Shoot Axis Research Articles

The Distribution of Nine Elements in Shoots of Lupinus albus L. and Lupinus angustifolius L. Compared with that of Silicon as a Measure of Passive Transport

The Ca, Mg, K, Na, P, Fe, Mn, Zn, Cu and opaline-Si contents of leaves, stems and inflorescences from each order of shoot axis was determined in Lupinus albus L. and Lupinus angustifolius L. The distribution of Si was used as a base for passive transport in the transpiration stream. All of the elements investigated were redistributed among the leaves, stems and inflorescences of either L. albus or L. angustifolius. Most of the elements investigated were enriched in the inflorescences and depleted in either the leaves or the stems. Sodium was enriched in the stems whereas Ca and Mn were redistributed only in L. albus. The pattern of element redistribution was similar in each of the lateral shoot axes except for the youngest. For the elements enriched in the inflorescences, more than half was supplied by redistribution. Calcium redistribution was similar to that for K, which is regarded as phloem mobile, but a mechanism for Ca redistribution is uncertain.

Seasonal variations in nitrate content, total nitrogen, and nitrate reductase activities of macrophytes from a chalk stream in Upper Bavaria

11 macrophytic species from a groundwater influenced chalk stream in Upper Bavaria were investigated during a period of one year in order to determine differences in the endogenous nitrate content, in total nitrogen content and in nitrate reductase activity (NRA). Nitrate concentrations of different plants taken from the same site of the river varied by a factor of approximately 103. A maximum of 1,958 μmol NO 3- g-1 dry w. could be measured in the petioles of Nasturtium officinale, which accounts for 12% of plant dry w. Very high values were also found in Callitriche obtusangula and Veronica angallis-aquatica. In comparison to the ambient water, mean accumulation rates of up to 131 could be found. In Fontinalis antipyretica, the plant poorest in nitrate, the ratio was only 1.24:1. Elodea canadensis belonged to a group of plants having very low nitrate concentrations. Since NRA was very low too, it is assumed that nitrogen nutrition of this species depends rather on ammonia than on nitrate. With a few exceptions nitrate content of different plant organs varied markedly. In general they were lowest in leaves and highest in shoot axes. Appreciable amounts of nitrate were also found in the roots of plants. No correlation could be found between endogenous nitrate content and NRA. In contrast to endogenous nitrate content and NRA, total nitrogen concentrations of the plants did not differ significantly.

The Formation of Adventitious Organs V. The Ontogeny of the Apical Meristem of Shoots Formed by Nautilocalyx Explants

Summary When thin explants of Nautilocalyx leaves are grown on zeatin medium they produce shoot-forming meristems in or near trichomes. The stages of meristem and shoot formation were followed by light microscopy of the living explants. The meristems «differentiated after about 18 days in a more or less central, highly meristematic, pale zone, and in a surrounding green part. From the pale central part the future apex with tunica-corpus structure arose. The first leaf primordia were formed either from the pale zone or from a part of the meristem bordering this zone. The meristems remained flat until the first leaf primordia were formed. But when gibberellic acid was included in the medium a central bulge was formed from which later all parts of the shoot originated. The decussate phyllotaxis at the new shoot axis started with one leaf, or with two opposite leaves. In both cases a trichome played a role in the positioning of the first leaves.

Effects of Hormones on Morphogenesis and Cold Resistance in Berseem Clover (Trifolium alexandrinumL.)

Barnes, J. D. and Wilson, J. M. 1986. Effects of hormones on morphogenesis and cold resistance in berseem clover (Trifolium alexandrinum L.)—J. exp. Bot. 37: 1542-1551. Plants of berseem clover (Trifolium alexandrinum L.) cv. Tabor were raised under conditions inhibiting the acquisition of cold hardiness (non-hardened) or inducing cold hardiness (hardened). All non-hardened plants developed an elongated shoot and exhibited considerable frost sensitivity, as measured by the extent of the reduction in yield of variable chlorophyll fluorescence after exposure to sub-zero temperature. Hardened plants developed a shorter shoot, with fewer leaves and a greater percentage of dry matter in the root system. These parameters were associated with a marked increase in frost resistance. Exogenous application of ABA to plants effected similar morphological modifications in both hardening and non-hardening temperature regimes; plants developed a shorter primary shoot axis and leaves exhibited a marked increase in frost hardiness. In berseem clover ABA can thus substitute, at least partially, for the low temperature treatment required to induce cold hardiness. Spraying plants raised under hardening conditions with gibberellic acid reversed the effects of the hardening treatment, since they developed an elongated shoot and exhibited frost sensitivity comparable to non-treated plants grown under non-hardening conditions. It is concluded that these endogenous hormones are directly involved in triggering changes in morphogenesis which accompany physiological and metabolic events associated with the induction of plant cold hardiness.

A comparison of the growth and development of biculm wheat lines with freely tillering cultivars

SummaryThe growth, development and grain yield of two low-tillering lines of wheat of Israeli origin were compared with those of two freely tillering Australian wheat cultivars (Gamenya and Egret) in field plots. The majority of individuals from the low-tillering selections were uniculms or biculms. Detailed observations were made on the main shoot of the biculms. There was no difference in the duration of primordia production by the main shoot apex between genotypes but the rate of initiation of spikelet primordia in the lowtillering lines was significantly greater than that of the tillering cultivars and this resulted in a large ear with more spikelets. The rate of leaf appearance was very similar in all genotypes but the later-appearing leaves of the biculms were very large in comparison with those of the cultivars. The majority of the biculms produced the tiller in T3 position. At maturity the main shoot and tiller of biculm individuals produced 60 and 40% respectively more dry weight than the equivalent shoots of the tillering cultivars. The total biomass per plant of the biculms was similar to that of Egret but less than that of Gamenya. The grain yield of the main shoot of the biculms was 50% greater than that for the tillering varieties and this was associated with an increase in the number of grains per ear as there was little difference in grain size. In the biculm a high proportion of the spikelets in the mid part of the main shoot ear produced five grains; grains from basal florets were significantly larger than those of upper florets mainly because they had a longer duration of growth. Overall the grain yield of the two tillering cultivars, either per plant or per metre of row length, was approximately 30% greater than that of the low-tillering selections. The greater growth of the main shoot axis in the biculms therefore did not compensate for the grain contributed by the tillers of the freely tillering cultivars.

Effects of Leaf Age and Position on the Shoot Axis on Potassium Absorption by Tomato Leaf Slices

Effects of Leaf Age and Position on the Shoot Axis on Potassium Absorption by Tomato Leaf Slices

On the developmental morphology of the rosette galls ofAcacia leucophloea Willd., (Mimosaceae) induced byThilakothrips hablu Ramk. (Thysanoptera: Insecta)

Thilakothrips babuli induces rosette (artichoke) galls on the axillary buds ofAcacia leucophloea. As a result of feeding by the building populations of thrips, axillary shoot meristems are destroyed, and primordial palisade tissues of the leaflets and cortical tissues of the shoot axis are transformed into nutritive cells of specialised morphology. Very similar to the galls induced by mites, midges, chalcids, and chloropids,Thilakothrips-inducedAcacia galls also have a characteristic morphology, involving the inhibition of elongation of the shoot axis and crowding of maldeveloped leaflets. While describing the cecidogenesis in relation to the biology of the gall maker, an attempt has been made to discuss the morphological convergence among shoot apex galls.

THE PRIMARY THICKENING MERISTEM: DEFINITION AND FUNCTION IN MONOCOTYLEDONS

The PTM should be defined as a diffuse primary meristem which decreases in cross‐sectional extent (i.e., becomes a thinner‐walled cylinder) in a basipetal direction. It is associated with extensive anticlinal cell files and consists of cell initials that divide predominantly in periclinal planes. This meristem occurs typically in monocotyledons, especially those with thick, compact stems in species with rosette shoot axes. The PTM is also associated with a wide crown, so that the apical meristem is either slightly above the level of youngest leaf primordia, at approximately the same level as the leaf primordia, or distinctly sunken below surrounding stem tissue and the youngest leaf primordia. The location is dependent on the extent of primary thickening growth occurring in a particular species. A meristem associated with primary thickening of other plant groups should not be called a primary thickening meristem unless all of the above characteristics are shown to be associated with the meristem being examined. The primary thickening meristem is responsible for primary thickening of a stem axis. Its ontogenetic relationship with the STM needs further investigation. Extensive primary stem thickening has been observed in non‐monocotyledons (ferns, lycopods, cycads, and dictyledons). Some of these organisms appear to undergo primary thickening from a PTM in a similar process as that which occurs in monocotyledons. Further research is necessary to establish the mechanisms of primary thickening in these cases.

MORPHOGENESIS OF POLLEN CALLUS CULTURES OF HYOSCYAMUS NIGER

Morphogenesis of calluses of single pollen grain origin shed from anthers of Hyoscyamus niger cultured in a liquid medium containing 2,4‐dichlorophenoxyacetic acid (2,4‐D) was followed upon their transfer to a solid medium with or without 2,4‐D. In a solid medium lacking 2,4‐D, small calluses consisting of one to five nodular groups of cells at the time of inoculation differentiated root and shoot systems and formed miniature seedlings. In the same medium large calluses with several nodules initially formed a crop of bipolar somatic embryoids with well‐defined root and shoot axes which subsequently differentiated into seedlings. Irrespective of their size at the time of transfer, calluses grown in a solid medium containing 2,4‐D continued to proliferate without showing signs of organogenesis or embryogenesis.

Use of the Ureide Technique to Describe the Nitrogen Economy of Field-Grown Soybeans

Nitrogen fixation was estimated in ;Bragg,' ;Forrest,' and ;Bethel' soybean (Glycine max [L.] Merrill) from seven locations northwest of New South Wales, Australia, by relating ureide and nitrate contents of plant parts sampled at regular intervals during growth to standard curves derived under controlled nitrate regimes. Estimates were combined with data on crop growth and mineral N contents of soils to (a) determine the total requirements for N by the crops, (b) determine the contributions of N(2) fixation to crop growth, and (c) relate symbiotic dependence ([N(2) fixed/total plant N] x 100) of the crops to levels of mineral N in the soil at sowing. At two locations, Myall Vale and Glenara, levels of ureides in the shoot axes and roots of unnodulated seedlings were surprisingly high at the first time of sampling, perhaps reflecting effects of uptake of ammonium-N by the soybeans or breakdown and remobilization of cotyledonary protein. Ureides in plant parts declined significantly by the second (V5 to V7 growth stage) sampling. Subsequently, ureide contents increased whereas levels of nitrate in plant parts decreased. The relative abundance of ureides ([ureide-N/ureide-N + nitrate-N] x 100) in the shoot axes and nodulated roots of both crops increased linearly from almost zero during mid-vegetative growth (V5 to V7) to virtually 100% during late reproductive growth (R4 to R5, Myall Vale and R6, Glenara). The data suggest a steady transition in soybeans at both locations from dependence upon mineral N for early growth to complete reliance upon fixed N during late reproductive growth. Estimates of seasonal N(2) fixation for soybeans at the seven locations ranged from 73 to 288 kilograms per hectare N (shoot axes ureides) and from 147 to 337 kilograms per hectare N ha (nodulated roots ureides).

Relative Abundance of Ureides and Nitrate in Plant Tissues of Soybean as a Quantitative Assay of Nitrogen Fixation

The relationship between the relative abundance of ureides ([ureide-N/ureide-N plus nitrate-N] x 100) in the shoot axis (stems plus petioles), nodulated roots and leaflets of "Bragg" soybean (Glycine max [L.] Merrill) and the symbiotic dependence of these plants was examined under glass-house conditions. Plants, inoculated with effective Rhizobium japonicum CB1809, were grown with their roots exposed continuously to a nutrient solution containing either 0, 1.5, 3.0, 6.0 or 12.0 millimolar NO(3)-N per liter. Nodulation and N(2)-acetylene fixation were correlated inversely with the level of nitrate. Seasonal acetylene reduction profiles for each of the nitrate treatments were integrated and the symbiotic dependence ([N(2) fixed per total plant N] x 100) determined using a conversion ratio of 1.5:1 (acetylene reduced:N(2) fixed), calculated from the zero NO(3) treatment. Examination of the nitrogenous solutes of the shoot axis and nodulated roots showed linear relationships between the relative abundance of ureides and the symbiotic dependence of the plants. Two standard curves, depicting these relationships during vegetative and reproductive growth, were drawn for each plant part. The overriding effect of plant age invalidated any attempt to develop a standard relationship for leaflets. Data from two diurnal studies suggested that relative ureides were insensitive to diurnal fluctuations, thus simplifying sampling procedures. Plant material could be stored at ambient temperatures (20-30 degrees C) for up to 24 h without affecting the relative concentration of ureides and nitrate. It is suggested that the shoot axis provides the most suitable target organ when using this technique as a quantitative assay for N(2) fixation because of ease of sampling of these tissues, especially with field-grown plants.

Sites of Enzymatic Synthesis of Quinolizidine Alkaloids and Their Accumulation in Lupinus polyphyllus

Summary The distribution of the first two enzymes of the biosynthetic pathway of quinolizidine alkaloid biosynthesis, lysine decarboxylase and 17-oxosparteine synthase, was studied in the various organs of a flowering Lupinus polyphyllus plant. Lysine decarboxylase activity is present in all plant parts, whereas the activiy of the key enzyme 17-oxosparteine synthase is only expressed in leaf extracts. This indicates that alkaloid synthesis is bound to the leaves, where both enzyme had been localized in chloroplasts previously. The alkaloid content, alkaloid concentration and the alkaloid composition was quantitatively evaluated for the various organs of two flowering L. polyphyllus plants. The highest alkaloid content was found in the roots (38-45% of total alkaloids) and leaves (27-31%), but alkaloids are virtually present in all parts of a plant. Relatively high alkaloid concentrations were found in leaves, in younger parts of the shoot axis and in mature seeds. The alkaloid content of leaves is reduced during senescence by 90% as compared with young leaves. The alkaloid pattern evaluated quantitatively by capillary gas chromatography for the organs of two plants and seeds includes the following compounds: lupanine, sparteine, angustifoline, N-methylangustifoline, dehydrolupanine, 17-oxolupanine, 13-hydroxylupanine and its esters (13-tigloyl-, 13-angeloyl-, 13-benzoyl- and 13-cis and 13-transcinnamoyl-oxylupanine). A high percentage of ester alkaloids and a low content of 13-hydroxylupanine was found in leaves. Roots and seeds, the main sites of alkaloid accumulation, displayed the opposite pattern, i.e. high concentration of 13-hydroxylupanine and low concentration of ester alkaloids.

The Development of Leaves and Axillary Flowers along the Primary Shoot Axis of Cyclamen persicum 'F-1 Rosemunde' (Primulaceae)

Leaf emergence in Cyclamen persicum 'F-1 Rosemunde' followed a sigmoid pattern which was linear between 12 and 33 wk after planting. The early elongation of leaf laminae and petioles was exponential. The rates of lamina and petiole elongation along the axis exhibited heteroblastic patterns, but maxima occurred in different leaves. A shift in allometry constants (leaf lamina vs. petiole) from 1 occurred at leaves 6 and 7. Flowers were initiated at the same rate as leaves. Elongation of flower buds and peduncles was exponential until just prior to anthesis. The rates of bud elongation in the first 20 flowers were essentially constant, but the rate of peduncle elongation decreased at successive nodes. The maximum rate of lamina elongation at leaf 6, as well as the shift in allometry at leaves 6 and 7, may be associated with floral induction. Although the subtending leaf had an important role in the initiation of floral primordia, its importance in later floral development may be minimal. Use of the ...

Variation in isoabienol content in Pinus sylvestris needles

The diterpene alcohol isoabienol occurs in some individual pine (Pinus sylvestris L.) trees, in which it constitutes 0.6–1.0% of the needle dry weight, and is totally lacking in others. Isoabienol can be found only in the needles, mainly in fully outgrown needles, not in shoot axis tissue, wood, or cortex oleoresin. If sampling is limited to mature needles, within-tree, within-clone, and seasonal variations are insignificant, making isoabienol a suitable marker substance for studies of chemotaxonomy and population genetics. Isoabienol occurs more frequently in northerly provenances than in southerly. No correlation could be shown between isoabienol occurrence and the monoterpene or resin acid composition of the needles. There was no family-level correlation between isoabienol occurrence and resistance towards the pathogenic fungus Gremmeniella abietina.

Fibro-vascular Strands in the Great Millet (Sorghum vulgare Pers.)

Morphology of various types of vascular bundles in shoot axis of jowar— the great millet has been studied. Mesocotyl internode and coleoptile have four to six collateral endarch vascular strands. In the vegetative internode three strata of vascular bundles can be recognized. All vascular bundles of internode have a sclerenchyma sheath around them. Peripheral bundles of the internode have a heavy sclerenchyma sheath. The amount of sclerenchyma sheath gradually decreases in the central vascular bundles. Nodal vasculature is most complex. Some bundles in the node lack sclerenchyma sheath, whereas some of them have a radiating parenchyma sheath around them. The fibro-vascular system varies not only in various parts of the axis but also in a radial plane of any given point in the axis.

Herbicidal effects of metolachlor (2-chloro- N-[2-ethyl-6-methylphenyl]- N-[2-methoxy-1-methylethyl]acetamide) at the cellular level in Sorghum

The coleoptile node cells of sorghum [ Sorghum bicolor (L.) Moench] are sensitive to metolachlor (2-chloro- N-[2-ethyl-6-methylphenyl]- N-[2-methoxy-1-methylethyl]acetamide) in that lateral growth is stimulated at the expense of growth in length. This lateral growth may be induced by ethylene which is released from the herbicide-treated seedling. The bundle sheath cells of the first leaf develop pronounced cell walls after metolachlor treatment. Starch is accumulated in the chloroplasts. This points to the conclusion that starch-mobilizing enzymes (their synthesis or activity) are affected by metolachlor. Newly developing and differentiating cells of the shoot axis come under the direct influence of the herbicide. In these cells, mitochondria, chloroplasts, and other membranous structures become only weakly discernible. This seems to indicate that plastids and other membranous structures are not formed or that through membrane damage the fixatives and stains used for transmission electron microscopy are no longer suitable. The electron microscope pictures support the theory that one possible mode of action of the acetanilide herbicides is an inhibition of starch mobilization in the chloroplasts and of lipid synthesis.

Distribution of Polyploidy in Elongating and Non-Elongating Shoot Axis of Pisum sativum

In the shoot of the dwarf pea Pisum sativum «Kleine Rheinländerin» the ploidy level of the cortex cells in the first 5 internodes was determined after treatment with GA 3 and FdUrd. GA 3 has a similar effect as darkness in enhancing the ploidy level in these cells. The hormone will provide this effect at concentrations up to 2.5 × 10 -6 M. DNA content per cell of non growing internodes is not altered by this treatment. However in growing internodes an increase in DNA-content can be recorded immediately after the treatment. The growth and fresh weight do not increase proportionally to the DNA-content. Employing FdUrd as an inhibitor of DNA-synthesis will however terminate growth entirely. The results demonstrated that shoot growth of peas - as in many other plants - is always followed by a higher DNA content of the individual cells.

Über das ätherische Öl in den Öldrüsen and im aulßendrüsischen Bereich von Monarda fistulosa

The composition of the essential oil in the glands, which is characterized by the highest content of thymol in comparison with all other plant parts investigated, is in good accordance with that of the cotyledons, of the leaves, and of the shoot axis. These oils, rich in thymol and monoterpene hydrocarbons, clearly differ from the oil of roots, having much less thymol and hydrocarbons, but showing oxygenated compounds. Those parts of the shoot that lack glands do contain volatile substances, too. This is also true for the tissues of the phloem. The occurrence of volatile substances in plant tissues not specialized in secretion shows that even, in plants wich normally do have glands and oil-containing idioblasts the latter tissues are no prerequisite for oil synthesis. A sequential synthesis of the oil components can only be observed in quite young plantlets. The oil composition of ten days old seedlings already resembles that of grown-up leaves. The native glandular oil agrees with that extracted from leaves by steam destiliation. This means that in the case of Monarda degradation during destillation may be neglected.

THE POSSIBLE ROLE OF MEMBRANE ELECTROPHORESIS IN THE POLAR TRANSPORT OF IAA AND OTHER SOLUTES IN PLANT TISSUES

SummaryPolar transport of IAA in young higher plant shoot tissue requires an asymmetric distribution of membrane‐transport sites in the plasmalemma of the cells. The ‘chemiosmotic’ hypothesis of IAA transport requires that IAA‐ uniporters be largely on the basal side of the cells. It is suggested that the longitudinal gradient of electrical potential difference (PD, base positive to apex) which may result from activation of plasmalemma H+ efflux in the basal cells by transported IAA, may serve to maintain and reinforce this asymmetric distribution of carriers by the process of membrane electrophoresis of the carriers. The origin of this asymmetric distribution (and hence of polar IAA transport) may lie in electrical potential differences in maternal tissue around the developing embryo. Maintenance of polarity through seed dormancy may be related to gradients in cell‐wall fixed charges (and hence of electrical potential difference) along the shoot axis related to the uronate content of cell walls at different stages of cell development. The possibility of testing this hypothesis, and its relevance to other polar transport phenomena in plants, are briefly discussed.

AN INVESTIGATION OF THE MORPHOGENETIC MECHANISMS WHICH CONTROL THE DEVELOPMENT OF ZONATION IN SEEDLING SHOOT APICAL MERISTEMS

The development of zonation in the shoot apical meristems of 28 species of cacti was examined. At germination the embryonic apex may have one of three types of organization: 1) tunica/corpus; 2) tunica/central mother cells/corpus; 3) tunica/central mother cells/peripheral zone/pith‐rib meristem. Apices of the third type have complete zonation and undergo little or no further structural development. Both of the other types develop the missing zones. First, the apices become mitotically active, and peripheral zone characters develop in the outer corpus. Simultaneously, or slightly later, the central mother cells differentiate if they are not yet present. The final step is the formation of the pith‐rib meristem. The sequence of appearance of the zones was constant throughout all species examined, but the time of appearance of only one zone could be correlated with any other morphogenetic process: the development of peripheral zone characteristics in the outer corpus occurs with or before the beginning of leaf production. The development of zonation appears to be independent of apical size, shape, or age, either real age or plastochron age. This has been interpreted to indicate that the metabolic mechanism controlling the development of zonation in shoot apical meristems is largely autonomous and independent of other aspects of morphogenesis occurring in the seedling. Also, the fact that leaf initiation and shoot axis production can both occur before the development of either the central mother cells or the pith‐rib meristem indicates that neither of these zones is essential for these two apical morphogenetic activities.