Flag Leaf Anatomy of Triticum and Aegilops Species in Relation to Photosynthetic Rate

Quantitative anatomical and other measurements were made onfully expanded flag leaves of a series of diploid, tetraploidand hexaploid Triticum and Aegilops species, and photosyntheticrates per unit leaf area were measured at light saturation (P_max). Diploids had the highest P_max, hexaploids the lowest with tetraploidsbeing intermediate. The anatomical features of tetraploids andhexaploids were generally similar, but different from the diploids.The diploids had thinner leaves with less dry matter and chlorophyllper unit area. The surface area of the mesophyll cells per unitvolume of mesophyll tissue was similar for all ploidy levels,as was the ratio mesophyil cell surface area per unit leaf area.It is argued that while these anatomical features are unlikelyto account for the observed variation in Pmax, it is possiblethat other structural factors with which they are correlatedmay causally influence P_max. One such feature is the averagediffusion path length from the plasmalemma at the cell surfaceto the sites of carboxylation. Anatomy, photosynthesis, mesophyll, cell size, Triticum, Aegilops, polyploidy     

Genome-Dependent Factors in the Development of Leaf Phototrophic Tissues in Diploid and Alloploid Wheat Species

Growth and mesostructure of the photosynthetic apparatus were studied in leaves of ten Triticum L. species. Plants with the A^u genome were shown to develop larger leaf assimilation areas due to expanding areas of individual leaves and an increase in the absolute growth rate. Leaf and mesophyll thickness and mesophyll cell size decreased in the G-genome species. Leaf compactness, which depended on cell size and number per unit leaf area and leaf folding, determined the specific patterns of internal leaf organization in wheat species with diverse genotypes. These patterns did not affect cell plastid-to-cytoplasm ratio as shown by the stable indices of cell surface area/cell volume, cell surface area per chloroplast, and cell volume per chloroplast. The structural indices of leaf phototrophic tissues, mesophyll density, and mesophyll CO₂ conductance in alloploids, as compared to diploid species, depended on both ploidy and genome constitution.     

Variation in Mesophyll Cell Number and Size in Wheat Leaves

The numbers of mesophyll cells in wheat leaves were determinedin a variety of wheat species differing in ploidy level andin leaves from different positions on the wheat plant. Leafsize and mesophyll cell number are linearly related in bothcases but differences were observed in mesophyll cell numberper unit leaf area with changing leaf size. Where changes incell size are caused either by nuclear ploidy or leaf position,differences in mesophyll cell number per unit leaf are negativelycorrelated with mesophyll cell plan area. The decrease in cellsize with increasing leaf position also results in a greaternumber of chloroplasts per unit leaf area. These results arediscussed in relation to anatomical variation of the wheat leaf. Mesophyll cell, cell numbers, leaf size, Triticum     

Changes in Size and Number of Mesophyll Cells, Nitrogen Content and Photosynthesis with Leaf Order in Brassica spp.

Numbers of mesophyll cells per unit leaf area decreased progressivelyfrom an upper leaf with a width of 3 cm towards the lower leaves.Enlargement of mesophyll cell size with leaf order accountedfor an increase or maintenance of mesophyll cell surface areaper unit leaf area. Increase of photosynthetic rates was correlatedwith increases of mesophyll cell surface area and nitrogen contentper unit leaf area. Therefore, in spite of an increase in cellsurface area to volume ratio with increase of mesophyll cellsize, it appears that increase of mesophyll cell surface areaand nitrogen content per unit leaf area enables a high rateof photosynthesis to be maintained. Brassica, photosynthesis, mesophyll surface area, nitrogen content, cell size, mesophyll resistance, leaf age     

Relationship between Leaf Structure and Gas Exchange in Wheat Leaves at Different Insertion Levels

Net photosynthesis rate (P_n), stomatal conductance to CO₂ andresidual conductance to CO₂ were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO₂ and O₂ levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (V_mes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm² of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. P_n per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm^–2 h^–1 and32·32±1·61 mg dm^–2 h^–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in P_n per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in V_mes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin P_n per unit leaf area was studied. Key words: Photosynthesis, structure, wheat     

Stomata and Mesophyll Characteristics of Barley Leaf as Affected by Light: Stereological Analysis

The anatomical structure of the second leaf blade of barley{Hordeum vulgare L. cv. Koral) was studied in plants exposedto a photosynthetic photon flux density (PPFD) of 200 µmolm^–2 s^–1 compared with those grown under 25µmolm^–2–11. Design-based stereological methods wereused for the estimation of various leaf anatomical characteristicssuch as mesophyll volume, proportion of intercellular spaces,number of mesophyll cells, mean mesophyll cell volume, and internalleaf surface area. The structure of the mesophyll was more affectedby different levels of PPFD than were the stomatal characteristics.Increased PPFD produced thicker leaves with a larger mesophyllvolume having a higher number of less elongated mesophyll cellsand a larger internal leaf surface area. Key words: Hordeum vulgare, light effect, mesophyll, stereology, stomata     

The Uptake and Utilization of Phosphorus and Nitrogen by Diploid, Tetraploid and Hexaploid Wheats (Triticum spp.)

Twenty genotypes of Triticum and Aegilops wheats including diploid,tetraploid and hexaploid types, were grown under contrastingphosphorus (P) regimes (control and low P) at 15 °C by dayand 10 °C at night. Dry-matter production and phosphorusand nitrogen uptake and distribution were measured on matureplants. Phosphorus efficiency (PE) was considered in terms of yieldper unit of P in the main shoot and concentration of phosphorusin grain (per cent P). In the low-P set, PE, which ranged from110 to 715 mg grain mg^–1 P, increased as the yield perculm and dry-matter partitioning (harvest index) increased,with hexaploid > tetraploid > diploid. In both the controland low-P plants percentage P in grain decreased in the orderdiploids > tetraploids > hexaploid wheats. Grain phosphoruswas highly negatively correlated with the log of grain yield(r = –0.74; –0.88) and the log of harvest index(r = –0.80 and –0.88) for control and low-P plants,respectively. This suggests that future gains in plant harvestindex will cause smaller reductions in grain phosphorus concentrations.But, within either a high or low phosphorus supply, wheats witha given grain harvest index have significantly different grainphosphorus concentrations, and conscious selection for thischaracter is feasible. Low-P plants had similar grain nitrogen concentrations but lowernitrogen harvest indexes than control plants. Aegilops spp., Triticum spp., wheat, yield components, harvest index, polyploidy, evolution, phosphorus efficiency     

Cytokinin Effects on Leaf Architecture in Phaseolus vulgaris L.

Treatment of expanding primary leaves of bean plants (Phaseolnsvulgaris L. cv. Limburgse vroege) with benzyladenine (BA) orkinetin at 0.5 mM for five consecutive days resulted in thickerleaves showing a significant decrease in intercellular air spacevolume. Compared with control plants, exposed mesophyll cellsurface area was lower per unit tissue volume, but unchangedwhen expressed per unit leaf surface area. Stomata of treatedplants were not fully closed in the dark and they did not openas wide as controls in the middle of the light period, suggestingthat the treatment resulted in impaired stomatal action. Allthe effects mentioned were more pronounced after treatment withBA, compared to kinetin. In spite of their magnitude, the observedchanges in leaf structure and function did not seem to havean important effect on total leaf diffusion resistance to carbondioxide during the course of the light period. Key words: Cytokinins, Leaf architecture     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 1. General Characteristics of the Leaf Mesophyll and a Comparison with Terrestrial Plants

The structure of photosynthetic elements was investigated in leaves of 42 boreal plant species featuring different degrees of submergence (helophytes, neustophytes, and hydatophytes). The mesophyll structure types were identified for all these species. Chlorenchyma tissues and phototrophic cells were quantitatively described by such characteristics as the sizes of cells and chloroplasts in the mesophyll and epidermis, the abundance of cells and chloroplasts in these tissues, the total surface area of cells and chloroplasts per unit leaf area, the number of plastids per cell, etc. The hydrophytes typically had thick leaves (200–350 m) with a well-developed aerenchyma; their specific density per unit area (100–200 mg/dm²) was lower than in terrestrial plants. Mesophyll cells in aquatic plants occupied a larger volume (5–20 × 10³m³) than epidermal cells (1–15 × 10³m³). The number of mesophyll cells per unit leaf area was nearly 1.5 times higher than that of epidermal cells. Chloroplasts were present in the epidermis of almost all species, including emergent leaves, but the ratio of the chloroplast total number to the number of all plastids varied depending on the degree of leaf submergence. The total number of plastids per unit leaf area (2–6 × 10⁶/cm²) and the surface of chloroplasts per unit leaf area (2–6 cm²/cm²) were lower in hydrophytes than in terrestrial plants from climatically similar habitats. The functional relations between mesophyll parameters were similar for hydrophytes and terrestrial plants (a positive correlation between the leaf weight per unit area, leaf thickness, and the number of mesophyll cells per unit leaf area), although no correlation was found in hydrophytes between the volume of mesophyll cells and the leaf thickness. Phototrophic tissues in aquatic plants contributed a larger fraction to the leaf weight than in terrestrial plants, because the mechanical tissues were less developed in hydrophytes. The CO₂assimilation rates by leaves were lower in hydrophytes than in terrestrial plants, because the total surface area of chloroplasts per unit leaf area is comparatively small in hydrophytes, which reduces the conductivity for carbon dioxide diffusion towards the carboxylation sites.     

Photosynthetic carbon metabolism in wild, primitive and cultivated forms of wheat at three levels of ploidy: Role of the glycolate pathway

¹⁴CO₂ assimilation was studied with diploid, tetraploid, hexaploidspecies of the genera Triticum and their wild relatives Aegilops.Attached mature leaves of 3–4 weekold plants were allowedto undergo photosynthesis under air at ambient temperature.The pattern of distribution of ¹⁴C was notably similar in Triticumand Aegilops species whatever the level of ploidy. Sucrose wasthe sink for photosynthetic carbon. ¹⁴C for sucrose synthesis was supplied either through the glycolatepathway by glycolate, the product of the photorespiration orby the Calvin cycle intermediates exported into the cytoplasm.Depending on the species, the glycolate pathway provided 40to 75%of the sucrose ¹⁴C. The higher labeling of sucrose was associated with the greaterparticipation of the glycolate pathway in the wild diploid (DD)A. squarrosa and in the cultivated hexaploid (AABBDD) T. aestivum.The results suggest that the expression of the male D genomeis dominant over the female AB genome in T. aestivum. In T. aestivum under ambient conditions lowering (low temperature)or hindering (1% O₂ ) photorespiration, sucrose labeling decreased,but serine and glycine labeling was favoured. We propose thatin wheat leaves, the role of photorespiration is to drain artof the carbon exported from the chloroplast as glycolate, towardssucrose synthesis. (Received March 16, 1979; )     

Diversity and evolution of chloroplast DNA in Triticum and Aegilops as revealed by restriction fragment analysis

Summary Restriction fragment analysis of chloroplast (cp) DNAs from 35 wheat (Triticum) and Aegilops species, including their 42 accessions, was carried out with the use of 13 restriction enzymes to clarify variation in their cpDNAs. Fourteen fragment size mutations (deletions/insertions) and 33 recognition site changes were detected among 209 restriction sites sampled. Based on these results, the 42 accessions of wheat-Aegilops could be classified into 16 chloroplast genome types. Most polyploids and their related diploids showed identical restriction fragment patterns, indicating the conservatism of the chloroplast genome during speciation, and maternal lineages of most polyploids were disclosed. This classification of cpDNAs was principally in agreement with that of the plasma types assigned according to phenotypes arising from nucleus-cytoplasm interactions. These mutations detected by restriction fragment analysis were mapped on the physical map of common wheat cpDNA, which was constructed with 13 restriction endonucleases. Length mutations were more frequently observed in some regions than in others: in a 16.0 kilo base pairs (kbp) of DNA region, including rbcL and petA genes, 6 of 14 length mutations were concentrated. This indicates that hot spot regions exist for deletions/insertions in chloroplast genome. On the other hand, 33 recognition site mutations seemed to be distributed equally throughout the genome, except in the inverted repeat region where only one recognition site change was observed. Base substitution rate (p) of cpDNA was similar to that of other plants, such as Brassica, pea and Lycopersicon, showing constant base substitution rates among related taxa and slow evolution of cpDNA compared with animal mitochondrial DNA. Phylogenetic relationships among Triticum and Aegilops species were discussed, based on the present data.Contributions no. 45 and no. 490 from the Kihara Institute for Biological Research, Yokohama City University and the Laboratory of Genetics, Faculty of Agriculture, Kyoto University, respectively.     

Salt Tolerance in the Triticeae: K/Na Discrimination in Aegilops Species

Inorganic ion concentrations were measured in the leaves ofAegilops species growing in 50 or 75 mol m^–3 NaCl (+2.5or 3.75 mol m–3 CaCl₂). The low leaf Na and high leafK concentrations characteristic of the enhanced K/Na discriminationcharacter, originally found in Aegilops squarrosa and in hexaploidwheat, were also found in other Aegilops species containingthe D genome, but not in Ae. ventricosa. The S genome diploidAegilops species (section Sitopsis) all lacked the enhancedK/Na discrimination trait, as did the C genome species Ae. caudataand the N genome species Ae. uniaristata. Most of the U genomespecies (section Polyeides), except Ae. biuncialis, Ae. kotschyiand Ae. variabilis, also exhibited the trait. Examination ofamphiploid hybrids suggested that the trait was dominant incrosses involving Ae. squarrosa or Ae. umbellulata with otherspecies in which the trait was absent. Key words: Salt, ion transport, D genome, Aegilops spp     

Dry Matter Yields and Photosynthetic Rates of Diploid and Hexaploid Triticum Species

The above ground dry matter yields of two wild diploid Triticumspecies averaged 76 per cent of that of two hexaploid breadwheat varieties in field trials carried out over five years.A cultivated diploid species, T. monococcum, gave similar drymatter yields to the bread wheat varieties but had a longergrowth cycle. The flag leaves of wild diploid species had higher rates ofphotosynthesis than those of the bread wheat varieties bothwhen expressed per unit area of leaf or per unit weight of chlorophyll.Photosynthetic rates of other organs, expressed per unit weightof chlorophyll were also greater for the wild diploids thanfor hexaploids. For snoots at the stage when their flag leaveswere fully expanded, the investment in photosynthetic machinery,as measured by chlorophyll concentration, was less in the twowild diploids than in the hexaploids. This compensated for thehigh photosynthetic rate of the former, such that the specificgrowth rates, assessed by carbon-14 fixation per unit shootdry matter, were similar. Triticum spp., wheat, dry matter yield, photosynthesis, carbon-14, ploidy     

Restriction Fragment Length Polymorphism (RFLP) for protein disulfide isomerase (PDI) gene sequences in Triticum and Aegilops species

RFLP variation revealed by protein disulfide isomerase (PDI) coding gene sequences was assessed in 170 accessions belonging to 23 species of Triticum and Aegilops. PDI restriction fragments were highly conserved within each species and confirmed that plant PDI is encoded either by single-copy sequences or by small gene families. The wheat PDI probe hybridized to single EcoRI or HindIII fragments in different diploid species and to one or two fragments per genome in polyploids. Four Aegilops species in the Sitopsis section showed complex patterns and high levels of intraspecific variation, whereas Ae. searsii possessed single monomorphic fragments. T. urartu and Ae. squarrosa showed fragments with the same mobility as those in the A and D genomes of Triticum polyploid species, respectively, whereas differences were observed between the hybridization patterns of T. monococcum and T. boeoticum and that of the A genome. The single fragment detected in Ae. squarrosa was also conserved in most accessions of polyploid Aegilops species carrying the D genome. The five species of the Sitopsis section showed variation for the PDI hybridization fragments and differed from those of the B and G genomes of emmer and timopheevi groups of wheat, although one of the Ae. speltoides EcoRI fragments was similar to those located on the 4B and 4G chromosomes. The similarity between the EcoRI fragment located on the 1B chromosome of common and emmer wheats and one with a lower hybridization intensity in Ae. longissima, Ae. bicornis and Ae. sharonensis support the hypothesis of a polyphyletic origin of the B genome. Received: 25 June 1999 / Accepted: 14 September 1999     

Leaf expansion and carbon assimilation in cotton leaves grown at two photosynthetic photon flux densities

Increasing photosynthetic photon flux density (PPFD) received during development from 5.5 to 31.2 mol m^-2 d^-1 resulted in greater leaf and mesophyll cell surface areas in cotton (Gossypium hirsutum L.). The relationships between the amounts of these surface areas and potential CO₂ assimilation by these leaves were evaluated. Leaf area (epidermal surface area of one side of a leaf), mesophyll cell surface area, and net rate of CO₂ uptake (P_n) were measured from the time leaves first unfolded until P., was substantially reduced. At the higher PPFD, leaf and mesophyll surface areas increased more rapidly during expansion, and P_n per unit leaf area was greater than at the lower PPFD. Although leaves at the higher PPFD reached the maximum P., per unit mesophyll cell surface area 4 to 5 days earlier than leaves at the lower PPFD, the maxima for these P., were similar. Leaves grown at the higher PPFD had the potential to assimilate 2.2, 3.5, or 5.8 times the amount of CO₂ as leaves from the lower PPFD when P., was expressed per unit mesophyll surface, per unit leaf surface, or per whole leaf, respectively. Greater and earlier development of both P., and mesophyll cell surface area at higher PPFD apparently had a compounding effect on the potential for carbon assimilation by a leaf.     

Shading-induced changes in the leaf mesophyll of plants of different functional types

Changes in the structural characteristics of mesophyll induced by shading were investigated in ten species of wild plants of diverse functional types. In all plant types, shading reduced leaf thickness and density by 30–50% and total surface of mesophyll, by 30–70%. The extent and mechanisms of mesophyll structural rearrangement depended on the plant functional type. In the ruderal plants, integral parameters of mesophyll, such as the surface of cells and chloroplasts and mesophyll resistance, changed threefold predominantly because of changes in the dimensions of the cells and chloroplasts. In these plants, shading reduced the volume of chloroplasts by 30%, and the chloroplast numbers per cell declined. The competitor plants showed a twofold increase in mesophyll resistance due to a decrease in the number of photosynthesizing cells per leaf area unit. Moreover, these plants maintained constant dimensions of mesophyll cells, ratios mesophyll surface/mesophyll volume and chloroplast surface/cell surface. In stress-tolerant plants, diffusion resistance of mesophyll remained the same irrespective of the growing conditions, and mesophyll rearrangement was associated with inversely proportional changes in the dimensions of the cells and cell volume per chloroplast. Noteworthy of these plants were relatively constant chloroplasts number per cell, per leaf area unit and total surface area of chloroplasts. The nature of relationship between the mesophyll diffusion resistance and structural parameters of leaf mesophyll differed in plants of diverse functional types.     

Photosynthesis in relation to leaf characteristics of cotton from controlled and field environments

In situ and light-saturated net photosynthetic rates per unit leaf area were greater in cotton (Gossypium hirsutum L.) plants grown in pots in the field than in similar plants from a phytotron growth chamber. Light-saturated stomatal resistances did not differ in leaves of similar age and exposure on field and chamber plants; lower photosynthetic rates in chamber leaves were associated with greater mesophyll resistance. Differences in net photosynthetic rates were related to differences in leaf thickness. When the photosynthetic rates were expressed per unit of mesophyll volume or per unit chlorophyll differences between field and chamber plants were much less than when rates were expressed per unit leaf area. Characterization of the chloroplast lamellar proteins showed that the field leaves had smaller photosynthetic units than the chamber leaves. Since the field leaves also contained more chlorophyll per unit area, this resulted in a much larger number of photosynthetic units per unit area in the field leaves.     

Inflorescence Initiation and Leaf Size in Some Gramineae

The morphology of successive leaves on the flowering shoot wasstudied in species of Glyceria, Lolium, and Triticum. The bladesof successive leaves were progressively longer, eventually reachinga maximum, after which the blades of the last few leaves producedbefore heading were shorter. When the longest leaf blade waselongating, dissection of the shoot apices showed that inflorescenceinitiation was taking place. Epidermal cell measurements inTriticum indicate that differences in blade length are due todifferences in the amount of cell extension. It appears that a correlated change occurs in blade morphologyassociated with the onset of the reproductive state of the shootapex, brought about via changes in the amount of cell extension. A study of the effect of different amounts of low-temperatureand different day-lengths on the relation between inflorescenceinitiation and the production of the longest leaf blade showedthat, under some conditions, this relation can be disturbed.     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis II. Morphology and Anatomy of Evolution Forms

Morphological and anatomical parameters which are variable underroot anaerobiosis in Triticum aestivum were checked on fivetaxa of primitive and modern wheats (and the related genus Aegilops).The plants were grown in nutrient solution which was eitheraerated or flushed with nitrogen. When the plants were flushedwith nitrogen a general retardation in longitudinal root growthoccurred in all of them, but only Triticum aestivum showed aclear promotion of growth of later appearing roots enablingit to maintain the same root/shoot ratio even under stress conditions.There was an increase in the volume of intercellular space inthe root cortex of nearly all the plants investigated. The diameterand the lignin content of the roots and the form of their corticalcells also varied. All these changes were expressed in the primitivewheats to a lesser extent than in the advanced Triticum aestivumindicating that there is a clear increase in the adaptive responsein the latter. Triticum species, Aegilops species, wheat, roots, anatomy, anaerobiosis, stress, intercellular space, selection     

COMPARISON OF TETRAPLOID AND SINGLE GENE-INDUCED GIGAS VARIANTS IN CHICKPEA (CICER ARIETINUM). II. MORPHOLOGICAL AND ANATOMICAL LEAF CHARACTERS

Two genomic variants of a chickpea (Cicer arietinum L.) parental line have been developed which exhibit gigas characters. The two genotypes were the result of a single-gene mutation (gigas) and induced tetraploidy of a single parental line. The two genotypes plus parental strain were investigated to determine the similarity-of-effect of polyploidy and this single-gene mutation on leaf anatomy and morphology. Leaves consisted of two rows of alternatively arranged leaflets. Both the tetraploid and parental lines had the same mean number of leaflets per leaf while the gigas plants had fewer, but mean total leaf surface area was greater in the gigas plants. Quantitative comparison of mesophyll and vascular tissue and air space volume density (V_v) showed that leaves of the tetraploid plants had the greatest mesophyll cell density (V_vm) and least air space density. Mesophyll cell density was equal in the parental and single-gene mutant while parental leaves had the greatest vascular tissue density. The greater mesophyll cell density values of the polyploid were due to larger mean mesophyll cell size, not to greater cell numbers per unit area. Leaf models based on tissue density and leaflet size showed tetraploid plants had the greatest productivity potential per unit of leaflet surface area. However, if models were based on a whole leaf, gigas plants had the greatest productivity potential since they had larger total leaf area. The effectiveness of using structural models to predict physiological potential in plant tissues will be tested in future studies.