Rotational mobility of the photoreaction center in chromatophore membranes of Rhodospirillum rubrum

We investigated the rotational mobility of the photoreaction center in chromatophores of Rhodospirillum rubrum by studying the photoinduced linear dichroism of absorption changes at 865 nm. The study was carried out in suspensions of chromatophores treated with ferricyanide in order to bleach their antenna bacteriochlorophyll and thus minimize depolarization by energy transfer. Very little depolarization of the photoinduced absorbance change at 865 nm was observed at room temperature for chromatophores immersed in a highly viscous medium over the time range 0–10 ms following an exciting light flash. In the light of independent evidence for transmembrane arrangement of the photoreaction center, we conclude that the photoreaction center protein is immobilized in the chromatophore membrane for at least 10 ms.     

Changes in biochemical composition of vacuoles isolated from Acer pseudoplatanus L. during cell culture

Vacuoles were isolated from Acer pseudoplatanus cell suspension culture using a one-step procedure involving the lysis of the protoplast plasmalemma through a gradient of Ficoll containing DEAE-Dextran. The vacuole suspensions were slightly contaminated by other organelles (less than 5%) and the isolated vacuoles readily accumulated neutral red. Since α-mannosidase was located exclusively in the vacuoles it was used as a convenient marker. It was shown that the number of vacuoles per protoplast decreased as the cell aged. Studies on the biochemical composition of the isolated vacuoles indicated that amino acids, organic acids and protein contents varied with the cell culture cycle, emphasizing the dynamic status of the vacuolar system in cell suspension cultures of Acer pseudoplatanus.     

Phenological match drives pollen‐mediated gene flow in a temporally dimorphic tree

• Variation in flowering phenology is common in natural populations, and is expected to be, together with inter‐mate distance, an important driver of effective pollen dispersal. In populations composed of plants with temporally separated sexual phases (i.e. dichogamous or heterodichogamous populations), pollen‐mediated gene flow is assumed to reflect phenological overlap between complementary sexual phases. In this study, we conducted paternity analyses to test this hypothesis in the temporally dimorphic tree Acer opalus.
• We performed spatially explicit analyses based on categorical and fractional paternity assignment, and included tree size, pair‐wise genetic relatedness and morph type as additional predictors. Because differences between morphs in flowering phenology may also influence pollination distances, we modelled separate pollen dispersal kernels for the two morphs.
• Extended phenological overlap between male and female phases (mainly associated with inter‐morph crosses) resulted in higher siring success after accounting for the effects of genetic relatedness, morph type and tree size, while reduced phenological overlap (mainly associated with intra‐morph crosses) resulted in longer pollination distances achieved. Siring success also increased in larger trees.
• Mating patterns could not be predicted by phenology alone. However, as heterogeneity in flowering phenology was the single morph‐specific predictor of siring success, it is expected to be key in maintaining the temporal dimorphism in A. opalus, by promoting not only a prevalent pattern of inter‐morph mating, but also long‐distance pollination resulting from intra‐morph mating events.

     

Japanese maple (Acer palmatum var. Matsumurae, Aceraceae) recruitment patterns: seeds, seedlings, and saplings in relation to conspecific adult neighbors

We analyzed the spatial patterns among seeds, seedlings, saplings, and conspecific adult trees of the cool-temperate tree species Acer palmatum var. Matsumurae in a conifer-hardwood mixed forest in northern Japan, using two models that consider the influence of each adult within the neighborhood of the offspring. The results showed that recruitment patterns of each stage could be characterized and that significant shifts occur between successive stages. Sound seeds were more widely dispersed than unsound seeds; the mean dispersal distance (MDD) was 41.5 m for sound seeds, but only 12.6 m for unsound seeds. Most seedlings were located near conspecific adult trees, with a MDD of 14.3 m. Saplings, however, were more dispersed away from conspecific adult trees, with an MDD of more than 35 m. Light and gap distributions did not strongly affect the spatial distribution of the offspring; most saplings were located under nonconspecific canopies. These results suggest that the recruitment pattern of Japanese maple offspring is strongly affected by conspecific adult neighbors, rather than by light and gap distributions, with close proximity to conspecific adult trees reducing the growth and survival of seedlings during the transition to saplings.     

Temporal variation in the woody understory of an old-growth Fagus-Acer forest and implications for overstory recruitment

Abstract. Changes in woody vegetation were examined over eight years, using a 1.05-ha permanent plot in which the location of every shrub and tree > 1m height was mapped. There was little change in the overstory vegetation, as expected for an old-growth forest. Much greater change occurred in the understory, primarily related to a 40 % increase in density. Differences occurred among species in the under-story, as Acer saccharum and Prunus serotina increased and Fraxinus americana and Fagus grandifolia decreased. Canopy gap dynamics are implicated in differences among species in the establishment and growth of individuals in the understory and their recruitment into the overstory. It is concluded that because understory is temporally variable, overstory recruitment from the understory may take different courses at different times in the same forest.     

Norway Maple (Acer platanoides) Invasion of a Natural Forest Stand: Understory Consequence and Regeneration Pattern

Norway maple (Acer platanoidesis) is invasive in a natural stand in suburban Ithaca, NY. To determine the understory pattern and consequences of a Norway maple invasion, I compared density and species richness under Norway maples and sugar maples (Acer saccharum). Mean sapling density was significantly lower (P<0.0027) under Norway maples (3.64/100 m²±1.6 SE) than under sugar maples (19.4/100 m²±4.4 SE). Mean sapling species richness was significantly lower (P<0.0018) under Norway maples (0.7/32 m²±0.18 SE) than under sugar maples (2.6/32 m²±0.48 SE). Likewise, Norway maple regeneration is more frequent under sugar maples than sugar maple regeneration: 57% of sugar maple plots had Norway maple saplings while 0% of Norway maple plots had sugar maple saplings. Two significant plot effects were found for presence–absence: Norway maple saplings grow under Norway maples with a significantly lower frequency (P<0.03) than under sugar maples; sugar maple saplings grow under Norway maples with a significantly lower frequency (P<0.000) than under sugar maples. Across the site, Norway maple saplings were the most abundant (29 saplings for 480 m²). The success of Norway maple regeneration and the reductions in total stem density beneath Norway maples is most likely the result of its strong competitive abilities, notably its high shade tolerance and abundant seed crops.