ROLE OF STEM GROWTH IN LINUM USITATISSIMUM LEAF TRACE PATTERNS

Linum usitatissimum stem growth parameters were quantified by computer-assisted analyses of scanning electron micrographs of shoot apical meristems throughout ontogeny. There were progressive decreases in the plastochron and relative plastochron rates of radial and vertical stem growth which resulted in the generation of progressively higher orders of contact parastichy phyllotaxis throughout ontogeny. The change in the relative spacing of primordia initiation on the stem coupled with the iterative differentiation of leaf gap and interfascicular ray parenchyma associated with each leaf primordium resulted in the delimitation of progressively higher orders of leaf trace interconnections throughout ontogeny. A set of developmental rules was generated which should permit simulation of many leaf trace patterns.     

MEGAGAMETOPHYTE ORGANIZATION IN A POLYEMBRYONIC LINE OF LINUM USITATISSIMUM

A haploid-diploid twin-producing polyembryonic line “RA91” of Linum usitatissimum L., flax, known to produce twin embryos with a frequency in excess of 32% was employed to determine the cytological factors relating to the production of haploid embryos using light and transmission electron microscopy. Potentially polyembryonic flax megagametophytes contain at maturity either a conventional 3-celled egg apparatus (36% of megagametophytes), or contain supernumerary eggs forming either a 4- (50%) or 5-celled (14%) egg apparatus. In megagametophytes with supernumerary eggs, one egg cell appears to occupy the conventional position, whereas additional supernumerary eggs surmount the synergids and are smaller cells presumably derived from division of the true egg. Although supernumerary eggs appear similar in ultrastructure, they differ in location, size, and unlike typical egg cells, appear to have a complete, contiguous cell wall adjacent to the synergid. Such supernumerary cells are postulated as the origin of such haploid embryos, with the diploid member formed by conventional fertilization events with the micropylar egg.     

亚麻下胚轴离体培养和转化的研究

报道了亚麻（Ｌｉｎｕｍ　ｕｓｉｔａｔｉｓｓｉｍｕｍ）的高频率植株再生和细胞转化。亚麻下胚轴切段培养在ＭＳＢ分化培养基上,诱导分化出不定芽。最佳的激素组合是ＢＡ２ｍｇ／Ｌ＋ＩＡＡ０．５ｍｇ／Ｌ,分化频率可达９７％。在附加ＢＡ１ｍｇ／Ｌ和ＮＡＡ０．０２ｍｇ／Ｌ的ＭＳＢ培养基上,亚麻下胚轴外植体的不定芽分化频率也可达９０％以上。用根癌农杆菌（Ａｇｒｏｈａｃｔｅｒｉｕｍ　ｔｕｍｅｆａｃｉｅｎｓ）感染亚麻下胚轴外植体,在含卡那霉素５０ｍｇ／Ｌ的选择培养基上筛选获得卡那霉素抗性苗,并检测到ＧＵＳ基因活性表达。表明它们是转化植株,转化频率约为２％。     

CELLULAR BASIS FOR GROWTH AND TISSUE DIFFERENTIATION PATTERNS IN LINUM USITATISSIMUM (LINACEAE) STEMS: THE STEM UNIT

The stem unit is defined as the smallest portion of a stem that can duplicate the stem in toto through regular rotations and dilations over successive plastochrons. In stems exhibiting k(m, n) contact parastichy phyllotaxis, the stem unit is delimited vertically and tangentially by the boundaries of four successive leaf primordia along the m-, n-, and (m + n)- parastichies and radially by these boundaries extended to the centroid of the stem. With the stem unit concept, node refers only to the region of actual leaf insertion, rather than the entire transverse level of insertion. Many of the conflicting and complicating aspects of the traditional node-intemode subdivisions of stems are demonstrated, and the utility of the stem unit in circumventing these is illustrated. The stem unit is proposed as a more useful analytic subunit of the stem with which to examine stem growth and tissue differentiation processes than the more traditional node-intemode subdivisions of stems.     

亚麻原生质体培养及植株再生

试验分别采用四个纤维用亚麻(Linumusitatissimum)品种7309,948,Belinka和Viking的无菌苗的茎尖为材料游离原生质体。以萌发10天的无菌苗茎尖游离获得的原生质体得率和活性最高,分别达到1．8×106／gFW和85．5％。以V-KM为培养基,采用琼脂岛法培养的原生质体,可在培养3天后发生第一次分裂,10天后统计细胞分裂频率为36％,20天后统计植板率达到5．2％。品种7309和Belinka再生的愈伤组织接种在均附加o．6mg/L6-BA和0．1mg／LNAA的B5-1和MS3固体培养基上,都有芽苗分化,并分别获得再生植株。品种Viking和948分别仅分化获得了不定根或叶状体。     

COMPARISON OF EARLY LATERAL VEIN FORMATION IN LINUM USITATISSIMUM LEAVES WITH THEORETICAL NETWORK MODELS

The plastochron age of the Linum leaf that first exhibited lateral leaf vein divergences, the divergent leaf, increased through shoot ontogeny, but the size of the divergent leaf remained constant. There were progressive decreases in the plastochron and relative plastochron rate of leaf elongation, but no significant change in relative chronological rate of leaf elongation, through ontogeny. Thus, divergent leaves of similar sizes occupied different relative positions in the array of leaves on stems of different plastochron ages. These observations are partially consistent with theoretical network model predictions on early leaf vein development. The empirical data of this study suggest additional features of leaf development that should be incorporated into future simulation models for leaf vein development.     

MODIFIED REMNANTS OF CENTRIPETAL XYLEM IN THE LEAF TRACE OF CEPHALOTAXUS

A study of the leaf traces at the nodes in various species and varietal forms of Taxus, Torreya, Amentotaxus and Cephalotaxus reveals, only in Cephalotaxus, an unusual type of parenchymatous tissue associated with the xylem of the leaf trace. The cells of this tissue occur in one to three layers, have abundant cytoplasm and conspicuous nuclei. The thin walls of these cells are devoid of pits and show spiral or spiral-reticulate thickenings. These thickenings, although readily taking the counterstain, reveal the presence of lignin as determined by the phloroglucin test and by fluorescence microscopy. This tissue is always internal—that is, adaxial—to the protoxylem of the trace. From the node it accompanies the trace for a short distance into the leaf base, where it gives way centrally to the typical leaf parenchyma and laterally to the transfusion tissue on the flanks of the bundle. In the basipetal direction it is in contact with the inner face of the annular protoxylem of the stele, eventually disappearing in the typical pith parenchyma. This tissue occasionally reveals instances of well-lignified tracheid-like centripetal elements. On the basis of the characteristics of this tissue, it is suggested that its origin lies in former centripetal xylem. The significance of this tissue to the evolution of the stele and the systematic position of Cephalotaxus is discussed.     

SEASONAL PATTERNS OF LEAF PHOTOSYNTHETIC CAPACITY IN SUCCESSIONAL NORTHERN HARDWOOD TREE SPECIES

Seasonal patterns of leaf photosynthetic capacity and conductance were determined for deciduous hardwood tree species in natural habitats in northern lower Michigan. Leaves of bigtooth aspen and red oak at the top of the canopy had higher maximum CO₂ Exchange Rate (CER) (10–15 μmol m ² s ¹) than leaves of sugar maple, red maple, red oak, and beech growing in the understory (4–5 μmol m ² s ¹). In all leaves, CER measured at light-saturation increased to a maximum near the completion of leaf expansion in early June, was constant until mid-September, and then rapidly declined until leaf death. A similar pattern was seen for CER measured in low light (1.5% full sun). Respiration rate in the dark was highest in young leaves and decreased during leaf expansion; a relatively constant rate was then maintained for the rest of leaf lifespan. The seasonal pattern of the initial slope of the light response of CER paralleled the pattern of light-saturated CER. The initial slope in midsummer ranged from values of 37 to 44 μmol/mol for species in the understory to 51 and 56 μmol/mol for red oak and bigtooth aspen, respectively, at the top of the canopy. Leaf conductance was constant throughout most of leaf lifespan, with some decline occurring in autumn. Leaves at the top of the canopy had higher conductances for water vapor (2–5 mm/s) than leaves in the understory (1–2 mm/s). All species maintained leaf intercellular CO, mole fractions (c,) near 200 uML/L until autumn, when c, increased during leaf senescence.     

暖温带地区主要树种叶片凋落物分解过程中主要元素释放的比较

应用分解网袋法对暖温带落叶阔叶林内分布较为优势的辽东栎（Quercus liaotungensis)、五角枫（Acermono)、蒙椴（Tilia mongolica)、糠椴（T.mandshurica)等4种植物叶片凋落物第一年的分解速率损失过程基本符合Olson的指数降解模型。4种凋落物的分解速率（凋落物的年重量损失）依次为五角枫＞糠椴＞蒙椴＞辽乐栎。N、P、Na、Fe、Cu、Mn在几种凋落物残留物中各自有不同程度的富集。C、K含量显著单调下降,其它几种元素含量变化不太规律。可以看出,元素的初始含量对其释放速率有很大影响,当微生物固持作用使C与其它元素比升高到某一阈值时,元素开始释放;初始含量较高的元素则从最初开始释放。高含量的木质素对元素的净释放有一定抑制作用,而在凋落物分解初期影响不大。     

LEAF PARENCHYMA WITH TRANSFER CELL-LIKE CHARACTERISTICS IN THE MOSS,POLYTRICHUM COMMUNE HEDW

Mature leaves of Polytrichum commune Hedw. were examined in regard to structural features and possible solute transport mechanisms. The leaf bundle is organized into several parenchyma layers which are termed passage cells, deuters, and socci. The deuters (leptoids of some authors) are large-diametered parenchymatic elements which exhibit papillate wall ingrowths characteristic of transfer cells. The deuter cytoplasm is typical of transfer cells, including a large number of mitochondria, numerous polysomes, and a peripheral network of ER associated with the wall ingrowths. Deuters show little ultrastructural similarity to leptoids (sieve elements of bryophytes) of the stem. Socci parenchyma and passage cells have a distinct inner wall layer which is convoluted in places, and therefore, these cells as well as the deuters might be involved in intensive short-distance fluxes of solutes. A possible translocation mechanism involving an active, carrier-mediated loading of leaf parenchyma is discussed in relation to these structural features.     

PATTERNS IN LEAF MORPHOLOGY AND PHOTOSYNTHESIS IN SHOOTS OF SASSAFRAS ALBIDUM (LAURACEAE)

Trees of Sassafras albidum (Nuttall) Nees. display leaves that fall into discrete categories of form. Unlobed leaves, with undissected margins, predominate at proximal and distal nodes of shoots, while lobed leaves are most common at intermediate nodes. In this study we investigated the hypothesis that shoots of sassafras respond to environmental changes over the growing season by generating predictable nodal patterns for leaf morphology and physiology. We recorded leaf shape category and measured leaf surface area, node number, chlorophyll content, nitrogen content, and photosynthesis in four trees. Over 1,000 measurements of photosynthesis were made in situ, using the LI-Cor LI 6200 portable photosynthesis system. The two trees growing under heavy shade had few lobed leaves (2.0% and 18.8%) and often had negative carbon balance, with positive net photosynthesis occurring during sun flecks. The two trees growing in more open conditions had many more lobed leaves (56.3% and 61.0%) and higher, less variable net photosynthetic rates. As indicated by chlorophyll and nitrogen contents, the highest leaf photosynthetic rates occurred at intermediate nodes (nodes six to nine), and this was shifted distally along the shoot during the growing season. Leaves at intermediate nodes also had the largest surface areas and the greatest frequency of lobing. In comparative experiments with models, lobing was shown to enhance free-convectional heat loss relative to unlobed leaves of the same surface area. Due to their large surface area, these leaves also have the highest rates of whole leaf photosynthesis. Under conditions of equivalent photosynthetically active radiation, lobed leaves had higher rates of net photosynthesis than did unlobed leaves. We conclude that shoots of sassafras produce groups of leaves with predictably different morphological and physiological specializations.     

QUANTITATIVE PATTERNS OF LEAF EXPANSION: COMPARISON OF NORMAL AND MALFORMED LEAF GROWTH IN VITIS VINIFERA CV. RUBY RED

Developmental patterns produced during normal expansion of the leaf of Vitis vinifera cv. Ruby Red are quantitatively characterized from the distribution of relative growth rates and growth velocity vectors and are compared to patterns produced during the development of an abnormally shaped leaf. The bilateral symmetry of the V. vinifera leaf, which is present in the normal leafand absent in the malformed leaf, is shown during growth by the patterns of velocity isolines. Ellipses formed by the isolines around the midrib during normal development are distorted during development of the malformed leaf. During normal growth, tissue elements are displaced in rather straight lines, resulting in streamlines which radiate outward from the petiole. Element motion in the abnormally developing leaf causes curving of streamlines. Relative growth in area of elements located in an area in the normal leaf are higher than those in the malformed leaf. The most frequently observed category of relative area growth in the normal leaf is 40%-59% d~¹, while 20%–39% d^−-1 predominates in the abnormal leaf. A spatial gradient in growth appears during normal development with lowest relative growth (20%–39% d^−-1) present in the tip region, intermediate values (40%–59% d^−-1) in the midsection, and maximum growth (> 60% d^−-1) appearing in the basal region. During development of the abnormally shaped leaf, the gradient along the midrib is disrupted with low magnitudes of growth (<20% d^−-1) appearing in the midsection of the leaf where intermediate values are expected. The theoretical and numerical distinctions between two common expressions for relative growth (relative elemental growth and exponential growth rate) are discussed. Relative elemental growth is shown to become increasingly larger than the exponential growth rate as the magnitude of growth increases relative to initial size of the tissue element. Numerical methods for evaluating relative growth based on finite element areas are compared to methods based on displacement and velocity gradients and are shown to produce similar results.     

2,4—D在玉米幼叶培养中的歧义作用

本文报道,在玉米幼苗第二片叶的组织培养中:1.接近叶基的细胞对2,4-D敏感性强,而离叶基较远的细胞对2,4-D敏感性则相对弱;2.在0.02—6mg/L浓度下,2,4-D能刺激细胞进行分裂,而在20—40mg/L浓度时,2,4-D则起抑制作用;3.离叶基21mm以上的叶细胞失去对各种浓度2,4-D的反应能力;4.2,4-D诱导的愈伤组织,大多是由一些原先处于抑制状态的根原基形成的。