Dissecting components of flowering pattern: size effects on female fitness

Flowering synchrony is essential for plant reproductive success, especially in the case of small‐sized populations of self‐incompatible species. Closely related to synchrony, flowering intensity influences pollinator attraction and pollinator movements. Thus, a high flowering intensity may increase pollinator attraction but, at the same time, may also increase the probability of geitonogamous pollinations. Depending on the mating system, the female fitness of plants in small populations may be affected by both the positive effects of higher flowering synchrony and pollinator attraction and the negative effects of geitonogamous pollinations induced by a high flowering intensity. It was hypothesized that different‐sized plants in a population would show contrasting flowering patterns, resulting in differences in pollinator behaviour. These influences could result in differences in mating and female reproductive success. This hypothesis was tested by studying the flowering pattern of Erodium paularense (Geraniaceae), a rare and endangered endemic of central Spain. The temporal distribution of flower production was explored throughout the reproductive season, and the probability of xenogamy and geitonogamy and their relationship to plant size and fitness components were calculated. The analysis of this partially self‐compatible species showed diverse flowering patterns related to different plant sizes. Small plants produced a larger number of seeds per fruit in spite of having lower values of flowering synchrony. By contrast, large plants produced a larger number of seeds from geitonogamous pollinations. The effect of different flower displays and outcrossing rates on seed set varied throughout the season in the different groups. Our findings highlight the relevance of individual plant size‐dependent phenology on female reproductive success and, in particular, on the relationship between flowering synchrony and fitness. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156 , 227–236.     

Development and Experimental Validation of a Fluid/Structure-Interaction Finite Element Model of a Vacuum-Driven Cell Culture Mechanostimulus System

A new fluid/structure-interaction finite element formulation is reported, by means of which reactive fluid stresses can be determined for what is currently the most widely used laboratory apparatus (the Flexercell Strain Unit) for delivering controlled in vitro mechanical stimuli to cultured cells. The apparatus functions by means of cyclic vacuum application to the undersurface of a membrane-like circular rubber substrate. When operated in its original embodiment (i.e., without axial constraint to substrate motion), the pulsatile vacuum causes appreciable pulsatile excursions (often several millimeters) of the substrate. The mechanical stimuli experienced by cells attached atop the substrate include not only substrate distention, but also potentially confounding reactive fluid stresses due to coupled motions of the overlying liquid culture nutrient medium. Since it is impractical to directly measure reactive fluid stress in such environments, a corresponding mathematical model has been developed. The formulation involves transient continuum finite element solutions for the nutrient medium flow field and for the deformation of the substrate, coupled at their mutual interface (the substrate culture surface). Besides the nonlinearities inherent in the flow field and substrate treatments per se, the numerical problem is complicated by the presence of moving boundaries at the nutrient free surface and at the nutrient/substrate interface, as well as by the need to enforce fluid/structure interaction throughout the duty cycle. Algorithmic considerations appropriate to achieving physically realistic numerical performance are reported, and a confirmatory laboratory validation experiment is described.     

SOME OBSERVATION ON AIR-ION-ENHANCED IRON CHLOROSIS IN BARLEY (HORDEUM VULGARIS) SEEDLINGS

The air ion effects on "active" and "residual" iron distributionin barley seedlings were studied in the course of the developmentof ironchlorosis in an iron-free culture medium. "Active" or"acid soluble" iron plays an important role for chlorophyllbiosynthesis and is extractable with 1.0 N HCl from dried tissues,and "residual" or "acid insoluble" iron does not participatein this chlorophyll formation process and is not extracted with1.0 N HCl. Ions of either charge induced a significant decrease in activeiron content which was associated with a decrease in chlorophyllcontent. Concomitantly, there occurred an increase in both theresidual iron and the cytochrome c fractions. The increase inresidual iron content may involve not only cytochrome c butalso other cytochromes and ironcontaining enzymes as well. Theauthors have proposed a hypothesis that the site of air ionaction in the experiments reported may be the regulatory systemscontrolling iron metabolism in the seed and young seedling.Through this action air ions apparently divert more endogenousfree-state iron to residual iron (consisting of cytochromesand Fe-containing enzymes) than to active iron. Tracer experiments showed that air ions enhanced the uptakeof exogenous iron by early germinating barley seeds. The increasedincorporation of iron was not influenced by light. (Received December 10, 1964; )