Initiation of Procambial Strands in Leaf Primordia of Dactylis glomerata L. as an Example of a Temperate Herbage Grass

This study is concerned with the examination of shoots of herbagegrasses, particularly Dactylis glomerata L., for comparisonwith earlier investigations on this species and on the cerealTriticum aestivum L. The main features of procambial strandinitiation are found to be the same in all the herbage grassesexamined and to be very similar to those in Triticum. Thus,in a vegetative shoot, all the procambial strands originatein the leaf primordia independently of the vascular system ofthe older parts of the plant, and extend downwards from theirfirst point of origin. For the median strands, the first pointof origin is in the disc of insertion of the primordium, butfor later strands it is progressively higher, so that the laststrands are initiated well up in the free portion of the primordium.The course of the median and first and second lateral strands,in the first two discs of insertion that they penetrate, isvery regular and predictable. However, two discs of insertionbelow the point of initiation of strands, their course is interruptedby the strands of the primordium directly below (there is onealternating primordium between them), and from this point downwardsvariations, both specific and between individual plants andprimordia, occur. This is the region where connexion with thevascular supply of the rest of the plant is first established.The timing of the arrival of young strands from above and ofthe development of successive nodal plexi from below, via whichmost interconnexions are established, will give some variationto the early development of this region.     

Floret Initiation and Development in Spring Wheat (Triticum aestivum L.)

The number and developmental stages of florets were determinedin each spikelet of the spike in the main shoots of spring wheat.Samples were taken frequently from plants grown in a phytotronand in a nitrogen application field-test. Ten stages of development,from floret initiation until anthesis, were recognized and described. Inter-spikelet variation in the total number of initiated floretswas rather small. However, the number of florets at advancedstages of development, as well as the number of grains, washighest in the central spikelets in which florets initiatedfirst. Floret initiation did not proceed beyond spike emergence,whereafter the distal florets and the spikelet apex degenerated.Grain-set was restricted to florets which had developed at leastto the stage of visible anther lobes at spike emergence. Thenumber of these florets was increased significantly by nitrogenapplication. Wheat, Triticum aestivum L., spikelet, floret, grain set, nitrogen     

Nitrogen and Photosynthesis in the Flag Leaf of Wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L. cv Yecora 70) plants were grown with various concentrations of nitrate nitrogen available to the roots. Sampling of flag leaves began after they had reached full expansion and continued throughout senescence. Rates of gas exchange, ribulose-1,5-bisphosphate (RuP₂) carboxylase activity, and the amounts of chlorophyll, soluble protein, nitrogen, and phosphorus were determined for each flag leaf. Rate of CO₂ assimilation was uniquely related to total leaf nitrogen irrespective of nutrient treatment, season, and leaf age. Assimilation rate increased with leaf nitrogen, but the slope of the relationship declined markedly when leaf nitrogen exceeded 125 millimoles nitrogen per square meter. Chlorophyll content and RuP₂ carboxylase activity were approximately proportional to leaf nitrogen content. As leaves aged, RuP₂ carboxylase activity and calculated Hill activity declined in parallel. With normal ambient partial pressure of CO₂, the intercellular partial pressure of CO₂ was always such that rate of assimilation appeared colimited by RuP₂ carboxylation and RuP₂ regeneration capacity.

The initial slope of rate of CO₂ assimilation against intercellular partial pressure of CO₂ varied nonlinearly with carboxylase activity. It is suggested that this was due to a finite conductance to CO₂ diffusion in the wall and liquid phase which causes a drop in CO₂ partial pressure between the intercellular spaces and the site of carboxylation. A double reciprocal plot was used to obtain an estimate of the transfer conductance.

     

Developmental Anatomy of the Inflorescence of Bread Wheat (Triticum aestivum L.) during Normal Initiation and when Affected by 2, 4-D

In wheat, the tip of the shoot apex normally consists of a coreof irregularly arranged cells covered by two uniseriate, selfperpetuating, layers (the dermatogen and the hypodermal layer):no third, inner layer (sub-hypodermal layer) is present. Leafinitiation involves periclinals in the cells of the dermatogenand hypodermal layers, but not the core. Buds involve many periclinalsin the outer cells of the core, a few occasionally in the hypodermallayer but never any in the dermatogen. The appearance of ‘double-ridges’signals inflorescence initiation. Each double-ridge is the equivalentof an axillary bud (the future spikelet bud) and its subtendingleaf primordium. The initiation of the subtending leaf is normal:the initiation of the spikelet bud is characterized by periclinaldivisions in the outer cells of the core, though some may alsooccur in cells of the hypodermal layer immediately outside:no periclinals are observed in the neighbouring dermatogen cells.All the above events concerned with leaf and bud initiationoccur in an easily recognizable, strictly distichous, pattern.In plants affected by 2, 4-dichlorophenoxyacetic acid the cellularpattern where double-ridges would have been arising, is badlydisrupted, due mainly to increased cell divisions in the hypodermallayer and outer part of the core, though possibly includingsome in the dermatogen. The apex tip itself is unaffected, probablyexplaining why, when growth is resumed, it produces a successionof normal spikelets in the normal phyllotaxis. Triticum aestivum L, bread wheat, shoot apex, double-ridge primordia, inflorescence initiation, spikelet buds, 2, 4-dichlorophenoxyacetic acid     

High Frequency Divisions in Leaf Base Protoplasts of Wheat (Triticum aestivum L.)

Protoplasts were isolated from the basal meristematic region of leaves from 6-day-old seedlings of wheat (Triticum aestivum). Protoplasts divided when cultured on MS medium (as agarose beads) in presence of nurse tissue. Donor seedlings when grown on BAP-supplemented MS medium were found to be considerably superior for protoplast isolation and culture than when grown on MS basal medium, in terms of protoplast viability, cell wall formation and cell division frequency. In addition, reduction of ammonium content of the culture medium, together with a dark Incubation, led to a high protoplast division frequency of about 70%. Microcolonies of 10-to 12-celled stages were obtained in Triticum aestivum, varieties HD 2329, HD 2285, Kalyan Sona, Arjun and CPAN 1676.     

Morphogenesis of 2,4-D Induced Abnormalities of the lnflorescence of Bread Wheat (Triticum aestivum, L.).

Treatment of Triticum plants with 2,4-D profoundly affects inflorescencemorphogenesis and results in the production of various abnormalities,amongst which are branched heads, whorls of spikelets. superimposedpairs of spikelets (‘banana’ twin spikelets) andpaired spikelets borne at the same level (‘yoked’spikets). Often more than one kind of abnormality is observedin a single head. Except for ‘banana’ twin spikelets,none of the induced abnormalities are duplicated by abnormalitieswhich occur spontaneously in untreated plants. Disturbance dueto treatment is only temporary and later the terminal regionof the apex recommences growth along a normal pattern of morphogenesis.     

Initiation of Procambial Strands in Axillary Buds of Dactylis glomerata L., Secale cereale L., and Lolium perenne L.

In axillary buds of Dactylis glomerata L., Secale cereale L.,and Lolium perenne L., the first two procambial strands of theprophyll and the median strand of the first normal leaf areinitiated in the bud in isolation from the vascular system ofthe parent axis. They rapidly form connections with the vascularsystem of the parent axis, presumably by downward extension,as is the case of the strands of leaf primordia on the mainaxis.     

QTL Mapping of Diffuse Reflectance Indices of Leaves in Hexaploid Bread Wheat (Triticum aestivum L.)

Russian Journal of Plant Physiology - Quantitative trait loci (QTL) mapping of diffuse reflectance indices of laminas in bread wheat (Triticum aestivum L.) has been first performed under controlled...     

The Morphology and Development of Cross Veins in the Leaves of Bread Wheat (Triticum aestivum L.)

In the leaves of bread wheat Triticum aestivum L. the longitudinalvascular bundles are linked by small transverse bundles Pairsof similar small vascular bundles also link the upper ends ofminor longitudinal bundles to their neighbours in a Y-shapedarrangement The cross-vein procambial strands arise from unexpanded cellsof one layer of the mesophyll tissue. Lines of these cells connectone longitudinal procambial strand to the next The procambialcells subsequently undergo two tangential divisions to producecells which differentiate to form the conducting and parenchymatouselements of the mature cross veins. Anomalous cross veins are sometimes found. possible modes oforigin of these anomalous cross veins are considered.     

Development and Characterization of a New TILLING Population of Common Bread Wheat (Triticum aestivum L.)

Mutagenesis is an important tool in crop improvement. However, the hexaploid genome of wheat (Triticum aestivum L.) presents problems in identifying desirable genetic changes based on phenotypic screening due to gene redundancy. TILLING (Targeting Induced Local Lesions IN Genomes), a powerful reverse genetic strategy that allows the detection of induced point mutations in individuals of the mutagenized populations, can address the major challenge of linking sequence information to the biological function of genes and can also identify novel variation for crop breeding. Wheat is especially well-suited for TILLING due to the high mutation densities tolerated by polyploids. However, only a few wheat TILLING populations are currently available in the world, which is far from satisfying the requirement of researchers and breeders in different growing environments. In addition, current TILLING screening protocols require costly fluorescence detection systems, limiting their use, especially in developing countries. We developed a new TILLING resource comprising 2610 M(2) mutants in a common wheat cultivar 'Jinmai 47'. Numerous phenotypes with altered morphological and agronomic traits were observed from the M(2) and M(3) lines in the field. To simplify the procedure and decrease costs, we use unlabeled primers and either non-denaturing polyacrylamide gels or agarose gels for mutation detection. The value of this new resource was tested using PCR with RAPD and Intron-spliced junction (ISJ) primers, and also TILLING in three selected candidate genes, in 300 and 512 mutant lines, revealing high mutation densities of 1/34 kb by RAPD/ISJ analysis and 1/47 kb by TILLING. In total, 31 novel alleles were identified in the 3 targeted genes and confirmed by sequencing. The results indicate that this mutant population represents a useful resource for the wheat research community. We hope that the use of this reverse genetics resource will provide novel allelic diversity for wheat improvement and functional genomics.     

Genetic Diversity and Population Structure Analysis of European Hexaploid Bread Wheat (Triticum aestivum L.) Varieties

Progress in plant breeding is facilitated by accurate information about genetic structure and diversity. Here, Diversity Array Technology (DArT) was used to characterize a population of 94 bread wheat (Triticum aestivum L.) varieties of mainly European origin. In total, 1,849 of 7,000 tested markers were polymorphic and could be used for population structure analysis. Two major subgroups of wheat varieties, GrI and GrII, were identified using the program STRUCTURE, and confirmed by principal component analysis (PCA). These subgroups were largely separated according to origin; GrI comprised varieties from Southern and Eastern Europe, whereas GrII contained mostly modern varieties from Western and Northern Europe. A large proportion of the markers contributing most to the genetic separation of the subgroups were located on chromosome 2D near the Reduced height 8 (Rht8) locus, and PCR-based genotyping suggested that breeding for the Rht8 allele had a major impact on subgroup separation. Consistently, analysis of linkage disequilibrium (LD) suggested that different selective pressures had acted on chromosome 2D in the two subgroups. Our data provides an overview of the allele composition of bread wheat varieties anchored to DArT markers, which will facilitate targeted combination of alleles following DArT-based QTL studies. In addition, the genetic diversity and distance data combined with specific Rht8 genotypes can now be used by breeders to guide selection of crossing parents.     

Acid Carboxypeptidases in Grains and Leaves of Wheat, Triticum aestivum L

Extracts of resting and germinating (3 days at 20°C) wheat (Triticum aestivum L. cv Ruso) grains rapidly hydrolyzed various benzyloxycarbonyldipeptides (Z-dipeptides) at pH 4 to 6. Similar activities were present in extracts of mature flag leaves. Fractionation by chromatography on CM-cellulose and on Sephadex G-200 showed that the activities in germinating grains were due to five acid carboxypeptidases with different and complementary substrate specificities. The wheat enzymes appeared to correspond to the five acid carboxypeptidases present in germinating barley (L Mikola 1983 Biochim Biophys Acta 747: 241-252). The enzymes were designated wheat carboxypeptidases I to V and their best or most characteristic substrates and approximate molecular weights were: I, Z-Phe-Ala, 120,000; II, Z-Ala-Arg, 120,000; III, Z-Ala-Phe, 40,000; IV, Z-Pro-Ala, 165,000; and V, Z-Pro-Ala, 150,000. Resting grains contained carboxypeptidase II as a series of three isoenzymes and low activities of carboxypeptidases IV and V. During germination the activity of carboxypeptidase II decreased, those of carboxypeptidases IV and V increased, and high activities of carboxypeptidases I and III appeared. The flag leaves contained high activity of carboxypeptidase I and lower activities of carboxypeptidases II, IV, and V, whereas carboxypeptidase III was absent.     

The Initiation, Growth, and Emergence of Leaf Primordia in Fragaria

The leaf initiation rate in Fragaria vesca (var. ‘RoyalSovereign’) has been compared with the elongation rateof the leaf primordia at different seasons. Certain conceptionsof growth correlation within the bud are presented. Experimentson the nature of elongation and emergence of primordia are described,and the causes of emergence are discussed.     

Novel Structural and Functional Motifs in cellulose synthase (CesA) Genes of Bread Wheat (Triticum aestivum,L.)

Cellulose is the primary determinant of mechanical strength in plant tissues. Late-season lodging is inversely related to the amount of cellulose in a unit length of the stem. Wheat is the most widely grown of all the crops globally, yet information on its CesA gene family is limited. We have identified 22 CesA genes from bread wheat, which include homoeologs from each of the three genomes, and named them as TaCesAXA, TaCesAXB or TaCesAXD, where X denotes the gene number and the last suffix stands for the respective genome. Sequence analyses of the CESA proteins from wheat and their orthologs from barley, maize, rice, and several dicot species (Arabidopsis, beet, cotton, poplar, potato, rose gum and soybean) revealed motifs unique to monocots (Poales) or dicots. Novel structural motifs CQIC and SVICEXWFA were identified, which distinguished the CESAs involved in the formation of primary and secondary cell wall (PCW and SCW) in all the species. We also identified several new motifs specific to monocots or dicots. The conserved motifs identified in this study possibly play functional roles specific to PCW or SCW formation. The new insights from this study advance our knowledge about the structure, function and evolution of the CesA family in plants in general and wheat in particular. This information will be useful in improving culm strength to reduce lodging or alter wall composition to improve biofuel production.     

Chlorophyll Fluorescence Detected Passively by Difference Reflectance Spectra of Wheat （Triticum aestivum L.） Leaf

The chlorophyll fluorescence （CF） signature emitted from vegetation provides an abundance of information regarding photosynthetics activity and has been used as a powerful tool to obtain physiological information of plant leaves in a non-invasive manner. CF is difficult to quantify because the CF signal is obscured by reflected light. In the present study, the apparent reflectance spectra of wheat （Triticum aestivum L.） leaves were measured under illuminations with and without filtering by three specially designed long-wave pass edge filters; the cut-off wavelengths of the three filters were 653.8, 678.2, and 694. l nm at 50% of maximum transmittance. The CF spectra could be derived as the reflectance difference spectra of the leaves under illuminations with and without the long wave pass edge filters. The ratio of the reflectance difference at 685 and 740 nm （Dif685/Dif740） was linear correlated with the CF parameters （maximal photochemical efficiency Fv/Fm, and the yield of quantum efficiency） measured by the modulated fluorometer. In addition, the ratio reflected the water stress status of the wheat leaf, which was very high when water deficiency was serious. This method provides a new approach for detecting CF and the physiological state of crops.     

Free Polyamines in Senescing Wheat(Triticum aestivum L.)

The free polyamine content of flag leaves, peduncles, rachis,glumes, and grains of wheat (Triticum aestivum L., cv. Castell)plants, ripening under field conditions, has been investigatedduring three consecutive growing seasons. Putrescine was quantitativelythe most important of all polyamines detected in these organs.Concentrations were highest in the grains, glumes and flag leaves.No correlation was found between polyamine content and the onsetof senescence of flag leaves and other organs. Excised primaryleaves, however, showed a decrease in polyamine content in thedark and also in light/dark cycles, but in the latter case onlyafter an initial increase. Sink removal of otherwise intactwheat plants caused an accumulation of putrescine in flag leavesat the later stages of senescence, whereas removal of all otherleaves was without any significant effect. Putrescine was alsorecovered in phloem-exudate samples collected throughout theperiod of grain development. In both grains and glumes, peakconcentrations of polyamines were found early during seed development. Key words: Triticum aestivum, polyamines, ripening, senescence     

Leaf wax of Triticum aestivum

Leaf waxes from spring wheat varieties Selkirk and Manitou contain hydrocarbons (6%, 10%), long chain esters (14%, 13%), free acids (5%, 8%), free alcohols (19%, 21%), β-diketone (16%, 20%), hydroxy β-diketones (8%, 10%), unidentified gum (29%, 16.5%) and minor amounts of diol diesters, glycerides and aldehydes. The major hydrocarbon is nonacosane and major esters are octacosyl esters of C₁₄–C₃₂ acids but C₂₀ and C₂₂ alcohol esters of trans 2-docosenoic and tetracosenoic acids are also present (Selkirk 20%, Manitou 10% of total esters). Previously unknown trans 2-docosen-1-ol is present as an ester (Selkirk 5%, Manitou 2.5% of total esters). Free acids are C₁₄–C₃₂ acids and trans 2-docosenoic and tetracosenoic acids (Selkirk 30%, Manitou 9% of free acids). Octacosanol is the principal free alcohol. Hentriacontane-14,16-dione is the β-diketone and the hydroxy β-diketones are a 1:1 mixture of 8- and 9- hydroxyhentriacontane-14,16-diones.