bluuebunny/crossref_metadata_2025 huggingface dataset:
THE TOLERANCE OF TREE ROOTS TO WATERLOGGING
Authors: COUTTS M. P.
Published: May 2006

Rooted cuttings of Picea sitchensis and Pinus contorta were grown with split roots in plastic troughs of soil, to produce 500 mm long woody roots on either side of each plant with the distal parts of the root system growing out into pots at the ends of the troughs. Some roots of primary structure were also present in the troughs. The soil in the trough on one side of the plant was waterlogged while all other parts of the root system remained in freely drained soil. The waterlogging treatment was applied out of doors from April to November.

In both species all roots of primary structure in the waterlogged soil were killed, whereas most of the woody roots survived. In the pine, radial growth of the waterlogged part of the woody root was reduced relative to the freely drained control side, and the root tapered from the plant stem towards the centre of the waterlogged zone, then increased again towards the distal end. Growth of pine roots of primary structure in freely drained soil at the distal end of the waterlogged woody root was not reduced compared with the control side. Spruce was more sensitive, and growth of xylem and phloem of the woody root almost ceased at the centre of the waterlogged zone; there was also a carry‐over effect of the waterlogging treatment into other parts of the root system. Growth of the woody root proximal to the waterlogged zone and of the primary roots distal to it were reduced.

Enlarged lenticels became abundant on the woody roots of both species at the ends of the waterlogged zone and their frequency decreased towards the centre.

The results are discussed in relation to differences in oxygen transport known to occur in woody roots of the two species.
SENESCENCE IN SUBMERGED AQUATIC ANGIOSPERMS: EFFECTS OF HEAVY METALS
Authors: JANA SASADHAR , CHOUDHURI MONOJIT A.
Published: May 2006

The effects of mercuric chloride, lead acetate, cadmium chloride and cupric sulphate on the senescence of isolated mature leaves of three submerged aquatic angiosperms, Potamogeton pectinatus L., Vallisneria spiralis L. and Hydrilla verticillata (L.f.) Royle, were studied. All four compounds decreased the rate of respiration of all the species except that Cu increased the respiration rate of Potamogeton. All the heavy metals hastened senescence of all three species as measured by decreases in the contents of chlorophyll, RNA, protein and dry wt and increases of free amino acid content, tissue permeability, the ratio of acid to alkaline pyrophosphatase activity and the activities of protease and RNase. All metals decreased the ratio of chlorophyll a to b in Potamogeton and Vallisneria but increased it in Hydrilla. Cu seemed to be the most effective metal in inducing deleterious effects in Potamogeton and Vallisneria. Pretreatment of leaves of these plants with kinetin for 12 h or more, significantly reduced the senescence promoted by the heavy metals. Of the three species studied, Hydrilla was most tolerant to the heavy metals applied.
CATABOLITE REPRESSION OF THE SYNTHESIS OF PECTIN‐DEGRADING ENZYMES BY SUILLUS LUTEUS (L. EX FR.) S. F. GRAY AND HEBELOMA OCULATUM BRUCHET
Authors: GILTRAP N. J. , LEWIS D. H.
Published: May 2006

The synthesis of pectin‐degrading enzymes in vitro by both Suillus luteus (L. ex Fr.) S. F. Gray, a proven ectomycorrhizal fungus, and Hebeloma oculatum Bruchet, a saprotrophic, non‐mycorrhizal species of a frequently ectomycorrhizal genus, is repressed by glucose. The possibility that a control mechanism, which is based on catabolite repression and which prevents extensive intracellular fungal infection, operates in ectomycorrhizas is discussed.
FACTORS AFFECTING THE SPREAD OF VESICULAR MYCORRHIZAL FUNGI IN SOIL
Authors: WARNER A. , MOSSE B.
Published: May 2006

The effect of root density on the spread of vesicular‐arbuscular mycorrhizal infection was measured using Trifolium repens (clover) and Festuca rubra (fescue). Seeds of both host species were sown in large troughs at three different distances apart, which resulted in different root densities that persisted for up to 15 weeks. For clover, colonization (i.e. total length of infected root) and linear spread were favoured by greater root densities, and at the greatest root density colonization seemed to proceed faster than root extension. In fescue, root density was positively related to linear spread up to about 23 cm root cm−3 soil, but greater root density was supra‐optimal for linear spread but not for colonization. Although root density had important effects on the spread of infection, effects of plant species were much greater. Fescue had more total root (five times that of clover), but it supported less linear spread and less than half the total length of infected root.
RELATIONSHIPS BETWEEN HOST AND ENDOPHYTE DEVELOPMENT IN MYCORRHIZAL SOYBEANS
Authors: BETHLENFALVAY G. J. , BROWN M. S. , PACOVSKY R. S.
Published: May 2006

Symbiotic associations of soybeans and the vesicular–arbuscular mycorrhizal fungus Glomus fasciculatus were grown to maturity in a sand‐perlite rooting medium watered with a nutrient solution containing growth‐limiting amounts of soluble phosphorus. Development of fungal mycelia external and internal to the host plant's root system was measured by determining chitin in isolated fungal mycelium, in the rooting medium, and in the mycorrhizae. The biomasses of the extra‐ and intraradical mycelia were calculated from the values of chitin obtained spectrophotometrically. The amount of total fungal biomass relative to that of the host plant varied throughout the lifespan of the association and reached a maximum of 2.3 % 10 weeks after planting. The amount of intraradical mycelium increased throughout the host plant's life span. Extraradical fungal structures attained a maximum weight at the onset of logarithmic growth of the soybean pods and decreased thereafter. Cessation of the rapid growth phase of G. fasciculatus lagged behind that of the host plant's vegetative structures, but appeared to be related to pod development. The fungus to root dry wt ratio was 12–3% at senescence. The ratio of extra‐ to intraradical mycelium decreased throughout the association's lifespan. Since the extraradical hyphae are the organs responsible for enhanced nutrient uptake this ratio is proposed as an index of the endophyte's usefulness to the host. High values for this usefulness index coincided with significant growth enhancement of the host plant. Source–sink relationships in the host appear to be a determining factor in the growth of the fungal endophyte.
AMINO ACID NUTRITION IN THE BLUE‐GREEN ALGA NOSTOC MUSCORUM
Authors: VAISHAMPAYAN A.
Published: May 2006

The L‐isomers of 21 amino acids have been screened for their ability to serve as carbon or nitrogen sources for growth of the het+ nif−11 heterocystous and non‐nitrogen fixing mutant strain of the blue‐green alga Nostoc muscorum by a simple test system combining the use of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) (an inhibitor of photosynthetic assimilation of CO2) and the auxotrophic (non‐nitrogen fixing) characteristic of the mutant. The amino acids glutamate, alanine, tyrosine and cysteine were toxic; glutamine, histidine, asparagine, tryptophan and serine were utilized as nitrogen sources; arginine, proline and phenylalanine were utilized as carbon sources; leucine, isoleucine, lysine, methionine, valine and citrulline were utilized as sources of both carbon and nitrogen; aspartate, threonine and glycine served neither as carbon nor nitrogen sources.
EFFECTS OF TWO SPECIES OF V A MYCORRHIZAL FUNGI ON DROUGHT TOLERANCE OF WINTER WHEAT*
Authors: ALLEN MICHAEL F. , BOOSALIS MICHAEL G.
Published: May 2006

Summary

Roots and soils from western Nebraska fields of native and planted grasslands, and winter wheat of varied fallow‐wheat cultivation duration, were evaluated for vesicular–arbuscular (VA) mycorrhizal root infection and spore numbers and types. Increased cultivation decreased percentage mycorrhizal infection in wheat and reduced spore numbers of Glomus fasciculatus, the dominant VA mycorrhizal fungus in these soils. Spore numbers of other VA mycorrhizal fungi did not change significantly with cultivation although mean numbers of G. mosseae increased with continued wheat production. Water relations and growth were determined for greenhouse‐grown non‐raycorrhizal, G. fasciculatus‐infected, and G. mosseae‐infected wheat in wet and dry soils. Stomatal conductances were higher in mycorrhizal than in non‐mycorrhizal plants in both wet and dry treatments. Stomatal closure in‐mycorrhizal plants occurred at lower leaf water potentials (Ψ1) and after greater desiccation than in non‐mycorrhizal plants, but some leaves of G. mosseae‐infected plants showed no stomatal response to drought and continued to transpire at Ψ as low as ‐4.1 MPa. Leaf osmotic adjustment was greatest for G. fasciculatus‐infected plants. Non‐mycorrhizal and G. fasciculatus‐infected plants had equal dry wts in both wet and dry conditions. Infection by G. fasciculatus appeared to increase wheat drought tolerance while infection by G. mosseae did not.
THE DYNAMICS OF GROWTH AND NUTRIENT ACCUMULATION BY FRUITS OF GREVILLEA LEUCOPTERIS MEISSN., A PROTEACEOUS SHRUB, WITH SPECIAL REFERENCE TO THE COMPOSITION OF XYLEM AND PHLOEM SAP
Authors: HOCKING PETER J.
Published: May 2006

Summary

Grevillea leucopteris is a large xeromorphic shrub from nutrient‐deficient sandy heathland in south‐western Australia. The fruit of G. leucopteris is a follicle which contains two seeds. Leaves and follicles have very low levels of essential nutrients, but seeds have very high levels, especially N, P and trace elements, as well as substantial oil reserves (30% w/w). Grevillea leucopteris appears to be a Ca accumulator because of the very high concentrations of this element in leaves, follicles and seeds.

Phloem exudate from incisions in fruiting branches and xylem sap were used to study transport of nutrients to fruits. Phloem sap had 14 to 17% sugar. Glutamine was the major amino compound in xylem and phloem sap. Arginine comprised 37% of the N in xylem sap but was absent in phloem, suggesting its release from storage pools in roots and stems and metabolism in leaves. K dominated the mineral spectrum of phloem sap, and Ca that of xylem. Ca levels in xylem and phloem sap were very high (200 and 500 μg cm−2 respectively), and K: Ca ratios were very low: xylem 0.5: phloem 3.7. The phloem: xylem concentration ratio for all minerals was 8.7. Reduced transpiration by enclosing fruits in plastic bags or foil changed their K: Ca ratios from 0.95 to 3.13 or 4.48.

Each fruit used 11.5 cm3 of water during growth, 76% estimated to arrive in the xylem, the rest via the phloem. The water use efficiency of G. leucopteris fruits was 29.9 cm−3 g−1 dry matter produced, close to values reported for mesomorphic species such as lupin and pea. The high levels of Ca in G. leucopteris fruits are due to high levels of Ca in transport fluids rather than elevated transpiration.
MODULATION, BY PHENOLIC COMPOUNDS, OF ENDOGENOUS MANGANESE DURING IAA‐INDUCED GROWTH IN AVENA COLEOPTILE SEGMENTS: AN ELECTRON SPIN RESONANCE STUDY
Authors: KRISHNA T. MOHAN , BHARTI SUDHAKAR
Published: May 2006

Summary

The behaviour of endogenous manganese (Mn2+) was studied by electron spin resonance spectroscopy during growth induced by indol‐3‐ylacetic acid (IAA) and modulated by phenolic acids in Avena coleoptile segments. Oat coleoptile segments show a characteristic sextet hyperfine spectrum which is similar in appearance to the sextet of Mn2+ In aqueous solution. Endogenous Mn2+ shows a concentration response to IAA, Coleoptile segments treated with p‐hydroxy benzoic acid and 2,4‐dicblorophenol, which inhibit IAA‐induced growth, show a decline in the concentration of endogenous Mn2+. Chlorogenic acid and caffeic acid, which synergize IAA‐induced growth, keep endogenous manganese in the reduced state (i.e. Mn2+) probably by donating electrons in the reaction. It appears that conditions inhibitory to IAA‐induced growth are associated with a decreased level of tissue Mn2+ while those stimulatory to growth seem to be associated with a higher level of endogenous Mn2+. The changes in endogenous Mn2+ may be mediated either by complex formation or by a change in the redox state.
INFECTION DEVELOPMENT AND INTERACTIONS BETWEEN VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI
Authors: WILSON J. M. , TRINICK M. J.
Published: May 2006

Summary

The response of mycorrhizal infection to changes in inoculum density was similar in form forGlomus tenuisandGlomus monosporus. Nevertheless,G. tenuisproduced considerably more infection per propagule unit than did G.monosporus, probably due to a greater ability ofG. tennisto produce secondary infection points. When mixed inocula of the two fungi were used, both the time of harvest and the frequency of each fungus in the inoculum influenced the competitive effects.Glomus tenuiswas slow to form infection points, and was less aggressive thanG. monosporusat 12‐ and 24‐day harvests. By 36 days the two fungi were equally aggressive and the amount of infection produced by each fungus was directly proportional to its frequency in the inoculum.
EVIDENCE FOR THE PARTICIPATION OF GLUTAMATE DEHYDROGENASE IN AMMONIUM ASSIMILATION BY STICHOCOCCUS BACILLARIS
Authors: EVEREST S. A. , SYRETT P. J.
Published: May 2006

Summary

Cells of the green alga, Chlorella vulgaris (strain 21l/8k) have high NADPH‐glutamate de‐hydrogenase (GDH) activity when grown on ammonium (NH4+); activity is low in nitrate (NO3−)‐grown or nitrogen‐depleted cells. In contrast, cells of Stichococcus bacillaris (strain 379/5) contain little NADPH‐GDH activity when grown on NH4+ but much when grown on NO3− or depleted of nitrogen. Despite the high NADPH‐GDH activity in NH4+‐grown cells of C. vulgaris, NH4+ assimilation by this organism is strongly inhibited by methionine sulphoximine (MSO), an inhibitor of glutamine synthetase. NH4+ assimilation by NH4+‐grown S. bacillaris is similarly almost completely inhibited by MSO. However, NH4+ assimilation by NQ3‐grown S. bacillaris is much less inhibited by MSO and it is suggested that the high NADPH‐GDH activity of these cells is partly responsible for the remaining NH4+ assimilation.
HYBRIDIZATION, PGLYPLGIDY AND APOMIXIS IN ANDROPOGON TECTORUM SCHUM. AND THONN. (GRAMINEAE)
Authors: OKOLI BOSA E.
Published: May 2006

Summary

Natural populations of Andropogon tectorum from various parts of Nigeria have been investigated and found to contain diploid and triploid chromosome races. Intraspecific hybrids were obtained between two morphologically and cytologically distinct diploids. Meiosis in the triploids was characterized by a high frequency of univalents in one collection and of multivalents in another. At meiosis in the diploid hybrid, multivalents and non‐disjunction ‘bridge‐and‐fragment’ configurations were discovered. The triploid collections and the hybrids were observed to reproduce apomictically. The relationship between hybridization and polyploidy on the one hand and apomixis on the other is examined in the light of the available information.
CRYSTALS OF CALCIUM COMPOUNDS IN GRAMINEAE
Authors: LERSTEN NELS R.
Published: May 2006

Summary

From reviews of the anatomy and cell contents of grasses it would appear that crystals of calcium compounds do not occur. However, 13 scattered reports of such crystals in grasses have been discovered in the literature. As a result of observations made by the author, calcium oxalate crystals have been found in bundle sheath cells and adjacent mesophyll in leaves of Melinis minutiflora (Panicoideae).
DO LEMON COTYLEDONS GREEN IN THE DARK?
Authors: WHATLEY JEAN M. , PRICE D. N.
Published: May 2006

Summary

In general angiosperms do not synthesize chlorophyll in the dark. It has, however, been pointed out that the large or woody fruits of a few species may be opaque, but that, nevertheless, their embryos become green. In some species of citrus, seeds occasionally germinate within the intact, ripe fruit. The cotyledons of such seedlings expand and become dark green. An electron microscope investigation showed that the cotyledons contained chloroplasts with few stroma lamellae but with true grana. The quality of light reaching the seeds and embryos in ripe lemons was found to be poor in blue light but rich in the red wavelengths necessary for the conversion of protochlorophyll to chlorophyll. The quantity of light penetrating to the embryos was low but of an order of magnitude known to be adequate for chlorophyll synthesis and chloroplast development in a number of species.
CONTACT ANGLES OF WATER DROPLETS ON NEEDLES OF SCOTS PINE (PINUS SYLVESTEIS) GROWING IN POLLUTED ATMOSPHERES
Authors: CAPE J. N.
Published: May 2006

Contact angles of 1 μl droplets of distilled water were smaller on old than young needles of Pinus sylvestris. The decrease from c. 110° on young needles was larger for needles of trees growing in atmospheres with c. 40 μ SO2 m−3 than for those from trees in atmospheres with < 10 μg SO2 m−3 (c. 70° and c. 80° respectively on 3‐year‐old needles). Although there were small changes in the wettability of the needle cuticle, the decreases in contact angle are largely attributable to changes in epicuticular waxes.
THE ADAPTIVE ARCHITECTURE OF SHRUB CANOPIES: LEAF DISPLAY AND BIOMASS ALLOCATION IN RELATION TO LIGHT ENVIRONMENT
Authors: NICOLA A. , PICKETT S. T. A.
Published: May 2006

Leaf display features and biomass allocation were investigated in four dominant shrubs of forest and old‐field habitats in central New Jersey, USA, to determine whether differences exist between species which reach optimum development in different successional environments. Late‐successional shrubs were found to possess larger leaves, greater leaf area expansion (ratio of leaf area to leaf weight), and increased allocation of total energy to leaves versus wood, compared to early‐successional shrubs. The shrubs appeared to deviate from patterns of biomass allocation expected in trees, possibly as a result of relative ease of horizontal exploitation of space through cloning. In addition, there appears to be a great deal of flexibility in features of leaf display which may play an important role in shrub adaptation to particular light regimes.
EFFECTS OF FLOODING ON LEAF WATER POTENTIAL AND STOMATAL RESISTANCE INBRUGUIERA GYMNORRHIZA(L.) LAM
Authors: NAIDOO G.
Published: May 2006

The effects of 10, 20, 40 and 80 days of flooding on stomatal responses in the halophyte,Bruguiera gymnorrhiza(L.) Lam were investigated. Measurements were made of leaf water potential and stomatal resistance (rg) during the period of flooding, and continuing for 12 to 14 days after its termination.

Generally, plants flooded for prolonged periods had lower leaf water potentials than the controls both during and after flooding. Prolonged flooding also resulted in higherrgduring flooding and continuing for 8 to 10 days afterwards. Leaf water potentials decreased with increase in the duration of flooding. Decrease in leaf water potential was also associated with an increase inrg.

Prolonged flooding also resulted in ultrastructural modifications. The chloroplasts had smaller grana and the lamellae were considerably swollen. There also appeared to be some degradation of thylakoid membrane structure.
PRODUCTIVITY OF FIELD‐GROWN SOYBEANS EXPOSED TO SIMULATED ACIDIC RAIN
Authors: EVANS LANCE S. , LEWIN KEITH F. , PATTI MITCHELL J. , CUNNINGHAM ELIZABETH A.
Published: May 2006

Two experiments were performed during the summer of 1981 to determine the effects of simulated acidic rain on seed yields of soybeans grown using standard agronomic practices. In one experiment, plants were shielded from all ambient rainfall and exposed to simulated rainfall in quantities equal to the average amount of rainfall that occurs at the site. Seed yields of soybeans exposed twice weekly to simulated rain of pH 4.1, 3.3 and 2.7 were, respectively, 10.7, 16.8 and 22.9 % below yields of plants exposed to simulated rain of pH 5.6. A treatment‐response function of seed yield vs rainfall pH was y= 7.40 +1.025x and had a correlation coefficient of 0.997 (y is seed mass per plant and x is the pH of the simulated rain). In a second experiment, soybean plants were not shielded from ambient rainfall (weighted mean hydrogen ion concentration equal to pH 4.04) and received only small volumes of simulated rainfall three times weekly. Plants exposed to simulated rainfall of pH 4.1, 3.3 and 2.7 exhibited yield reductions of 2.7, 7.0 and 7.6%, respectively, below yields of plants exposed to simulated rainfall of pH 5.6. By best fit analyses, the equation describing this relationship is expressed by y= 9.68 + 0.318x, and the correlation coefficient is 0.97. In both experiments, the observed decrease in seed yields was due to a decrease in number of pods per plant.
ULTRASTRUCTURE OF ACTIVE AND DORMANT CAMBIAL CELLS IN TEAK (TECTONA GRANDIS L. f)
Authors: RAO K. S. , DAVE Y. S.
Published: May 2006

Cytological changes in the ultrastructure of cambial cells of teak (Tectona grandis) during active and dormant periods have been studied after glutaraldehyde‐osmium tetroxide fixation. The fusiform and ray initials are essentially alike in their ultrastructure and all have cellular organelles. Active cambial cells are highly vacuolated and are rich in all organelles. They contain rough endoplasmic reticulum (ER), polysomes, dictyosomes with hypertrophied cisternae, mitochondria and plastids with starch. The plastids are characterized by the presence of varying amounts of a dark intralamellar inclusion which is considered to be a protein. Microfilament bundles, 0.05 to 0.2 üm in width, occur frequently in the parietal cytoplasm. Dormant cambial cells have numerous small vacuoles, smooth ER, free ribosomes and a few inactive dictyosomes. In addition to the dark inclusion, plastids contain what are thought to be phytoferritin granules and prolamellar bodies. Branched plasmodesmata and paramural bodies are associated with the cambial cell walls.
DIFFERENTIATION OF THE PHOTOSYNTHETIC APPARATUS IN PHYLLITIS SCOLOPENDRIUM (L.) NEWMAN
Authors: MARIANI COLOMBO P. , RASCIO N. , CASADORO G.
Published: May 2006

Chloroplast development in both coiled and uncoiling croziers of Phyllitis scolopendrium has been studied. An interesting stage of chloroplast ontogenesis appears to be that characterized by the presence of very long thylakoid stacks. It resembles the final stage of organization attained by the chloroplasts of many green algae at maturity even if, in P. scolopendrium, it represents only an intermediate stage in thylakoid system ontogenesis.

Growing the plants in the dark has a pronounced effect on the morphogenesis of the frond and on plastid differentiation. In both dark‐ and light‐grown plants we could observe, even if in different amounts, prolamellar body‐like structures interconnected with the thylakoids. The presence of such structures is discussed, especially in view of the fact that ferns are able to synthesize chlorophylls in the dark.
THE INFLUENCE OF LIGHT QUALITY ON CARBOHYDRATE TRANSLOCATION WITHIN CORN LEAF STRIPS
Authors: HODDINOTT J.
Published: May 2006

To test the effect of light quality on carbohydrate translocation, leaf strips of Phaseolus vulgaris L. cv. Black Valentine were prepared before or after exposure to a 48 h dark pretreatment. Central portions of the strips were labelled with 14CO2 and translocate was allowed to move acropetally and basipetally along the strips. The portions of the strips on either side of the labelling region were exposed to red or far‐red light, or darkness. Translocation in darkened strips was predominantly basipetal. When portions of the strips were given red light, translocation to that region was suppressed. It is suggested that Ptr does not promote unloading. Pr formation induced by far‐red light, or dark decay of phytochrome, promotes unloading and long distance transport in a high irradiance response, but does not alter the normal polar transport in the strips.
EFFECT OF KINETIN AND CYCLIC 3′, 5′‐ADENOSINE MONOPHOSPHATE ON BUD INDUCTION IN THE MOSS TIMMIELLA ANOMALA
Authors: KAPOOR (néeREKHI) ANITA , CHOPRA R. N.
Published: May 2006

Kinetin enhances bud formation in Timmiella anomala. Cyclic 3′, 5′‐adenosine monophosphate (cAMP) and theophylline inhibit bud formation, but stimulate growth of gametophores. N8, O2‐dibutyryl adenosine 3′, 5′‐cyclic monophosphate has no appreciable effect. ATP, ADP, 2′, 3′‐cAMP, 5′‐AMP, adenosine and adenine stimulate bud formation. Kinetin in combination with cAMP further increases bud number and also the length of gametophores. This effect appears to be specific, since it is not observed when kinetin is added along with 2′, 3′‐cAMP, 5′‐AMP or adenosine.
MERCURY VAPOUR: A HEALTH HAZARD IN HERBARIA
Authors: BRIGGS D. , SELL P. D. , BLOCK M. , I'ONS R. D.
Published: May 2006

Metallic mercury vapour is released from herbarium specimens poisoned with mercuric chloride, in quantities which might constitute a health hazard. By increasing the ventilation in the Cambridge University Herbarium, the concentration of mercury vapour in the air has been reduced to a safer level. Even if herbaria no longer use mercuric chloride to protect specimens against insect attack, botanists might wish to consider the health hazard involved by release of mercury from older herbarium specimens which might have been poisoned in the traditional manner.
POTATO INTRODUCTIONS AND BREEDING UP TO THE EARLY 20TH CENTURY
Authors: GLENDINNING D. R.
Published: May 2006

Following an outline of the great variation in the primitive cultivars and wild species of potatoes in Latin America, the history of introductions and breeding procedures is discussed. Although two introductions occurred in the 16th century there were only few early introductions, and only very few varieties were grown in the early 18th century. The appearance of virus diseases, which debilitated established varieties but did not pass through true seed, led to widespread selection among seedlings and a vast increase in the number of varieties grown in the late 18th and early 19th centuries. The seedlings were from naturally‐set berries and most would be selfed derivatives; selection among them may have reduced the gene‐pool.

Improvements made by this selection were such that most 19th century introductions appeared primitive and, with only two known exceptions, they were discarded. Blight appeared in the mid 19th century and eliminated almost all varieties, including a number which were probably virus resistant, thus further reducing the gene‐pool.

T. A. Knight commenced deliberate crossing before 1810 but this practice did not become widespread until the second half of the 19th century. Breeding among the few survivors of the blight epidemics and the few new introductions led, by the early 20th century, to a great many varieties being grown, e.g. over 500 in Britain and over 50 in North America, but they represented only a very limited gene‐pool.

The pedigrees of modern potato varieties show that, although several 20th century introductions may occur in their ancestries, generally 80% or more of their genes are derived from varieties grown early this century. An appendix illustrates this for the recent varieties Pentland Dell and Croft. It follows that the gene‐pool is still rather limited, and that modern varieties are somewhat inbred due to relationships between their parents and ancestors.
BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF LEAF DEVELOPMENT IN COCOA (THEOBROMA CACAO L.)
Authors: ABO‐HAMED S. , COLLIN H. A. , HARDWICK K.
Published: May 2006

Summary

The flush leaves of seedling cocoa plants were assessed at each stage of the flush cycle from leaf unfolding to maturity for differences in leaf lamina presentation angle, surface hairs, stomatal number and development and leaf cuticle thickness. Changes in these parameters were then correlated with cuticular and stomatal diffusive resistance of the leaves. It is suggested that perpendicular positioning of the young flush leaves, the presence of surface hairs, the rapid synthesis of the cuticle and the limited stomatal development during the early stages of leaf expansion, restrict water loss from the developing leaves. Maximum rate of water loss from the leaves of a new flush was only attained after leaves were fully expanded, stomata fully developed and the leaves horizontally positioned. It is suggested that the large increase in water loss from the flush leaves following these changes might lead to an internal water deficit in the plant and hence to increased synthesis of abscisic acid in the shoot which, in turn, will maintain dormancy of the shoot apex in at least part of the interflush period.
AN ULTRASTRUCTURAL STUDY OF RESERVE LIPID MOBILIZATION IN STEM ROOT PRIMORDIA AND POPLAR
Authors: ČIAMPOROVá MILADA
Published: May 2006

Summary

Structural aspects of reserve lipid mobilization have been investigated in cells following the initiation of rhizogenesis from root primordia in stem cuttings of poplar. The number of spherosomes decreases during the first hours of initiation indicating that the reserve lipids are utilized during rhizogenesis. The lipid is removed from some spherosomes in the cytoplasm, the other spherosomes being incorporated into the vacuole. Cytochemical reactions show that the cells of root primordia do not contain glyoxysomes. The process of reserve lipid utilization differs from that in germinating seeds in both the absence of glyoxysomes and the participation of vacuoles in lipid degradation.
THE MECHANISM OF ROOT CONTRACTION IN GYMNARRHENA MICRANATHA, A DESERT PLANT
Authors: ZAMSKI E. , UCKO ORNA , KOLLER D.
Published: May 2006

Summary

The taproot of the ephemeric desert annual Gymnarrhena micranatha (Asteraceae) starts to contract soon after emergence and continues to do so at a constant rate over a period of 50 days or longer. This causes retraction of the main shoot apex from the soil surface to a depth of about 10 mm. Contraction takes place in cells of the endodermis, pericycle and primary phloem which expand radially while contracting longitudinally to about one‐half their initial length. This results in a wavy pattern in their radial walls. Partial hydrolysis of the cell wall is probably associated with secretion of multivesicular bodies from the cytoplasm. Contracted cell walls appear wavy where dissolution is incomplete or straight with undulated microfibrils where it is more complete.
VANADIUM AS A TRACE ELEMENT IN THE BLUE‐GREEN ALGA, NOSTOC MUSCORUM: INFLUENCE ON NITROGENASE AND NITRATE REDUCTASE
Authors: VAISHAMPAYAN A.
Published: May 2006

Summary

Molybdenum (Mo), a group VI B element (applied in the form of sodium molybdate at a concentration of 0.0177 ppm), is required for the nitrogenase and nitrate reductase activities of Nostoc muscorum and hence for growth on N2 and NO−3. These enzymic activities, as well as the growth of Mo‐containing cultures, are significantly enhanced by the addition of 0.0125 ppm vanadium (V), an element belonging to group V (applied in the form of sodium vanadate). At concentrations above 0.0125 ppm. V addition inhibits nitrogenase and nitrate reductase activities and ultimately leads to a retardation of growth on N2 and NO−3. Molybdenum and/or V has no effect on the growth of N. muscorum with NO−2 as nitrogen source.
PLANT‐INDUCED CHANGES IN THE RHIZOSPHERE OF RAPE (BRASSICA NAPUS VAR. EMERALD) SEEDLINGS
Authors: HEDLEY M. J. , NYE P. H. , WHITE R. E.
Published: May 2006

Summary

Additions of soluble phosphate to P‐deficient Begbroke sandy loam delayed or completely prevented the fall in rhizosphere pH observed when rape was grown at high root densities in this soil (Parts I to III, this series). Whereas the pH of the unamended rhizosphere soil fell from 6–6.5 to 5.1–5.3 by day 41, the rhizosphere pH of soil with an extra 2 μmol P g−1 remained steady (6 to 6.5) until day 35, and that of soil with an extra 20 μmol P g−1 increased slightly from pH 6 to 6.4 during 41 days of growth. The increase in rhizosphere phosphatase activity with increasing severity of P deficiency appeared to be a response to increasing root density and decreasing concentration of soluble inorganic P in the soil. No significant change in levels of soil organic P was detected.

Plants that acidified their rhizosphere (low P status) depleted acid‐soluble forms of soil P and absorbed twice the amount of P which could be desorbed from the control soil in 10−2 M Ca(NO3)2at pH 6.1. Uptake of P by plants which did not acidify their rhizosphere (high P status) was never greater than the amount of P desorbable in 10−2m Ca(NO3)2 at pH 6.1, and was derived from alkali‐soluble and resin‐extractable forms of soil P. Cation uptake exceeded anion uptake in both low and high P plants, but the difference was greater in low P plants. These differences in cation and anion uptake (mEq) were approximately equal to the milliequivalents of H+ (OH−) required to produce the observed changes in rhizosphere pH. These results explain why models for P uptake based on in vitro measurements of physicochemical parameters governing phosphate diffusion in soil work well for P sufficient plants, but tend to underestimate P uptake by P deficient plants growing in soils in which soluble P levels are sensitive to pH change.
THE ROLE OF ECTOMYCORRHIZAS IN DROUGHT TOLERANCE OF DOUGLAS‐FIR SEEDLINGS *
Authors: PARKE ENNIFER L. , LINDERMAN R. G. , BLACK C. H.
Published: May 2006

Summary

Experiments were conducted to test the relative ability of mycorrhizal and non‐mycorrhizal Douglas‐fir [Pseudotsuga menziesii(Mirb.) Franco] seedlings to tolerate and recover from drought conditions, using reduction in CO2fixation as an overall indicator of plant moisture stress. Seedlings were watered daily or conditioned to cyclic drying and re‐wetting of the soil. Net photosynthetic rates of mycorrhizal and non‐mycorrhizal seedlings watered daily did not differ significantly; however, drought‐stressed mycorrhizal seedlings fixed CO20at a rate ten times that of non‐mycorrhizal seedlings. Total leaf water potentials of mycorrhizal plants were lower (more negative) than those of non‐mycorrhizal plants but they recovered more rapidly.

Non‐mycorrhizal seedlings and seedlings inoculated with four ectomycorrhizal fungus species were allowed to become desiccated, then were rewatered and compared for their ability to tolerate and recover from drought. Seedlings inoculated withRhizapogon vintcolorwere less affected by drought than any of the other mycorrhizal or non‐mycorrhizal treatments. Net photosynthetic rate ofRhizopogon‐inoculated seedlings 24 h following re‐watering was seven times that of non‐mycorrhizal seedlings. The transpiration rate ofRhizopogon‐inoculated seedlings was low before desiccation, declined rapidly during the drought period and, after re‐watering, quickly resumed a rate higher than that for other treatments.
USE OF VESICULAR‐ARBUSCULAR MYCORRHIZAL ROOTS, INTRARADICAL VESICLES AND EXTRARADICAL VESICLES AS INOCULUM *
Authors: BIERMANN BRENDA , LINDERMAN R. G.
Published: May 2006

Summary

The presence of intraradical vesicles increases the inoculum potential of excised mycorrhizas. High infectivity was obtained with root pieces colonized by species of vesicular‐arbuscular (VA) mycorrhizal fungi that formed intraradical vesicles (i.e. Glomus fasciculatum, Glomus mosseae and Acaulospora spinosa). Root pieces colonized by mycorrhizal fungi which generally do not form intraradical vesicles (i.e. Gigaspora margarita and Gigaspora gigantea) were not infective. Extraradical vesicles of Gigaspora margarita were also not infective propagules. Intraradical vesicles separated from the colonized roots remained highly infective but hyphae and cell debris from the same roots were not. Mycorrhizal fungi in root pieces treated for short times in sodium hypochlorite were apparently killed.
A PROCEDURE FOR ISOLATION OF SINGLE‐SPORE CULTURES OF CERTAIN ENDOMYCORRHIZAL FUNGI
Authors: FANG YU‐CHENG , McGRAW A.‐C. , MODJO HAKAM , HENDRIX J.W.
Published: May 2006

Summary

A procedure for the isolation of single‐spore cultures of endomycorrhizal fungi is described. A single spore is placed on plant roots with a Pasteur pipette by use of a binocular microscope, and the plant is transplanted into sand in a 50 ml growth tube. Plants are incubated for 6 to 8 weeks in a greenhouse and are continuously subirrigated by capillarity with dilute (5 to 10%) Hoagland's solution. Forty to 80% of plants inoculated by this technique with single spores of Glomus macrocarpus, G. etunicatus and G. caledonius became infected. Cultures of G. constrictus and G. microcarpus were not obtained. Hoagland's solutions of up to 25% were equally effective for isolating G. macrocarpus, but limiting plant size by using only 5 or 10% Hoagland's solution was advantageous. The presence of spores on living root systems was the most reliable indicator of fungal development. Non‐inoculated control plants incubated in a common Hoagland's solution reservoir with inoculated plants never became mycorrhizal. The procedure uses readily available materials, is easy to use in the laboratory and conserves greenhouse space and labour.
THE IDENTITY AND ORIGINS OF PICEA ABIES (L.) KARSTEN FROM THE CHELFORD INTERSTADIAL (LATE PLEISTOCENE) OF ENGLAND
Authors: HOLYOAK D. T.
Published: May 2006

Summary

Pollen and macrofossils of Picea from the Chelford Interstadial (Early Devensian) of England are described. All leaves and cones were referred to P. abies (L.) Karsten, and the unimodal size distribution of pollen also suggests only this species was present. The fossil leaves are mostly similar to those of P. abies subspecies obovata (Ledeb.) Hultén, but the cones are intermediate between subspecies obovata and abies. Occurrence of forms approaching the north‐east European subspecies obovata does not necessarily imply immigration of Picea into England from the east or north‐east during the Early Devensian because similar intermediate forms also occur in the Alps.
TWO POSTGLACIAL POLLEN PROFILES FROM THE UPLANDS OF SNOWDONIA, GWYNEDD, NORTH WALES
Authors: INCE J.
Published: May 2006

Summary

Pollen diagrams are presented from two upland cwms in Gwynedd, North Wales. The profiles provide a detailed record of vegetational and environmental changes in the uplands of Snowdonia during the early and later postglacial (Flandrian) periods. Radiocarbon dates indicate that at both sites organic sedimentation commenced at around 10000 B.P., and support geomorphological evidence of cwm glaciation during the Loch Lomond (Younger Dryas) Stadial. Pollen analysis of basal minerogenic sediments, deposited sometime before 10000 B.P., reveal the colonization of the recently deglaciated uplands by grassland communities rich in Rumex and other open habitat taxa. Early herbaceous communities were invaded by Juniperus and Betula, and then replaced by Betula—Corylus woodland, and later by forests of birch, pine, oak, elm and alder. Altitudinal factors ensured the survival of many open habitat taxa in the uplands throughout the Flandrian period. Deteriorating environmental conditions and human interference during mid‐ to late‐Flandrian times resulted in the gradual decline of forests in the uplands and the development of open grassland and heathland communities characteristic of Snowdonia today.
LOCALIZATION OF POLYPHENOLOXIDASES DURING THE ESTABLISHMENT OF OPHRYS LUTEA ENDOMYCORRHIZAS
Authors: PAIS M. SALOMÉ S. , BARROSO J.
Published: May 2006

The cytochemical location of polyphenoloxidases in Ophrys lutea during invasion by Rhizoctonia repens suggests that the fungus is able to synthesize or activate polyphenoloxidases.

The dense product of its reaction is observable in the fungal cytoplasm during the first stages of fungal invasion. Later on, it is located in small quantities in the hyphal cytoplasm and great amounts are seen at the interface.

Our results suggest that the enzymes, synthesized in the fungal cytoplasm, are translocated across the plasmalemma and the cell wall of the fungus. These enzymes are accumulated in the interface close to the host plasmalemma, where they are likely to promote the oxidation of phenols from the host.
ULTRASTRUCTURE OF INTRAHYPHAL HYPHAE OF GLOMUS FASCICULA TUM (THAXTER) GERDEMANN AND TRAPPE IN ROOTS OF WHITE CLOVER (TRIFOLIUM REPENS L.)
Authors: LIM L. L. , FINERAN B. A. , COLE A. L. J.
Published: May 2006

Intrahyphal hyphae are reported in roots of white clover (Trifolium repens) infected with Glomus fasciculatum, this being the first unequivocal description of the phenomenon in coarse vesicular–arbuscular mycorrhizal associations. Various configurations of the hyphae are illustrated by transmission electron micrographs. The simplest situation is where the intercellular hypha contains a single intrahyphal hypha that may be either thin‐ or thick‐walled and which may also show different degrees of association with the enclosing hypha, the relationship often varying along the length of the two hyphae. The wall of the surrounding hypha may also be either thin‐or thick‐walled. Degenerate remnants of protoplasm frequently persist between the walls of the two hyphae. Compound intrahyphal hyphae also occur which may represent either branches of a single hypha or successive re‐invasion of a hypha with close adposition of walls so that in transverse section the wall appears to be concentrically layered.
INTERPRETING THE EVOLUTION OF A TRIAZINE‐RESISTANT POPULATION OF POA ANNUA L.
Authors: DARMENCY H. , GASQUEZ J.
Published: May 2006

The frequency of esterase isozyme genotypes was analysed both in a triazine‐resistant population and in susceptible populations. The main findings were (i) a low polymorphism, (ii) a high rate of heterozygotes at one particular locus; this polymorphism being related to the growth form, (iii) a higher proportion of prostrate plants then would usually be expected in an open habitat. This genetic structure could result from a recent founder event in a triazine‐treated area followed by an increase of polymorphism through gene migration from adjacent populations. The importance of environmental conditions (other than triazine treatments) on the evolution of populations is discussed.
THE SIGNIFICANCE OF INTERSPECIFIC DIFFERENCES IN SPECIFIC LEAF AREA TO THE GROWTH OF SELECTED HERBACEOUS SPECIES FROM DIFFERENT ALTITUDES
Authors: WOODWARD F. I.
Published: May 2006

Field measurements of selected upland and lowland species have demonstrated a decline in specific leaf area with altitude, probably due to changes in both air temperature and wind‐speed.

Both field and controlled environment experiments have demonstrated that the upland species have lower specific leaf areas than the lowland species, under similar environmental conditions.

Leaf growth and turgor of the upland species, Phleum alpinum, are insensitive to changes in wind‐speed in the range of 0.2 to 3 m s−1, while both growth and turgor decline with wind‐speed for the lowland P. pratense. Leaf turgor of P. pratense declined with increasing specific leaf area but no such relationship was found for P. alpinum.
THE ECOLOGY OF SHORT‐LIVED FORBS IN CHALK GRASSLANDS: DISPERSAL OF SEEDS
Authors: VERKAAR H. J. , SCHENKEVELD A. J. , Van de KLASHORST M. P.
Published: May 2006

Wind dispersal of some characteristic short‐lived species in Dutch chalk grasslands was studied. Field observations were in agreement with a model and indicated a rather limited dispersal of seeds (0.3 to 3.5 m).

Species with inherently short inflorescences have more extensive and less concentrated dispersal in open vegetation than in dense turf despite the fact that they are slightly taller in dense turf. In dense turf the slight increase in plant height does not sufficiently compensate for the reduced wind velocity in that habitat. In contrast, in species which have inherently longer inflorescences, dispersal is usually more extensive and less concentrated in dense turf. Apparently, in this case additional height more than counterbalances the reduced wind velocity in such turf. In all cases dispersal seems to be more affected by the interaction of stem height and wind profile at each site, and by the terminal vertical movement of seeds, than by other factors.

Heterogeneity in the seed bank in the soil is partly explained by limited dispersal of seeds but may also be due to variation in seed production and to the pattern of distribution of fruiting individuals.
THE INFLUENCE OF SOIL AERATION ON THE EFFICIENCY OF VESICULAR‐ARBUSCULAR MYCORRHIZAS
Authors: SAIF S. R.
Published: May 2006

Oxygen concentrations in the soil atmosphere influenced growth and mineral uptake in Eupatorium odoratum L., Sorghum bicolor (L.) Moench and Guizotia abyssinica (L.f.) Cass. inoculated with Glomus macrocarpus, Glomus mosseae and ‘white reticulate’. Shoot and root dry weights of mycorrhizal plants increased with O2 concentration up to 16%. Dry weights of roots and shoots of non‐mycorrhizal plants were lower than those of mycorrhizal plants at all O2 concentrations except at 2 %. Mycorrhizal and non‐mycorrhizal plants at 21 % O2, or non‐aerated controls, were smaller than those at 16%. Generally, mycorrhizal plants contained higher quantities of mineral elements than did non‐mycorrhizal plants and took up more nutrients as soil O2 concentrations increased. Phosphorus concentrations of mycorrhizal plants were mostly significantly higher than those in non‐mycorrhizal plants. Soil O2 generally did not influence the P concentrations of plants. Inoculation increased the concentrations of K and Mg in E. odoratum, but only the concentration of Mg in S. bicolor and the concentrations of Ca and Mg in Guizotia abyssinica. Only the concentrations of K and Mg in E. ordoratum, the concentrations of Ca and Mg in S, bicolor and the concentration of Mg in Guizotia aybssinica showed positive responses to increase in soil O2. The development of Glomus macrocarpus, Glomus mosseae and ‘white reticulate’ exhibited quantitative and qualitative responses to different soil O2 concentrations.
TRIMORPHIC INCOMPATIBILITY IN MEXICAN POPULATIONS OF PONTEDERIA SAGITTATA PRESL. (PONTEDERIACEAE)
Authors: GLOVER D. E. , BARRETT S. C. H.
Published: May 2006

Populations of Pontederia sagittata from the northern coastal plain of Mexico possess a tristylous breeding system. Styles and stamens are reciprocally arranged in the three floral morphs. Differences in anther size, pollen size and pollen production are associated with the three anther levels. Controlled pollinations performed in the glasshouse indicate that physiological self‐incompatibility accompanies floral trimorphism. Pollinations between morphs with anthers and stigmas at equivalent heights are highly productive of seed in comparison with self‐ or intra‐morph pollinations. In each floral morph, substantial differences in seed production result from self‐pollination with alternate anther levels. Overall, the mid‐styled morph exhibits weak self‐incompatibility whereas the long‐ and short‐styled morphs are more strongly self‐incompatible. In all pollen‐stigma combinations pollen germinated readily and pollen tubes penetrated stigmatic tissue. Inhibition of pollen tubes occurs in the style and possibly the ovary. The rate of pollen tube growth differs between anther levels following self‐pollination.

The three floral morphs were represented in eight populations examined although there was a tendency for the long‐styled morph to be under‐represented. Strong pollen trimorphism allows the origin of pollen deposited on naturally pollinated stigmas to be determined. Considerable variation in the amount and composition of pollen deposited on stigmas by syrphid flies was recorded. The likelihood of legitimate pollination appears to be highest in the long‐styled morph, intermediate in the mid‐styled morph and lowest in the short‐styled morph. Tristyly in P. sagittata is compared with the closely related P. cor data and P. rotundifolia. Implications of weak self‐incompatibility in the mid‐styled morph for the breakdown of tristylous breeding systems in the Pontederiaceae are discussed.