Unintended effects of genetic transformation on photosynthetic gas exchange, leaf reflectance and plant growth properties in barley (Hordeum vulgare L.)

Characterization of different component processes of photosynthesis is useful to understand the growth status of plants and to discover possible unintended effects of genetic modification on photosynthesis in transgenic plants. We focused on the changes in photosynthetic gas-exchange properties, reflectance spectra, and plant growth traits among groups of different transgenic barley T1 (Tol_T1) and its isogenic controls (Tol_NT1), Tol_T1, and group of its own transgenic progenies T2 (Tol_T2), Tol_NT1 and its wild type (WT), respectively. Gas-exchange measurements showed that only the net photosynthetic rate (P _N) and the light-use efficiency (LUE) differed significantly between Tol_T1 and Tol_T2 with no obvious changes of other characteristics. Reflectance measurements indicated that the reflectance ratio was sensitive to identify the differences between two barley groups. Differences in reflectance expressed on an index basis depended on barley groups. The relationship between LUE and the photochemical reflectance index (PRI) at a leaf level among different barley groups of WT, Tol_NT1, Tol_T1 and Tol_T2 did not changed obviously. The differences in the total leaf area per plant (LA) between WT and Tol_NT1 as well as between Tol_T1 and Tol_T2 were significant. This study finally provided a plausible complex explanation for the unintended effects of genetic transformation on photosynthesis-related properties in barley at different levels. Furthermore, it was concluded that the photosynthesis-related properties of transgenic plants based on gas exchange, leaf reflectance, and plant growth measurements responded to the same environment in a more different way between two subsequent generations than to the processes of the gene insertion by Agrobacterium and associated tissue culture.     

Indole acetic acid (IAA) induced changes in growth, relative water contents and gas exchange attributes of barley (Hordeum vulgare L.) grown under water stress conditions

Effect of different concentrations of indole acetic acid (IAA) under varying soil water deficit conditions on two barley cultivars viz. B-99094 and Jau-87 was investigated in soil filled earthen pots. There were six treatments including control each with four replicates. Three concentrations of IAA (0, 15 and 30 mg l⁻¹) were applied as foliar spray 30 days after germination. After hormone application, half of the pots were subjected to one cycle of water stress (withholding of water till incipient wilting), followed by regular watering. Plant height, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency relative water content, dry biomass, and grain yield/plant were significantly reduced by water stress. However, IAA treatments alleviated the adverse effect of water stress and successful in enhancing the plant growth and yield of barley cultivars. Barley cultivar Jau-87 performed better than B-99094. IAA application␣was effective in enhancing growth and photosynthetic efficiency of barley both under normal and water stress conditions.     

The effects of DNA hypomethylating drugs on androgenesis in barley (Hordeum vulgare L.)

Summary The effects of DNA hypomethylating drugs (azacytidine and ethionine) on induction of microspore-derived calluses and embryos were studied in barley (Hordeum vulgare L.) ev. Igri. The results were as follows: (1) Yield of calluses and embryos pretreated with the different concentrations of azacytidine for 3 d was several-fold higher than that of the control. The highest yield of calluses and embryos in all treatments appeared at a concentration of 3 mg l⁻¹, which reached 11.03 per anther. It was 110-fold higher than the control. (2) There was a significant difference in yield of calluses and embryos between the different days of pretreatment. The highest yield was obtained at a 3-d pretreatment. If the period of pretreatment was shorter or longer than 3 d, yield of calluses and embryos was reduced sharply, and was similar to that of the control. (3) The data obtained with ethionine pretreatment were very similar to those obtained with azacytidine. (4) Tests on the different methods of pretreatment showed that yield of calluses and embryos pretreated with distilled H₂O, mannitol, azacytidine, and ethionine was much higher than other pretreatments and the control, and reached 6.53–11.39 per anther. The yield of calluses and embryos pretreated with DNA hypomethylating drugs was higher than with mannitol. However, pretreatment with hypomethylation drugs supplemented with induction medium was not effective.     

Phosphorus concentration in barley (Hordeum vulgare L.) seed: Influence on seedling growth and dry matter production

The effect of phosphorus (P) concentration in barley seed on seedling growth has not been much investigated. Consequently, two experiments were conducted in the greenhouse to determine the effect of P concentration in barley seed (Hordeum vulgare L., cv. Empress) on the seedlings grown in sand-filled boxes receiving a culture solution without P. Seeds were selected with three P concentrations: high-P (113.0 mmol P kg⁻¹), medium-P (80.7 mmol P kg⁻¹) and low-P (54.9 mmol P kg⁻¹). At 21 days after sowing, the shoot and root yield or shoot height was the least with seedlings from low-P seed. In the other experiment, high-P and low-P seeds were wetted with distilled water or with a solution of 25.8 cmol L⁻¹ of NaH₂PO₄ for 24 h, and then grown for 31 days. Solution P had been imbibed by seeds whether low or high in native P, but only the imbibed P held by low native P seed benefited seedling dry matter accumulation and shoot elongation. The lack of benefit from seed-imbibed P on seedlings grown from high-P barley seed was associated with low recovery of the imbibed P in those seedlings.     

Gene expression and activity of antioxidant enzymes in barley (Hordeum vulgare L.) under controlled severe drought

The objective of the present study was to determine the activity of antioxidant enzymes: superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) and the expression of their genes in two barley genotypes under controlled severe drought. To fulfill this objective, 21-day-old barley plants of two genotypes: Rum and Yarmouk were exposed to controlled severe drought (25% field capacity) for 2, 9, and 16 days. The activity of SOD was significantly high in Rum genotype after 2 days of drought treatment. In Yarmouk genotype, the activity of APX was significantly high after 2 and 9 days of drought treatment. In Rum genotype, CAT2 was upregulated after 9 days of drought treatment and SOD and APX were upregulated after 16 days of drought treatment, whereas CAT2, SOD, and APX were upregulated in Yarmouk genotype after 2 days of drought treatment. The results indicate a unique pattern of activity and gene expression of the antioxidant enzymes in the two barley genotypes under controlled severe drought. Moreover, the data suggest that each genotype utilizes different molecular and biochemical responses under the same drought conditions.     

Interactive effect of salt (NaCl) and nitrogen form on growth, water relations and photosynthetic capacity of sunflower (Helianthus annum L.)

The effects of the ammonium (NH₄⁺) and nitrate (NO₃^-) forms of nitrogen and NaCl on the growth, water relations and photosynthesis performance of sunflower (Helianthus annuus L.) were examined under glasshouse conditions. Eight-day-old plants of cv. Hisun 33 were subjected for 21 days to Hoagland's nutrient solution containing 8 mol m^-3N as NH₄⁺or NO₃^-, and salinised with 0, 60, or 120 mol m^-3NaCl. Fresh weights of shoots and roots, and leaf area of NO₃^-supplied non-salinised plants were significantly greater than those of NH₄⁺-supplied non-salinised plants. But addition of NaCl to the rooting medium of these plants had more inhibitory effect on the growth of NO₃^--supplied plants than on NH₄⁺-supplied plants. Both leaf water and osmotic potentials of plants grown with NH₄⁺were lower than those of plants given NO₃^-under both non-saline and saline conditions. Chlorophylls a and b concentrations were higher in plants grown with NH₄⁺than N0₃^--supplied plants at the lower two levels of salinisation. The rate of photosynthesis in plants was considerably higher in non-salinised plants grown with NO₃^-than with NH₄⁺, but with increase in salinisation the photosynthesis rate decreased in NO₃^--supplied plants, but not in those given NH₄⁺. The rate of transpiration was increased significantly by salinisation in NO₃^--supplied plants, but not consistently so in NH₄⁺-supplied plants. The stomatal conductances were much higher in plants given NO₃^-than with NH₄⁺when grown under non-saline conditions, but not when salinised. As a consequence, water-use efficiency in NO₃^--supplied control plants was better than in NH₄⁺-supplied under non-saline conditions, but worse under saline conditions. The different forms of nitrogen and the addition of NaCl to the growing medium did not affect the relative intercellular concentrations of CO₂ (C_i/C_a). Overall, the NH₄⁺form of nitrogen inhibited the growth of sunflowers under non-saline conditions, but NO₃^-and NaCl interacted to inhibit growth more than did NH₄⁺under saline conditions.     

Interactive effects of seed availability,water depth,and phosphorus enrichment on cattail colonization in an Everglades wetland

The relative importance of seed availability, waterdepth, and soil phosphorus (P) concentrations oncattail (Typha domingensis pers.) earlyestablishment in an Everglades wetland area wasexamined using seed bank analysis and controlledexperiments. The experiments measured seed germinationand seedling growth in tanks with cattail seedaddition subjected to two P concentrations(un-enriched vs. enriched) and water depth (saturatedvs. flooded soils). A limited seed bank (223 ± 69m²) of cattail was found in the surface soil ofthe area studied. The germination of added seeds wasinhibited under flooded conditions, and only 0.6% ofthe germination was found. In contrast,under-saturated soil conditions, a maximum of 6% and15% germination was observed in P-un-enriched andP-enriched treatments, respectively. High mortality ofseedlings occurred regardless of P treatments followinga cold spell. However, P enrichment resulted inincreased seedling growth and asexual propagation.These results suggested the importance of theconcurrence of appropriate hydrologic regimes, Penrichment, and air temperature on the recruitment ofplant species.     

The effect of cefotaxime on the growth and regeneration of callus from four varieties of barley (Hordeum vulgare L.)

Recently it has been reported that the cephalosporin antibiotic cefotaxime increases growth, regeneration and embryogenesis in wheat calli. We investigated the effect of cefotaxime on callus initiated from immature embryos of four barley (Hordeum vulgare L.) varieties. In calli cultured in the presence of antibiotic callus growth was up to 45% greater than in controls and the frequency of regenerating calli was increased by up to 80%. There was an apparent interaction of the antibiotic with genotype and the 2,4-D in the medium.     

Effects of salinity and nitrogen on growth,ion relations and proline accumulation in Triglochin bulbosa

The effects of salinity and nitrogen on growth, ion relations and prolineaccumulation in the monocotyledonous halophyte, Triglochin bulbosa,was investigated in hydroponic culture over 5 months. The experimentaldesign was a 3 × 3 factorial with three salinity treatments (0, 150 and 300 mol m^-3 NaCl) and three levels of N (5, 10 and 20 gml^-1 N as NaNO₃). Total and root dry biomass accumulationwere significantly affected by salinity, but not by N or N × salinityinteraction. Increase in NaCl from 0 to 150 mol m^-3 had no effecton total or root dry biomass, while further increase in salinity to 300mol m^-3 significantly reduced biomass by 21% and 25%respectively. Shoot dry biomass, which was significantly affected by N andnot by salinity, increased with increase in N from 5 to 10 gml^-1. Ion concentrations in roots and shoots were significantlyaffected by salinity, but not by N or N × salinity interaction. Theconcentration of Na⁺ and Cl^- in roots and shoots increasedprogressively with an increase in salinity, while that of K⁺ decreased. Under non-saline conditions, Na⁺/K⁺ ratios were low (0.41to 0.44) and increased significantly with an increase in salinity in both rootsand shoots. Shoot sap osmotic potentials decreased progressively with anincrease in salinity. Increase in N in the hydroponic solution from 5 to20 g ml^-1 significantly increased root and shoot N by 66%and 41% respectively. Tissue concentrations of proline were significantlyaffected by salinity and substrate N but not by N × salinity interaction. Theconcentration of proline in roots and shoots increased significantly by334% and 48%, respectively, with an increase in salinity from 0 to 300mol m^-3 NaCl. Increase in substrate N from 5 to 20 g ml^-1 significantly increased proline in roots and shoots by 66% and41% respectively. The significance of substrate N on the accumulationof proline is discussed in relation to salt tolerance.     

Photoinhibition of Photosystem I in field-grown barley (Hordeum vulgare L.): Induction, recovery and acclimation

The effects of exposure of a field-grown winter cultivar of barley (Hordeum vulgare L.) to Photosystem I (PS I) photoinhibitory conditions in the form of bright day-light combined with chilling conditions were investigated. PS I photoinhibition was manifested by damage to the Fe-S centers of PS I and to the PS I-A/B polypeptides. Up to 20% of the PS I complexes were photoinactivated. Upon transfer to room temperature, the plants partially recovered from PS I photoinhibition, although damage was still detectable after one week. These results demonstrate that PS I photoinhibition is a physiologically relevant phenomenon in chilling-tolerant plants grown under field conditions. In order to study the induction of cyclic electron transport around PS I by PS I photoinhibitory conditions, antibodies raised against the NDH-I subunit of the NDH complex (a component of cyclic electron transport) were used to measure NDH levels in the exposed plants. A marked increase in the amount of NDH complex and a corresponding increase in NADPH dehydrogenase activity in the thylakoids were observed. The data indicate that the response to PS I-photoinhibitory conditions may involve regulated changes in cyclic electron transport around PS I. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of salinity, pH, organic solutes, anaerobic conditions, and the presence of other microbes on production and survival of Lagenidium giganteum (Oomycetes: Lagenidiales) zoospores

The effects of several environmental factors on the production of viable zoospores by Lagenidium giganteum were determined by counts of germlings produced after induction of zoosporogenesis by suspension of mycelium in various substances. NaCl at a concentration of 0.6 g/liter virtually eliminated zoosporogenesis. At 0.2 g/liter NaCl there was a significant reduction in four of the five fungal isolates tested. Transmission of fungus between mosquito larvae at 0.8 g/liter NaCl suggests that estimates of solute effects from in vitro studies are exaggerated. Zoosporogenesis took place from pH 4.5 to 8.4 by three isolates and from 4.5 to 8 by two other isolates (±0.2). Anaerobic conditions halted zoosporogenesis. Reintroduction of oxygen within 7 days allowed the process to resume, but with reduced production for each day under anaerobic conditions. Five species of bacteria inhibited zoosporogenesis at concentrations of 10⁷–10⁸ cells/ml. The yeast, Saccharomyces cerevisiae, was inhibitory at 10⁶ cells/ml. Three sugars, a sugar alcohol, three amino acids, and peptone all reduced zoosporogenesis at levels that generally correlated positively with their nutritional values for the fungus. Peptone, which can support lush vegetative growth of L. giganteum in the absence of other nutrients, was far more effective in inhibiting zoosporogenesis than the other solutes.     

Formation of early-light-inducible-protein complexes and status of xanthophyll levels under high light and cold stress in barley (Hordeum vulgare L.)

In our previous work we found considerable accumulation of early light-inducible proteins (ELIPs) in barley during adaptation to combined high light and cold stress, an accumulation which occurred preferentially in the apical part of the leaves (M.-H. Montané et al., 1997, Planta 202: 293–302). Here we studied, under the same conditions, the effect of adaptation on the composition of thylakoid membrane proteins and pigments, particularly xanthophylls and chlorophyll, and their distribution within the barley leaf. It was observed that high light fluxes appeared to favour the trimerization of the light-harvesting complex of photosystem II (LHC II) whereas cold appeared to favour the monomers of LHC II. High light, cold or the combination of both factors had only a small effect on the protein composition of the thylakoid membranes except for the proteins of LHC II which were found to decrease under high light to a greater extent at 25 °C than at 5 °C. The total xanthophyll-cycle carotenoid content increased linearly with cellular development, the highest amount being observed in the apical part of the leaf. Cold and high light acted synergistically to induce less than a doubling in the amount of total xanthophylls, while chlorophylls a and b remained nearly constant. The fraction consisting of antheraxanthin plus zeaxanthin was up to 4- to 5-fold higher at 5 °C than at 25 °C. As determined previously (Montané et al. 1997), the same conditions caused a 15-fold increase in the accumulation of ELIPs. Consequently, neither the distribution of total xanthophylls nor that of antheraxanthin plus zeaxanthin along the leaf followed the same pattern as ELIP. Thus, the accumulation of xanthophylls cannot be stoichiometrically correlated with that of ELIPs. Using electrophoresis in the presence of decylmaltoside, we could demonstrate for the first time that ELIPs of 13.5 kDa are contained in high-molecular-mass complexes of >100 kDa, which are located in the unstacked stroma lamellar region of the thylakoid membranes. Received: 6 April 1998 / Accepted: 26 January 1999     

The influence of genotype and temperature pre-treatment on anther culture response in barley (Hordeum vulgare L.)

The influence of temperature stress pre-treatment on anther culture response has been examined in eight commercially desirable barley cultivars. Spikes were pre-treated in darkness at 4°C for periods of 0, 7, 14, 21 and 28 days. Overall, the optimum pre-treatment period was 21 days, although there were large genotype by pre-treatment interactions. The most responsive cultivar was Igri, with a mean of 38% anthers responding, and relatively little effect of pre-treatment. The greatest effect of pre-treatment was in cv. Heriot, which had 3% response with no pre-treatment and 52% response from 14 days pre-treatment.     

The effect of potassium application on leaf water relations characteristics of field grown barley plants (Hordeum distichum L.)

Leaf water relations characteristics were studied in spring barley fertilized at low (50 kg ha^-1) or high (200 kg ha^-1) levels of potassium applied as KCl. The leaf water relations characteristics were determined by the pressure volume (PV) technique.Seasonal analysis in fully irrigated plants showed that within 2 weeks from leaf emergence the leaf osmotic potential at full turgor ( ¹⁰⁰) decreased from about –0.9 to –1.6 MPa in leaf No 7 (counting the first leaf to emerge as number one) and from about –1.1 to –1.9 MPa in leaf No 8 (the flag leaf) due to solute accumulation. ¹⁰⁰ was 0.05 to 0.10 MPa lower in high K than in low K plants. Thus, an ontogenetically determined accumulation of solutes occurred in the leaves independent of K application. The ratio of leaf weight at full turgor to dry weight (TW/DW) decreased from about 5.5 in leaf No 6 to 4.5 in leaf No 7 and 3.8 in leaf No. 8. The TW/DW ratio was 4 to 10% higher in high K than in low K plants indicating larger leaf cell size in the former. The tissue modulus of elasticity () was increased in high K plants. The main effect of high K application on water relations was an increase in leaf water content and a slight decrease in leaf During drought limited osmotic adjustment and increase in elasticity of the leaf tissue mediated turgor maintenance. These effects were only slightly modified by high potassium application.     

Nitrogen fixation and plant growth of common bean (Phaseolus vulgaris L.) at different levels of phosphorus availability

The efficacy of the alumina system for differentiating between bean (Phaseolus vulgaris L.) genotypes for growth at different levels of phosphorus availability was determinated. In addition to response to P levels, comparisons were made between plants receiving N either from fertilizer or nitrogen fixation. When the cv. Carioca was provided with either 100 ppm of N or inoculated withRhizobium leguminosarum biovarphaseoli, differences in shoot dry weight and nodule number were related to P level. There was a greater proportion of green, ineffectivevs. red, active nodules at the low P concentration than at the higher P concentration. In a second experiment, two cvs., Puebla 152 and Carioca and the breeding line UW 24-21, either were inoculated with rhizobia or provided with 150ppm of N. Each genotype-nitrogen combination was grown at 8 levels of P. There was a positive effect of P level on shoot dry weight, nodule number and nodule mass. Root mass was affected less than nodule or shoot mass by the P level of the growth medium. Nodule mass, but not P concentration in the nodules, was affected by P level, whereas in the other plant tissues, P concentrations were lower at lower P levels in the media.     

Influence of light intensity on the distribution of carbon and consequent effects on mineralization of soil nitrogen in a barley (Hordeum vulgare L.)-soil system

A pot experiment was conducted in a ¹⁴C-labelled atmosphere to study the influence of living plants on organic-N mineralization. The soil organic matter had been labelled, by means of a 200-days incubation, with ¹⁵N. The influence of the carbon input from the roots on the formation of microbial biomass was evaluated by using two different light intensities (I). Mineralization of ¹⁵N-labelled soil N was examined by following its fate in both the soil biomass and the plants. Less dry matter accumulated in shoots and roots at the lower light intensity. Furthermore, in all the plant-soil compartments examined, with the exception of rhizosphere respiration, the proportion of net assimilated ¹⁴C was lower in the low-I treatment than in the high-I treatment. The lower rates of ¹⁴C and ¹⁵N incorporation into the soil biomass were associated with less root-derived ¹⁴C. During the chamber period (¹⁴CO₂-atmosphere), mineralized amounts of ¹⁵N (measured as plant uptake of ¹⁵N) were small and represented about 6.8 to 7.8% of the initial amount of organic ¹⁵N in the soil. Amounts of unlabelled N found in the plants, as a percentage of total soil N, were 2.5 to 3.3%. The low availability of labelled N to microorganisms was the result of its stabilization during the 210 days of soil incubation. Differences in carbon supply resulted in different rates of N mineralization which is consistent with the hypothesis that roots induce N mineralization. N mineralization was higher in the high-I treatment. On the other hand, the rate of mineralization of unlabelled stable soil N was lower than labelled soil ¹⁵N which was stabilized. The amounts of ¹⁵N mineralized in planted soil during the chamber period (43 days) which were comparable with those mineralized in unplanted soil incubated for 210 days, also suggested that living plants increased the turnover rate of soil organic matter.     

Novel approaches for examining the effects of differential soil compaction on xylem sap abscisic acid concentration, stomatal conductance and growth in barley (Hordeum vulgare L.)

Novel techniques were devised to explore the mechanisms mediating the adverse effects of compacted soil on plants. These included growing plants in: (i) profiles containing horizons differing in their degree of compaction and; (ii) split-pots in which the roots were divided between compartments containing moderately (1·4 g cm ^{? 3}) and severely compacted (1·7 g cm ^{? 3}) soil. Wild-type and ABA-deficient genotypes of barley were used to examine the role of abscisic acid (ABA) as a root-to-shoot signal. Shoot dry weight and leaf area were reduced and root : shoot ratio was increased relative to 1·4 g cm ^{? 3} control plants whenever plants of both genotypes encountered severely compacted horizons. In bartey cultivar Steptoe, stomatal conductance decreased within 4 d of the first roots encountering 1·7 g cm ^{? 3} soil and increased over a similar period when roots penetrated from 1·7 g cm ^{? 3} into 1·4 g cm ^{? 3} soil. Conductance was again reduced by a second 1·7 g cm ^{? 3} horizon. These responses were inversely correlated with xylem sap ABA concentration. No equivalent stomatal responses occurred in Az34 (ABA deficient genotype), in which the changes in xylem sap ABA were much smaller. When plants were grown in 1·7 : 1·4 g cm ^{? 3} split-pots, shoot growth was unaffected relative to 1·4 g cm ^{? 3} control plants in Steptoe, but was significantly reduced in Az34. Excision of the roots in compacted soil restored growth to the 1·4 g cm ^{? 3} control level in Az34. Stomatal conductance was reduced in the split-pot treatment of Steptoe, but returned to the 1·4 g cm ^{? 3} control level when the roots in compacted soil were excised. Xylem sap ABA concentration was initially higher than in 1·4 g cm ^{? 3} control plants but subsequently returned to the control level; no recovery occurred if the roots in compacted soil were left intact. Xylem sap ABA concentration in the split-pot treatment of Az34 was initially similar to plants grown in uniform 1·7 g cm ^{? 3} soil, but returned to the 1·4 g cm ^{? 3} control level when the roots in the compacted compartment were excised. These results clearly demonstrate the involvement of a root-sourced signal in mediating responses to compacted soil; the role of ABA in providing this signal and future applications of the compaction procedures reported here are discussed.     

Organ-specific changes in the activity and subunit composition of glutamine-synthetase isoforms of barley (Hordeum vulgare L.) after growth on different levels of NH+ 4

One cytosolic glutamine synthetase (GS, EC 6.3.1.2) isoform (GS 1a) was active in the germinating seeds of barley (Hordeum vulgare L.). A second cytosolic GS isoform (GS 1b) was separated from the leaves as well as the roots of 10-d-old seedlings. The chloroplastic isoform (GS 2) was present and active only in the leaves. The three GS isoforms were active in N-supplied (NH⁺ ₄ or NO ₃ ^– ) as well as in N-free-grown seedlings. This indicates (i) that a supply of nitrogen to the germinating seeds was not necessary for the induction of the GS isoforms and (ii) that no nitrogen-specific isoforms appeared during growth of seedlings with different nitrogen sources. The activity of GS, however, depended on the seedlings' nitrogen source: the specific activity was much higher in the leaves and much lower in the roots of NH⁺ ₄-grown barley than in the respective organs of NO ₃ ^– -fed or N free-grown plants. With increasing concentrations of NH⁺ ₄ (supplied hydroponically during growth), the specific activity of GS 1b increased in the leaves, but decreased in the roots. The activity of GS 2 (leaf) also increased with increasing NH⁺ ₄ supply, whereas GS 1a activity (leaf and root) was not affected. The changes in the activities of GS 1b and GS 2 were correlated with changes in the subunit compositions of the active holoenzymes: growth at increased levels of external NH⁺ ₄ resulted in an increased abundance of one of the four GS subunits, and of two of the five GS 1b subunits in the leaves. In the roots, however, the abundance of these two GS 1b subunits was decreased under the same growth conditions, indicating an organ-specific difference either in the expression of the genes coding for the respective GS 1b subunits or in the assembly of the GS 1b holoenzymes. Furthermore, growth at different levels of NH⁺ ₄ resulted in changes in the substrate affinities of the isoforms GS 1b (root and leaf) and GS 2 (leaf), presumably due to the changes in the subunit compositions of the active holoenzymes.Abbreviations FPLC fast protein liquid chromatography - GHA -glutamyl hydroxamate - GS glutamine synthetase Dr. Roger Wallsgrove's (Rothamsted Experimental Station, Harpenden, UK) generous gift of GS antiserum is greatly appreciated.     

The effect of genotype and environment on the fatty acid content of barley (Hordeum vulgare L.) grains

Abstract A comparison was made of the content of total and some individual fatty acids in grains of nine barley varieties grown at six sites in Belgium. The varieties represented six- and two-rowed winter types and two-rowed spring types. The results showed that the winter types contain more linolenic acid (C18 : 3) than spring types and that six-rowed barleys have less total fatty acids than two-rowed barleys, due mainly to a low concentration of palmitic (C16:0), oleic (CI8 : 1) and linoleic (C18 : 2) acids. Analysis of variance showed that fatty acid content is affected by both the genotype and the environment and multiple regression analysis suggested that weather conditions before and after flowering affected lipid composition.