Polyamine levels in buds and twigs of Tilia cordata from dormancy onset to bud break

The fluctuations of free and bound polyamines (PAs) were studied in vegetative buds and underlying twigs of linden (Tilia cordata L.) from August to May, to assess the connection between PA levels and seasonal cycles of growth and dormancy. Outer and inner bud scales and shoot tips (short shoot tips with leaf initials in contiguous short internodes) were analyzed separately, as were phloem with cortex and xylem with pith tissue from twigs. Seasonal variations in PA levels were present in buds and twigs during the research period. The most abundant PA in buds and twigs in free and bound forms was spermidine followed by putrescine. PA amounts were low in buds and twigs in autumn. In twig tissues, free PAs were predominant whereas in bud scales, bound PAs accumulated over free PAs in autumn, first in inner scales and later in outer scales as well. PA levels did not increase dramatically during the onset of dormancy in autumn but lower temperatures and probable cold hardening correlated positively with bound PAs in bud scales. In shoot tips with leaf initials, and contiguous short internodes, free putrescine and spermidine levels rose simultaneously with bud burst and new growth, while bound PAs diminished quite radically from temporary bud scales and from growing shoot tips.     

Flower Morphogenesis in Rosa hybrida 'Mercedes' as Studied by Cryo-scanning Electron and Light Microscopy. Effects on Light and Shoot Position on a Branch

Flower bud development in Rosa hybrida cv. 'Mercedes' was studied in shoots grown at different irradiances and sprouting from axillary buds at different branch positions. Cryo-scanning electron microscopy and light microscopy were used to visualize, characterize and determine flower morphogenesis during early shoot development. Up to the moment of visible flower bud appearance on the plant, flower morphogenesis was divided into nine stages. This classification was based on external and internal characteristics of the primordium. All shoots of the rose 'Mercedes' whether positioned uppermost or second on a branch and whether grown at 300 or 150 μmol m^-2 s^-1 PAR (12 h d^-1) developed equally up to flower stage 7, i.e. the stage just before visible initiation of stamen and pistils. Signs of flower bud abortion were the compactness of the flower bud at developmental stage 7 (height/width < 1·5) and the sprouting of axillary buds positioned just below the flower bud primordium. It was concluded that once a flower bud has reached a height to width ratio larger than 1·5, and once stamen and pistil developmental has started, it has passed the critical developmental stage in which abortion may occur. Flower developmental stage was closely related to shoot length. This relationship was not affected by irradiance level nor by shoot position on a branch. Therefore, cultivation treatments aimed to improve flower production by reducing flower abortion, such as supplementary lighting, will be most effective when applied during the first 2 weeks of shoot growth in which the flower develops up to stage 7.     

Plant regeneration,origin, and development of shoot buds from root segments of <Emphasis Type="Italic">Melia azedarach</Emphasis> L. (<Emphasis Type="Italic">Meliaceae</Emphasis>) seedlings

Summary In vitro regeneration of plants from root culture of Melia azedarach seedlings was obtained. The origin and mode of development of the regenerated shoot buds were studied by means of histological analysis and scanning electron microscopy (SEM). Maximum shoot bud regeneration was achieved when root segments were cultured on Murashige and Skoog (MS) medium at quarter strength with 3% sucrose and 0.44 μM benzyladenine (BA) and kept under light (116 μmol m⁻² s⁻¹). Shoot bud elongation was achieved on MS with 0.44 μM BA, 0.46 μM kinetin (KIN), and 3.26 μM adenine sulphate (AD). Regenerated shoots were rooted on MS with 12.26 μM indole-3-butyric acid (IBA) for 4 d and subsequently in MS lacking plant growth regulators for 26 d. Plants were established in a potting substrate. Histological analysis of roots from intact seedlings (without treatment) demonstrated that during the early life of the roots, M. azedarach lacks preformed buds. In contrast, when the roots were excised and cultured in vitro, the histology and SEM observations revealed that buds originated from meristematic groups of cells, which had been formed from the pericycle and several layers beneath. These meristematic groups of cells grew towards the periphery of the cortex by crushing the outer layer of cortical cells. Further develoment led to the differentiation of leaf primordia and a shoot apical meristem.     

Inhibitory Effect of Methyl Jasmonate on Flowering and Elongation Growth in Pharbitis nil

The effect of methyl jasmonate (JA-Me) on the floral bud formation and elongation growth in the short-day plant Pharbitis nil was investigated. The placing of 4-day-old seedlings of P. nil in a solution of JA-Me for a period of 24 h before an inductive (16 h or 14 h of darkness) night led to a dramatic reduction in the number of flower buds formed by the plant. Plants treated with JA-Me also totally lost their capacity to form a generative terminal bud. JA-Me applied after photoinduction does not inhibit flowering. Gibberellic acid (GA3) partly reverses the inhibitory effect of JA-Me. Plants treated simultaneously with JA-Me and GA3 formed about 3 flower buds more than plants treated with JA-Me only. JA-Me at a concentration of 10-7 M stimulates slightly, but at higher concentrations it inhibits root growth and shoot growth. A distinct lack of correlation between the effect of JA-Me on inhibition of flowering and shoot and root growth was noted. This indicates the independent action of JA-Me in controlling both processes.     

Inhibitory Effect of Methyl Jasmonate on Flowering and Elongation Growth in Pharbitis nil

The effect of methyl jasmonate (JA-Me) on the floral bud formation and elongation growth in the short-day plant Pharbitis nil was investigated. The placing of 4-day-old seedlings of P. nil in a solution of JA-Me for a period of 24 h before an inductive (16 h or 14 h of darkness) night led to a dramatic reduction in the number of flower buds formed by the plant. Plants treated with JA-Me also totally lost their capacity to form a generative terminal bud. JA-Me applied after photoinduction does not inhibit flowering. Gibberellic acid (GA3) partly reverses the inhibitory effect of JA-Me. Plants treated simultaneously with JA-Me and GA3 formed about 3 flower buds more than plants treated with JA-Me only. JA-Me at a concentration of 10-7 M stimulates slightly, but at higher concentrations it inhibits root growth and shoot growth. A distinct lack of correlation between the effect of JA-Me on inhibition of flowering and shoot and root growth was noted. This indicates the independent action of JA-Me in controlling both processes.     

THE SHELL ZONE: ITS DIFFERENTIATION AND PROBABLE FUNCTION IN SOME DICOTYLEDONS

Thirty-five species belonging to various dicotyledonous families were investigated to study the origin, development, and probable function of the shell zone, which is defined as an arcuate zone of cambiform cells delimiting the early axillary bud meristem. It is present in the majority of the investigated plants and five intergrading patterns of origin are described: (i) from the parenchymatized derivatives of the cells of the peripheral meristem of the shoot apex, adaxial to the bud meristem, (ii) from the peripheral meristem of the shoot apex along with the initiation of the early bud meristem, (iii) from the adaxial cells of the bud meristem, (iv) from the derivatives of the cells of the bud meristem at its base, and (v) partly from the parenchymatized cells of the peripheral meristem adaxial to the bud and partly from the adaxial derivatives of the bud meristem. The shell zone loses its identity at different stages of bud development in various species. Its cells ultimately contribute to the ground meristem, procambium, and pith cells of the axis. In Cuminum cyminum and lpomoea cairica the shell zone contributes in bringing about the axillary position of the bud from its early lateral position. In Solarium melongena, derivatives of the shell zone initiate the internodal elongation between the flower or inflorescence and the shoot apex, ultimately shifting the bud to an extra-axillary position on the internode.     

Morpho-Histological Investigation of Plantlet Formation In Vitro in Taiwania flousiana Gaussen

Histological events during adventitious shoot formation in cultured shoot apex of 10–12-day-old seedlings and adventitious root formation in the elongated shoot of Taiwania floudana Gaussen were examined. Ceils of the peripheral subsurface layers of the shoot apex responded to cytokinin and divided into meristematic cells from which the shoot primordia were proliferated. A few bud primordia also originated from the epidermis and hypodermis of the adaxial surface of the cotyledon. The parenchyma of leaf gap of the shoots cultured in rooting medium dedifferentiated to regain the capacity of division and form adventitious root. Besides, cells that had relatively low potential of differentiation, such as the cortex parenchyma, pith ray, phloem parenchyma and cambium zone, albeit initiated to divide, but seldom formed root primordium. The origin of the adventitious roots in the leaf gap facilitated the establishment of the vascular connection between the shoot and root.     

Histogenesis of the transmitting tract in Strelitzia reginae

Organisation and development of the stigmatic, stylar and ovarian parts of the transmitting tract in Strelitzia reginae were evaluated. They were characterised by 1) cell shape, 2) appearance of distal cell wall, 3) type of plastid, 4) and vacuolar system. The long stigmatic trichomes have a secondary irregular wall layer separated from the primary wall. Cell structures include pleomorphic plastids with vesiculated thylakoids and frequently a crystal or a lipidic globule. In early stages of bud development the extensive endoplasmic reticulum (ER) is smooth, whereas it is mainly rough in older buds. Coated vesicles are frequent, as are dictyosomes. Prominent invaginations along the plasma membrane contain floccular deposits in the older flower buds. These deposits are similar in structural appearance to material in the large vacuoles. The basal part of the stigma has wedge-shaped cells with wall ingrowths. Three stages of stigmatic secretion during the development were characterised. The stylar canal is initially narrow but widens subsequently. The cuticle is detached and the apical cell walls show a fringed surface; from this wall inbuddings develop shortly before anthesis. At this stage sheets of rough ER are evident in the cell cortex. The plastids have a few vesiculated thylakoids, proteinaceous crystals and starch grains. The epithelial cells of young buds have numerous vacuoles, the volume of which decreases in more mature cells. The stylar canal is filled with a secretion at all stages of bud development. The face of the ovarian transmitting tract, lining the placenta, is smooth in young buds but lobed in older ones due to the division pattern of the epithelial cells. These cells are large, elongated and culumnar as young but narrow and wedge-shaped when more mature. Cell wall inbuddings are formed late during bud development.     

Shoot bending promotes flower bud formation by miRNA‐mediated regulation in apple (Malus domestica Borkh.)

Flower induction in apple (Malus domestica Borkh.) trees plays an important life cycle role, but young trees produce fewer and inferior quality flower buds. Therefore, shoot bending has become an important cultural practice, significantly promoting the capacity to develop more flower buds during the growing seasons. Additionally, microRNAs (miRNAs) play essential roles in plant growth, flower induction and stress responses. In this study, we identified miRNAs potentially involved in the regulation of bud growth, and flower induction and development, as well as in the response to shoot bending. Of the 195 miRNAs identified, 137 were novel miRNAs. The miRNA expression profiles revealed that the expression levels of 68 and 27 known miRNAs were down‐regulated and up‐regulated, respectively, in response to shoot bending, and that the 31 differentially expressed novel miRNAs between them formed five major clusters. Additionally, a complex regulatory network associated with auxin, cytokinin, abscisic acid (ABA) and gibberellic acid (GA) plays important roles in cell division, bud growth and flower induction, in which related miRNAs and targets mediated regulation. Among them, miR396, 160, 393, and their targets associated with AUX, miR159, 319, 164, and their targets associated with ABA and GA, and flowering‐related miRNAs and genes, regulate bud growth and flower bud formation in response to shoot bending. Meanwhile, the flowering genes had significantly higher expression levels during shoot bending, suggesting that they are involved in this regulatory process. This study provides a framework for the future analysis of miRNAs associated with multiple hormones and their roles in the regulation of bud growth, and flower induction and formation in response to shoot bending in apple trees.     

Anatomical Structures of the VA Mycorrhiza in the Apocynaceae (Gentianales)

Roots of 19 Apocynaceae species were studied anatomically with respect to their symbiosis with VAM-fungi. In plants collected from the field, VAM-fungi were established in the root cortex. Also, inoculations with different Glomus species on the cultured plants are very successful in the infection and colonization of the root cortex. After penetration of the rhizodermis, the special exodermal short cells become colonized by winding hyphae. Then, in the root cortex of many Apocynaceae species, the VAM-fungi produce intercellular running hyphae which leads to extensive colonization of the root. Arbuscules develop on intracellular running hyphae, whereas vesicles develop mainly on intercellular hyphae. Except for some special details, this is the most common type of colonization of VAM fungi in flowering plants. But in Amsonia tabernaemontana, Nerium oleander, and Thevetia peruviana, another type of colonization could be observed. In these species, the colonization of the hyphae within the root cortex is only possible by intracellular growth. Intercellular running hyphae in the root are lacking. Therefore, after penetration the colonization in the cortex is cluster-like and strictly limited. Only by additional penetrations from hyphae in the soil, will roots show heavy infestations. This type of growth of the VAM fungi in the root is well known from the Gentianaceae and was explained as a structural incompatibility. In Catharanthus roseus, Pachypodium lamerei, and Trachelospermum jasminoides, intermediate stages of both types of colonization could be described. The results are discussed in the search for possible stimulants for structural incompatibility.     

白鲜根的发育解剖学研究

应用半薄切片、常规石蜡切片并结合离析法,对药用植物白鲜(Dictamnus dasycarpus Turcz.)根的发生发育过程进行了研究。结果表明:白鲜根的发生发育过程包括4个阶段,即原分生组织阶段、初生分生组织阶段、初生结构阶段以及次生结构阶段。原分生组织位于根冠内侧及初生分生组织之间,衍生细胞分化为初生分生组织。初生分生组织由原表皮、基本分生组织以及中柱原组成。原表皮分化为表皮,基本分生组织分化为皮层,中柱原分化为维管柱,共同组成根的初生结构;在初生结构中,部分表皮细胞外壁向外延伸形成根毛,皮层中分布有油细胞,内皮层有凯氏带,初生木质部为二原型或偶见三原型,外始式;根初生结构有髓或无。次生结构来源于原形成层起源的维管形成层的活动以及中柱鞘起源的木栓形成层的活动;白鲜次生韧皮部宽广,其中多年生根中可占根横切面积的85%,另外除基本组成分子外,还分布有油细胞;周皮发达,木栓层厚;初生皮层、次生木质部和次生韧皮部薄壁细胞中常充满丰富的淀粉粒。     

Development and Growth Potential of Axillary Buds in Roses as Affected by Bud Age

The effect of axillary bud age on the development and potentialfor growth of the bud into a shoot was studied in roses. Ageof the buds occupying a similar position on the plant variedfrom 'subtending leaf just unfolded' up to 1 year later. Withincreasing age of the axillary bud its dry mass, dry-matterpercentage and number of leaves, including leaf primordia, increased.The apical meristem of the axillary bud remained vegetativeas long as subjected to apical dominance, even for 1 year. The potential for growth of buds was studied either by pruningthe parent shoot above the bud, by grafting the bud or by culturingthe bud in vitro. When the correlative inhibition (i.e. dominationof the apical region over the axillary buds) was released, additionalleaves and eventually a flower formed. The number of additionalleaves decreased with increasing bud age and became more orless constant for axillary buds of shoots beyond the harvestablestage, while the total number of leaves preceding the flowerincreased. An increase in bud age was reflected in a greaternumber of scales, including transitional leaves, and in a greaternumber of non-elongated internodes of the subsequent shoot.Time until bud break slightly decreased with increasing budage; it was long, relatively, for 1 year old buds, when theysprouted attached to the parent shoot. Shoot length, mass andleaf area were not clearly affected by the age of the bud thatdeveloped into the shoot. With increasing bud age the numberof pith cells in the subsequent shoot increased, indicatinga greater potential diameter of the shoot. However, final diameterwas dependent on the assimilate supply after bud break. Axillarybuds obviously need a certain developmental stage to be ableto break. When released from correlative inhibition at an earlierstage, increased leaf initiation occurs before bud break.Copyright1994, 1999 Academic Press Age, axillary bud, cell number, cell size, pith, shoot growth, Rosa hybrida, rose     

SHOOT APEX ORGANIZATION AND ORIGIN OF THE RHIZOME-BORNE ROOTS AND THEIR ASSOCIATED GAPS IN DENNSTAEDTIA CICUTARIA

The shoot apex of Dennstaedtia cicutaria consists of three zones—a zone of surface initials, a zone of subsurface initials, and a cup-shaped zone that is subdivided into a peripheral region and central region. A diffuse primary thickening meristem, which is continuous with the peripheral region of the cup-shaped zone, gives rise to a broad cortex. The roots occurring on the rhizomes are initiated very near the shoot apex in the outer derivatives of the primary thickening meristem. The roots that occur on the leaf bases also differentiate from cortical cells. Eventually, those cortical cells situated between the newly formed root apical cell and the rhizome procambium (or leaf trace) differentiate into the procambium of the root trace, thus establishing procambial continuity with that of the rhizome or leaf trace. Parenchymatous root gaps are formed in the rhizome stele and leaf traces when a few of their procambial cells located directly above the juncture of the root trace procambium differentiate into parenchyma. As the rhizome procambium or leaf trace continues to elongate, the parenchyma cells of the gap randomly divide and enlarge, thus extending the gap.     

Role of hormones on flower bud formation in thin-layer expiants of tobacco

Flower bud formation was studied in thin-layer tissue expiants of epidermis plus subepidermal cortex from the inflorescence ramifications ofNicotiana tabacum cv. Samsun. With appropriate hormone concentrations of BA and NAA expiants from flowerv and fruitbearing stalks regenerate flower buds only, while those from the internodes of the inflorescence ramifications produce generative as well as vegetative buds. In both types of expiants the number of buds formed depend mainly on the hormone concentrations but, in addition, the age of stalks and internodes from which expiants are taken also affects bud formation. Both ABA and JA inhibit flower bud formation in expiants of flower stalks. JA was shown to particularly inhibit bud initiation.     

银杏LEAFY同源基因的时空表达

以银杏雄株、雌株成年树和还未开过花的幼树的根、茎、叶,雌株幼果和不同时期的雄花芽、雌花芽为材料,利用同位素标记,制备Ginlfy和GinNdly两个特异探针,进行Northern分子杂交,研究银杏LFY同源基因Ginlfy、GinNdly在银杏不同器官,花芽不同生长发育时期的时空表达情况。结果显示,无论是幼树,还是成年的雌株、雄株,Ginlfy基因在各个器官,如根、茎、叶、雌花芽、雄花芽、幼果以及雌花芽、雄花芽的不同发育时期都有表达,属组成型表达,而GinNdly基因只在叶和不同时期的雄花芽、雌花芽中表达,其他器官都不表达,属特异性表达。银杏双拷贝LFY同源基因中的GinNdly基因可能与开花关系更为密切。 Abstract: Expressions of Ginlfy and GinNdly gene were studied by northern blotting in different organs and stages of Ginkgo Biloba. Ginlfy gene was expressed in different organs such as root, stem, leaf of juvenile tree, male tree and female tree, and in different stages of male flower bud and female flower bud. It was inferred that Ginlfy gene could be expressed constitutionally. GinNdly gene was only expressed in leaf of juvenile tree, male tree and female tree and in different stages of male flower bud and female flower bud, while GinNdly gene was not expressed in the other organs. Therefore it was thought that GinNdly gene could be expressed differentially and be a close relation to development of flower.     

<Emphasis Type="Italic">In vitro</Emphasis> organogenesis of chestnut (<Emphasis Type="Italic">Castanea sativa</Emphasis> Mill.) cotyleodon explants: responses to growth regulators and developmental aspects

Summary Adventious root and shoot formation was obtained from cotyledon fragments of chestnut (Castanea sativa Mill.) and these processes followed two phases. In a first stage after detachment of the embryonic axis, the cotyledon fragments in culture formed a cotyledon petiole, which elongated for about 6d. Thereafter, root primordia arose at the tip of the cotyledon petioles, followed by normal root development. In some cases, the cotyledon, petioles showed adventitious shoot regeneration from a nodular structure previously formed at the end of the petioles. The presence or absence of growth regulators did not significantly influence root regeneration, whereas cytokinins stimulated shoot formtion. The processes of root and shoot differentiation were studied also at the histological level. Observation with a light microscope showed that the developing root apical meristems were connected with a vascular bundle of the cotyledon petiole. Similarly, shoot bud meristem connections were observed with vascular tissue inside the nodular structure.     

Winter bud content according to position in 3-year-old branching systems of 'Granny Smith' apple

An investigation was made of the number of preformed organs in winter buds of 3-year-old reiterated complexes of the 'Granny Smith' cultivar. Winter bud content was studied with respect to bud position: terminal buds were compared on both long shoots and spurs according to branching order and shoot age, while axillary buds were compared between three zones (distal, median and proximal) along 1-year-old annual shoots in order 1. The percentage of winter buds that differentiated into inflorescences was determined and the flowers in each bud were counted for each bud category. The other organ categories considered were scales and leaf primordia. The results confirmed that a certain number of organs must be initiated before floral differentiation occurred. The minimum limit was estimated at about 15 organs on average, including scales. Total number of lateral organs formed was shown to vary with both bud position and meristem age, increasing from newly formed meristems to 1- and 2-year-old meristems on different shoot types. These differences in bud organogenesis depending on bud position, were consistent with the morphogenetic gradients observed in apple tree architecture. Axillary buds did not contain more than 15 organs on average and this low organogenetic activity of the meristems was related to a low number of flowers per bud. In contrast, the other bud categories contained more than 15 differentiated organs on average and a trade-off was observed between leaf and flower primordia. The ratio between the number of leaf and flower primordia per bud varied with shoot type. When the terminal buds on long shoots and spurs were compared, those on long shoots showed more flowers and a higher ratio of leaf to flower primordia.     

栝楼不定根尖分化不定芽过程中的细胞组织学研究

将栝楼（Trichosanthes kirilowii)长约0.5-1cm不定根尖（连同原外植体茎段或根段一起,或不连）培养在MS附加6－BA5mg/L的培养基上光照培养15d,可在根尖分化出大量不定芽。不定根尖培养过程中每隔2－3d取材,用FAA固定液固定1次,通过石蜡切片观察,将栝楼的不定根尖端分化不定芽的细胞组织学变化分为4个时期。1．启动期（0-3d),根尖分生组织细胞、中柱鞘细胞起动分裂。2“根茎转变区”原形成层形成期（4－6d0。起动细胞分裂后形成2－3层体积小、核大、质浓、近似扁平形的细胞层,组成“杯形”的“根茎转变区”原形成层。3．“根茎转变区”形成期（7－10d)。原形成层不同部位加速分裂使根尖膨大成半球形、球形或梭形,并在膨大区进行维管组织的转变。4．芽分化形成期（11－15d)。原形成层在不同部位向外形成“突起”即分生细胞团,每个“突起”发育为1个芽原基。作者还讨论了栝楼与其它植物根芽产生的异同。     

Translocation of 14C-Assimilates in Roses

Movement of ¹⁴C-assimilates from young and mature leaves to young rose shoots (Rosa hybrida cv. Marimba) was examined in two developmental stages. In the first stage after bud breaking the young shoot, especially its tip, depends for its supply of assimilates mainly on the mature foliage. At this stage young leaves are powerful sinks and retain 97% of their own photosynthates. The translocated 3% move mainly to the roots. At a later stage, just after the appearance of the flower bud, most of the leaves on the shoot become a source. The upper leaves supply assimilates to the flower bud and to the upper part of the stem. The ¹⁴C-assimilates from the lower leaves move in two directions, the larger part being directed downward.     

Factors Affecting Flower Abortion and Malformation in Roses

The formation of blind shoots and malformed flowers in rose plants grown under various temperatures and light intensities, and subjected to different cut back procedures has been studied. Low temperature, low light intensity and low cut back promoted blind shoot formation. Hybrid tea cultivars are more sensitive for unfavourable temperature, light and cut back treatments than Floribunda cultivars. The process of floral abortion is initiated during the early stages of shoot growth before the differentiation of floral parts has been completed. Low temperatures (12–15°C) in this critical stage of development strongly promote blind shoot formation, but have no effect when stamen and pistil primordia had been formed in the apical flower bud. The formation of malformed flowers, so-called “bullheads”, which have significantly more petals than normal flowers, is also promoted by low temperature and low cut back. Light intensity seems to have no effect. Shoots subjected to low temperature (12°C) during the early stages of development, before the differentiation of the floral organs are fully completed, produce malformed flowers to a greater extent than shoots subjected to high temperature (18–24°C) during this period. It is suggested that blind shoot formation in roses is subject to hormonal control.