Treatment with the herbicide granstar induces oxidative stress in cereal leaves

Disks excised from leaves and intact 7-day-old plants of winter wheat (Triticum aestivum L., cv. Mironovskaya 808), winter rye (Secale cereale L., cv. Estafeta Tatarstana), maize (Zea mays L., hybrid Kollektivnyi 172 MV), and common wild oat (Avena fatua L.) were treated with the xenobiotic (herbicide Granstar, 3–300 μg/l), and the effects of short-term action (up to 3 h) and long-term aftereffect (up to 3 days) on physiological and biochemical indices related to oxidative stress development were studied. Changes (predominantly toward increase) of lipid peroxidation intensity, superoxide anion-radical (O₂^·−)generation, total antioxidant activity, and antioxidant enzymes (superoxide dismutase, catalase, and ascorbate peroxidase) under the action of the herbicide were observed. Plant responses depended nonlinearly on the herbicide concentration and duration of treatment. Winter wheat and winter rye turned out to be more tolerant, and maize and common wild oat were less tolerant. It is concluded that oxidative stress is the basis for cereal plant responses to the herbicide action.     

Ice segregation in the crown of winter cereals: Evidence for extraorgan and extratissue freezing

Meaningful improvements in winter cereal cold hardiness requires a complete model of freezing behaviour in the critical crown organ. Magnetic resonance microimaging diffusion‐weighted experiments provided evidence that cold acclimation decreased water content and mobility in the vascular transition zone (VTZ) and the intermediate zone in rye (Secale cereale L. Hazlet) compared with wheat (Triticum aestivum L. Norstar). Differential thermal analysis, ice nucleation, and localization studies identified three distinct exothermic events. A high‐temperature exotherm (?3°C to ?5°C) corresponded with ice formation and high ice‐nucleating activity in the leaf sheath encapsulating the crown. A midtemperature exotherm (?6°C and ?8°C) corresponded with cavity ice formation in the VTZ but an absence of ice in the shoot apical meristem (SAM). A low‐temperature exotherm corresponded with SAM injury and the killing temperature in wheat (?21°C) and rye (?27°C). The SAM had lower ice‐nucleating activity and freezing survival compared with the VTZ when frozen in vitro. The intermediate zone was hypothesized to act as a barrier to ice growth into the SAM. Higher cold hardiness of rye compared with wheat was associated with higher VTZ and intermediate zone desiccation resulting in the formation of ice barriers surrounding the SAM.     

Selectivity of diclofop-methyl between wheat and wild oat: growth and herbicide metabolism

Abstract Growth of the second leaf of susceptible wild oat (Avena fatua L.) was inhibited within 2 days after treatment with the herbicide, diclofop-methyl, in the 1-1/2 leaf stage. Leaf growth of resistant wheat (Triticum aestivum L.) was unaffected by diclofop-methyl. In wild oat. chlorosis developed 1 day after leaf growth was inhibited. Foliar absorption of diclofop-methyl was similar between wild oat and wheat with 67 and 61% of the recovered radioactivity from [¹⁴C]diclofop-methyl being absorbed by wild oat and wheat, respectively, after 4 days. Wild oal was equally sensitive to the methyl ester and acid forms of the herbicide when the compounds were injected into the stem. Wheat was unaffected by both forms when treated similarly. Very little diclofop-methyl and diclofop (combined total of 10 to 12% in wild oat and 5 to 7% in wheat) remained in plant tissues 2 days after leaf treatment in both susceptible and resistant plants. Therefore, the active form of the herbicide must inhibit growth of susceptible plants very rapidly and at relatively low concentrations. Diclofop-methyl was rapidly hydrolyzed to diclofop by wild oat and wheat. Wild oat predominantly conjugated diclofop to an ester conjugate but wheat hydroxylated the 2,4-dichlorophenyl ring and formed a phenolic conjugate. The formation of the different conjugates between wild oat and wheat was the most significant difference in metabolism between the two species. Nearly 60 and 70% of the methanol-soluble radioactivity was present as water-soluble conjugates in wild oat and wheat, respectively, 4 days after treatment.     

Effect of simulated rain on retention, distribution, uptake, movement and activity of difenzoquat applied to Avena fatua

In glasshouse studies the degree of control of A vena fatua increased as the period between application of difenzoquat and the onset of simulated rain was prolonged. 0.5 mm of ‘rain’ removed 29% of the herbicide deposit without adversely affecting performance at the recommended dose of 1 kg/ha. A further 30% was removed by 2.0 mm of ‘rain’, resulting in a marked reduction in acrivity. With lower amounts of ‘rain’ (0.16 mm), some of the spray deposit was redistributed from the leaf lamina to the leaf base/ligule area. The rate of penetration of ¹⁴C-difenzoquat was much greater when applied to the inner surface of the leaf sheath than when the leaf blade and outer sheath areas were treated. Translocation from the ‘inner sheath’ to other parts of the plant was up to 100 times greater than from other areas. It is suggested that the performance of difenzoquat is not reduced by low amounts of rain because: (1) the spray deposit is removed principally from the leaf blade, whilst in the more responsive ligule/leaf sheath area the herbicide remains in solution, (2) the recommended dose of 1 kg/ha allows for some loss of active ingredient without reduction in performance. The practical implications of the work are discussed and further topics for research are outlined.     

Chlorophyll fluorescence technique as a rapid diagnostic test of the effects of the photosynthetic inhibitor chlorotoluron on two winter wheat cultivars

A modified chlorophyll fluorescence technique was evaluated as a rapid diagnostic test of the susceptibility of wheat cultivars to chlorotoluron. Two winter wheat cultivars (Maris Huntsman and Mercia) exhibited differential response to the herbicide. All of the parameters of chlorophyll fluorescence examined were strongly influenced by herbicide concentration. Additionally, the procedure adopted here for the examination of winter wheat cultivar sensitivity to herbicide indicated that the area above the fluorescence induction curve and the ratio F_V/F_M are appropriate chlorophyll fluorescence parameters for detection of differential herbicide response between wheat cultivars. The potential use of this technique as an alternative to traditional methods of screening new winter wheat cultivars for their response to photosynthetic inhibitor herbicide is demonstrated here.     

STRUCTURE AND DEVELOPMENT OF LEAVES IN CARLUDOVICA PALMATA (CYCLANTHACEAE) WITH REFERENCE TO OTHER CYCLANTHACEAE AND PALMAE

The adult leaf of Carludovica palmata consists of a plicate lamina, adaxial hastula, petiole, and sheath. The leaf is unusual in the angiosperms because about two-thirds of the apical meristem is utilized in its initiation. The adult leaf requires about 4–5 plastochrons to mature. Shortly after its initiation the adult leaf and apical meristem collectively appear pyramid-shaped and various parts of the mature adult leaf may be traced back to particular portions of the pyramid. Plications develop by differential growth within the lamina, not by splitting of leaf tissue. Quantitative studies indicate that certain regions of the developing adult leaf elongate more rapidly or slowly than other regions depending upon the stage of leaf development. The adult leaf of C. palmata develops differently from those of previously studied palms in various ways. It therefore appears less justifiable to consider the superficial similarity between the adult leaves of various Cyclanthaceae (particularly those of Carludovica sensu strictu) and those of fan palms as evidence of especial affinity between the Cyclanthaceae and Palmae. Juvenile leaves of C. palmata differ from adult leaves both in their mode of origin and appearance at maturity. The juvenile leaf appears homologous to the entire adult leaf.     

Adventitious shoot formation in decapitated dicotyledonous seedlings starts with regeneration of abnormal leaves from cells not located in a shoot apical meristem

Regeneration of new shoots in plant tissue culture is often associated with appearance of abnormally shaped leaves. We used the adventitious shoot regeneration response induced by decapitation (removal of all preformed shoot apical meristems, leaving a single cotyledon) of greenhouse-grown cotyledon-stage seedlings to test the hypothesis that such abnormal leaf formation is a normal regeneration progression following wounding and is not conditioned by tissue culture. To understand why shoot regeneration starts with defective organogenesis, the regeneration response was characterized by morphology and scanning electron and light microscopy in decapitated cotyledon-stage Cucurbita pepo seedlings. Several leaf primordia were observed to regenerate prior to differentiation of a de novo shoot apical meristem from dividing cells on the wound surface. Early regenerating primordia have a greatly distorted structure with dramatically altered dorsoventrality. Aberrant leaf morphogenesis in C. pepo gradually disappears as leaves eventually originate from a de novo adventitious shoot apical meristem, recovering normal phyllotaxis. Similarly, following comparable decapitation of seedlings from a number of families (Chenopodiaceae, Compositae, Convolvulaceae, Cucurbitaceae, Cruciferae, Fabaceae, Malvaceae, Papaveraceae, and Solanaceae) of several dicotyledonous clades (Ranunculales, Caryophyllales, Asterids, and Rosids), stems are regenerated bearing abnormal leaves; the normal leaf shape is gradually recovered. Some of the transient leaf developmental defects observed are similar to responses to mutations in leaf shape or shoot apical meristem function. Many species temporarily express this leaf development pathway, which is manifest in exceptional circumstances such as during recovery from excision of all preformed shoot meristems of a seedling.     

A single nucleotide substitution in TaHKT1;5-D controls shoot Na+ accumulation in bread wheat

Improving salinity tolerance in the most widely cultivated cereal, bread wheat (Triticum aestivum L.), is essential to increase grain yields on saline agricultural lands. A Portuguese landrace, Mocho de Espiga Branca accumulates up to sixfold greater leaf and sheath sodium (Na⁺) than two Australian cultivars, Gladius and Scout, under salt stress in hydroponics. Despite high leaf and sheath Na⁺ concentrations, Mocho de Espiga Branca maintained similar salinity tolerance compared to Gladius and Scout. A naturally occurring single nucleotide substitution was identified in the gene encoding a major Na⁺ transporter TaHKT1;5-D in Mocho de Espiga Branca, which resulted in a L190P amino acid residue variation. This variant prevents Mocho de Espiga Branca from retrieving Na⁺ from the root xylem leading to a high shoot Na⁺ concentration. The identification of the tissue-tolerant Mocho de Espiga Branca will accelerate the development of more elite salt-tolerant bread wheat cultivars.     

Biological control of winter wheat pathogens with the use of antagonistic Sphingomonas bacteria under greenhouse conditions

This paper describes, for the first time, the effect of bacteria of the genus Sphingomonas on healthiness of winter wheat. The effect of the application of Sphingomonas cell suspension on development of disease symptoms of powdery mildew and Fusarium head blight (FHB) of winter wheat cv. Bogatka was studied under greenhouse conditions. The abundance of populations of yeast and fungi producing mycelium as well as bacteria of the genus Azotobacter and pseudomonads was determined on wheat kernels. The biocontrol agent reduced the population size of Fusarium poae, and it contributed to better grain filling. The tested Sphingomonas isolate reduced the severity of flag leaf infection caused by pathogenic biotroph Blumeria graminis f. sp. tritici.     

Composition of leaf surface waxes of Triticum species: Variation with age and tissue

The composition of cuticular wax from plants of spring wheat (varieties Selkirk and Manitou) and of durum wheat (variety Stewart 63) at various stages of growth, and of wax from different parts of the plants varies considerably. Wax was analysed, without preliminary separation, by GLC using Dexsil 300 as liquid phase. Alcohols are major components of wax from leaf blades and β-diketones are major components of wax from leaf sheaths, especially the flag leaf sheath. Glaucousness of the leaf sheath is due to the high β-diketone content. In the first 50 days after germination, before sheaths and flag leaf are completely developed, the major component is octacosanol (> 50%). At 66 days, when sheath development is complete, β-diketone content is greatest. Hydrocarbon composition differs for wax from leaf blade and leaf sheath and also for different leaf blades and between adaxial and abaxial sides of the flag leaf. From 66 to 100 days ester content of wax increases, especially in Selkirk wheat, apparently due to formation of wax containing high proportions of esters of trans-α,β-unsaturated C₂₂ and C₂₄ acids. The content of these acids in the free fatty acids and of diesters based on these acids also increases during this period.     

Field Studies of Cereal Leaf Growth: II. THE RELATION BETWEEN AUXANOMETER AND DISSECTION MEASUREMENTS OF LEAF EXTENSION AND THEIR RELATION TO CROP LEAF AREA EXPANSION

Destructive measurements of laminar, sheath, and internode lengthmade on spring barley and winter wheat enabled the contributionof these phytomer components to apparent leaf extension rate(R_E), as measured by auxanometer or rule, to be determined.R_E for early formed leaves consisted entirely of laminar andsheath extension. However, during stem extension, internodeextension also contributed to measured R_E. For the last twoleaves of winter wheat, the extension of internode below thephytomer being measured contributed to R_E. For these leaves,R_E should therefore be interpreted cautiously. Calculating mainstem and tiller leaf areas, and allowing for changes of leafwidth with leaf number, showed that leaf extension was closelyrelated to crop leaf area expansion.     

Wheat acetyl-CoA carboxylase

The acetyl-CoA carboxylase present in both wheat germ and total wheat leaf protein contains ca. 220 kDa subunits. It is the major biotin-dependent carboxylase present in wheat chloroplasts. Active acetyl-CoA carboxylase purified from wheat germ is a homodimer with an apparent molecular mass of ca. 500 kDa. The enzyme from wheat germ or from wheat chloroplasts is sensitive to the herbicide haloxyfop at micromolar levels. The incorporation of ¹⁴C-acetate into fatty acids in freshly cut wheat seedling leaves provides a convenient in vivo assay for both acetyl-CoA carboxylase and haloxyfop.     

Characterization of a dominant mutation for the liguleless trait: Aegilops tauschii liguleless (Lgt)

Background

Leaves of Poaceae have a unique morphological feature: they consist of a proximal sheath and a distal blade separated by a ligular region. The sheath provides structural support and protects young developing leaves, whereas the main function of the blade is photosynthesis. The auricles allow the blade to tilt back for optimal photosynthesis and determine the angle of a leaf, whereas the ligule protects the stem from the entry of water, microorganisms, and pests. Liguleless variants have an upright leaf blade that wraps around the culm. Research on liguleless mutants of maize and other cereals has led to identification of genes that are involved in leaf patterning and differentiation.

Results

We characterized an induced liguleless mutant (LM) of Aegilops tauschii Coss., a donor of genome D of bread wheat Triticum aestivum L.. The liguleless phenotype of LM is under dominant monogenic control (Lg^t). To determine precise position of Lg^t on the Ae. tauschii genetic map, highly saturated genetic maps were constructed containing 887 single-nucleotide polymorphism (SNP) markers derived via diversity arrays technology (DArT)seq. The Lg^t gene was mapped to chromosome 5DS. Taking into account coordinates of the SNP markers, flanking Lg^t, on the pseudomolecule 5D, a chromosomal region that contains this gene was determined, and a list of candidate genes was identified. Morphological features of the LM phenotype suggest that Lg^t participates in the control of leaf development, mainly, in leaf proximal–distal patterning, and its dominant mutation causes abnormal ligular region but does not affect reproductive development.

Conclusions

Here we report characterization of a liguleless Ae. tauschii mutant, whose phenotype is under control of a dominant mutation of Lg^t. The dominant mode of inheritance of the liguleless trait in a Triticeae species is reported for the first time. The position of the Lg^t locus on chromosome 5DS allowed us to identify a list of candidate genes. This list does not contain Ae. tauschii orthologs of any well-characterized cereal genes whose mutations cause liguleless phenotypes. Thus, the characterized Lg^t mutant represents a new model for further investigation of plant leaf patterning and differentiation.

     

An Evaluation of Some Parameters Required for the Enzymatic Isolation of Cells and Protoplasts with CO2 Fixation Capacity from C3 and C4 Grasses

Variable factors affecting the enzymatic isolation of mesophyll protoplasts from Triticum aestivum (wheat), a C₃ gras, and mesophyll protoplasts and bundle sheath strands from Digitaria sanguinalis (crabgrass), a C₄ grass, have been examined with respect to yields and also photosynthetic capacity after isolation. Preparations with high yields and high photosynthetic capacity were obtained when small transverse leaf segments were incubated in enzyme medium in the light at 30°C, without mechanical shaking and without prior vacuum infiltration. Best results were obtained with an enzyme medium that included 0.5 M sorbitol, 1 mM MgCl₂, 1 mM KH₂PO₄, 2% cellulase and 0.1% pectinase at pH 5.5. In gerneral, leaf age and leaf segment size were important factors, with highest yields and photosynthetic capacities obtained from young leaves cut into segments less than 0.8 mm. To facilitate the cutting of such small segments, a mechanical leaf cutter is described that uniformly (± 0.05 mm) cuts leaf tissue into transverse segments of variable size (0.4–2 mm). Isolations that required more than roughly 4 h gave poor yields with reduced photosynthetic capacity; however, using the optimum conditions described, functional preparations could be roughly 2 h. High rates of light dependent CO₂ fixation by the C₄ mesophyll protoplasts required the addition of pyruvate and low levels of oxalacetate, while isolated bundle sheath strands and C₃ mesophyll protoplasts supported CO₂ fixation without added substrates. Rates of CO₂ fixation by isolated wheat protoplasts generally exceeded the reported rates of whole leaf photosynthesis. Wheat mesophyll protoplasts and crabgrass bundle sheath strands were stable when stored at 4°C while C₄ mesophyll protoplasts were stable when stored at 25°C.     

HETEROPHYLLIC DEVELOPMENT IN MUEHLENBECKIA (POLYGONACEAE)

Flowering shoots of Muehlenbeckia platyclados Meisn. bear only reduced scale leaves which resemble the membranous sheath portion (ochrea) of leaves of other members of the Polygonaceae. Shoots propagated from cuttings bear enlarged foliage leaves with distinct lamina, petiole, and ochrea zones. The developmental basis for this heterophylly is explored in order to determine whether scale leaves resemble foliage leaves in their pattern of ontogeny or are developmentally unique. SEM and histological analyses have shown that scale leaves and foliage leaves are distinctive from inception. The scale leaf arises as a collarlike growth and extends over the shoot apex as a hooded sheath without evidence of blade initiation. By contrast, the first stage of foliage-leaf ontogeny is the differentiation of the distal lamina from the future leaf base. As the foliage-leaf ochrea encircles the stem axis, the lamina grows erect and projects from the abaxial surface of the sheath. Lamina reduction coupled with ochrea elaboration in intermediate leaf types indicate a homology between the entire scale leaf and foliage-leaf ochrea. Despite this homology, the production of the bladeless scale leaf does not involve a mere suppression of the foliage-leaf lamina. Erect growth of the saccate ochrea of the foliage leaf contrasts with the hooded expansion of the scale. Early histological differences, including contrasting rates of cell differentiation, also distinguish the two organs. This disparity in modes of growth and differentiation from inception results from separate, predetermined courses of ontogeny. Unlike other plants studied, leaf size and degree of leaf elaboration decrease with shoot meristem enlargement in Muehlenbeckia. Leaf packing does increase with shoot development and may contribute to variations in leaf morphology. It is concluded that the peculiarities of the heterophyllic leaf sequence in Muehlenbeckia are a property of the shoot system as a whole.     

The Effect of Speckled Leaf Blotch on Apical Development and Yield in Winter Wheat in New Zealand

Speckled leaf blotch (Mycosphaerella graminicola) reduced yieldin a winter wheat trial by 18 per cent. Detailed analyses ofthe effects of disease on yield components showed that diseasereduced both grain number per ear and grain weight. The reductionin grain number per ear was due to a decrease in grain numberper spikelet, and this occurred for both main stem and tillers,and occurred equally at each spikelet position on the ear. The effect of disease on grain number was traced back to anearlier reduction in floret primordium number per ear, especiallyfloret number per spikelet. It was suggested that floret primordiumproduction was affected by the reduced assimilate supply tothe developing apex. The effects of disease on yield could therefore be attributedto effects on plant development both before and after anthesis.The disease effects on yield were not necessarily associatedwith the time of maximum disease severity. Plots with the early phase of disease epidemic only showed asignificant reduction in yield, but there was some evidenceof compensation for early reductions to yield potential in thelater-determined yield components. We suggest, therefore, thatan effective disease-control programme must take into accountthe possible early effects of disease on yield potential. Mycosphaerella graminicola, speckled leaf blotch, winter wheat, yield loss, apical development