SOME EPIDERMAL CHARACTERISTICS OF PALEAS OF DICHANTHELIUM,PANICUM, AND ECHINOCHLOA

The apical portion of paleas of the perfect (upper) floret of 11 species of Dichanthelium, 10 species of Panicum, and one species of Echinochloa were examined with a scanning electron microscope. The surfaces of the Dichanthelium palea tips uniformly had simple, rounded papillae, widely spaced in regular rows, whereas the palea tips of most Panicum species had irregularly arranged, compound or aggregated papillae. Unusual epidermal features were observed in P. obtusum, P. hians, and P. hemitomon. The Echinochloa crusgalli palea surface exhibited a pattern of papillae or spicule development similar to that of P. hians. Transverse sections of Dichanthelium palea showed the papillae to be little if at all thickened. An electron beam x-ray microanalysis indicated a high concentration of silicon in the papillae.     

Developmental Morphology and Histogenesis of Reproductive Structures of the Millet,Panicum miliaceum L. Histogenesis of the Inflorescence and Flower

The branches of successive orders of the inflorescence of Panicum miliaceum L. arise in the axils of the bracts of the branches of next lower order. Their initiation is evidenced by periclinal division of sub-hypodermal cells. The primordia of branches arise in initiation like a normal axillary bud. The floral histogenesis of Panicum miliaceum L. is similar to that of Triticum. Primordia of the spikelet, flower and stamen are initiated by the activity of the periclinal division of the sub-hypodermal cell or cells. Sometimes, periclinal divisions also occur in a few hypodermal cells during these primordial developments; such divisions are more frequent in the formation of the flower and stamen primordia than in the formation of the spikelet primordia. The periclinal division of the dermatogen ceils never occurs in the formation of these organs. Glumes and lemma are initiated in the periclinal division of the dermatogen and hypodermal cell or cells. The primordia of the palea, lodicule and carpel are initiated by means of the periclinal division in the dermatogen cell or cells. In the formation of the palea and carpel, periclinal divisions also occur in hypodermat cells, but their derivatives are protruding into the bases of the primordia and do not constitute the tissues of the palea and carpel. The growing point of the flower axis develops into the ovule. The integuments arise from the periclinal division of dermatogen cells. The periclinal division of dermatogen cells is characteristic of the initiation of the phylloid organs in the Gramineae.     

INITIATION OF THE VASCULAR SYSTEM IN THE FERTILE FLORET OF ANTHOXANTHUM ODORATUM (GRAMINEAE)

Procambium was initially isolated near the insertions of lemma and stamen primordia in the grass Anthoxanthum. The palea was initiated before its procambium. The acropetal, continuous differentiation of procambium involved in the siting of leaves on shoots of many other megaphyllous plants, does not occur in the rachilla of this grass. A portion of the vascular system of the fertile floret of Anthoxanthum became connected with the vascular system of the rest of the spikelet by basipetal differentiation of the procambial trace of the fertile lemma. A core of residual meristem persisted in the fertile floret above the procambial trace to the fertile lemma. Vascular continuity between the procambial trace to the fertile lemma and the procambial traces of the stamens was achieved by the differentiation of procambium from this core of residual meristem.     

The Morphology of Germination in Setaria lutescens (Gramineae): The Effects of Covering Structures and Chemical Inhibitors on Dormant and Non-dormant Florets

The sequence of organ emergence in embryos of the yellow foxtailgrass (Setaria lutescens) is similar to that reported for othergrasses: coleorhiza, radicle, coleoptile and first leaf. Thecoleorhiza emerges by forcing open a hinged flap on the lemma.Coleorhiza trichomes form soon after emergence. The radicleprotrudes through the abaxial surface of the coleorhiza. Thecoleoptile elongates in a downward direction initially as itpasses between the lemma and palea, but immediately turns upward.The first leaf emerges by protruding through a slit-like creaseon the adaxial surface of the coleoptile. Embryos excised fromdormant florets are shown to germinate as well as those fromnon-dormant florets. Experiments are described which show theinhibitory effects of the embryo covering structures; the lemma,palea and caryopsis coat. Other experiments are discussed concerningthe effects on germination of the inhibitors abscisic acid andcycloheximide. An intermediate concentration of cycloheximide(10^–4 M) does not decrease germination percentage, butrather inhibits radicle growth but no coleoptile elongation.The significance of these observations is discussed.     

VASCULAR SYSTEM OF THE FLORET OF LEERSIA VIRGINICA (GRAMINEAE-ORYZOIDEAE)

The vascular system of the floret of Leersia is unified yet is segmented according to the appendages it serves. The rachilla at the floret base contains a collateral bundle related to the median trace of the lemma. The palea median trace joins the posterior of this bundle in the rachilla as the lemma laterals merge with the anterior. Although the stamen traces enter at the flanks of this rachilla bundle, they do not become fully incorporated into the system until near the floret base where the rachilla bundle, lemma laterals, and palea laterals converge. Traces from the lodicules attach to the anterior of the stamen traces. The base of the vascular system of the pistil, the pistil plexus, attaches tenuously by a bundle to the lower system between the entrance of the stamen traces. A bundle from each style attaches near the anterior of the pistil plexus below the level where the posterior of the pistil plexus rises, as the placental bundle, to merge with the ovule. Characteristics of the vascular system of Leersia, such as the relative discreteness of the staminal and stylar traces and the lack of both the anterior pistil bundle and the xylem discontinuity, are useful for delimiting the Oryzoideae from the Festucoideae.     

Seed dormancy and longevity in <Emphasis Type="Italic">Stipa tenacissima</Emphasis> L. (Poaceae)

In the present paper we studied the life history traits related to seed germination of Stipa tenacissima, a key species in semiarid environments of western Mediterranean areas. S. tenacissima is a perennial tussock grass, which has traditionally been considered to expand mainly by vegetative propagation with little or no sexual reproduction. We analysed seed longevity as well as the type of seed dormancy and the role of the seed covers from seeds collected from different populations in SE Spain. We also studied the variation in seed germinability among populations, individuals, and years and the ability of seeds of S. tenacissima to form soil seed banks. There was significant variation in seed germination among individuals, populations and years. Lemma and palea were the main factor controlling these differences since their removal promoted higher and faster germination and eliminated the differences in germination parameters among populations. However, the control of dormancy by lemma and palea was independent of their weight, suggesting that their chemical nature plays a more important role than does size in controlling seed germination. Mechanical scarification treatments (via abrasion with sand) did not affect seed germination. The decay in seed germinability two years after seed collection and the low density of viable seeds in soils one year after seed dispersal indicated that S. tenacissima forms transient soil seed banks.     

ANATOMY OF THE CARYOPSIS OF BRIZA MAXIMA (POACEAE)

Briza maxima (quaking grass) is a cosmopolitan grass common to Europe and North and South America. It grows in disturbed soils and on roadsides. The hemispherical caryopsis is embedded between a leaflike lemma and flattened palea. The embryo is of the festucoid type. The scutellum shows two surrounding ridges at the edge of the scutellum/endosperm boundary, and has lateral lobes. A broad epiblast extends toward the embryo apex and is continuous with the dorsal surface of the coleorhiza. The single-layered aleurone surrounds the starchy endosperm and is discontinuous around the embryo. The caryopsis coat is thin, except at the placental pad where it is thickened by the pigment strand and the nucellar projection.     

Seed Dormancy,Seedling Establishment and Dynamics of the Soil Seed Bank of Stipa bungeana (Poaceae) on the Loess Plateau of Northwestern China

Studying seed dormancy and its consequent effect can provide important information for vegetation restoration and management. The present study investigated seed dormancy, seedling emergence and seed survival in the soil seed bank of Stipa bungeana, a grass species used in restoration of degraded land on the Loess Plateau in northwest China. Dormancy of fresh seeds was determined by incubation of seeds over a range of temperatures in both light and dark. Seed germination was evaluated after mechanical removal of palea and lemma (hulls), chemical scarification and dry storage. Fresh and one-year-stored seeds were sown in the field, and seedling emergence was monitored weekly for 8 weeks. Furthermore, seeds were buried at different soil depths, and then retrieved every 1 or 2 months to determine seed dormancy and seed viability in the laboratory. Fresh seeds (caryopses enclosed by palea and lemma) had non-deep physiological dormancy. Removal of palea and lemma, chemical scarification, dry storage (afterripening), gibberellin (GA₃) and potassium nitrate (KNO₃) significantly improved germination. Dormancy was completely released by removal of the hulls, but seeds on which hulls were put back to their original position germinated to only 46%. Pretreatment of seeds with a 30% NaOH solution for 60 min increased germination from 25% to 82%. Speed of seedling emergence from fresh seeds was significantly lower than that of seeds stored for 1 year. However, final percentage of seedling emergence did not differ significantly for seeds sown at depths of 0 and 1 cm. Most fresh seeds of S. bungeana buried in the field in early July either had germinated or lost viability by September. All seeds buried at a depth of 5 cm had lost viability after 5 months, whereas 12% and 4% seeds of those sown on the soil surface were viable after 5 and 12 months, respectively.     

Identification and fine mapping of a mutant gene for palealess spikelet in rice

In grass, the evolutionary relationship between lemma and palea, and their relationship to the flower organs in dicots have been variously interpreted and wildely debated. In the present study, we carried out morphological and genetic analysis of a palealess mutant (pal) from rice (Oryza sativa L.), and fine mapping the gene responsible for the mutated trait. Together, our findings indicate that the palea is replaced by two leaf-like structures in the pal flowers, and this trait is controlled by one recessive gene, termed palealess1 (pal1). With a large F2 segregating population, the pal1 gene was finally mapped into a physical region of 35 kb. Our results also suggest that the lemma and palea of rice are not homologous organs, palea is likely evolutionarily equivalent to the eudicot sepal, and the pal1 should be an A function gene for rice floral organ identity.     

Ectopic expression of <Emphasis Type="Italic">OsMADS1</Emphasis> caused dwarfism and spikelet alteration in rice

In rice, an E-class gene, OsMADS1, acts to specify the identities of the lemma and palea. In this study, the OsMADS1 gene with a CaMV35S promoter was transformed into a japonica cultivar, Zhonghua 11. All transgenic plants successfully showed similar phenotypes, including dwarfism, distorted panicles, decreased numbers of branches and spikelets, and elongated sterile lemma. Histological analysis showed that the elongated sterile lemma developed with silicified epidermal and sclerenchymal cells, which were lacking in the wild-type sterile lemma, suggesting that the elongated sterile lemma had assumed the identity of the lemma or palea. Some marker genes were subjected to a detailed analysis of the distribution of their expression among the lemma, palea and sterile lemma. DROOPING LEAF (DL) and OsMADS6 genes were only expressed in the normal lemma or palea, respectively. In the elongated sterile lemma, a high level of DL gene expression was detected, while no expression of OsMADS6 was found, implying that the sterile lemma transformed into the lemma but not the palea. These results provide clues to elucidate the mechanism of evolution from lemma to sterile lemma in rice. qPCR analysis also suggested that the ectopic expression of OsMADS1 induced abnormal brassinosteroid and gibberellin acid activation, and then resulted in developmental defects in the stem and panicle.     

SCANNING ELECTRON MICROSCOPY AND ELECTRON MICROPROBE ANALYSIS OF SILICIFICATION PATTERNS IN INFLORESCENCE BRACTS OF AVENA SATIVA

Using scanning electron microscopy, we determined the kinds and distribution of epidermal cell types in Avena inflorescence bracts (glume, lemma, and palea). Electron microprobe analysis of silica deposition in these epidermal cells showed that silica cells constitute one of the important deposition sites. Probe ratio data indicate that the silica deposited is 74 % pure. Significant amounts of silica also become deposited in the trichomes and lesser amounts in the walls of long epidermal cells. None could be detected in the stomata. The possible functional significance of silica deposition in epidermal cells of these bracts is discussed.     

SURFACE CONFIGURATION OF THE LORICA OF THE EUGLENOID TRACHELOMONAS AS REVEALED WITH SCANNING ELECTRON MICROSCOPY

The surface of Trachelomonas was examined readily with SEM at magnifications up to X 20,000 in unfixed or fixed material. Cells were placed directly on specimen holders without washing, air dried, and coated with aluminum or gold. Clones of T. grandis, T. hispida var. coronata, and T. oblonga var. punctata and three species from a natural collection showed the following features: the lorica was punctate or solid, and the surface projections, when present, consisted of minute papillae (0.1 μm), larger, often globose papillae (up to 0.8 μm), and spines which tapered to a point or which had parallel sides and ended bluntly; spines appeared hollow or solid. Pringsheim's clone of T. oblonga var. punctata, which he described as a new spineless variety, possessed short tapering spines and globose papillae. Such observations suggest that a major problem in delimiting species may be in discovering the ornamentation potential of a clone. The discovery of new features of the lorica (e.g., minute papillae and hollow projections), the clarification of shapes of surface features, and, in general, the excellent resolution at 10 times the usable magnification of light microscopy dictate a reexamination of known species with SEM. We suggest that a SEM study of the variation in the lorica surface in clonal material will lead to a recognition of polymorphism and eventually to a clearer understanding of taxonomic entities described from natural collections.     

Self-incompatibility and interspecific incompatibility: relationships in intra- and interspecific crosses of Zinnia elegans Jacq. and Z. angustifolia HBK (Compositae)

Summary Intraspecific and reciprocal interspecific crosses involving Zinnia angustifolia clones and Z. elegans lines showed that in both species, sporophytic self-incompatibility (SI) systems were present. Intensity of SI varied among clones and lines, and high self seed set was associated with a concomitant decrease in callose fluorescence in papillae and pollen tubes. Incomplete stigmatic inhibition of pollen germination and tube growth was observed in reciprocal interspecific crosses and associated with callose synthesis, suggesting S-gene activity. Seed set and progeny obtained following Z. angustifolia×Z. elegans matings was comparable to intraspecific compatible matings of Z. angustifolia although the rate of pollen tube growth through the style was slower. In Z. elegans × Z. angustifolia matings, additional prezygotic barriers were present and acted between pollen tube penetration of the stigma and syngamy. SI X SI interspecific incompatibility was essentially unilateral, with no embryos or progeny obtained when Z. elegans was the pistillate parent. It was hypothesized that nonfunctioning of Z. elegans × Z. angustifolia crosses was due to S-gene expression at the stigmatic surface and to other isolating mechanisms in the stylar or ovarian transmitting tissue.Scientific Article No. A-4448, Contribution No. 7439 of the Maryland Agricultural Experiment Station, Department of HorticultureA portion of this paper was presented in the report: Boyle TH, Stimart DP (1986) Incompatibility relationships in intra- and interspecific crosses of Z. elegans Jacq. and Z. angustifolia HBK (Compositae). In: Mulcahy D (ed) Biotechnology and ecology of pollen. Springer, New York     

小麦种子成熟和萌发过程中的假萌发素活性

用SDS-PAGE方法研究了假萌发素(ψG)在小麦种子成熟和萌发过程中活性的变化.结果表明:在种子成熟过程中只有ψG表达,扬花后10 d,在颖壳、内外桴、种皮和果皮中皆可检测到ψG的草酸氧化酶活性,随着发育进程的推进,ψG的活性增大.在种子萌发过程中,在小麦品种中育5号的维管束过渡区中除了萌发素G和G'外,还可检测到ψG的草酸氧化酶活性.由于ψG在种子成熟过程中主要存在于颖壳、内外桴、果皮及种皮这些保护组织中,且开始大量表达的时间正是生长接近停止时,于是推测ψG很可能通过降解草酸产生H2O2而推动这些组织细胞壁的木质化.     

THE ROLE OF INTROGRESSIVE HYBRIDIZATION IN THE EVOLUTION OF THE GILA ROBUSTA COMPLEX (TELEOSTEI: CYPRINIDAE)

Abstract The extent and impact of introgressive hybridization was examined in the Gila robusta complex of cyprinid fishes using mitochondrial DNA (mtDNA) sequence variation. Lower Colorado River basin populations of G. robusta, G. elegans, and G. cypha exhibited distinct mtDNAs, with only limited introgression of G. elegans into G. cypha. The impact of hybridization was significant in upper Colorado River basin populations; most upper basin fishes sampled exhibited only G. cypha mtDNA haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence. Analysis of the geographic distribution of variation identified two distinctive G. elegans lineages; however, the small number of individuals and localities sampled precluded a comprehensive analysis. Analysis of haplotype and population networks for G. cypha mtDNAs from 15 localities revealed low divergence among haplotypes; however, significant frequency differences among populations within and among drainages were found, largely attributable to samples in the Little Colorado River region. This structure was not associated with G. cypha and G. robusta, as morphotypes from the same location are more similar than conspecific forms in other locations. This indicates that morphological and mtDNA variation are affected by different evolutionary forces in Colorado River Gila and illustrates how both hybridization and local adaptation can play important roles in evolution.     

Infection Process of Burkholderia glumae in Rice Spikelets

Burkholderia glumae, which causes bacterial panicle blight of rice (BPBR), is a well‐known pathogen. The pathogen‐induced symptoms include seedling rot, grain rot and leaf‐sheath browning in rice plants. B. glumae can incubate in rice plants as endophytes before booting stage of rice. In this study, we constructed a gfp‐labelled system of B. glumae LMG 2196 and used SEM to clarify the colonization course of B. glumae at the heading stage. New locations of B. glumae were found. The pathogens initially distributed on the surface of the glumes and colonized in the glume hairs and cells of the edge of sterile lemma, palea and lemma. The base of glume hairs was the initial position for colonization. Bacterial population raised around glume hairs, penetrated into the inner surface of the palea and lemma, and spread on the gynoecium and stamens through contact. The spreading of B. glumae among the panicles mainly occurred through the contact or friction among glumes or leaf sheaths, but the inner spread of the stamens mainly occurred through the connective tissue of anther. We also detected the differences of bacterial content in stamens, gynoecia and glumes. The growing stage of B. glumae in spikelets could be divided into two sections. The biomass of all parts continued to increase to nearly 10⁸ CFU/g at 10 DAI. This caused wilt symptoms and stopped the pollination. This work showed that glume hairs played an important role in the initial colonization of B. glumae, and provides a foundation for further studies of the infection manner of B. glumae and other pathogenic bacteria.     

Morphology of caryopses,seedlings and seedling emergence of the grass Calamovilfa longifolia from various depths in sand

Summary The spikelets of the grass Calamovilfa longifolia (Hook) Scribn. are one flowered and the dispersal unit is composed of a caryopsis (3.5 mm long and 0.9 mm wide) enclosed in lemma and palea. The highest germination of caryopses and emergence of seedlings occurred from 1–2 cm depths and seedling emergence decreased with increasing depth of burial. The maximum depth of sand from which a seedling can emerge is about 8 cm. Seedlings emerging from deep locations had first internodes which were more elongated than those of seedlings from more shallow plantings. Coleoptile lengths of seedlings from shallow or deeply buried caryopses were similar.