Soft-part anatomy of the siphuncle in Permian prolecanitid ammonoids

Exceptionally well-preserved remains of phosphatized siphuncles were discovered in four specimens of a Permian prolecanitid ammonoid Akmilleria electraensis (Plummer and Scott) from Buck Mountain, Nevada. These structures occur as truncated segments within the siphuncular tube. The outer surface of the siphuncle is sculptured by numerous equally spaced longitudinal ridges and furrows; the ridges represent an infolded basement membrane of epithelial cells which corresponds to the distal ends of individual canaliculi between epithelial cells. In cross-section, the siphuncle of A. electraensis consists of a large central vein, possibly two pairs of arteries, porous connective tissue with reticulate hemocoelic spaces, and a thin epithelium. In the presence of two pairs of arteries and porous connective tissue, the siphuncle of A. electraensis is more like that of Nautilus pompilius than that of Spirula spirula, which has nine arteries and dense connective tissue. However, Nautilus possesses relatively smaller and more numerous epithelial cells around the siphuncle than does Akmilleria. These observations strongly suggest that the siphuncular epithelium of Akmilleria served as the salt-­concentrating organ for buoyancy regulation of the living animal, just as in Nautilus and Spirula.     

Diversification in flowering time due to tandem FT-like gene duplication, generating novel Mendelian factors in wild and cultivated rice

The complex structure of a single Mendelian factor widespread in the Asian cultivated rice ( Oryza sativa ) and its wild progenitor ( Oryza rufipogon ) that caused diverse phenotypes in the timing of flowering under natural field conditions was investigated in near isogenic lines. These near isogenic lines showed differences in flowering time despite all eight accessions collected from tropical regions possessing a recessive gene allelic to the se-pat gene. Fine mapping in two of these near-isogenic lines revealed that cultivated (Patpaku) and wild (W593) accessions had three and two linked quantitative trait loci (QTL) in the candidate regions, respectively, showing that Patpaku and W593 possessed linked QTLs with different effects in addition to the commonly-observed recessive gene ( se-pat ). Molecular dissection suggested that the tandemly duplicated FT-like genes ( Hd3a and RFT1 ) could be the candidate genes for these QTLs. Interestingly, the linked QTLs differed in their epistases, degree of dominance, and genotype × environment interactions. The nucleotide sequences showed that RFT1 has diverged more rapidly than Hd3a during rice evolution, suggesting phenotypic diversification of the two genes. Phylogenetic analysis implied that the se-pat ⁺ alleles might have emerged in different lineages within O. sativa . The present results strongly suggest that nucleotide divergence and shuffling of the linked QTLs by recombination might have created novel Mendelian factors that probably contribute to responding to local environments.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 2: Analysis of Ligament Function

A three-dimensional model of the knee is used to study ligament function during anterior-posterior (a-p) draw, axial rotation, and isometric contractions of the extensor and flexor muscles. The geometry of the model bones is based on cadaver data. The contacting surfaces of the femur and tibia are modeled as deformable; those of the femur and patella are assumed to be rigid. Twelve elastic elements are used to describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit represented as a three-element muscle in series with tendon. The calculations show that the forces applied during a-p draw are substantially different from those applied by the muscles during activity. Principles of knee-ligament function based on the results of in vitro experiments may therefore be overstated. Knee-ligament forces during straight a-p draw are determined solely by the changing geometry of the ligaments relative to the bones: ACL force decreases with increasing flexion during anterior draw because the angle between the ACL and the tibial plateau decreases as knee flexion increases; PCL force increases with increasing flexion during posterior draw because the angle between the PCL and the tibial plateau increases. The pattern of ligament loading during activity is governed by the geometry of the muscles spanning the knee: the resultant force in the ACL during isometric knee extension is determined mainly by the changing orientation of the patellar tendon relative to the tibia in the sagittal plane; the resultant force in the PCL during isometric knee flexion is dominated by the angle at which the hamstrings meet the tibia in the sagittal plane.     

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.     

Utilization of Seed Reserves and Currently Produced Photosynthates by Embryonic Tissues of Pine Seedlings

The importance of seed reserves for growth of Pinus resinosaAit. during and shortly after seed germination was studied undercontrolled conditions. Tissues in the resting embryo were notcompletely differentiated. Many small, presumably reserve particleswere present in the embryo in addition to reserves in the megagametophyte.During seed germination, procambia in the embryo first differentiatedprotophloem 2 days after seeds were sown. The radicle beganto emerge from the seed coat at 5 days, at which time initialxylem formation was observed. Also, at approximately the sametime, primordia of primary needles were forming in the peripheralzone of the apex. Elements of the photosynthetic apparatus,including stomata and mesophyll with chloroplasts, were differentiatedfirst in the hypocotyl and then in cotyledons between 5 and8 days after seeds were sown. Photosynthetic rates of youngseedlings were correlated with rates of cotyledon expansion.During early developmental stages, reserve particles in megagametophytecells and embryo cells gradually disappeared. Surgical removalof megagametophytes at various stages of seed germination resultedin subsequent growth inhibition of the hypocotyl-radicle axis,with early removal of cotyledons suppressing most growth. Growthof primary needles appeared to be influenced indirectly by megagametophytereserves, probably by changes in amount of photosynthetic tissue.The embryo alone possessed capacity to differentiate such tissuesas primary needle primordia, stomata, and primary and secondaryvascular systems. Megagametophyte reserves appeared to contributeto growth of embryonic tissues only after the embryo itselfinitiated growth. Both current photosynthesis of seedlings andseed reserves contributed importantly to seedling development.     

Dopamine influences locomotor activity in honeybee queens: implications for a behavioural change after mating

Abstract Dopamine has been suggested to be involved in physiological and/or behavioural changes triggered by mating in European honeybee (Apis mellifera) queens but its specific role remains unclear. In the present study, the amounts of dopamine (DA) and its metabolite, N‐acetyldopamine (NADA) are measured, in queens of various ages to clarify the association with locomotor activity. The effects of DA receptor agonist/antagonist drugs on locomotor activity are further investigated. Brain levels of DA and NADA are relatively constant during the period before mating when locomotor activity reportedly increases with age but decreases in 1‐year‐old laying queens with low locomotor activity. Reduced DA and NADA levels are also found in haemolymph of 1–3‐month‐old laying queens. When a DA receptor agonist or antagonist is injected into 6‐day‐old virgin queens, locomotor activity levels increase significantly with 2‐amino‐6,7‐dihydroxy‐1,2,3,4‐tetrahydronaphthalene (agonist), and decreased with cis(Z)‐flupenthixol (antagonist). These results suggest that DA systems are involved in the motor control of honeybee queens, and that the decline in DA levels reduces locomotor activity after mating but increased locomotor activity before mating may be independent of DA levels.     

Leaf Anatomy and Carbon Discrimination in NAD-malic Enzyme Panicum Species and their Hybrids Differing in Bundle Sheath Cell Ultrastructure

The relationship between leaf anatomy, ultrastructure and carbondiscrimination was investigated in leaves of two F₁hybrids (F₁-1and F₁-2) between two different types of the grassPanicum [anNAD-malic enzyme (ME) C₄species], which differ in bundle sheathultrastructure. The female parent was Kabulabula grass, whichhas centrifugal chloroplasts in bundle sheath cells and is designatedan NAD-ME(F) species, while the male parent was Makarikari grass,which has centripetal chloroplasts in the bundle sheath cellsand is designated an NAD-ME(P) species. Suberin lamellae arepresent in Kabulabula grass but are lacking in Makarikari grass.Both F₁hybrids had the same chromosome number (2n =36) as theparents but exhibited both univalent (about 45%) and bivalent(about 55%) chromosome pairing which was the major basis forthe identification of F₁hybrids. In F₁-1, elongated bundle sheathcell chloroplasts are arranged mainly in a centripetal position,similar to those in the male parent, Makarikari grass. In contrast,most of the bundle sheath cells in F₁-2 are packed with starch-containingchloroplasts, although in some cells chloroplasts tended tobe centripetally arranged. In both F₁hybrids, suberin lamellaewere found in the bundle sheath cell walls, similar to the femaleparent, Kabulabula grass. The ¹³C values of both F₁hybrids were-11.4 to -11.7, almost the same as those of Kabulabula grass(-11.4), but significantly higher than those of Makarikari grass(-12.7). These results indicate that the chloroplast orientationin the bundle sheath cells and the presence of suberin lamellaeare not obligatorily linked in their expression and suggestthat suberin lamellae may play an important role in discriminationagainst¹³C. Panicum ; NAD-malic enzyme species; hybrid; chloroplast position; ¹³C discrimination; suberin lamellae     

Polysome formation in Pinus resinosa at initiation of seed germination

Ribonucleic acid systems present in dormant embryos of red pine(Pinus resinosa Ait.) were studied. Sucrose gradient centrifugationwas used to isolate ribosomes of dormant embryos and embryosimbibed for various times in the light. In dormant embryos,ribosomes existed as monomers. After imbibition, a gradual decreasein the monomers was observed, with subunits and polymers ofribosomes detected within 4 hr. When poly U was added to homogenatesof dormant embryos, formation of polysomes was observed aftera 15-min incubation at 25°C. However, artificial polysomeformation required some factors from heavy particles in thehomogenates. ¹ Contribution from the Missouri Agricultural Experiment Station,Journal Series No. 7079. ² Present address: Government Forest Experiment Station, Meguro,Tokyo, Japan. (Received April 20, 1971; )