The light-induced unrolling of the grass leaf — A study of polarity, light-piping and stimulus transmission

Primary leaves of dark-grown barley ( Hordeum vulgare L. cv. Weibull's Ida) unroll in darkness when cut into sections shorter than about 2 cm; the shorter the more unrolling. The unrolling pattern of irradiated leaf sections longer than about 2 cm indicates a polarity in the leaves: the top end of the basal section of a divided leaf unrolls more than the base end of the distal section. Earlier reported findings of a stimulus transmission from irradiated to non-irradiated areas can be fully explained by light-piping and by mechanical, mutual influence between irradiated and non-irradiated areas.     

Barley leaf unrolling. The proline connection

Unrolling of 1 cm sections, taken between 3 and 4 cm from the apex, of 6-day-old, etiolated barley leaves, was promoted by blue (426 nm) and red (658 nm) light. Accompanying such unrolling was a reduction in the level of the free proline of the tissue. When leaf unrolling was prevented by irradiation with far-red (728 nm) light, or treatment with abscisic acid (ABA) following red light irradiation, the level of proline remained more or less unchanged, at the level of the untreated, dark controls. The proline analogue, azetidine carboxylic acid (AZC) powerfully inhibited the light induced leaf opening, emphasizing the significance of proline-containing, structural and functional proteins in barley leaf unrolling. The inhibition imposed by AZC is partially reversible by added proline.     

Waterlogging tolerance in the tribe Triticeae: the adventitious roots of Critesion marinum have a relatively high porosity and a barrier to radial oxygen loss

Nine species from the tribe Triticeae – three crop, three pasture and three ‘wild’ wetland species – were evaluated for tolerance to growth in stagnant deoxygenated nutrient solution and also for traits that enhance longitudinal O₂ movement within the roots. Critesion marinum (syn. Hordeum marinum) was the only species evaluated that had a strong barrier to radial O₂ loss (ROL) in the basal regions of its adventitious roots. Barriers to ROL have previously been documented in roots of several wetland species, although not in any close relatives of dryland crop species. Moreover, the porosity in adventitious roots of C. marinum was relatively high: 14% and 25% in plants grown in aerated and stagnant solutions, respectively. The porosity of C. marinum roots in the aerated solution was 1·8–5·4‐fold greater, and in the stagnant solution 1·2–2·8‐fold greater, than in the eight other species when grown under the same conditions. These traits presumably contributed to C. marinum having a 1·4–3 times greater adventitious root length than the other species when grown in deoxygenated stagnant nutrient solution or in waterlogged soil. The length of the adventitious roots and ROL profiles of C. marinum grown in waterlogged soil were comparable to those of the extremely waterlogging‐tolerant species Echinochloa crus‐galli L. (P. Beauv.). The superior tolerance of C. marinum, as compared to Hordeum vulgare (the closest cultivated relative), was confirmed in pots of soil waterlogged for 21 d; H. vulgare suffered severe reductions in shoot and adventitious root dry mass (81% and 67%, respectively), whereas C. marinum shoot mass was only reduced by 38% and adventitious root mass was not affected.     

Glycine oxidation in mitochondria isolated from light grown and etiolated plant tissue

Mitochondria were isolated from light grown and dark grown monocotyledonous (wheat- Triticum aestivum and barley- Hordeum vulgare ) and dicotyledonous (pea- Pisum sativum ) plants and their capacity to oxidize glycine was measured. In all of the studied plant species the rate of mitochondrial glycine oxidation was high in light grown leaves. Glycine oxidation in mitochondria from etiolated leaves was also very substantial; the rate of glycine oxidation relative to the oxidation of other substrates was about half as compared to green tissue. In etiolated non-photosynthetic tissues the relative glycine oxidation was only ca 20% of that measured in green leaves. The effect of light on the development of glycine oxidation capacity was studied using etiolated barley which was transferred to light for 6 to 24 h. During this time the rate of glycine oxidation as compared to the oxidation of NADH and malate increased, approaching the ratio observed in light grown leaves. It is concluded that the synthesis of proteins involved in glycine oxidation is regulated both in a light dependent and in a tissue specific manner. Monocotyledonous plants should be very useful for further studies of this aspect due to the relatively small developmental difference between etiolated and light grown leaf tissue.     

Effects of red, far-red and blue light on the viscosity of the cytoplasm of wheat leaf cells

The displacement by centrifugation of the cell contents of wheat ( Triticum aestivum L. cy. Weibull's Starke) was studied after various light treatments. In dark-grown leaves the viscosity of the cytoplasm, measured as the time necessary to displace the cell contents, is low, but increases slowly during continuous red irradiation as well as after a short red pulse. The increase after a red light pulse can be nullified by a short far-red irradiation which in itself has no effect. Unlike that found earlier for Elodea densa Casp., and verified in the present study, the cytoplasm of wheat leaves does not show any rapid response to blue light, not even after pretreatment with red light.     

The effect of δ-aminolevulinic acid on red light-induced unrolling of dark-grown barley leaf sections

Unrolling of sections from dark grown barley leaves ( Hordeum vulgare L. cv. Klages) was stimulated by red irradiation. The unrolling started after a lag phase of 6-8 h and was completed after 24 h. The effect of several keto and amino acids on leaf unrolling was compared with their effect on coleoptile segment expansion growth. Of the substances tested δ-aminolevulinic acid had the most inhibitive effect on leaf unrolling and the least inhibitive effect on coleoptile segment expansion growth. Prolonged treatment caused a strong inhibition of the unrolling but with a short tretment, a stimulation of the unrolling occurred. The inhibitive effect of δ-aminolevulinic acid was only found if the treatment started within 6-8 h after the red irradiation. Kinetin and gibberellic acid could decrease the inhibitory effect of δ-aminolevulinic acid. A possible role for δ-aminolevulinic acid working as a triggering substance for leaf unrolling is discussed.     

Presence of molybdenum cofactor in seeds of wheat and barley

Molybdenum cofactor (Mo-co) was determined in seeds of wheat and barley by its ability to restore nitrate reductase (NR) activity in extracts of nitrate reductase-deficient mutants. Its activity was compared with that of wheat roots and leaves. Conditions for assay of Mo-co from different sources in the presence of molybdate and reduced glutathione (GSH) were optimised. The effect of heat-treatment of cell-free extracts from seeds, roots and leaves was also investigated. Mutant extracts of Neurospora crassa nit-1 and Nicotiana tabacum CnxA68, used as apoprotein source for in vitro complementation, were shown to give comparable results. The Mo-co activity, extracted from wheat and barley seeds, could be separated into two peaks by gel chromatography.     

Effect of Increasing Concentrations of Heavy Metals on the Growth of Barley and Wheat Seedlings

The tolerance to increasing doses of lead and cadmium salts on the growth and survival of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) seedlings were studied. Seedlings grown under controlled conditions were treated with dilute (0.001–0.005 mM) solutions of either lead nitrate or cadmium bromide for 1, 4, or 7 days. Subsequently, they were incubated for 7 days in solutions of the same compounds, but at sublethal or lethal concentrations (0.05–10 mM). Plant pretreatment with low concentrations of heavy metals induced an increase in their tolerance to the metals, because pretreated plants could tolerate heavy metals at high concentrations. It is concluded that plant tolerance to increasing concentrations of heavy metals is related to the activation of protective and adaptive processes in their tissues.     

Salinity stress and cytoplasmic factors. A comparison of cell permeability and lipid partiality in salt sensitive and salt resistant cultivars and lines of Triticum aestivum and Hordeum vulgare

Salinity effects on the cell membranes of four lines of wheat ( Triticum aestivum L.). and two cultivars of barley ( Hordeum vulgare L.), differing in salt resistance were investigated. Plants were grown for 10 days in 1/4-strength Hoagland solution and then for 5 more days in 1/4-strength Hoagland with and without NaCl (100 m M ) or (for Hordeum only) polyethylene glycol (PEG). Permeability to three non-electrolytes (urea, methylurea and ethylurea) of subepidermal cells of leaf sheaths ( Triticum ) and coleoptiles ( Hordeum ) was determined and membrane partiality calculated, a parameter which numerically indicates the degree of lipophilicity of a membrane. Non-electrolyte permeability significantly increased and membrane partiality decreased in the salt sensitive cultivars or lines under salt stress. Neither parameter changed significantly in the salt resistant lines and cultivar in a saline environment. Osmotic stress in Hordeum by PEG 10000 had no significant effect on permeability and thus membrane partiality neither in sensitive nor in resistant cultivars.
The osmotic component of salinity stress did not seem to be a major factor causing injury, rather ion toxicity may be a cause of cell damage. The results indicate differences in the membrane between salt sensitive and salt resistant genotypes. Salt resistance seems to be controlled by genetic factors independent of external salinity levels.     

Plant Breeding and Drought in C3 Cereals: What Should We Breed For?

Drought is the main abiotic constraint on cereal yield. Analysingphysiological determinants of yield responses to water may helpin breeding for higher yield and stability under drought conditions.The traits to select (either for stress escape, avoidance ortolerance) and the framework where breeding for drought stressis addressed will depend on the level and timing of stress inthe targeted area. If the stress is severe, breeding under stress-freeconditions may be unsuccessful and traits that confer survivalmay become a priority. However, selecting for yield itself understress-alleviated conditions appears to produce superior cultivars,not only for optimum environments, but also for those characterizedby frequent mild and moderate stress conditions. This impliesthat broad avoidance/tolerance to mild–moderate stressesis given by constitutive traits also expressed under stress-freeconditions. In this paper, we focus on physiological traitsthat contribute to improved productivity under mild–moderatedrought. Increased crop performance may be achieved throughimprovements in water use, water-use efficiency and harvestindex. The first factor is relevant when soil water remainsavailable at maturity or when deep-rooted genotypes access waterin the soil profile that is not normally available; the twolatter conditions become more important when all available wateris exhausted by the end of the crop cycle. Independent of themechanism operating, a canopy able to use more water than anotherwould have more open stomata and therefore higher canopy temperaturedepression, and ¹³C discrimination (¹³C) in plant matter. Thesame traits would also seem to be relevant when breeding forhot, irrigated environments. Where additional water is not availableto the crop, higher water-use efficiency (WUE) appears to bean alternative strategy to improve crop performance. In thiscontext ¹³C constitutes a simple but reliable measure of WUE.However, in contrast to lines performing better because of increasedaccess to water, lines producing greater biomass due to superiorWUE will have lower ¹³C values. WUE may be modified not onlythrough a decrease in stomatal conductance, but also throughan increase in photosynthetic capacity. Harvest index is stronglyreduced by terminal drought (i.e. drought during grain filling).Thus, phenological traits increasing the relative amount ofwater used during grain filling, or adjusting the crop cycleto the seasonal pattern of rainfall may be useful. Augmentingthe contribution of carbohydrate reserves accumulated duringvegetative growth to grain filling may also be worthwhile inharsh environments. Alternatively, extending the duration ofstem elongation without changing the timing of anthesis wouldincrease the number of grains per spike and the harvest indexwithout changing the amount of water utilized by the crop.     

Application to wheat and barley of two leaf photosynthesis models for C3 plants

Abstract Two models describing the relationship between net photosynthesis of leaves of C₃ plants, light intensity and CO₂ concentration in the substomatal cavities are described and fitted to data obtained in a constant environment cabinet and in the field. The first model, based on a resistance analogue for gaseous diffusion and Michaelis-Menten biochemistry, gave the best fit to the data. For the field data, four parameters were required–quantum yield, mesophyll resistance, ‘dayrsquo; respiration and a photorespiration constant. For the cabinet data, a parameter representing the limiting photosynthesis rate was required. The second model, based on a recent more rigorous biochemical analysis of photosynthesis, contains five parameters–quantum yield, maximum carboxylation rate, ‘day’ respiration, a photorespiration constant and a maximum electron transport rate. It fitted the data less well.     

The effects of O3 fumigation during leaf development on photosynthesis of wheat and pea: An in vivo analysis

Previous studies have shown that short exposure of plants to high doses of ozone decreases subsequent photosynthesis; initially by reducing carboxylation capacity. This study tests the hypothesis that this is also the primary cause of loss of photosynthetic capacity in leaves affected by development under a low level of ozone. Triticum aestivum and Pisum sativum plants were exposed from germination to ozone in air (80 nmol mol^-1 for 7 hours per day, for 18 days. Leaves that had completed lamina expansion at this time were free of visible injury and light absorptance was unaffected. However, some significant changes in photosynthetic gas exchange were evident. Photosynthetic CO2 uptake at light saturation was decreased significantly by 35% in T. aestivum but was unchanged in P. sativum. The reduction in photosynthesis of T. aestivum was accompanied by a 31% decline in the maximum velocity of carboxylation measured in vivo. Decreased stomatal conductance did not contribute to this reduction of photosynthesis because there was no significant change in the stomatal limitation to CO2. Processes directly dependent upon photochemical reactions; that is, the quantum yield of CO2 uptake and capacity for regeneration of ribulose 1,5-bisphosphate were not affected by O3 fumigation in either species. This suggests that for wheat, the quantitative cause of decreased photosynthetic rate in vivo is a decrease in the quantity of active ribulose-1,5- bisphosphate carboxylase-oxygenase.     

Calcium and phytochrome control of leaf unrolling in dark-grown barley seedlings

The red light-stimulated component of unrolling in sections from 7-d-old dark-grown barley (Hordeum vulgare L.) leaves is inhibited by ethyleneglycol-bis-(-aminoethyl ether)-N,N,N,N-tetracetic acid (EGTA). A free-Ca²⁺ activity of less than 40 M restores the ability to respond to red light, but only if supplied within 1 h of red light. Magnesium ions are an ineffective substitute. At least two processes in unrolling appear to be Ca²⁺-sensitive.Fluence-response measurements indicate that the levels of the far-red-absorbing from of phytochrome (Pfr) still present 4 h after red-light treatment should be above saturation for the unrolling response; consequently, loss of Pfr does not explain the loss in effectiveness of Ca²⁺ during prolonged EGTA treatment. However, if a further red-light treatment is given simultaneously with Ca²⁺ addition 4 h after the initial light stimulus, then full unrolling occurs in EGTA-treated sections. These data indicate that, under normal circumstances, a functional change in the properties of Pfr must occur, uncoupling it from the transduction chain.Abbreviations EGTA ethyleneglycol-bis-(-aminoethylether)-N,N,N,N,-tetracetic acid - FR far-red light - Mes 2-(N-morpholino)ethanesulphonic, acid - Pfr far-red absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light     

Stored xylem sap from wheat and barley in drying soil contains a transpiration inhibitor with a large molecular size

Xylem sap was collected from wheat and barley growing in a drying soil, and the effect of the sap on transpiration was detected by a bioassay with detached wheat leaves. The inhibitory activity of fresh sap was small, and could be largely accounted for by the abscisic acid content (about 2×10^-5mol m^-3). When fresh sap was stored at -20°C for several days, the activity increased. Maximum activity developed after a week. This increase in activity was due to a compound that increased in size with storage at -20°C. When fresh sap was fractionated with filters of different molecular size exclusion characteristics, and the separated fractions stored at -20°C for a week, activity developed only in the fraction containing compounds smaller than 0·3 kDa. However, when sap already stored at -20°C was fractionated, activity was only in fractions containing compounds larger than 0·3 kDa. The increase in activity and in size did not occur with storage in liquid nitrogen (-196°C) or at -80°C. These results suggest that storage at -20°C causes the aggregation or polymerization of a small compound with low activity to form a large compound with high activity. This change is not catalysed by an enzyme because it can occur in a fraction from which molecules larger than 0·3 kDa are removed. It is probably promoted by high solute concentrations when ice crystals form. Sap collected from plants in soils of high water potential had little or no activity after storage at -20°C.     

Changes in chloroplast peroxidase activities in relation to chlorophyll loss in barley leaf segments

Total peroxidase activity increased during senescence of excised barley ( Hordeum vulgare L. cv. Kashimamugi) leaves. Kinetin treatment furter increased total peroxidase activity but repressed chlorophyll degradation in excised barley leaves. When isoperoxidases were extracted from barley leaf segments. 4 cationic and 4 anionic isozymes were found in polyacrylamide gel electrophorests during leaf senescence. The chloroplasts contained only two cationic isoperoxidase activities. One (designated C4) was repressed by kinetin. and the other (C3) was increased by kinetin. Glucosamine, which also repressed the degradation of chlorophyll, completely repressed C4 activity but did not affect C3 activity. The induction with senescence, and the repression with kinetin and glucosamine, suggest chat chloroplast isoperoxidase C4 may function as a chlorophyll-degrading enzyme during barley leaf senescence.     

Movement of fluorescein into isolated caryopses of wheat and barley

Abstract. The movement of fluorescein, a symplastic fluorescent tracer, into isolated caryopses of wheat and barley is described. The dye followed the pathway to the endosperm which has been proposed previously from anatomical studies, namely a movement from the phloem, through cells of the pigment strand and nucellar projection, followed by a radial spread of the dye from the endosperm cavity into the starchy endosperm. By contrast, the fluorochromes calcofluor white M2R and ANS remained confined to the apoplast and failed to cross the 'xylem discontinuity' at the base of the caryopses.     

Conversion of AFLP markers to sequence-specific PCR markers in barley and wheat

 Conversion of amplified fragment length polymorphisms (AFLPs) to sequence-specific PCR primers would be useful for many genetic-linkage applications. We examined 21 wheat nullitetrasomic stocks and five wheat-barley addition lines using 12 and 14 AFLP primer combinations, respectively. On average, 36.8% of the scored AFLP fragments in the wheat nullitetrasomic stocks and 22.3% in the wheat-barley addition lines could be mapped to specific chromosomes, providing approximately 461 chromosome-specific AFLP markers in the wheat nullitetrasomic stocks and 174 in the wheat-barley addition lines. Ten AFLP fragments specific to barley chromosomes and 16 AFLP fragments specific to wheat 3BS and 4BS chromosome arms were isolated from the polyacrylamide gels, re-amplified, cloned and sequenced. Primer sets were designed from these sequences. Amplification of wheat and barley genomic DNA using the barley derived primers revealed that three primer sets amplified DNA from the expected chromosome, five amplified fragments from all barley chromosomes but not from wheat, one amplified a similar-sized fragment from multiple barley chromosomes and from wheat, and one gave no amplification. Amplification of wheat genomic DNA using the wheat-derived primer sets revealed that three primer sets amplified a fragment from the expected chromosome, 11 primer sets amplified a similar-sized fragment from multiple chromosomes, and two gave no amplification. These experiments indicate that polymorphisms identified by AFLP are often not transferable to more sequence-specific PCR applications. Received: 30 June 1998 / Accepted: 26 October 1998