Plant Internode Research Articles

QTL mapping of stalk bending strength in a recombinant inbred line maize population

Stalk bending strength (SBS) is a reliable indicator for evaluating stalk lodging resistance of maize plants. Based on biomechanical considerations, the maximum load exerted to breaking (F max), the breaking moment (M max) and critical stress (σ max) are three important parameters to characterize SBS. We investigated the genetic architecture of SBS by phenotyping F max, M max and σ max of the fourth internode of maize plants in a population of 216 recombinant inbred lines derived from the cross B73×Ce03005 evaluated in four environments. Heritability of F max, M max and σ max was 0.81, 0.79 and 0.75, respectively. F max and σ max were positively correlated with several other stalk characters. By using a linkage map with 129 SSR markers, we detected two, three and two quantitative trait loci (QTL) explaining 22.4, 26.1 and 17.2% of the genotypic variance for F max, M max and σ max, respectively. The QTL for F max, M max and σ max located in adjacent bins 5.02 and 5.03 as well as in bin 10.04 for F max were detected with high frequencies in cross-validation. As our QTL mapping results suggested a complex polygenic inheritance for SBS-related traits, we also evaluated the prediction accuracy of two genomic prediction methods (GBLUP and BayesB). In general, we found that both explained considerably higher proportions of the genetic variance than the values obtained in QTL mapping with cross-validation. Nevertheless, the identified QTL regions could be used as a starting point for fine mapping and gene cloning.

Spectral Sensitivity of the Extension Growth of Tulips Grown with Night Lighting under a Natural Photoperiod

The effect of light quality on the extension growth of tulips was investigated for 4 tulip (Tulipa gesneriana) cultivars “Leen van der mark,” “Murasaki suisho,” “Come back,” and “Kikomachi.” The exposure of tulips to ultraviolet-A (UV-A), blue (B), red (R) or far-red (FR) fluorescent tubes throughout the entire night (a process called “night lighting”) was found to promote lengthening of the stem and first internode of plants grown under natural photoperiod conditions in a greenhouse. The effectiveness of FR night lighting was consistently observed across 4 cultivars, although the effectiveness of illumination within the UV-A, B and R wavelength ranges was found to vary with respect to stem length, the first internode and among different cultivars. Elevated photon flux densities of FR light were found to quantitatively increase the extension growth of “Leen van der mark,” but the effect of FR night lighting reached saturation point at 0.59 μmol m-2 s-1. A 4-h end-of-day lighting period and night-break FR lighting period were also found to promote extension growth, but these effects were less pronounced than that induced by FR night lighting. A 4-h end-of-night FR lighting period had no effect on extension growth. Apart from these findings, the effects of the light quality on extension growth are discussed.

Effects of fragmentation on the survival and growth of the invasive, clonal plant Alternanthera philoxeroides

The capacity of small clonal fragments to survive and grow is a major factor in the spread of clonal plants, especially aquatic species. This study of the introduced, invasive, amphibious, stoloniferous herb Alternanthera philoxeroides in China tested the effects of fragment size, of loss of the stolon apex, and of the original position of a fragment within a clone before fragmentation on the survival and growth of fragments in a greenhouse experiment. The stolon internodes of plants consisting of one stolon with 5 ramets were severed in all 16 possible patterns, generating fragments of 1–5 ramets. These 16 fragmentation treatments were crossed with removal of the stolon apex. Fragmentation and apex removal did not affect total growth of plants, but more highly fragmented plants produced smaller, more numerous ramets. The survival of fragments consisting of one original ramet was about 85%, compared to 100% survival of fragments with 5 original ramets. Fragments consisting of the youngest ramets along the original stolon grew more than fragments of the same size that consisted of older ramets. These effects of fragmentation on growth provide new evidence for clonal integration of the rate at which connected ramets produce new ramets and novel evidence that fragments produced from different portions of clones have different potential for spread. They further suggest that detachment of small groups of distal ramets along stolons in the field might be very effective in spreading the species and that a trade-off between the number and the size of new ramets produced by fragments may represent an adaptive, plastic response to disturbance. Results do not recommend intentional fragmentation of clones as a means of controlling the rate of growth of this invasive species but suggest that incidental fragmentation may not increase its growth in mass, although it may increase its rate of spread.

Cytogenetic effect of Alternanthera philoxeroides (alligator weed) on Agasicles hygrophila (Coleoptera: Chrysomelidae) in its native range

Plant genotypic effects can alter insects’ ability of utilizing their host plant. Alligator weed, Alternanthera philoxeroides, is a South American amphibious Amaranthaceae, which invades aquatic and terrestrial habitats. Populations with varying morphotypes and cytotypes were identified and further associated with a polyploid hybrids complex in Argentina, which probably is the centre of origin and diversification of alligator weed. The current model of the hybrid complex formation proposes that diploid ancestors gave rise to allotetraploids and allohexaploids. Agasicles hygrophila is a monophagous chrysomelid beetle which successfully controls A. philoxeroides in regions with mild winters and where the weed grows in aquatic habitats. However, plant genetic characteristics could constrain insect development and reproduction, providing an alternative explanation for the restricted success of biological control of alligator weed with A. hygrophila. We investigated the effect of four A. philoxeroides populations with varying cytogenetical characteristics on plant–insect interaction with A . hygrophila in the native range of the weed. The insect’s life cycle on each host population was studied. In addition, the genetic relationships among the weed populations was explored using dot blot analysis. Plant population affected insect survival and fecundity, but not life cycle length nor third larval instar mortality, pupal mortality or female proportion. Plant internode diameter was not a restriction for insect pupation. All hexaploid populations of A. philoxeroides, as well as the close related A. aquatica, hybridized with the tetraploid population probe with similar intensity, meaning that this population is a component of their polyploid genome.

Effects of Plant Growth Promoting Bacterium on Yield Components of Tomato

This study was conducted to determine the effects of growth promoting bacterium on yield and yield components of tomato (Lycopersicon lycopersicum L.). Different strains of bacteria, 52/1-E43, 21/3F, 17/3N, E43 F, 637 Ca, MFDCa1, 52/1, 21/3+637Ca, 52/1 were used. Tulin F1 tomato cultivar was used as plant material. In result, there were significant important differences in terms of yield/h, plant length, between nod lengths, average fruit weight, pH and root stem diameter in among the applications. However, there were no important differences in regardless of fruit length, fruit number per plant, fruit diameter, total soluble solid content (TSS) and fruit firmness based on the applications. Yield per hectare changed from 74,099 kg/ha to 46,034 kg/ha and the best results were taken from 21/3F, 52/1 and 21/3+637 Ca applications, respectively. Plant length was determined between 212.2 cm and 197.5 cm and the effective results were reported in 21/3+637 Ca, 52/1 Zeatin, 17/3N and control, respectively. Between plant internodes lengths ranged from 8.9 cm to 8.0 cm. Average fruit weight was determined as 183.0 g and 131.5 and the highest value was found in 17/3N application. pH changed between 4.43 and 4.00 and the best results were reported in 53/1 Zeatin and control, respectively. Root collar diameter was found between 19.69 and 15.91 mm, and the highest value was determined in 21/3+637 Ca application. As a result, different Plant Growth Promoting Bacterium (PGPB) applications have different effects on yield and yield components. Especially 21/3F, 21/3+637 Ca and 17/3N applications had positive effect on yield and yield components, respectively.

Effect of fungicide seed treatments on root pathogens of cereal crops under field conditions

It is of importance to reduce the spread of Fusarium graminearum to western regions of the Canadian prairies where Fusarium head blight has so far occurred to a limited extent. Determining the effectiveness of fungicides against F. graminearum in infected seed under various growing conditions will help design a comprehensive strategy for preventing the spread of this pathogen. Field trials at various locations in eastern Saskatchewan were conducted (2003-2005) to examine the performance of registered and experimental fungicides on Fusarium colonization of subcrown internodes (SIs) of plants derived from Fusarium-infected barley (Hordeum vulgare L.), common (Triticum aestivum L.) and durum [T. turgidum L. ssp. durum (Desf.) Husn.] wheat seed, and on SI discoloration. Among the fungi isolated from discolored SIs were Fusarium spp., including F. graminearum, and Cochliobolus sativus. Fusarium graminearum infections were mostly seed-borne whereas infection by other fungi appeared to be mostly soil-borne. Compared with the untreated infected control, the combined seed treatments reduced discoloration of SIs, but no single fungicide reduced discoloration consistently across site-years or crops. Similarly, no product consistently reduced the isolation of F. graminearum or other Fusarium pathogens, although some fungicides appeared to be more effective than others in reducing isolation of F. graminearum or C. sativus. Our observations agree with results from a controlled-environment study of effects of seed treatments on F. graminearum colonization of plants derived from infected common and durum wheat seed, thus confirming that treatment of F. graminearum-infected seed with fungicides will not likely prevent the spread of this pathogen.

Systemic Infection by Fusarium verticillioides in Maize Plants Grown Under Three Temperature Regimes.

Fusarium verticillioides causes seedling decay, stalk rot, ear rot, and mycotoxin contamination (primarily fumonisins) in maize. Systemic infection of maize plants by F. verticillioides can lead to kernel infection, but the frequency of this phenomenon has varied widely among experiments. Variation in the incidence of systemic infection has been attributed to environmental factors. In order to better understand the influence of environment, we investigated the effect of temperature on systemic development of F. verticillioides during vegetative and reproductive stages of plant development. Maize seeds were inoculated with a green fluorescent protein-expressing strain of F. verticillioides, and grown in growth chambers under three different temperature regimes. In the vegetative-stage and reproductive-stage experiments, plants were evaluated at tasseling (VT stage), and at physiological maturity (R6 stage), respectively. Independently of the temperature treatment, F. verticillioides was reisolated from nearly 100% of belowground plant tissues. Frequency of reisolation of the inoculated strain declined acropetally in aboveground internodes at all temperature regimes. At VT, the high-temperature treatment had the highest systemic development of F. verticillioides in aboveground tissues. At R6, incidence of systemic infection was greater at both the high- and low-temperature regimes than at the average-temperature regime. F. verticillioides was isolated from higher internodes in plants at R6, compared to stage VT. The seed-inoculated strain was recovered from kernels of mature plants, although incidence of kernel infection did not differ significantly among treatments. During the vegetative growth stages, temperature had a significant effect on systemic development of F. verticillioides in stalks. At R6, the fungus reached higher internodes in the high-temperature treatment, but temperature did not have an effect on the incidence of kernels (either symptomatic or asymptomatic) or ear peduncles infected with the inoculated strain. These results support the role of high temperatures in promoting systemic infection of maize by F. verticillioides, but plant-to-seed transmission may be limited by other environmental factors that interact with temperature during the reproductive stages.

Expression of cell wall related genes in basal and ear internodes of silking brown-midrib-3, caffeic acid O-methyltransferase (COMT) down-regulated, and normal maize plants

BackgroundSilage maize is a major forage and energy resource for cattle feeding, and several studies have shown that lignin content and structure are the determining factors in forage maize feeding value. In maize, four natural brown-midrib mutants have modified lignin content, lignin structure and cell wall digestibility. The greatest lignin reduction and the highest cell wall digestibility were observed in the brown-midrib-3 (bm3) mutant, which is disrupted in the caffeic acid O-methyltransferase (COMT) gene.ResultsExpression of cell wall related genes was investigated in basal and ear internodes of normal, COMT antisens (AS225), and bm3 maize plants of the INRA F2 line. A cell wall macro-array was developed with 651 gene specific tags of genes specifically involved in cell wall biogenesis. When comparing basal (older lignifying) and ear (younger lignifying) internodes of the normal line, all genes known to be involved in constitutive monolignol biosynthesis had a higher expression in younger ear internodes. The expression of the COMT gene was heavily reduced, especially in the younger lignifying tissues of the ear internode. Despite the fact that AS225 transgene expression was driven only in sclerenchyma tissues, COMT expression was also heavily reduced in AS225 ear and basal internodes. COMT disruption or down-regulation led to differential expressions of a few lignin pathway genes, which were all over-expressed, except for a phenylalanine ammonia-lyase gene. More unexpectedly, several transcription factor genes, cell signaling genes, transport and detoxification genes, genes involved in cell wall carbohydrate metabolism and genes encoding cell wall proteins, were differentially expressed, and mostly over-expressed, in COMT-deficient plants.ConclusionDifferential gene expressions in COMT-deficient plants highlighted a probable disturbance in cell wall assembly. In addition, the gene expressions suggested modified chronology of the different events leading to cell expansion and lignification with consequences far beyond the phenylpropanoid metabolism. The reduced availability of monolignols and S units in bm3 or AS225 plants led to plants also differing in cell wall carbohydrate, and probably protein, composition. Thus, the deficiency in a key-enzyme of the lignin pathway had correlative effects on the whole cell wall metabolism. Furthermore, the observed differential expression between bm3 and normal plants indicated the possible involvement in the maize lignin pathway of genes which up until now have not been considered to play this role.

Comparison of antioxidant activities and endogenous hormone levels between bush and vine-type tropical pumpkin ( Cucurbita moschata Duchesne)

A bush-type plant was selected from a cultivar ‘Cga’ of tropical pumpkin ( Cucurbita moschata Duchesne) in order to study and compare the bush and vine habit of C. moschata in terms of various physiological and biochemical characteristics. During the internode development of the bush and vine-type plants in C. moschata, the metabolism of reactive oxygen species (hydrogen peroxide, H 2O 2; and superoxide anion radical, O 2 − ), the activities of some antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; and ascorbate peroxidase, APX), and the levels of some endogenous hormones (gibberellin A 3, GA 3; gibberellin A 4, GA 4; and indole-3-acetic acid, IAA) were compared. Bush plants were found to have a significantly higher O 2 − level than vine plants at 28 days after germination (DAG) and onwards. Moreover, there was no significant difference of H 2O 2 level between the two genotypes until 32 DAG, in which the difference was significant at 32 DAG. In both genotypes, no significant differences of SOD activity were observed, and this was opposite to APX activity in which significant differences were observed during almost the whole sampling stages. What's more, APX activity of bush plants was significantly higher than that of vine plants at 24, 28, 32, and 36 DAG. CAT activity showed the same trend for the two genotypes. Quantitative analysis by enzyme-linked immunosorbent assay (ELISA) indicated that the internodes of bush plants contain lower levels of GA 3, IAA, and GA 4 than those of vine plants in C. moschata. In addition, GA 3 deficiency was also found in the leaves and roots of bush plants. In conclusion, this work provided some new information about different levels of endogenous chemicals in pumpkins with differing growth habits.

Note: Corn stalk borer (Sesamia nonagrioides) infestation on sorghum in central Greece

Sweet sorghum (Sorghum bicolor (L.) Moench) was introduced recently into Greece and is being cultivated experimentally for the production of liquid biofuel. A pilot survey was conducted in October 2005 to provide information on the species composition and density of its lepidopterous stem borers, which appear to cause severe losses in production. The dominant pest in that season wasSesamia nonagrioides Lefebvre, with a mean density of 1.41 larvae per plant. Larvae were sampled from various plant internodes and found to have a preference for the lower ones. Analysis of variance showed no significant effects on larval density of the irrigation levels or of the organic — conventional soil fertilization method. A significant negative correlation was found between the body length ofS. nonagrioides larvae and the internode from which they were retrieved. This is the first published report of sorghum borer pests in Greece.

Engineering of gibberellin levels in citrus by sense and antisense overexpression of a GA 20-oxidase gene modifies plant architecture

Carrizo citrange (Citrus sinensisxPoncirus trifoliata) is a citrus hybrid widely used as a rootstock, whose genetic manipulation to improve different growth characteristics is of high agronomic interest. In this work, transgenic Carrizo citrange plants have been produced overexpressing sense and antisense CcGA20ox1 (a key enzyme of GA biosynthesis) under control of the 35S promoter to modify plant architecture. As expected, taller (sense) and shorter (antisense) phenotypes correlated with higher and lower levels, respectively, of active GA1 in growing shoots. In contrast, other phenotypic characteristics seemed to be specific to citrus, or different from those described for similar transgenics in other species. For instance, thorns, typical organs of citrus at juvenile stages, were much longer in sense and shorter in antisense plants, and xylem tissue was reduced in leaf and internode of sense plants. Antisense plants presented a bushy phenotype, suggesting a possible effect of GAs on auxin biosynthesis and/or transport. The main foliole of sense plants was longer, although total leaf area was reduced. Leaf thickness was smaller in sense and larger in antisense plants due to changes in the spongy parenchyma. Internode cell length was not altered in transgenic plants, indicating that, in citrus, GAs regulate cell division rather than cell elongation. Interestingly, the phenotypes described were not apparent when transgenic plants were grafted on non-transgenic rootstock. This suggests that roots contribute to the GA economy of aerial parts in citrus and opens the possibility of using the antisense plants as dwarfing rootstocks.

Adaptation to a ‘home’ site by white clover (Trifolium repens) in sown swards in Uruguay

Climatic and soil conditions in Uruguay are marginal for white clover (Trifolium repens L.). Plants were collected from four sites, in different parts of the country, multiplied vegetatively, and the populations planted into each of the four sites. Plant survival and internode length (indicating growth potential) were recorded at intervals during the 55-week period after planting. On the site with the highest annual rainfall and lowest summer water deficit, one fifth of the plants survived at least 55 weeks, whereas on the site with the highest annual evaporation almost all the plants had died within 20 weeks. There was some evidence of adaptation to a ‘home’ site in both plant survival and growth potential. Thus, on three of the four sites, populations from the ‘home’ site survived better than the average of the non-‘home’ populations. Also, internode length was greatest (9·5 mm on average, compared with a mean of 5·6 mm for the experiment as a whole) in a population from a site with soil relatively high in available P, when planted into its ‘home’ site. Plant breeders could consider producing different white clover cultivars to suit different conditions of moisture supply and available P.

Evaluation of Maize Hybrids for Resistance to Fusarium Stalk Rot

Stalk rot is one of the main diseases of maize, causing stalk lodging and trouble for harvesting. The most effective way for controlling the disease is cultivation of resistant hybrids. In order to determine the susceptibility of maize hybrids, to stalk rot, an experiment was conducted with 60 hybrids arranged in RCBD at Karaj and Sari Research Stations in 1998. Inoculation was carried out by using Drill/ toothpick method in the first extentded internode of maize plants at tasseling stage. Inoculated Plants were cut at the third internode after physiological maturity and vertical stalk sections of each hybrid were used for disease assessment using disease severity index based on the discoloration of pith tissue. Significant differences in response to stalk rot were observed among the hybrids. The majority of the hybrids were highly susceptible to stalk rot. The most susceptible hybrids were K1263/14-2 K1264/1 and B73 K12641. A few hybrids such as K3153 KC103/8 and K3153 K582/1-22 were moderately resistant. The overall results demonstrated that, early-maturing hybrids are more succeptible to stalk rot disease compared with late-maturing hybrids.

Type of Plant Architecture Can Conceal Fruit During Harvest of Okra

Abstract Fruit concealed by several plant parts are often overlooked during harvest in okra (Abelmoschus esculentus(L.) Moench), causing significant reductions in marketable yield. Effects of plant traits contributing to marketable fruit being missed during harvest were tested in 15 okra cultivars having different plant architectures. Significant correlations between the percentage of overlooked fruit (POF) and several traits were found. There were significant correlations between POF and leaf area, numbers of lateral branches, plant height, number of nodes/ plant and internode length. Correlations between POF and plant height and internode length were negative. Fruit diameter, length, and weight; fruit weight/plant and fruit number/plant; petiole length; and stem diameter were not related to POF. The calculated bias and the coefficient of determination revealed that leaf area accounted for 62% of the variability observed for POF among cultivars; while internode length accounted for only 9% of variability...

Identification of Casparian Bands in the Mesocotyl and Lower Internodes of Rice (Oryza sativa L.) Seedlings Using Fluorescence Microscopy

The mesocotyl and lower internodes of seedlings are underground organs that play a possible role in water absorption and transport. The aim of this study is to reexamine and understand further the anatomy and morphology of mesocotyls and lower internodes in rice, especially in terms of the existence of Casparian bands. Anatomical structures of mesocotyl and lower internodes tissue of rice seedlings were observed by light and fluorescence microscopy. The rice mesocotyl had two central cylinders, one is large and the other small, in the cross section. Casparian bands were observed in both the endodermis and exodermis of the mesocotyl, and also in the endodermis of the first internode. Furthermore, some bundles with intermediate xylem differentiation were observed between the exarch and endarch arrangement in the first internodes. Casparian bands were identified in the radial walls of cells surrounding each of these bundles. The second internode is quite similar to that of upper internodes in adult plants with respect to internal structure; scattered vascular bundles were seen as in monocotyledons. In the second internode, Casparian bands were seen in the radial cell walls of the bundle sheaths in each vascular bundle. Unlike the mesocotyl, Casparian bands were not observed in the hypodermis of the first or second internodes. The results show that the histological features of the mesocotyl and lower internodes of rice seedlings widely differed. In addition, the present study provides anatomical evidence for the existence of Casparian bands in both the mesocotyl and lower internodes of rice seedlings.

OsGLU1, A Putative Membrane-bound Endo-1,4-ß-D-glucanase from Rice, Affects Plant Internode Elongation

A dwarf mutant glu was identified from screening of T-DNA tagged rice population. Genetic analysis of the T1 generation of glu revealed that a segregation ratio of wild-type:dwarf phenotype was 3:1, suggesting that the mutated phenotype was controlled by a single recessive nuclear locus. The mutated gene OsGLU1, identified by Tail-PCR, encodes a putative membrane-bound endo-1,4-beta-D-glucanase, which is highly conserved between mono- and dicotyledonous plants. Mutation of OsGLU1 resulted in a reduction in cell elongation, and a decrease in cellulose content but an increase in pectin content, suggesting that OsGLU1 affects the internode elongation and cell wall components of rice plants. Transgenic glu mutants harboring the OsGLU1 gene complemented the mutation and displayed the wild-type phenotype. In addition, OsGLU1 RNAi plants showed similar phenotype as the glu mutant has. These results indicate that OsGLU1 plays important roles in plant cell growth. Gibberellins and brassinosteroids induced OsGLU1 expression. In rice genome, endo-1,4-beta-D-glucanases form a multiple gene family with 15 members, and each may have a distinct expression pattern in different organs. These results indicate that endo-1,4-beta-D-glucanases may play diverse roles in growth and developmental process of rice plants.

A new metabonomic strategy for analysing the growth process of the poplar tree

High-resolution, magic angle spinning, proton nuclear magnetic resonance (1H HR/MAS NMR) spectroscopy and multivariate data analysis using batch processing (BP) were applied to the analysis of two different genotypes of poplar tree (Populus tremula L. x tremuloides Michx.) containing an antisense construct of PttMYB76 and control (wild-type). A gene encoding a MYB transcription factor, with unknown function, PttMYB76, was selected from a cambial expressed sequence tag (EST) library of poplar tree (Populus tremula L. x tremuloides Michx.) for metabonomic characterization. The PttMYB76 gene is believed to affect different paths in the phenyl propanoid synthetic pathway. This pathway leads to the formation of S- and G-lignin, flavonoids and sinapate esters. Milled poplar samples collected at the internodes of the tree were analysed using 1H HR/MAS NMR spectroscopy. The application of multivariate BP of the NMR results revealed a growth-related gradient in the plant internode direction, as well as the discrimination between the trees with down-regulated PttMYB76 expression and wild-type populations. This paper focuses on the potential of a new analytical multivariate approach for analysing time-related plant metabonomic data. The techniques used could, with the aid of suitable model compounds, be of high relevance to the detection and understanding of the different lignification processes within the two types of poplar tree. Additionally, the findings highlight the importance of applying robust and organized multivariate data analysis approaches to facilitate the modelling and interpretation of complex biological data sets.

Jasmonates are essential factors inducing gummosis in tulips: mode of action of jasmonates focusing on sugar metabolism

The purpose of this study was to know the mechanism of jasmonates to induce gummosis in tulip (Tulipa gesneriana L. cv. Apeldoorn) shoots, especially on the focus of sugar metabolism. Gummosis in the first internode of tulip plants was induced by the application of methyl jasmonate (JA-Me, 1% w/w in lanolin) and jasmonic acid (JA, 1% w/w in lanolin) 5 days after application and strongly stimulated by the simultaneous application of ethylene-releasing compound, ethephon (2-chloroethylphosphonic acid, 1% w/w in lanolin), although ethephon alone had little effect. JA-Me stimulated ethylene production of the first internodes of tulips, ethylene production increasing up to more than 5 times at day 1 and day 3 after the application. On the other hand, application of ethephon did not increase endogenous levels of jasmonates in tulip stems. Analysis of composition of tulip gums revealed that they were consisted of glucuronoarabinoxylan with an average molecular weight of ca. 700 kDa. JA-Me strongly decreased the total amount of soluble sugars in tulip stems even in 1 day after application, being ca. 50% of initial values 5 days after application, but ethephon did not. However, both JA-Me and ethephon had almost no effect on the neutral sugar compositions of soluble sugars mainly consisting of glucose, mannose and xylose in ratio of 20:2:1 and traces of arabinose. Both JA-Me and ethephon applied exogenously stimulated senescence of tulip shoots shown by the loss of chlorophyll. These results strongly suggest that the essential factor of gummosis in tulips is jasmonates affecting the sugar metabolism in tulip shoots. The mode of action of jasmonates to induce gummosis of tulip shoots is discussed in relation to ethylene production, sugar metabolism and senescence.

Novel gene encoding a Ca2+-binding protein and under hexokinase-dependent sugar regulation.

A cDNA encoding a predicted 15-kDa protein was earlier isolated from sugar-induced genes in rice embryos (Oryza sativa L.) by cDNA microarray analysis. Here we report that this cDNA encodes a novel Ca2+-binding protein, named OsSUR1 (for Oryza sativa sugar-up-regulated-1). The recombinant OsSUR1 protein expressed in Escherichia coli had 45Ca2+-binding activity. Northern analysis showed that the OsSUR1 gene was expressed mainly in the internodes of mature plants and in embryos at an early stage of germination. Expression of the OsSUR1 gene was induced by sugars that could serve as substrates of hexokinase, but expression was not repressed by Ca2+ signaling inhibitors, calmodulin antagonists and inhibitors of protein kinase or protein phosphatase. These results suggested that Os-SUR1 gene expression was stimulated by a hexokinase-dependent pathway not mediated by Ca2+.

Variation between and within Trifolium repens L. populations collected from sown swards in Uruguay

Nineteen Trifolium repens L. (white clover) populations were collected in different parts of Uruguay (where conditions are marginal for the species) from swards sown 2–15 years earlier. Twenty five genotypes of each population were grown as spaced plants on a single site. Leaflet length and width, petiole length, plant height, plant diameter and internode length were recorded. In a second experiment, ten of the populations were studied in a similar way. Large genetic correlations were obtained among leaflet length, leaflet width, petiole length and plant height as one group, and among major plant diameter, minor plant diameter and internode length as another group, in both experiments. Collection site characteristics that tended to result in relatively short, small-leaved plants were: the sowing of cv. Bayucua or Santa Fe (rather than Zapican orYi); a relatively old sward; relatively high available soil P; overgrazing; and dry conditions. There was an indication that, in some respects, there was less variation within a population in older than in younger swards. Overall and within populations heritabilities were relatively high for leaflet length, leaflet width and petiole length and relatively low for plant diameter, with plant height intermediate. Genotypes from populations (such as that from Romero) that survived for 15 years in unfavourable conditions could be useful in a plant breeding programme. Selection for rather smaller-leaved types might enhance persistence.