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.     

The anatomy of the shoot apex of wheat (Triticutn aestivum L.) during transition from the vegetative to the reproductive state and the determination of the primordia

An investigation was made of the anatomical structure of the shoot apex of wheat in the first four stages of organogenesis according toKuperman (1961). It was found that the shoot apex is first covered only with dermatogen (first stage). Then the hypodermis gradually differentiates (second stage) followed by differentiation of the subhypodermis (third stage). In the first stage, the central core of the apex is formed by more or less uniform isodiametric cells so that no zones are distinguishable. During the initiation of the primordia of the assimilating leaves, i.e. in the second stage, a group of larger cells was observed in the apical part of the hypodermis and can be compared with the central zone described in dicotyledons. Under it there is a characteristic group of smaller cells. In the third stage the differences between these groups of cells become less clear and in the fourth stage are no longer observable. No differences were found in the manner of initiating the leaf and bud primordia during the period of ontogenesis studied. There is, however, an alteration in the extent of growth between the bud primordium and the corresponding leaves. Short-day photoperiodic inhibition, always started on the days when the shoot apices were collected for anatomical study, showed that the determination of the primordia of the leaves and axillary buds as parts of the inflorescence is complete by the end of the third stage, at the time when the primordia in the central part of the ear are initiated     

Spike initiation in Plantago ovata Forssk.

Histological studies on Plantago ovata indicated that spikeinitiation occurs from neither the shoot apex nor the axilsof young leaves. The first detectable inflorescence primordium,noticed in the axils of older leaves, gives rise to spike primordiumat later stages of development. Plantago ovata Forssk., inflorescence initiation, shoot apex     

Morpho-histogenic studies on tendrils of Passiflora

The ontogenetic development of the tendril and its associatedorgans is investigated in 17 species of Passiflora. The shootapex shows a single tunica layer though the second layer simulatestunica. The cytohistological zonation is not a constant feature.In P. caerulea Linn., it is distinct at leaf initiation butin P. pruinosa Mast., P. vespertilio Linn., and P. watsonianaMast., it is indistinct. The main axillary bud differentiatesfrom the peripheral meristem of the shoot apex. The differentiationof this bud into floral and tendril menstems occurs at a nodeimmediately below the shoot apex in P. minima Blanco. and Pracemosa Brot. In other species this differentiation generallyoccurs at the lower nodes. The floral meristem is initiatedas an accessory bud from this bud, thus forming a bud complex.The residuum of the bud complex develops as a tendril. The thirdaccessory bud which does not originate from this bud complex,develops into a vegetative branch. The fundamental nature ofthe vascular relationship between the flower, tendril, accessorybud, subtending leaf, and the axis is similar in most of theinvestigated species.     

Size of the Chrysanthemum Shoot Apex in Relation to Inflorescence Initiation and Development

The size of the apical dome of Chrysanthemum morifolium Ramat.at the transition to inflorescence initiation in continuouslight (long days) was not systematically influenced by eitherthe temperature or the irradiance under which the plants weregrown. It was generally 0.26 mm in diameter and c. 3.6 x 10^–3mm³ in volume when the first bract was initiated. The dimensionsof the apical dome of plants in short days were only slightlysmaller at this stage. Similarly, each step in the further developmentof the chrysanthemum inflorescence was associated with a narrowrange of apex sizes, indicating that inflorescence initiationand development are closely related to apex size. Chrysanthemum morifolium Ramat, shoot apex, inflorescence initiation     

Cell Cycle Patterns in the Shoot Apex of Lolium temulentum L. cv. Ceres During the Transition to Flowering Following a Single Long Day

Six-week-old Lolium temulentum cv. Ceres plants were inducedto flower by a single long day (day 1). The ‘double ridge’stage was reached on days 4/5. A detailed analysis of apicesevery 4 h on days 3 to 5 demonstrated synchronized cell divisionin the apex. However, this synchronized cell division occurredonly in the apical summit and axillary bud sites, i.e. onlyin those regions of the apex which give rise to the spikelets.This indicates a specific activation of the cells in these regions,rather than a general activation of the whole apex. Key words: Cell cycle, flowering, Lolium, shoot apex, spikelet     

The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

Some Aspects of Floral Histogenesis in Bajra (Pennisetum typhoides S. & H.)

The young reproductive apex in Bajra (Pennisetum typhoides S.& H.) possesses a biseriate tunica and a massive corpus.The cells of three or four peripheral layers and six to eightlayers at the summit of the apex are eumeristematic. The centralregion consists of elongated, highly vacuolated, and lightlystained cells arranged in files. The initiation of the spikeletbud is by periclinal divisions first in the corpus and laterin T₂ cells. Similarly the longer bristle or the extension ofthe fascicular axis develops from the corpus and T₂ cells. Theother bristles develop from the tunica layers. The chaff membersare initiated and develop like a leaf. The development of thestamen resembles that of a spikelet or an axillary bud. Thedevelopment of the carpel is similar to that of the leaf primordium.The origin and development of the male flower is like that ofan axillary bud.     

Sex expression as affected by N6-benzylaminopurine in staminate inflorescence of Luffa cylindrica

The effect of N⁶-benzylaminopurine (BA) on the sex expressionof staminate inflorescences of Luffa cylindrica was investigated.Direct application of BA to the staminate inflorescence inducedbisexual and pistillate flowers and finally caused the inflorescenceto develop into a shoot that was similar to the main shoot.Such modification in a staminate inflorescence from the proximalto the distal nodes is usually in the order of staminate flowers,bisexual flowers, pistillate flowers and foliage leaves (shoot).Pinching of the main stem also caused the inflorescence to developinto a shoot in the absence of lateral shoots. BA-induced femalenesswas strengthened when the number of leaves remaining on theplant was increased. On the other hand, application of BA tothe shoot apex of the main stem starting at the 2-leaf stagesuppressed differentiation of the flower bud on the main stem. (Received December 22, 1979; )     

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.     

Oxygen Distribution in Wetland Plant Roots and Permeability Barriers to Gas-exchange with the Rhizosphere: a Microelectrode and Modelling Study with Phragmites australis

Adventitious roots of intact Phragmites plantlets were securedhorizontally 2–3 mm below the surface of an oxygen-depletedfluid agar across which oxygen-free nitrogen was gently streamedto create a constant oxygen sink; the leafy shoot was fullyexposed to air. Radial oxygen profiles through rhizosphere androot at different distances from the apex were obtained polarographicallyusing Clark-type bevelled microelectrodes servo-driven in stepsof 10 µm (root) or 10–50 µm (rhizosphere).The pattern of radial oxygen loss (ROL) typical of wetland plants,viz. high at the apex and declining sharply sub-apically, wasrelated to synergism between ROL, and oxygen consumption andincreasing impedance to diffusion within the epidermal/hypodermalcylinder rather than to a surface resistance. The smallest oxygendeficit (2 kPa) to develop across the 80 µm thick epidermal/hypodermalcylinder was within the apical 10 mm and was consistent withtissue oxygen diffusivities similar to water. At 100 mm fromthe apex, consumption and impedance had increased the deficitto about 15 kPa and reduced ROL almost to zero. The developingimpedance within the epidermal/hypodermal cylinder was leastin cell layers immediately adjoining the cortex and increasedmost in the hypodermal cell layer abutting the epidermis. Thesub-apical decline in ROL appeared to coincide with the appearanceof aerenchyma in the cortex but thin walled ‘passage areas’(windows) in the hypodermal/epidermal cylinder persisted locallyand remained leaky to oxygen to some degree. It is through thesewindows that lateral roots emerge and the cortex in line withthe windows remains non-aerenchymatous. The radial and longitudinaloxygen profiles were consistent with modelling predictions.The shapes of the stelar oxygen profiles were consistent witha higher oxygen demand in the outer region (viz. pericycle,phloem, protoxylem and early metaxylem cylinder) than in theinner core (late metaxylem cylinder and medulla), but the deficitswere relatively small (     

Leaf Ontogeny in Digitaria eriantha

The shoot apex consists of two layers, the dermatogen and thehypodermis. The leaf primordia arise through periclinal divisionswithin these two layers on the side of the apex. Further divisionsof the dermatogen push the little protuberance upward and togetherwith divisions the hypodermis add internal tissues of the youngleaf. When the median and lateral bundles of the primordia arisein Digitaria eriantha they are isolated from the vascular supplyof the rest of the plant. The median strand, the first to form,and the first order laterals form at the disc of insertion ofthe primordium. The other laterals form higher up in the primordium.These strands extend both acropetally and basipetally to linkwith the vascular supply of the rest of the plant. Digitaria eriantha, apical meristem, leaf primordium, vascular bundle, orange G, tannic acid, iron alum     

Intracellular Silica Deposition in Immature Leaves in Three Species of the Gramineae

The formation of solid, discrete deposits of opaline silicawithin the cell lumen of leaf tissues is reported in speciesrepresenting three subfamilies of the Gramineae; the preparationof a silica-minimal nutrient solution is discussed. Opal phytolithnumbers are related to tissue age and to two external silicaconcentrations for tiller leaves over a period of 32 days followingbud initiation. Variations in silica deposition patterns among the individualleaves of a homologous series on the shoot apex are relatedto differential growth-rates. During ontogeny, deposition occursin an ordered sequence of cell types related to the basipetalmaturation gradient within the leaf. Initial deposition wasdetected in silica cells (idioblasts) of imbricated, bud leavesof Sieglingia decumbens, 1 mm long; phytoliths are confinedto these cells in expanding, basal portions of the leaf. Phytolithcounts/sq mm of epidermis vary with the degree of long-cellexpansion. The error is reduced by expressing silicificationas the number of phytoliths/100 silica cells. Post-expansiondeposition was initiated in epidermal long cells of the leafblade tip. The higher silica concentration resulted in a morerapid utilization of available deposition sites and larger phytoliths(P = 0.001). A passive cell influx of silicic acid is discussedin relation to cytodifferentiation.     

Changes in the anatomical structure of the shoot apex ofSenecio vulgaris L. during ontogenis in relation to the formation of leaves and inflorescence

An investigation was made of the anatomical structure of the shoot apex ofSenecio vulgaris L. a photoperiodically neutral plant, and compared with the formation of successive leaf primordia along the axis up to the initiation of the terminal inflorescence. In the shoot apex of a germinating plant a central zone can first be distinguished from the peripheral zone which is composed of small and intensely stained cells. Later, a rib meristem appears. At the time of the initiation of the middle (the largest) leaves, the shoot apex has a distinct small central zone and a well developed peripheral zone and rib meristem. Between these zones there is a group of cells dividing in all directions, the subcentral zone. At the time of initiation of the last leaves, the central zone extends to the flanks and gradually ceases to be distinguishable. At the same time, the subcentral zone increases in size. This is caused first by cell division and later, with the initiation of the last, most reduced leaves, by enlargement of the cells. Vacuolization in the inner part of the apex and the arrangement of the superficial cells in rows parallel to the surface of the apex, is a preparatory step to the initiation of the inflorescence.     

Reproductive Development of the Apex of Brachiaria decumbens Stapf

The development of Brachiaria decumbens tillers, as based onapex morphology, may be conveniently divided into six phases.These are the (1) vegetative, (2) raceme initiation, (3) spikeletinitiation, (4) spikelet differentiation, (5) inflorescenceexsertion and anthesis, and (6) seed maturation phases. Theonset of reproductive development is characterized by an increasein apex length and proceeds with the expansion of a bud in theaxil of the most recently initiated leaf primordium. This budgives rise to the first raceme and further racemes are formedin basipetal succession. Changes in apex morphology during thefirst four phases of development are described and illustratedwith scanning electron microscope and median longitudinal sectionphotomicrographs. Brachiaria decumbens, signal grass, apex morphology, SEM, median longitudinal sections, developmental phases     

Patterns of Assimilate Distribution and Source--sink Relationships in the Young Reproductive Tomato Plant (Lycopersicon esculentum Mill.)

Patterns of distribution of ¹⁴C were determined in 47-day-oldtomato plants (Lycopersicon esculentum Mill.) 24 h after theapplication of [¹⁴C]sucrose to individual source leaves fromleaves 1–10 (leaf 1 being the first leaf produced abovethe cotyledons). The first inflorescence of these plants wasbetween the ‘buds visible’ and the ‘firstanthesis’ stages of development. The predominant sink organs in these plants were the root system,the stem, the developing first inflorescence and the shoot ‘apex’(all tissues above node 10). The contribution made by individualsource leaves to the assimilate reaching these organs dependedupon the vertical position of the leaf on the main-stem axisand upon its position with respect to the phyllotactic arrangementof the leaves about this axis. The root system received assimilateprincipally from leaf 5 and higher leaves, and the stem apexfrom the four lowest leaves. The developing first inflorescencereceived assimilates mainly from leaves in the two orthostichiesadjacent to the radial position of the inflorescence on thevertical axis of the plant; these included leaves which weremajor contributors of ¹⁴C to the root system (leaves 6 and 8)and to the shoot apex (leaves 1 and 3). This pattern of distributionof assimilate may explain why root-restriction treatments andremoval of young leaves at the shoot apex can reduce the extentof flower bud abortion in the first inflorescence under conditionsof reduced photoassimilate availability. Lycopersicon esculentum Mill, tomato, assimilate distribution, source-sink relationships     

Shoot development ofAucuba japonica I. Morphological study

The shoot development ofAucuba japonica was studied morphologically. The shoot shows dichasial branching in connection with the formation of a terminal inflorescence and shows a decussate phyllotaxis even in the reproductive phase. The sequence of initiation of successive foliar appendages is very precise, hence the foliage leaf, scale leaf and bract can be compared with each other even at their stages of initiation. In the stage of proximal foliage leaf formation the shoot apex is flat, while in the stage of formation of distal foliage leaves, bud scales and proximal bracts, it becomes concave. In the stage of formation of distal bracts the apex becomes domed. Plastochron durations are relatively long in the vegetative phase in comparison with other plants, and the duration from initiation of the first pair of appendages to that of the second is about one and a half months. Both male and female inflorescences exhibit basically a thyrsoid type of monotelic synflorescence.     

Structural Organization of the Shoot Apex and Axillary Bud in Slipper Spurge (Pedilanthus tithymaloides Poit.) I

The slipper spurge (Pedilanthus tithymaloides) is a small cactus-likeherbaceous plant. The shoot apex has a single tunica layer andsometimes the second layer also simulates it. There is a centralmeristem zone whose significance could not be determined. Thefirst bud meristem differentiates at the second node. The earliestbud meristem has a procambium but no shell zone was observed.The node is trilacunar. There are three bud traces and threeprophyll traces. The single prophyll is situated at right anglesto the subtending leaf.