bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of microtubule organization in two polyhedral cell types in the gametophyte of the liverwort Marchantia paleacea Bert.
Authors: APOSTOLAKOS P. , GALATIS B.
Published: April 2006

summary

The typical scale cells (TSCs) of Marchantia paleacea Bert, contain a well‐developed cortical microtubule (Mt) cytoskeleton, particularly below the anticlinal walls and also display complete but broad preprophase‐prophase Mt bands (PMBs). In contrast, the cortical cytoskeleton of the inner thallus cells (ITCs) is less developed than that of TSCs and the PMBs are incomplete. The latter consist of one to four separate Mt bundles which lie on the cytokinetic plane, but do not form a complete Mt ring. In both cell types PMB formation precedes or keeps pace with the activation of the polar Mt‐organizing centres (MTOCs) and nuclear shaping. The Mts in the PMBs are more numerous and densely packed at the cell edges than on the cell face. The polar MTOCs persist up to late prophase‐prometaphase. Afterwards, the spindle Mts are focused on several minipoles, where endoplasmic reticulum is localized. In postcytokinetic cells the cortical Mts first reappear on the daughter wall surface.

Our findings suggest that: (a) The formation of complete or incomplete PMBs in TSCs and ITCs of M. paleacea is related to differences in the development of the interphase cortical Mt arrays, (b) The cell edges are able to form or at least arrange the Mts of the PMB. (c) Tight mature PMBs like those found in flowering plant cells are not formed in the cells examined in the present study. (d) The final orientation of the cell plate is controlled by the PMB cortical zone. (e) The cytoplasm abutting on the postcytokinetic daughter wall has the ability to assemble cortical Mts.
Pollen dispersal and representation on an offshore island
Authors: JACKSON STEPHEN T. , DUNWIDDIE PETER W.
Published: April 2006

summary

The effects of spatial isolation on pollen representation were examined in a study of seven small kettle ponds on Block Island, a small, unforested island 19 km off the New England Coast (USA). Modern pollen assemblages from the ponds were compared with modern assemblages from similar ponds on the adjacent, partly forested mainland and in extensively forested northern New York. Representation of pollen from local and extralocal sources was amplified on the island owing to spatial isolation. However, variation among pollen assemblages on the island was not clearly related to spatial variation in vegetation composition. Significant transport of pollen from the mainland to the island was observed. There appeared to be little or no decrease in representation of large, poorly dispersed mainland pollen types between the mainland and island. This latter result may indicate differences between the mainland and island in the predominant modes of pollen transport, or alternatively, effects of local pollen source strength on representation of pollen from distant sources. Based on our results, we propose a theory of pollen representation on islands that can be tested and applied on offshore islands and patchy landscapes.
The Nostoc–Gunnera symbiosis
Authors: BERGMAN B. , JOHANSSON C. , SÖDERBÄCK E.
Published: April 2006

summary

Gunnera L. develops a complex and intimate symbiosis with N2‐fixing cyanobacteria of the genus Nostoc, which renders the plant independent of combined nitrogen. The Nostoc‐Gunnera symbiosis exhibits unique features compared to other cyanobacterial‐plant symbioses: it is for example the only one that involves a flowering plant (angiosperm), the cyanobacterium infects specialized gland organs located on the stems of the host and once it has passed into the interior of the gland the cyanobacterium also enters the Gunnera cells where it starts to differentiate the highest frequency of heterocysts (the N2‐fixing cells) recorded in any cyanobacterial population. Gunnera has attracted scientific attention also for the following reasons: the genus has a peculiar geographic distribution of its subgenera and species in the Southern Hemisphere. It differs morphologically and anatomically from related plants and also shows an anomalous polystelic vascular system (polystely). This review gives an updated account of present knowledge concerning the Nostoc‐Gunnera symbiosis. Emphasis will be on the development of the symbiotic tissue (the gland), the structure and function of the prokaryotic N2‐fixing cyanobacterium, the infection process and on the relationship between the pro‐ and eukaryotic partners prior to and following the establishment of symbiosis.

CONTENTS

Summary
379

I.
Introduction
379

II.
The Gunner a plant
380

III.
The microsymbiont(s)
383

IV.
The symbiosis
384

V.
The gland
385

VI.
The infection process
388

VII.
Specificity
391

VIII.
Impacts on the cyanobiont
392

IX.
N2 fixation and release
393

X.
Photosynthesis
396

XI.
Concluding remarks
397

Acknowledgements
398

References
398
Light‐activated plant defence
Authors: DOWNUM KELSEY R.
Published: April 2006

summary

Sunlight provides the energy required for all biochemical, physiological and developmental processes necessary for plant growth, reproduction and survival. The role of light in photosynthesis and photomorphogenesis has been appreciated for some time; however, the role of light in plant defence is a comparatively recent realization. Between 75–100 photosensitizers or phototoxins, molecules that become toxic in the presence of light, have been extracted from higher plant tissues. These biologically‐active compounds have diverse biosynthetic origins and belong to at least 15 different phytochemical classes (i.e. acetophenones, acetylenes, benzophenanthrenes, β‐carbolines, coumarins, extended quinones, furanochromones, furanocoumarins, furanoquinolines, isoquinolines, lignans, pterocarpans, quinolines, sesquiterpenes and thiophenes). Of more than 100 angiosperm families assayed, phototoxins and/or phototoxic activity have been reported inc.40 families representing 32 orders and 8 subclasses of the Magnoliophyta. Most of these allelochemicals are acute toxins with little organism‐specificity. As such, they are effective biocides capable of killing a wide‐range of potentially harmful organisms including: viruses, pathogenic bacteria and fungi, nematodes and herbivorous insects, as well as competing plant species. This review focuses on the phytochemistry, taxonomic occurrence and toxicological consequences of phototoxic metabolites in flowering plants. The available information suggests that phototoxic phytochemicals: (i) are broad‐spectrum allelochemicals capable of protecting plants against a variety of detrimental organisms in nature, (ii) represent a successful defensive strategy in both primitive and advanced plant taxa, and (iii) may be an effective defence under a variety of photoenvironmental conditions.

CONTENTSSummary401I.Introduction401II.Chemistry/biochemistry of plant photosensitizers402III.Botanical distribution of photosensitizers403IV.Toxicology405V.Biological activity/defensive role of photosensitizers408VI.Concluding remarks413References415
Content of carbohydrate and activities of fructosyltransferase and invertase in asparagus roots during the fructo‐oligosaccharide‐ and fructo‐polysaccharide accumulating season
Authors: SHIOMI N.
Published: April 2006

summary

Contents of fructo‐oligosaccharides and fructo‐polysaccharides and activities of fructosyltransferases and invertase in asparagus roots harvested between July and November were studied by gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC).

Contents of total sugar and fructo‐oligosaccharides and fructo‐polysaccharides were very low in July, and then increased until September. During this period, sucrose accumulated first, second trisaccharides, and then tetra‐, penta‐ and higher‐saccharides increased in that order. 1‐Kestose was the most predominant fructo‐ohgosacchande isomer [degree of polymerization (DP) 3 ∼ 6]. The fructo‐polysaccharide of DP ≥ 9 was 12.8 ∼ 21.7% of total sugar from September to November; polysaccharides estimated to be DP 20∼22 were just detectable.

SST activities were very low in July, rose to a maximum in September and then decreased. Change in activity of SST was responsible for change in contents of sucrose and 1‐kestose from July to November. 1F‐fructosyltransferase (1F‐FT) activities increased until September, were almost constant from October to November and then decreased slightly. 6G‐fructosyltransferase (6G‐FT) reached its highest activity early in October. 6r‐SST (6‐kestose producing enzyme) activity was very slight from July to November and was ∼ 1/1000 of SST activity in September. This activity does not contribute to the enzymatic synthesis of the saccharides of asparagus roots. Invertase activity was nearly constant throughout. The change of activities of SST, 1F‐FT and 6G‐FT paralleled closely the accumulation of sucrose, 1‐kestose, neokestose and other saccharides.

In vitro synthesis of fructo‐oligosaccharides from sucrose at 0.4, 0.1 and 0.05 M, or from 1‐kestose was investigated in a fraction prepared from asparagus roots harvested in September. 1‐Kestose (isokestose, 3a), neokestose (3b), nystose (4a), 1F (l‐β‐D‐fructofuranosyl)m‐6G(l‐β‐D‐fructofuranosyl)n‐sucrose (4b: m= 0, n= 2; 4c: m= 1, n=1; 5a: m=3, n0; 5b: m=0, n=3; 5c: M=2, n=1; 5d: m=1, n=2) and a mixture of hexasaccharide‐isomers were synthesized from 04 M sucrose in 60 h. In 0.05 and 0.1 M sucrose unidentified heptasaccharides were also produced. Octa‐ and higher‐saccharide, as well as the saccharides synthesized from sucrose, were formed from 0.1 M 1‐kestose. All of the saccharides synthesized from sucrose or 1‐kestose by the asparagus enzyme preparation were identical to saccharides occurring naturally in the roots of asparagus.
Non‐steady state ammonium‐limited growth of the marine phytoflagellate, Isochrysis galbana Parke
Authors: DAVIDSON K. , FLYNN K. J. , CUNNINGHAM A.
Published: April 2006

summary

The marine phytoflagellate Isochrysis galbana Parke was followed through two consecutive cycles of ammonium‐limited growth. There was a significant (48 h) lag in cell division following the resupply of ammonium but no discernible lag in biomass growth, which led to a transient increase in the mean biomass per cell. Cell carbon and Coulter volume were linearly correlated. Net chlorophyll synthesis was closely linked to the absorption of extracellular N, while carotenoid synthesis continued until C fixation ceased. Photosynthetic activity (C fixation per unit chlorophyll) varied significantly with the cellular N:C ratio. A rapid rise in the ratio of glutamine to glutamate (0.1–6) during the first 24 h after nitrogen supply indicated a temporary imbalance in the flux of C and N into biomass synthesis. Intracellular ammonium accounted for less than 4% of total cell N, while free intracellular amino acids accounted for 3–5%. Nevertheless, cell numbers were able to double after the medium became depleted of ammonium, presumably by recycling and redistributing high molecular weight intracellular N.
Transfer of symbiotically fixed nitrogen from berseem (Trifolium alexandrinumL.) to maize via vesicular—arbuscular mycorrhizal hyphae
Authors: FREY BEAT , SCHÜEPP HANNES
Published: April 2006

summary

In order to examine whether hyphae of VA mycorrhizal fungi may aid the transfer of symbiotically fixed nitrogen from a legume to a non‐legume, the roots of berseem plants inoculated with the VAM fungusGlomus intraradicesandRhizobium leguminosarumbiovar.trifolii(strain RCR 5) were separated by a 2 cm root‐free zone from the roots of maize plants. A 40 um pore size nylon net allowed VAM hyphae to pass through the root‐free zone but prevented root penetration. Replacement of this net by a 0.45 μm pore size membrane prevented penetration of VAM hyphae to the root‐free compartment. When the berseem plants were 63 d old, the plant chambers were sealed in plastic bags to allow the roots of the plants to be exposed to al0N2‐enriched atmosphere for 5 d.

Berseem plants that were exposed to a15N2‐enriched atmosphere fixed more15N than did berseem plants maintained under air at natural15N abundance. The total15N excess content of berseem was similar whether or not the mycorrhiza had access to the maize roots. Plant mass (dry weight) of maize was not affected by the mycorrhizal fungus, but total nitrogen content tended to be higher in VAM‐colonized maize than in non‐colonized maize. Furthermore, both atom %15N excess and15N excess content of mycorrhizal maize were significantly increased as compared with non‐mycorrhizal maize or with maize controls without berseem. The amounts of15N transferred were small, accounting for less than 4% of the15N in the N2‐fixing plant.

In spite of the 2 cm root‐free separating zone, the presence of the mycorrhizal fungus in the non‐legume increased the transfer of symbiotically fixed nitrogen from berseem to maize plants that were physiologically younger. The implications of these results for nitrogen transfer from a legume to an accompanying non‐legume via VAM hyphae are discussed.
The effect of magnesium ions on the vesicular—arbuscular mycorrhizal infection of maize roots
Authors: GRYNDLER M. , VEJSADOVÁ H. , VANČURA V.
Published: April 2006

summary

The effect of magnesium sulphate on the colonization of maize roots by a vesicular‐arbuscular mycorrhizal fungus was studied in hydroponic culture. Increased concentration of MgSO4 in the nutrient solution caused an increase in the percentage of root length infected. The highest infection levels were found when nutrient solutions contained 5 84–11.68 mmol 1−1 of MgSO4. Root colonization was stimulated by the increased concentration of magnesium but not calcium or potassium ions in the nutrient solution. No significant difference occurred in the percentage of root length infected when magnesium chloride was replaced by magnesium sulphate. A broad range of magnesium sulphate concentrations did not cause significant differences in plant biomass. The stimulation of root colonization by magnesium cannot be explained by changes in pH or osmotic pressure of the nutrient solution.
Hyphal growth promotion in vitro of the VA mycorrhizal fungus, Gigaspora margarita Becker & Hall, by the activity of structurally specific flavonoid compounds under CO2‐enriched conditions
Authors: CHABOT S. , BEL‐RHLID R. , CHÊNEVERT R. , PICHÉ Y.
Published: April 2006

summary

Plant phenolic compounds are known to be inducers of virulence genes in plant‐pathogen interactions such as those involving Agrobacterium, and flavonoids are known to be inducers or inhibitors of Nod genes in Rhizobium‐legume symbiosis. More recent studies suggest that some of these compounds act as molecular signals in the development of vesicular‐arbuscular mycorrhizas (VAM). The present study has shown that hyphal growth of the VAM fungus, Gigaspora margarita Becker & Hall, is affected by both stimulatory and inhibitory flavonoids, when applied at 10 μ together with an optimal carbon dioxide enrichment. Stimulatory compounds were all flavonols (kaempferol, quercetin and morin) and possessed at least one hydroxyl group on the B ring. Conversely, two isoflavones (biochanin A, and genistein), a single flavanone (hesperetin) and two compounds without any hydroxyl group on the B ring, galangin (flavonol) and chrysin (flavone), were all inhibitors of hyphal growth.
The evolutionary significance of the legume genus Chamaecrista, as determined by nodule structure
Authors: NAISBITT T. , JAMES E. K. , SPRENT J. I.
Published: April 2006

summary

Nodulated plants of 14 species of Chamaecrista (Leguminosae, sub‐family Caesalpinioideae) were grown. The structure of cells from the active N2‐fixing region of nodules varied greatly with species. At one extreme bacteroids were confined solely by peribacteroid membranes, typical of advanced papilionoid legumes such as soybean. At the other extreme, bacteroids were retained within sheath‐bounded persistent infection threads, previously reported as typical of the Caesalpinioideae and also found in certain of the base genera of the Papilionoideae. Other species had an intermediate nodule structure. Nodules of the genus Chamaecrista thus appeared to be at an evolutionary crossroads between the primitive and more advanced forms.
Activity of ribulose bisphosphate carboxylase/oxygenase from potato cultivars with differential response to ozone stress
Authors: ENYEDI ALEXANDER J. , ECKARDT NANCY A. , PELL EVA J.
Published: April 2006

summary

The effect of ozone (O3) on the carboxylation activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) from the fifth youngest leaf of four cultivars of Solarium tuberosum L. (potato) was investigated. Ozone‐tolerant cultivars ‘Superior’ (SP) and ‘Norgold Russet’ (NR), and O3‐sensitive cultivars ‘Cherokee’ (CK) and ‘Norland’ (NL) were exposed to O3 for five consecutive days in controlled‐environment chambers. Leaf samples were obtained during the O3‐exposure period and at 1, 5, and 10 d post‐exposure. For both charcoal‐filtered air (control) and O3‐treated foliage, total activity of Rubisco declined with increasing leaf age. Ozone induced an accelerated decline in the carboxylation activity of Rubisco in leaves obtained from CK and NL by the third day of O3 exposure. In contrast, O3 had no impact on the Rubisco activity from leaves of SP and NR as compared to non‐treated foliage. Differential foliar conductance could not account for the response of the sensitive and tolerant cultivars.

Rubisco was purified from cultivars SP and CK to determine whether protein sulphydryl content correlated with foliar O3 sensitivity. The number of SH groups did not differ between the two cultivars, either in chemically denatured or non‐denatured Rubisco. Consequently, neither number nor availability of SH groups appear to be factors controlling sensitivity of Rubisco to oxidative damage by O3.
The effects of the duration and timing of drought plus heat plus gibberellin A4/7 on apical meristem development and coning in Sitka spruce [Picea sitchensis (Bong.) Carr]
Authors: OWENS J. N. , PHILIPSON J. J. , HARRISON D. L. S.
Published: April 2006

summary

Coning was induced on container‐grown grafts of Picea sitchensis (Bong.) Carr. by stem injection of 2 mg per month or part of a month of gibberellin A4/7 in combination with drought and high temperatures. The treatments were applied in a polyethylene‐covered greenhouse at five different times or durations during spring and summer. Coning response was determined the following spring. Shoots were sampled every fortnight from early May until late August and buds were dissected and fixed for anatomical study of apical development. The best coning resulted from the May to June, and June treatments with lesser coning occurring in the May, July, and May (2 wk only) treatments (all received heat + drought + gibberellin A4/7). Both pollen cones and seed cones were induced. Apices from control trees began to initiate bud scales in early May and leaf primordia about mid‐July. Apices from May‐treated trees began to differentiate into vegetative, pollen‐cone or seed‐cone buds in mid‐June. Apices from the June‐treated trees showed the earliest stages of vegetative, seed‐cone and pollen‐cone bud differentiation in mid‐July, about 2 wk after treatment stopped. Apices from the May to June, and the July‐treated trees began to differentiate into vegetative, pollen‐cone and seed‐cone buds in mid‐June and mid‐July respectively. The 2 wk May treatment induced too few cones to warrant anatomical study. The long period (May‐July), during which apices can be induced to differentiate into cone buds, may be explained partly by variation in the stage of bud development and partly because treatments alter the time of differentiation and synchronize apical development. Thus the earliest treatment (May) produced earlier differentiation and promoted more buds to develop in a uniform and vigorous manner to the stage where differentiation occurs. Other treatments (May‐June, and June) which preceded the natural time of bud differentiation also promoted early and uniform bud development and the longer treatment stimulated many apices, which would otherwise have slowed or stopped their development, to continue developing. Later treatment, in July, delayed apical differentiation and allowed lagging and retarded apices to catch up and thus be susceptible to the inductive treatment.
An electron microscope study of resin production and secretion by the glands of seedlings of Betula pendula Roth
Authors: RAATIKAINEN O. J. , TAIPALE H. T. , PELTTARI A. , LAPINJOKI S. P.
Published: April 2006

summary

Transmission and scanning electron microscopy were used to study the ultrastructure and secretory processes of resin glands on shoot stems of Betula pendula seedlings during seasonal growth. The multicellular peltate glands possess a cortex of columnar cells surrounding a parenchymal medulla differing from the stem parenchyma below. Myelin‐like deposits comprising concentric layers of membranes and osmiophilic substances accumulate mainly in the cortical cells, while only the medullar cells have chloroplasts. Both of these deposits appear to be synthesized, initially, in the endoplasmic reticulum. The myelin‐like material is believed to consist of steroidal triterpenoids in cytoplasmic membranes, and the osmiophilic deposits to represent phenolics. Studies of glands of different ages suggest that the electron‐transparent resin ultimately exported is formed by combining the two initial products. In the cortical cells the secretion first accumulates in vesicles that fuse with larger ones and the periplasmatic space. From the latter the secretion diffuses through the cell wall and the resin is finally deposited in the subcuticular space. Secretion vesicles, but no periplasmatic deposits were seen in the medullar cells. At the end of seasonal growth the cortical cells are markedly vacuolate and appear to have lost their organelles. Some of the cells accumulate an electron‐opaque material not seen earlier. The medullar cells of the glands are suberized before winter dormancy, but usually later than in the surrounding stem bark.
Ribosomal DNA variation and population differentiation in Salicornia L.
Authors: NOBLE S. M. , DAVY A. J. , OLIVER R. P.
Published: April 2006

summary

Analysis of nuclear rDNA variation within and between populations of Salicornia from the salt marsh at Stiffkey, Norfolk has detected new patterns of genetic differentiation. Individual plants may have alternative 10.5 and 12 kb repeat units. A strong association between the frequency of particular genetic variants and the environmental gradient of tidal inundation was evident. Salicornia dolichostachya Moss from sandy flats on the lowest parts of the marsh, near to the seaward edge, and S. fragilis Ball & Tutin from deep creeks were both monomorphic for the 12 kb variant; in contrast, S. pusilla J. Woods, characteristic of the highest parts of the tidal range, was monomorphic for the 10–5 kb variant. The more phenotypically variable S. europaea L. and S. ramosissima J. Woods populations that are found in large areas of lower and upper marsh, respectively, were heterogeneous for rDNA variant type. Nevertheless, the frequency of the 12 kb variant was significantly higher in plants from the lower marsh than in those from upper marsh, and in plants from low‐lying pans than in those from raised interfluves; the 10.5 kb variant had the converse distribution. Variation in rDNA was not obviously associated with variation in morphology, or with variations in isozyme frequency established previously.

Comparison of these results with those for populations from an extensive study, ranging from Anglesey (N. Wales) to S.W. Spain and the Gulf coast of Saudi Arabia, suggested that the rDNA variation and its association with environmental variation are complex and site‐dependent. Plants from Anglesey had 10.5 and 11.5 kb variants, whereas only a 10–75 kb variant was detected in material from Spain and Saudi Arabia.

rDNA variants were used as genetic markers in order to test the hypothesis that Salicornia is predominantly an inbreeder; conventional breeding experiments have been hampered by its highly specialized morphology and this represents the first direct, sensitive test of an idea that has been suggested mainly on morphological and phenological grounds. Analysis of rDNA in 38 maternal plants from Stiffkey and 2112 of their progeny provided no evidence for out‐crossing.
Evidence that abaxial leaf glands are the sites of salt secretion in leaves of the mangrove Avicennia marina (Forsk.) Vierh
Authors: FITZGERALD MELISSA A. , ORLOVICH DAVID A. , ALLAWAY WILLIAM G.
Published: April 2006

summary

Pieces of leaf from the halophyte Avicennia marina (Forsk,) Vierh. were freeze‐substituted and sectioned with special precautions to keep specimens always dry. Spot energy dispersive X‐ray microanalysis and X‐ray mapping showed that vacuoles of water parenchyma and palisade mesophyll cells had much more sodium and chlorine than the cytoplasm of the same cells. Potassium and phosphorus were also found in the vacuoles of the palisade mesophyll cells but in the water parenchyma cell vacuoles, sodium and chlorine generated most of the X‐ray counts. This is consistent with a function for the water parenchyma cells of vacuolar salt storage. No sodium and chlorine were detected in the peltate cells of the abaxial epidermal hairs, and there was very little sodium in the vacuoles of their basal cells, potassium apparently being the major cation. Salt crystals were not detected in substomatal cavities. Abaxial epidermal glands contained sodium and chlorine in the collecting cell, stalk cell, secretory cells and the subcuticular cavity. Material just outside the glands gave extremely high X‐ray counts for sodium and chlorine. We conclude that the material was salt that had been secreted, and that the glands are the secretory apparatus on the abaxial surface of the leaves.
Drought‐induced changes in hydraulic conductivity and structure in roots of Ferocactus acanthodes and Opuntia ficus‐indica
Authors: NORTH GRETCHEN B. , NOBEL PARK S.
Published: April 2006

summary

Drought‐induced changes in hydraulic conductivity (Lp) and anatomy were investigated for 1‐, 3‐ and 12‐month‐old roots of Ferocactus acanthodes (Lem.) Britton & Rose and Opuntia ficus‐indica (L.) Miller. Responses were similar for the two species but varied for the three root ages. Drying in soil for 30 d caused little change in Lp or internal structure for 1‐month‐old roots, primarily due to the formation of soil sheaths in the root hair zone. For 3‐month‐old roots, Lp declined three‐ to five‐told after 30 d of drying, partly because of lacunae caused by rupture of cortical cells. For 12‐month‐old roots after 30 d of drying, the dehydration of suberized peridermal layers led to a two‐ to three‐fold decline in Lp. Measurements of axial hydraulic conductance per unit pressure gradient (Kh) before and after pressurization indicated that air embolism, caused by 30 d of drying, decreased Khby 53, 97, and 98% for 1‐ 3‐ and 12‐month‐old roots, respectively. Rewetting after 30 d of drying restored Kh to initial values within 7 d for all three root ages. Lpafter rewetting attained 100 % of its initial value for 1‐month‐old roots arid about 60% for 3‐ and 12‐month‐old roots. The formation of soil sheaths around young roots, the reduction in radial conductivity for older roots by cortical lacunae and peridermal dehydration, and the reduction in Kh by embolism thus caused a moderate, partly reversible decline in Lp that can help limit water loss from roots to the soil during drought.
The response of native, herbaceous species to ozone: growth and fluorescence screening
Authors: REILING K. , DAVISON A. W.
Published: April 2006

summary

Ozone concentrations in many parts of Europe exceed the proposed UN‐ECE Critical Levels for the protection of ecosystems but there is so little known about the effects on native, herbaceous species, that it is presently impossible to judge what effect, if any, these concentrations are having on this group of plants. This paper reports the results of an initial screening of 32 taxa that was used to select a small number of species for further work. All were exposed to 70 nl 1−1O3 given for 7 h d−1for two weeks and the response measured in terms of mean relative growth rate (R̄), the allometric root/shoot coefficient (K), and changes in induced chlorophyll fluorescence (FR).

Only six species showed visible symptoms but 14 showed a significant reduction in R̄. There was no relationship between the extent of visible symptoms and growth reduction, confirming that visible symptoms are often of little value in determining growth sensitivity to O3 stress. There were marked differences within genera and within species; a population of Plantago major collected in Athens showed no effects, while a Derbyshire population, with a 24% reduction in R̄, was the most sensitive of taxa tested, including Bel‐W3 tobacco which has been specifically bred for O3 sensitivity.

There was a significant regression of R% change on the R̄ of controls (R̄%= 12.4−10.4 ×R̄, P= 0.0007, r=−0.56), implying that > 30% of the variation in response between taxa was related to the inherent R̄; faster growing taxa tending to show a greater reduction in R̄ on exposure to O3. It is tentatively suggested that this may be related to differences in stomatal conductance.

Ozone caused a significant shift in K in 14 taxa, with many of the biggest changes being in grasses. Although O3 reduced K in some taxa, contrary to several published accounts, it increased it in others, and in some there was an effect on K with no effect on R̄. Possible reasons for this are discussed.

Chlorophyll fluorescence was examined as a tool for detecting O3 stress. The maximum rate of rise of induced fluorescence, FR, was very sensitive to O3 but showed a complex pattern of response dependent on species and time. Most taxa showed a significant change in FR, even when there was no effect of the O3 on R̄ or K. Whilst the sensitivity of FR makes it a useful method for in vivo detection of O3 stress, the complexity of the response makes it very difficult to quantify and use for comparisons between species.
The effect of long‐term ozone exposure on injury in seedlings of red spruce (Picea rubensSarg.)
Authors: FINCHER JEAN , ALSCHER RUTH G.
Published: April 2006

summary

The death of many mature red spruce (Picea rubensSarg.) trees in the northeastern United States has sparked controversy over the roles natural factors and air pollutants play. The goal of this work was to investigate the effects of long‐term ozone exposures on development of injury and, in particular, the expression of winter injury in red spruce. Red spruce seedlings were exposed to elevated levels of ozone during two growing seasons, starting just after budbreak, and continuing into the period of early frosts. Trees spent both winter periods under ambient conditions of light and temperature. No visible lesions on foliage that could be attributed to ozone developed during the growing seasons. Yellow and brown needles appeared each winter, with much more injury in the second year. However, in the spring after two seasons of ozone exposure, there was no significant effect of ozone on the overall appearance of the entire population of seedlings. Samples were taken for histology and ultrastructure approximately monthly. Ozone treatments increased mesophyll cell disruption after frosts in early winter in the first year, but not in the second. There was no correlation between histological injury in the autumn and visible symptoms in the spring, indicating that there may be different aspects of the winter injury syndrome. In the second summer from 20 to 40%, of all mesophyll cells were damaged. This damage was not related to ozone treatment, and probably resulted from high summer temperatures.
Differences in the spectral characteristics of white clover exposed to gaseous pollutants and acid mist
Authors: WILLIAMS J. H. , ASHENDEN T. W.
Published: April 2006

summary

White clover plants (Trifolium repensL. cv ‘Grasslands Huia’) were exposed to combinations of gaseous pollutants and acid mists similar to those found in many parts of upland Britain. The gaseous pollutant treatments were (a) charcoal‐filtered air (control), (b) SO2+ NO2(c) O3and (d) O3+ SO2+ NO2. The acid mist treatments were 6 mm per week of solutions at pHs of 2.5, 3.5, 4.5 and 5.6. After 12 weeks, canopy reflectance was measured at green, red, near infrared and middle infrared wavelengths using a portable radiometer. Distinct changes in the characteristic spectral reflectance of the clover canopies were noted. The effect of the gaseous pollutants was significant when examined by analysis of variance. The two treatments containing ozone showed particularly marked changes and were statistically separable from the control in a pairwise comparison; the sulphur and nitrogen dioxide treatment was not statistically separable from the control. The acid mists had no significant effect on canopy reflectance. Simple and 4‐waveband vegetation indices showed positive linear relationships with shoot dry weight. The O3+SO2+NO2, in particular, and O3treatments produced marked decreases in shoot dry weight and vegetation index. The green and near infrared wavebands were the best discriminators of change in canopy reflectance.
Structural responses of needles of conifer seedlings to acid rain treatment
Authors: BÄCK JAANA , HUTTUNEN SATU
Published: April 2006

summary

The mesophyll ultrastructure of needles of Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) seedlings was examined in the course of experimental acid rain treatment lasting three years. The pH 3‐treated needle mesophyll cells exhibited thicker granal packing in their chloroplasts than the dry control needles after one season's irrigation. Starch occurrence had decreased due to pH treatment when the whole hardening and rest period was considered. Chloroplast shapes were seen to vary from ellipsoid to irregular, especially in the pH 4 and pH 3‐treated needles, due to divisions during hardening. The mean area of mesophyll chloroplasts in the hardened state after three seasons, irrigation was largest (10.3 μm2) in the pH 3‐treated needles, which also contained the smallest number of dark‐stained plastoglobuli. Starch occurrence in the hardened mesophyll cells in October reflected disturbances in the hardening processes in the pH 3‐treated needles.
Stomatal response of mycorrhizal cowpea and soybean to short‐term osmotic stress*
Authors: AUGÉ R. M. , STODOLA A. J. W. , BROWN M. S. , BETHLENFALVAY G. J.
Published: April 2006

summary

Cowpea [Vigna unguiculata (L.) Walp.] and soybean [Glycine max (L.) Merr.] plants were grown in pots and either inoculated with the vesicular‐arbuscular (VA) mycorrhizal fungi, Glomus intraradices Schenck and Smith (cowpea) and G. mosseae (Nicol & Gerd.) Gerd. and Trappe (soybean), or provided with regular P fertilization (non‐VA mycorrhizal plants). When plants were six to ten weeks old, roots were exposed to osmotic stress and stomatal behaviour monitored for several hours. Leaves of VA mycorrhizal cowpea had higher stomatal conductance (gS) than those of non‐mycorrhizal cowpea before and after lowering soil water potential (Ψ) to −0.7 MPa with either sorbitol or macronutrient solutions. Pre‐stress gs and the initial decline in gs after exposure to − 0.5 MPa sorbitol were similar in mycorrhizal and non‐mycorrhizal soybean leaves. Stomatal conductance was higher in the latter after 2 h but higher in the former after 21 h. CO2 exchange rates and leaf water relations were similar in VA mycorrhizal and non‐mycorrhizal soybean before and after soil Ψ was lowered. Higher gs at equal soil Ψ suggests that mycorrhizal root systems either scavenged water of low activity more effectively or influenced nonhydraulic root‐to‐shoot communication differently from that in non‐infected root systems.
The growth of the extramatrical mycelium of ectomycorrhizal fungi and the growth response of Pinus sylvestris L.
Authors: COLPAERT JAN V. , VAN ASSCHE JOZEF A. , LUIJTENS KRISTEL
Published: April 2006

summary

Nine ectomycorrhizal fungi have been studied for their effect on the growth of Pinus sylvestris L. seedlings. The plants were kept growing for six months in root chambers with a changeable volume. All seedlings were cultivated under conditions of low substrate nutrient concentrations and they became strongly infected within a short time. We demonstrated the existence of an important negative correlation between the extent of the fungal development and the growth of the host plants. In most studies this reduced growth is attributed to an energy drain by the fungus. Fungi producing large amounts of fungal tissue are more energy consuming than species which only develop a sparse mycelium. However we suggest that also nitrogen acquisition by the plants might be altered by the fungus. Certain fungi probably retain a considerable amount of nitrogen for their own growth, thus reducing the amount transported to the host plant. A decreased N transport finally results in a slower growth. In this study the extramatrical mycelium in the rooting substrate was determined by wet oxidation and by nitrogen determination. This component of the fungal biomass showed the biggest variation among the different mycobiont species. The results are discussed in relation to the culture technique employed.
Fungal saprobes and pathogens as endophytes of rice (Oryza sativaL.)
Authors: FISHER P. J. , PETRINI O.
Published: April 2006

summary

Fungal endophytes have been isolated from inside the leaf blades, leaf sheaths, and roots of six‐week‐old plants as well as from seeds and ten‐day‐old seedlings ofOryza sativa(L.). The fungi isolated can be grouped in two categories; one containing organisms known mainly to be saprotrophic and the other comprising potential pathogens. Of the formerAlternaria alternata(Fr.) Keissler andEpicoccum purpurascensEhrenb. ex. Schlecht preferentially colonize the leaf blades of their host, whereasCladosporium tenuissimumCooke seems more generally distributed between leaf blades and leaf sheaths.Fusarium equiseti(Cords) Sacc.,F. oxysporumSchecht andPhoma sorghina(Sacc. Boerema) are latent in their hosts without causing disease symptoms.A. alternata, E. purpurascens, F, equiseti.andNigraspora oryzaehave also been frequently isolated from seeds and young seedlings and can be considered seed‐borne. Principal components analysis has shown a marked tissue specificity among rice endophytes. Leaf sheaths of the rice varieties grown under dry conditions are colonized by endophyte communities different from those of the wet cultivars.
Utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi (Lohmann) Kamptner
Authors: NIMER N. A. , DIXON G. K. , MERRETT M. J.
Published: April 2006

summary

Inorganic carbon‐dependent photosynthetic oxygen evolution was saturated at a photon flux density of 100 μmol m−2s−1for air‐grown cells of a low calcifying strain of Emittania huxleyi (Lohmann) Kamptner. Measurement of photosynthetic oxygen evolution at constant inorganic carbon concentration but varying pH showed that exogenous bicarbonate was not a major carbon source for photosynthesis. At pH 8.0 the concentration of dissolved inorganic carbon (DIC) required for the half‐maximal rate of photosynthetic O2 evolution (K0.5[DIC]) was 2.86 mm; the rate of non‐enzymic dehydration of HCO3 greatly exceeding the rate of CO2 fixation. Carbon dioxide uptake occurs by diffusive entry as shown by the K0.5 [DIC] of 12.5 μM at pH 5.0.

Bicarbonate uptake, measured by the silicone‐oil‐layer centrigual filtering technique, did not show Michaelis‐Menten type kinetics. The electrical membrane potential difference was determined from the distribution of the lipophilic cation tetra[3H]phenylphosphonium (TPP+) between cells and the media. Cells grown at pH 8.0 exhibited a negative membrane potential (inside of cell relative to outside) of about −60 mV.
Growth and carbon economy of a fast‐growing and a slow‐growing grass species as dependent on ontogeny
Authors: POORTER HENDRIK , POTHMANN PETER
Published: April 2006

summary

In previous experiments systematic differences have been found in the morphology, carbon economy and chemical composition of seedlings of inherently fast‐ and slow‐growing plant species. The present experiment was to investigate whether these differences persist when plants become larger. Plants of the inherently fast‐growing Holcus Lanatus L. and the inherently slow‐growing Deschampsia flexuosa (L.) Trin. were grown under standardized conditions and growth, photosynthesis, respiration and carbon and nitrogen content were followed over a period of 4 to 7 weeks. Differences in relative growth rate were mainly due to the higher leaf area ratio (leaf area; plant weight) of the fast‐growing species. Rates of photosynthesis differed substantially when expressed on a leaf weight basis, but only slightly when expressed per unit leaf area. Although most parameters showed some ontogenetic drift, differences found for young seedlings persisted at least until plants reached a dry weight of circa 3 g. Therefore, at least for these two species, the conclusions based on interspecific variation relative growth rate of young seedlings apply to larger plants as well.
Differences in fructan accumulated in induced and field‐grown wheat plants: an elongation‐trimming pathway for their synthesis
Authors: BANCAL P. , CARPITA N. C. , GAUDILLÈRE J. P.
Published: April 2006

summary

Mature blades of wheat seedlings were induced to form fructan by excision and continuous illumination, and their sugars were analyzed either 24 or 60 h after induction by both gel permeation and high performance liquid chromatography. The earliest accumulated fructan consisted mainly of 1‐kestose, nystose, bifurcose, and short oligomers rich in (2→1)‐linkages and branch point residues. After several days, fructan included more than fifty compounds, among which one‐half of the total were heptamers or larger. Oligomers accumulated during long‐term incubation contained a higher proportion of (2→6)‐linkages than those accumulated early after induction. Stems of field‐grown wheat contained about the same amount of fructan as blades of induced seedlings, but with larger proportions of phlein oligomers initiating with 6‐kestose, phlein‐like oligomers initiating with bifurcose, and other branched oligomers enriched in (2→6)‐linkages. An ‘elongation‐trimming’ pathway is proposed in which a (2→1)‐specific fructan fructosyl transferase and O‐6 branching activity produce branched oligomers rich in (2→1)‐linkages, and in which a fructan exo‐hydrolase cleaves 1‐linked terminal‐fructosyl units selectively to have phlein‐like oligomers resistant to further hydrolysis.
In situ studies of crassulacean acid metabolism in Kalanchoë beharensis Drake Del Castillo, a plant of the semi‐arid southern region of Madagascar
Authors: KLUGE MANFRED , RAZANOELISOA BAKOARSINA , RAVELOMANANA DIDIER , BRULFERT JEANNE
Published: April 2006

summary

The first comprehensive field study has been conducted of crassulacean acid metabolism in a Kalanchoë species, namely K. beharensis Drake Del Castillo, a plant of the flora of the semi‐arid southern part of Madagascar. The study includes measurements of diel patterns of CO2 exchange and transpiration, and of fluctuations in organic acid levels, PEP carboxylase properties and water relations.

In contrast to the other Kalanchoë species studied so far, the CAM behaviour of K. beharensis is very uniform. Regardless of whether the plants were naturally droughted for several months or had received 6 wk of daily watering, CO2 uptake was quantitatively the same and occurred entirely during the night. Watering also had no effect on the amplitude of the diel fluctuation of titratable acidity. The fluctuating citrate level was somewhat higher in the droughted plants. The data on PEP carboxylase indicate a diel change between an active night‐form and a less active day‐form of the enzyme known already from other CAM plants studied in the laboratory.

Experiments with leaves kept in situ artificially darkened during the day revealed that the onset of deacidification was under the control of an external stimulus, presumably of temperature. In the CAM performing leaves, neither water status nor seasons were associated with significant differences in leaf water potential, osmotic pressure and turgor pressure. The lower amplitude of titratable acidity found during the dry season is presumably more due to suboptimal night temperatures during this time than to plant water relations.

Altogether, the study shows that K. beharensis is capable of maintaining the full CAM performance throughout the entire arid seasons, and thus avoids CAM idling. It is assumed that this advantageous behaviour is based on the capability to maintain appropriate water status in the photosyntheticaily active leaves even during long‐lasting drought. This capability is due, on the one hand, to minimization of transpiration by the extreme CAM mode, accompanied by very low cuticular transpiration, and on the other hand due to water transfer from the older leaves which then wilt and are shed.
Tolerance of wheat (Triticum aestivum cvs Gamenya and Kite) and triticale (Triticosecale cv. Muir) to waterlogging
Authors: THOMSON C. J. , COLMER T. D. , WATKIN E. L. J. , GREENWAY H.
Published: April 2006

summary

Responses of two genotypes of wheat (Triticum aestivum cvs. Gamenya and Kite) and one genotype of triticale (Triticosecale cv. Muir) were evaluated in stagnant solution culture and in waterlogged soil, using 23‐ to 36‐d‐old plants. Stagnant nutrient solutions decreased shoot fresh weight of Gamenya by 21% compared with aerated plants, while shoot fresh weight of Muir was unaffected. Reductions in nodal root fresh weight under stagnant conditions were also less for Muir than Gamenya.

Aerenchyma in nodal roots of stagnantly grown plants accounted for 6.7 and 12.7% of the root cross sectional area for Gamenya and Muir, respectively. Oxygen supplied via this aerenchyma was substantially greater for Muir than Gamenya, and greatest for nodal roots of Kite. Elongation rates of stagnantly grown nodal roots in an Oa‐free medium reflected the amount of O2 supplied via the aerenchyma, and were 0.11, 0.17 and 0.27 mm h−1 for Gamenya, Muir and Kite, respectively.

Waterlogging in soil decreased the redox potential from +600 to − 200 mV after 35 d. Waterlogging decreased shoot fresh weight of Gamenya, Kite and Muir by 63–82% compared with drained plants, with similar reductions in growth of seminal roots. Nodal root growth was little affected by waterlogging in soil, although Muir had a 1.6‐2.4‐fold greater nodal root mass than Gamenya and Kite. Furthermore, after two cycles of 7 d waterlogging and 7 d drainage the seminal roots of Muir were at least double the length of Gamenya and Kite.

Under the same waterlogged conditions, the shoot growth of rice (Oryza sativa cv, Calrose) was much greater than for wheat and triticale, and this reflected differences in morphology and anatomy of the root systems. Nodal root/shoot ratios indicated the major factor limiting shoot growth of wheat was the small mass of nodal roots per plant. However, a possible additional factor is the poor function of nodal roots of wheat and triticale in waterlogged soil.