Phytochrome B dynamics departs from photoequilibrium in the field

Vegetation shade is characterized by marked decreases in the red/far‐red ratio and photosynthetic irradiance. The activity of phytochrome in the field has typically been described by its photoequilibrium, defined by the photochemical properties of the pigment in combination with the spectral distribution of the light. This approach represents an oversimplification because phytochrome B (phyB) activity depends not only on its photochemical reactions but also on its rates of synthesis, degradation, translocation to the nucleus, and thermal reversion. To account for these complex cellular reactions, we used a model to simulate phyB activity under a range of field conditions. The model provided values of phyB activity that in turn predicted hypocotyl growth in the field with reasonable accuracy. On the basis of these observations, we define two scenarios, one is under shade, in cloudy weather, at the extremes of the photoperiod or in the presence of rapid fluctuations of the light environment caused by wind‐induced movements of the foliage, where phyB activity departs from photoequilibrium and becomes affected by irradiance and temperature in addition to the spectral distribution. The other scenario is under full sunlight, where phyB activity responds mainly to the spectral distribution of the light.     

Mobilization of the gypsy and copia retrotransposons in Drosophila melanogaster induces reversion of the ovo dominant female-sterile mutations: molecular analysis of revertant alleles

The ovo locus is required for the maintenance of the female germ line in Drosophila melanogaster. In the absence of an ovo⁺ gene, males are completely normal but females have no germ-line stem cells. Three dominant mutations at the ovo locus, called ovo^D, were observed to revert towards recessive alleles at high frequency when ovo^D males were crossed to females of the strain y v f mal. We have found that this strain contains an inordinately high number of gypsy transposable elements, and crossing it with the ovo^D strains results in the mobilization of both gypsy and copia, with high-frequency insertions into the ovo locus: of 16 revertants examined 12 have gypsy and four have copia inserted at 4E, the ovo cytological site. Using gypsy DNA as a tag we have cloned 32 kb of wild-type DNA sequences surrounding a gypsy insertion and characterized molecular rearrangements in several independent revertants: in 10 of them gypsy appears to be inserted into the same site. The orientation of gypsy is strictly correlated with whether the neighbouring lozenge-like mutation appears in the revertants. A distal limit of the ovo locus was molecularly determined from the breakpoint of a deletion affecting closely flanking regions.     

Molecular phylogenies disprove a hypothesized C4 reversion in Eragrostis walteri (Poaceae)

Background and Aims

The main assemblage of the grass subfamily Chloridoideae is the largest known clade of C₄ plant species, with the notable exception of Eragrostis walteri Pilg., whose leaf anatomy has been described as typical of C₃ plants. Eragrostis walteri is therefore classically hypothesized to represent an exceptional example of evolutionary reversion from C₄ to C₃ photosynthesis. Here this hypothesis is tested by verifying the photosynthetic type of E. walteri and its classification.

Methods

Carbon isotope analyses were used to determine the photosynthetic pathway of several E. walteri accessions, and phylogenetic analyses of plastid rbcL and ndhF and nuclear internal transcribed spacer DNA sequences were used to establish the phylogenetic position of the species.

Results

Carbon isotope analyses confirmed that E. walteri is a C₃ plant. However, phylogenetic analyses demonstrate that this species has been misclassified, showing that E. walteri is positioned outside Chloridoideae in Arundinoideae, a subfamily comprised entirely of C₃ species.

Conclusions

The long-standing hypothesis of C₄ to C₃ reversion in E. walteri is rejected, and the classification of this species needs to be re-evaluated.     

Reversion of flowering in Glycine Max (Fabaceae)

Photoperiodic changes, if occurring before a commitment to flowering is established, can alter the morphological pattern of plant development. In this study, Glycine max (L.) Merrill cv. Ransom plants were initially grown under an inductive short-day (SD) photoperiod to promote flower evocation and then transferred to a long-day (LD) photoperiod to delay flower development by reestablishing vegetative growth (SD-LD plants). Some plants were transferred back to SD after 4-LD exposures to repromote flowering (SD-LD-SD plants). Alterations in organ initiation patterns, from floral to vegetative and back to floral, are characteristic of a reversion phenomenon. Morphological features that occurred at the shoot apical meristem in SD, LD, SD-LD, and SD-LD-SD plants were observed using scanning electron microscopy (SEM). Reverted plants initiated floral bracts and resumed initiation of trifoliolate leaves in the two-fifths floral phyllotaxy prior to terminal inflorescence development. When these plants matured, leaf-bract intermediates were positioned on the main stem instead of trifoliolate leaves. Plants transferred back to a SD photoperiod flowered earlier than those left in LD conditions. Results indicated that in plants transferred between SDs and LDs, photoperiod can influence organ initiation in florally evoked, but not committed, G. max plants.     

The Use of Mixtures of Sulfur and Bracken Litter to Reduce pH of Former Arable Soils and Control Ruderal Species

High soil pH has been highlighted as a constraint to the restoration of heathland on ex‐arable land. Previous studies at the Minsmere Reserve of the Royal Society for the Protection of Birds (RSPB) in England have shown that it is possible to acidify ex‐arable soils using elemental sulfur and bracken litter, although sulfur (S) is more effective. Current recommendations suggest that 4 tS/ha need to be applied to reduce soil pH below pH 4, control vigorous ruderal species, and create conditions suitable for Calluna vulgaris (heather) establishment. However, S is relatively expensive, and as bracken litter is moderately abundant within the reserve, it made economic sense to evaluate the potential for mixing S with bracken to see if adequate pH reductions could be achieved at lower S rates. Accordingly an experiment was designed to test the effects of combining S (0–8 t S/ha) and bracken litter (0–10 cm depth layers) on (1) soil pH, (2) cover of ruderal species, and (3) the developing plant community. Significant interactions were detected, especially in the period immediately after application. Where bracken litter was applied the soil pH fell immediately; in contrast, S took at least six months to start reducing pH. Where mixtures were applied there was a synergistic effect, which produced a lower pH than the S or bracken litter applied alone. These effects were most marked at low S application rates, between 0.5–4 t S/ha. The effects of the bracken litter addition also reduced the growth of ruderal species in the period immediately after application, probably through a combination of acidification and physical smothering. There is, therefore, a clear potential to acidify ex‐arable soils using combinations of S and bracken litter in schemes designed to restore Calluna heathland.     

The morphological basis of hallucal orientation in extant birds

The perching foot of living birds is commonly characterized by a reversed or opposable digit I (hallux). Primitively, the hallux of nonavian theropod dinosaurs was unreversed and lay parallel to digits II-IV. Among basal birds, a unique digital innovation evolved in which the hallux opposes digits II-IV. This digital configuration is critical for grasping and perching. I studied skeletons of modern birds with a range of hallucal designs, from unreversed (anteromedially directed) to fully reversed (posteriorly directed). Two primary correlates of hallucal orientation were revealed. First, the fossa into which metatarsal I articulates is oriented slightly more posteriorly on the tarsometatarsus, rotating the digit as a unit. Second, metatarsal I exhibits a distinctive torsion of its distal shaft relative to its proximal articulation with the tarsometatarsus, reorienting the distal condyles and phalanges of digit I. Herein, I present a method that facilitates the re-evaluation of hallucal orientation in fossil avians based on morphology alone. This method also avoids potential misinterpretations of hallucal orientation in fossil birds that could result from preserved appearance alone.     

Developmental morphology of branching flowers in Nymphaea prolifera

Nymphaea and Nuphar (Nymphaeaceae) share an extra-axillary mode of floral inception in the shoot apical meristem (SAM). Some leaf sites along the ontogenetic spiral are occupied by floral primordia lacking a subtending bract. This pattern of flower initiation in leaf sites is repeated inside branching flowers of Nymphaea prolifera (Central and South America). Instead of fertile flowers this species usually produces sterile tuberiferous flowers that act as vegetative propagules. N. prolifera changes the meristem identity from reproductive to vegetative or vice versa repeatedly. Each branching flower first produces some perianth-like leaves, then it switches back to the vegetative meristem identity of the SAM with the formation of foliage leaves and another set of branching flowers. This process is repeated up to three times giving rise to more than 100 vegetative propagules. The developmental morphology of the branching flowers of N. prolifera is described using both microtome sections and scanning electron microscopy.     

一个恢复力受单基因控制的水稻CMS育性回复突变体

利用￣（６０）Ｃｏ－γ射线对具有印尼水田谷细胞质的籼稻细胞质雄性不育系Ⅱ－３２Ａ干种子进行诱变处理,获得了一育性回复突变体Ｔ２４。育性基因未纯合的突变体分离出可育株和完全不育株,比例为３∶１;其与Ⅱ－３２Ａ和珍汕９７Ａ测交,Ｆ１代分离出１∶１的可育株和不育株。育性稳定株系与Ⅱ－３２Ａ和珍汕９７Ａ杂交,Ｆ２分离成３∶１的可育株和不育株。表明其育性回复是由一对基因显性突变所致。这一突变体对不育系的育性恢复机制不同于明恢６３、２０９６４等恢复系,后者表现为两对显性恢复基因作用。未观察到Ｔ２４与亲本Ⅱ－３２Ａ除育性以外的其他性状的差异,因而两者构成育性恢复基因的近等基因系。本文还对不育系育性回复类型和Ｔ２４的理论意义与育种价值进行了讨论。