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     

Observations of the Effect of Water on the Hyphal Apices of Fusarium oxysporum

When colonies of Fusarium oxysporum, growing on plates of mineral-sucroseagar, are flooded with the mineral-sucrose solution, withoutadded agar, or with solutions of any of the constituents ofthe mineral-sucrose mixture at a concentration of 0.076 M theleading hyphal apices at the agar surface continue to grow onunchecked. If, however, the colonies are flooded with solutionsof decreasing and increasing molarity from 0.076 M an increasingproportion of the leading hyphal apices at the agar surfacestop growing, and branch subterminally. In distilled water about50 per cent. of the apices branch and this branching is precededby swelling, whereas in 0.5 M sucrose more than 90 per cent.of the apices branch and the branching is not accompanied byswelling. In the distilled water those hyphae which do not branchswell a little and grow on from the apex within 40 seconds. When hyphal apices are flooded with distilled water for from10 to 40 seconds and then transferred to mineral-sucrose solutionmore than 90 per cent, of the hyphal apices branch, whereasflooding with distilled water for 60 seconds or longer givesthe same percentage of branched apices as does flooding withdistilled water alone. It is shown that swelling and branching of the hyphal apex arenot causally related but that branching always occurs followingarrestment of the hyphal apex for more than 60 seconds. It issuggested that the phenomena reported can be explained in termsof an irreversible change in the apical cap of the arrestedhypha such that continued extension can no longer take placein this region and fresh outlets for growth must then be foundsubterminally. Such a mechanism, however triggered, could accountfor a wide variety of morphogenetic forms in the fungi.     

Reproducibility of the cold-induced vasodilation response in the human finger.

Cold-induced vasodilation (CIVD) is a cyclic oscillation in blood flow that occurs in the extremities on cold exposure and that is likely associated with reduced risk of cold injury (e.g., frostbite) as well as improved manual dexterity and less pain while working in the cold. The CIVD response varies between individuals, but the within-subject reproducibility has not been adequately described. The purpose of this study was to quantify the within-subject variability in the CIVD response under standardized conditions. Twenty-one volunteers resting in a controlled environment (27 degrees C) immersed the middle finger in warm water (42 degrees C) for 15 min to standardize initial finger temperature and then in cold water (4 degrees C; CWI) for 30 min, on five separate occasions. Skin temperature (Tf) and blood flow (laser-Doppler; expressed as percent change from warm-water peak) responses that describe CIVD were identified, including initial nadir reached during CWI, onset time of CIVD, initial apex during CIVD, time of that apex, and overall mean during CWI. Within-subject coefficient of variation for Tf across the five tests for the nail bed and pad, respectively, were as follows: nadir, 9 and 21%; onset, 18 and 19%; apex, 12 and 17%; apex time, 23 and 24%; mean 10 and 15%. For blood flow, these values were as follows: nadir 52 and 64%; onset, 6 and 5%; apex, 33 and 31%; apex time 9 and 8%; and mean 43 and 34%. Greater variability was found in the temperature response of the finger pad than the nail bed, but for blood flow the variability was similar between locations. Variability in onset and apex time between sites was similar for both temperature and blood flow responses. The reproducibility of the time course of CIVD suggests this methodology may be of value for further studies examining the mechanism of the response.     

Respiration and Carbohydrate Accumulation in the Water-Stressed Wheat Apex

The effect of water stress on the respiration of the immaturefloral apex of wheat was studied in a controlled environmentand related to changes in water relations, growth, protein synthesis,and solute accumulation. Apex respiration measured in vitropolarographically showed no wounding response and was cyanide-and malonate-sensitive. It decreased with each decrease in apexwater potential _a reaching 40% of the non-stress control rateat –5·0 MPa, irrespective of whether the waterstress was induced by droughting in vivo or non-permeating osmoticain vitro. Apex respiration was not quantitatively related toturgor potential. During drought stress there was a conservation of ethanol-insolubledry matter and water in the apex while ethanol-soluble carbohydratesand amino acids accumulated. The calculated daily import ofsoluble carbohydrate into the apex during the whole droughtstress period remained nearly constant despite falling waterpotential. Respiration of the apex during a drought period wasnot limited by the suistrate supply within the apex.     

Rhythmic Circumnutation Movement of the Shoots in Phaseolus Vulgaris L

The apex of growing stems in twining plants describes a rhythmic movement in space called circumnutation. By the method of orthogonal projections, the position in space of the apex can be determined constantly. The mathematical analysis of data allowed us to determine that far Phaseolus vulgaris L. (cv. Mangetout Blanc de Juillet) grown under constant illumination and temperature (25°C) the period is about 100 min. This movement has been related to rhythmic changes in the osmotic potential of the cells located in the bending zone of the stem for a constant period. These variations are longitudinally and laterally coordinated. Treatment with a solution of LiCI at 7 × 10 'M supplied to the root system induces a lengthening of the period. The effect of the treatment is reversed by K⁺ ions. From these results we deduce that rhythmic changes of the membranes are implicated in the circumnutation movements of twining plants.     

Arrangement of cortical microtubules at the surface of the shoot apex inVinca major L.: Observations by immunofluorescence microscopy

Arrangements of cortical microtubules (MTs) and of cellulose microfibrils at the surface of the vegetative shoot apex ofVinca major L. were examined by immunofluorescence microscopy and polarizing microscopy, respectively. Cortical MTs adjacent to the outermost walls of the apex were arranged more or less randomly in individual cells: especially in cells in the central region of the apex the arrangement was almost completely random. However, in the peripheral region MTs tended to show parallel alignment in individual cells, and an overall pattern that was roughly concentric around the apical dome was discerned. Observations of birefringence of cell walls indicated that cellulose microfibrils in the peripheral region of the apex were also arranged in a pattern which was roughly concentric around the apical dome. These patterns of arrangements of MTs and microfibrils are understood to be perpendicular to the radial cell files observed in the peripheral region of the apex, and can be related to the radial expansion of the surface of the apex.     

Studies on a maize mutant sensitive to low temperature I. Influence of temperature and light on the production of chloroplast pigments

A mutant inbred line of Zea mays L. (M11) in which chlorophyll accumulation is particularly sensitive to low temperature is described. Under natural light conditions the chlorophyll content of seedlings is negligible below 17° but is normal at high temperature. Seedlings of M11 can synthesize chloroplast pigments at 16° but at a rate slower than normal. When photo-oxidation is minimized, chlorophyll accumulates, and seedlings can photosynthesize efficiently at low temperature. The primary site of low temperature sensitivity in M11 is the shoot apex where new leaves are developing and undergoing rapid cell expansion. It seems that there is impaired development and associated impaired function of chloroplasts in M11 grown at low temperatures which sensitizes them to rapid photo-oxidation in the light.     

Relationship of macrophyte-mediated changes in the water column to periphyton composition and abundance

SUMMARY. 1. Dense growths of Myriophyllum heterophyllum influenced temperature, dissolved oxygen, pH and light levels in the littoral waters of Lake Winnipesaukee, a soft-water. New England lake. Periphyton species composition and abundance (algal units cm' stem) were related to the macrophyte-mediated changes in the physicochemical environment.
2. Duringearlysummer, M. heterophyllum occupied onlythe lower part of the water column. Limnetic and littoral waters exchanged readily and were chemically similar. Early summer periphyton species composition was dominated by diatoms from the phytoplankton, entangled in the finely dissected leaves of M. heterophyllum.
3. By mid-summer, M. heterophyllum occupied the entire watercolumn of the littoral zone. The metabolic and photosynthetic activity and dense foliage of M. heterophyllum created marked vertical gradients in physicochemical conditions. Mid-day temperature, dissolved oxygen, pH and light levels were maximal in the surface waters of the M. heterophyllum mat during the summer. Concurrently, periphyton species composition shifted to blue-green and then to a filamentous green alga on the apex and mid-stem. On the lower stem, diatoms consistently dominated the periphyton.
4. Periphyton abundance on the apex was inversely related to apical elongation. Temporal fluctuations of periphyton abundance on the lower and mid-stem were small throughout the study. Periphyton abundance was lowest on the lower stem, where the deteriorating leaves provided less surface area for colonization.     

Effects of temperature and moisture on embryonic diapause of the veiled chameleon (Chamaeleo calyptratus)

The development of lizard embryos is typically initiated at fertilization and continues until birth or hatching. In contrast, embryonic development of some chameleons is arrested at the gastrula stage, and embryos remain at this stage for months after the eggs are laid. Our research tested the hypothesis that increased temperature, moisture, or both, are associated with the resumption of development by diapausing embryos of Chamaeleo calyptratus, the veiled chameleon. After 40 days of incubation at 25 degrees C in a relatively dry substrate, eggs were subjected to: 1) no change in temperature or moisture, 2) no change in temperature but change from a dry to a wet substrate, 3) change to a warmer temperature but no change in substrate moisture, or 4) an increase in both temperature and substrate moisture. Overall, embryos initiated development after 50-60 days to 80 or more days of incubation. Neither substrate moisture nor water uptake by eggs was related to the interval when development resumed. In contrast, development was initiated about 10 days earlier for eggs in the high temperature treatment compared to eggs in the low temperature treatment. Our results suggest that neither water availability nor water uptake by eggs affect the length of diapause but that an increase in ambient temperature initiates development of diapausing embryos of C. calyptratus.     

Temperature-driven plasticity in growth cessation and dormancy development in deciduous woody plants: a working hypothesis suggesting how molecular and cellular function is affected by temperature during dormancy induction

The role of temperature during dormancy development is being reconsidered as more research emerges demonstrating that temperature can significantly influence growth cessation and dormancy development in woody plants. However, there are seemingly contradictory responses to warm and low temperature in the literature. This research/review paper aims to address this contradiction. The impact of temperature was examined in four poplar clones and two dogwood ecotypes with contrasting dormancy induction patterns. Under short day (SD) conditions, warm night temperature (WT) strongly accelerated timing of growth cessation leading to greater dormancy development and cold hardiness in poplar hybrids. In contrast, under long day (LD) conditions, low night temperature (LT) can completely bypass the short photoperiod requirement in northern but not southern dogwood ecotypes. These findings are in fact consistent with the literature in which both coniferous and deciduous woody plant species’ growth cessation, bud set or dormancy induction are accelerated by temperature. The contradictions are addressed when photoperiod and ecotypes are taken into account in which the combination of either SD/WT (northern and southern ecotypes) or LD/LT (northern ecotypes only) are separated. Photoperiod insensitive types are driven to growth cessation by LT. Also consistent is the importance of night temperature in regulating these warm and cool temperature responses. However, the physiological basis for these temperature effects remain unclear. Changes in water content, binding and mobility are factors known to be associated with dormancy induction in woody plants. These were measured using non-destructive magnetic resonance micro-imaging (MRMI) in specific regions within lateral buds of poplar under SD/WT dormancing inducing conditions. Under SD/WT, dormancy was associated with restrictions in inter- or intracellular water movement between plant cells that reduces water mobility during dormancy development. Northern ecotypes of dogwood may be more tolerant to photoinhibition under the dormancy inducing LD/LT conditions compared to southern ecotypes. In this paper, we propose the existence of two separate, but temporally connected processes that contribute to dormancy development in some deciduous woody plant: one driven by photoperiod and influenced by moderate temperatures; the other driven by abiotic stresses, such as low temperature in combination with long photoperiods. The molecular changes corresponding to these two related but distinct responses to temperature during dormancy development in woody plants remains an investigative challenge.     

DIFFERENTIATION OF LATERAL SHOOTS AS THORNS IN ULEX EUROPAEUS

Ulex europaeus is a much-branched shrub with small, narrow, spine-tipped leaves and axillary thorn shoots. The origin and development of axillary shoots was studied as a basis for understanding the changes that occur in the axillary shoot apex as it differentiates into a thorn. Axillary bud primordia are derived from detached portions of the apical meristem of the primary shoot. Bud primordia in the axils of juvenile leaves on seedlings develop as leafy shoots while those in the axils of adult leaves become thorns. A variable degree of vegetative development prior to thorn differentiation is exhibited among these secondary thorn shoots even on the same axis. Commonly the meristems of secondary axillary shoots initiate 3–9 bracteal leaves with tertiary axillary buds before differentiating as thorns. In other cases the meristems develop a greater number of leaves and tertiary buds as thorn differentiation is delayed. The initial stages in the differentiation of secondary shoot meristems as thorns are detected between plastochrons 10–20, depending on vigor of the parent shoot. A study of successive lateral buds on a shoot shows an abrupt conversion from vegetative development to thorn differentiation. The conversion involves the termination of meristematic activity of the apex and cessation of leaf initiation. Within the apex a vertical elongation of cells of the rib meristem initials and their immediate derivatives commences the attenuation of the apex which results in the pointed thorn. All cells of the apex elongate parallel to the axis and proceed to sclerify basipetally. Back of the apex some cortical cells in which cell division has persisted longer differentiate as chlorenchyma. Although no new leaves are initiated during the extension of the apex, provascular strands are present in the thorn tip. Fibrovascular bundles and bundles of cortical fibers not associated with vascular tissue differentiate in the thorn tip and are correlated in position with successive incipient leaves in the expected phyllotactic sequence, the more developed bundles being related to the first incipient leaves. Some secondary shoots displayed variable atypical patterns of meristem differentiation such as abrupt conversion of the apex resulting in sclerification with limited cell elongation and small, inhibited leaves. These observations raise questions concerning the nature of thorn induction and the commitment of meristems to thorns.     

The Structure and Development of the Vegetative Shoot Apex in Glechoma hederacea L

The development of the vegetative shoot apex of Glechoma hederaceahas been followed through a double plastochron. During this period the apex grows from c. 20 to c. 260 µin height and c. 100 to c. 300 µ in width, whilst thepair of leaves inserted at the apex base increase from o toc. 600µ in height. The width of the apex and height ofthese leaves are directly related to apex height. Some variationoccurs in the average maximal dimensions of the apex with plastochronnumber but no regular increase or decrease in these dimensionsis apparent. Both a tunica-corpus organization and cytohistological zonationis visible within the apex throughout a double plastochron.The central initiation zone shows little change in size or appearanceduring this period but the rib and flank meristems grow considerablyand undergo some differentiation. The boundaries of these zonesare not sharply defined, but normally the rib meristem givesrise to the pith, and the flank meristem forms the epidermis,cortex, and provascular tissue. The provascular tissue differentiatesacropetally and in continuity with that in the axis below.     

The setting of rates of development of wheat plants at crop emergence: Influence of the environment on rates of leaf appearance

Examination of the time courses, expressed in terms of accumulated temperature over 0°C, of leaf appearance of fifteen sowings of winter wheat, including five cultivars, over three seasons at Auchincruive, revealed several examples of bi-linear rather than linear responses. Stepwise linear regression analysis, varying the temperature threshold by intervals of 1°C, showed that a linear relationship could be obtained for each sowing, but the appropriateness of this analysis is questioned. An alternative interpretation, that such changes in rate do have biological rather than purely statistical significance, is supported by the fact that, when they occurred, they coincided with the change in rate of spikelet initiation by the stem apex. Furthermore, similar relationships between leaf appearance and reproductive development have been demonstrated for perennial ryegrasses. Analysis of each sowing also revealed the existence of sub-populations of plants with different rates of leaf appearance and final leaf numbers, but with synchronous phenologies. These findings are discussed in relation to the coordination of the development of apex and leaves, and the environmental cues required to ensure this coordination.     

龙舌草果实和种子及其种苗发育形态学研究

采用形态观察和GMA切片相结合的方法,对龙舌草果实、种子及种苗发育的形态结构进行解剖学观察研究,探讨龙舌草个体发育中表现出的与水生环境相适应的结构特征.结果显示:(1)龙舌草由佛焰苞包被的果实通常由6心皮构成,心皮边缘不完全愈合,层片状胎座,水面形成的幼嫩果实被果柄拉入水中发育成熟;种子具毛,萌发时苗端先于根端发育,在胚根分化之前先出现单细胞的下胚轴毛,随后胚根发育为初生根,并在真叶的节处发育出不定根;果皮和叶肉内的维管束仅由少数细胞构成,且细胞分化不明显,有发达的通气道;叶表皮无角质层,细胞外凸,叶肉细胞数量少;表明龙舌草的结构特征与水生环境相适应.(2)研究还发现,龙舌草的种子无胚乳,下胚轴贮存种苗发育需要的大量淀粉粒,以及初生根和不定根均有根毛的结构,且与泽泻科的慈菇和泽泻的结构一致,证明水鳖科与泽泻科具有较近的亲缘关系.     

Some impacts of human activities on trout, Salmo trutta, populations

SUMMARY. 1. The life cycle of salmonid fishes is described.
2. The performance and environmental requirements of the various life stages of the trout ( Salmo trutta L.) are reviewed, (a) The literature gives predictive relationships between water temperature and rate of embryonic development, food requirements and growth rate, (b) Water temperature, intragravel oxygen supply rate, water pH, the occurrence of mechanical shock, disturbance of spawning gravels, sedimentation and water chemistry can all influence the survival of the intragravel stages, (c) The survival and/or well-being of the free-swimming stages and the success of spawning are influenced by such factors as dissolved oxygen concentration, pH, water depth, water velocity and water chemistry.
3. Human activities such as impoundment, river transfer, drainage works, land improvement, afforestation and deforestation can all influence trout populations via changes in flow regime (and related effects such as sedimentation), temperature regime and water chemistry.
4. Man can also influence trout populations directly by cropping for food and/or sport and by artificial stocking.
5. Examples of practical application of present knowledge are given and some future research needs are listed.     

Hydrogen peroxide treatment results in reduced curvature values in the Arabidopsis root apex

Curvature of a plane curve is a measurement related to its shape. A Mathematica code was developed [Cervantes E, Tocino A. J Plant Physiol 2005;162:1038-1045] to obtain parametric equations from microscopic images of the Arabidopsis thaliana root apex. In addition, curvature values for these curves were given. It was shown that ethylene-insensitive mutants (etr1-1 and ein2-1) have reduced curvature values in the root apex. It has also been shown that blocking ethylene action by norbornadiene, an ethylene inhibitor, results in reduced curvature values in the two outer cell layers of the root apex [Noriega A, Cervantes E, Tocino A. J Plant Physiol 2008, in press]. Because ethylene action has been related with hydrogen peroxide [Desikan R, Hancock JT, Bright J, Harrison J, Weir I, Hooley R, Neill SJ. Plant Physiol 2005;137:831-834], the effect of a treatment with hydrogen peroxide in the curvature values of three successive layers of the root apex in Arabidopsis thaliana was investigated by confocal microscopy. Treatment with 10mM hydrogen peroxide resulted in reduced curvature values in the three layers. The effect was associated with smaller cells having higher circularity indices. The results are discussed in the context of the role of ethylene in development.     

Endophyte transmission and activity in the Anabaena-Azolla association

Summary The survival of Azolla was studied in an artificial system which simulated the soil/water interface and the desiccation of soil during a fallow period in lowland rice culture. Tests with non-sporulating and sporulating Azolla fronds showed that Azolla only survives with sporulated fronds. At their reappearance the Azolla fronds already harboured the Anabaena endophyte. A detailed light microscopic and transmission electron microscopic study of macro- and micros-porocarp formation and development revealed that the endophyte is transmitted by the macrosporocarps and not by the microsporocarps. The Anabaena cells within the macrosporocarps are found just below the indusium cap. These cells are not nitrogen-fixing akinetes. The free-living Anabaena cells at the stem apex and below the overarching developing leaves do not bear heterocysts and accordingly are non nitrogen-fixing. During the development of the leaf the Anabaena enters the leaf cavity, but later the pore of this, cavity closes and the imprisoned cyanobacteria are lysed before the leaf decays. As the Azolla leaves age a nitrogen-fixing capability is successively built up concomittantly with the production of heterocysts. Heterocyst frequencies of 40–50% can be found inAnabaena azollae. Usually a gradient of nitrogen-fixing capacity occurs along the Azolla rhizome with two distinct peaks at leaf number 7/8 and at leaf number 13/14 from the apex.     

Studies on the developmental anatomy of Dioscorea sansibarensis Pax (Dioscoreaceae)

Certain developmental and anatomical studies on D. sansibarensis Pax are briefly reported. (1) Stem diameter, internodal length, vessel diameter, distribution and number of vascular bundles in internodes (from base to apex) are determined. There is no correlation between vessel size and stem diameter. Cut stems left in water develop tyloses. (2) Roots are all polyarch. The development and structure of the vessels are discussed. Xylem and phloem differentiation in the root tip is determined. A central meristem at the root apex gives rise to the different tissues in the root. Raphide development in root cortex is traced. (3) Both alternate and opposite leaf arrangements occur, sometimes on the same plant, and there is a correlation between stem thickness and leaf arrangement. During leaf development the lamina length exceeds the width, but the two dimensions reach their maximum size at the same time. The acuminate leaf-tip matures before the rest of the leaf. Stomatal development is traced.