells roughly correspond to those at 14, 14–12, 8–6 and 4–0 hr before the beginning of gastrulation. Using presumptive ectoderm of the early gastrula stage, 15 min was found to be the minimum time of contact necessary for the realization of induction. The reactivity of the presumptive ectoderm from pregastrula embryos was tested by 30 min contact. Presumptive ectoderm up to the 4–5 cell stage did not react to the inductor. It may become competent within the next 4–8 hr, since the ectoderm from embryos in the 6–7 cell stage was reactive.     

DIRECT ISOLATION OF NATIVE THIN FILAMENTS FROM EMBRYONIC MUSCLE CELLS*

A method is presented for the release of “native” thin filaments from 13-day old embryonic chick muscle without tryptic digestion or desoxycholate (DOC) solubilization of Z bands. The isolated filaments were 50–60 Å in diameter, of variable length, and formed “arrowhead-like” complexes with heavy meromyosin (HMM). In addition, the filaments interacted with purified myosin to form actomyosin as effectively as action extracted from an acetone powder of muscle. The Mg⁺⁺-dependent ATPase activity and extent of superprecipitation of the synthetic actomyosin required a low concentration of Ca⁺⁺, strongly suggesting the presence of troponin and tropomyosin on the thin filaments isolated from muscle at this stage of embryogenesis. The native thin filaments were more sensitive to trypsin than synthetic F-actin prepared from an acetone powder based on measurements of flow birefrengence, viscosity and the ability to activate myosin ATPase.     

Morphological and Physiological Acclimation Responses to Contrasting Light and Water Regimes in <Emphasis Type="Italic">Primula sieboldii</Emphasis>

The effects of the availability of light (high, medium and low) and soil water (wet and dry) on morphological and physiological traits responsible for whole plant carbon gain and ramet biomass accumulation were examined in a splitter-type clonal herbaceous species Primula sieboldii, a spring plant inhabiting broad range of light environments including open grassland and oak forest understory. Growth experiments were conducted for three genets originated from natural microhabitats differing in light and soil water availability. Ramets of a genet from high light and wet microhabitat, which were grown in low light (relative photon flux density: R-PPFD of 5%) showed 41% less light-saturated photosynthetic rate, 50% less dark respiration rate and earlier defoliation than the ramets in high light (R-PPFD of 61%). The estimation of daily photosynthesis revealed that the light acclimation response in leaf gas exchange contributes to efficient carbon gain of whole plants, irrespective of experimental light conditions. Water stress increased root weight ratio, decreased ramet leaf area, petiole length and photosynthetic capacity. These morphological effects of water stress were larger in high and medium light regimes than in low light regime. The consequence of the above responses was recognized in the relative growth rate of the ramets. The relative growth rate of the ramets in high light with wet regime was four-fold of that in low light plus wet regime, and was 1.5-fold of that in high light plus dry regime. However, even in low light and/or dry regimes, ramets kept positive relative growth rates and produced gemma successfully. We could not detect significant variation in growth responses among genets. The high photosynthetic plasticity revealed in the present study should enable Primula sieboldii to inhabit in a broad range of light and soil water availability.     

Regeneration failure of lakeshore plants under an artificially altered water regime

To reveal the effects of artificial alteration of water level regime on the regeneration of lakeshore plants from seeds, we examined the factors causing regeneration failure in Lake Kasumigaura, Japan. A survey of microtopography within and around a remnant fragment of lakeshore vegetation revealed that, over a large range, the habitat is frequently inundated in spring under the current water regime, although it was rarely inundated under past water regimes. Analysis of the patterns of seedling emergence and establishment at microsites at various elevations revealed a significant negative correlation between number of inundation days and abundance or species-richness of seedlings that emerged in the spring. Most seedling deaths occurred when the study site was inundated. We suggest that regeneration failure caused by the artificial raising of the lakes water level is one of the principal mechanisms of the recent vegetational decline in the lake.     

Germination responses of a seed population of Taraxacum officinale Weber to constant temperatures including the supra-optimal range

Abstract The germination responses of a nondormant fraction of a seed population of Taraxacum officinale Weber at constant temperatures in the range 7–34°C were analysed through a time-course study. Maximal percentage germination (approximately 90%) was attained at temperatures 10–18°C, where simple linear relationships were observed between the temperature and the germination rates, i.e. the reciprocals of the time taken to germinate by subpopulations with 20–80% germination. There was a variation in the required ‘thermal times’ (θ) which characterized the linear relationships, the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution, and A is a shape parameter characterizing the pattern of the distribution. Final percentage germination decreased with increasing temperature from 20 to 32°C, where the final percentage germination vs. temperature plotted on a normal probability scale yielded a straight line, indicating the normality of the distribution of the upper limit temperature in the seed population. The estimated mean and standard deviation were 27.25 ± 3.75°C. The rate of germination for the subpopulation with 20–80% germination also decreased with increases in the temperature from 22 to 30°C. If the relationships between the temperature within this range and the rate for the subpopulations with 20–80% germination were approximated by the regression lines, the negative ‘thermal time’ characterizing the yielded linear relationship would have a distribution which could be approximated by the same function with the required thermal time for the relationship of suboptimal range. The parameters m and A for the negative ‘thermal time’ were determined to be 2870 K h and 1.7 × 10^-10 K^-3 h^-3.