Journal of Experimental Botany

Napier, Richard, M.

doi: 10.1093/jxb/46.12.1787pmid: N/A

Abstract At the time of writing it is 10 years since the first putative auxin receptor was purified, the auxin-binding protein of maize seedlings (ABP1). Over these 10 years an enormous amount of work has been done to try and confirm that this protein is a receptor. Much of the effort has been in gathering descriptive information about the protein (its chemistry and its active sites), the genes encoding it (gene structure, promoter analysis) and the sites at which it is expressed. This information, and the probes generated during these investigations, have been put to use in functional assays to try to find out more directly what role ABP1 plays in auxin responsiveness. The key to defining a receptor is the suitability of the assay used to report on receptor occupancy and the choice of assays available for auxins is discussed in this review. It is shown how the various approaches have developed to complement each other and what they have told us about ABP1, but there are still some enigmas in the ABP1 story. Some problems appear to have been resolved, but more questions remain than have been answered and some of the ways in which these problems are being tackled are discussed. Auxin, receptor, protoplasts, antibodies, Zea mays L This content is only available as a PDF. Author notes 1Fax: +44 1789 470552. © Oxford University Press

Kutík,, Jaromír;Nátr,, Lubomír;Demmers-Derks,, H.H.;Lawlor, David, W.

doi: 10.1093/jxb/46.12.1797pmid: N/A

Abstract Sugar beet (Beta vulgaris L., cultivar Celt) plants were grown under simulated field conditions in pots and supplied with adequate or deficient nitrogen (HN and LN, respectively) combined with two CO2 concentrations, ambient (c. 350μmol mol−1 C02—AC), or elevated CO2 (c. 600 μmol mol−1 CO2—HC). Chloroplast structure in mesophyll palisade cells of mature leaves (leaf number 19 in HN and 9 in LN), sampled at midday on 16 August 1993 was studied by transmission electron microscopy and quantified stereologically. The ultrastructure of palisade parenchyma chloroplasts was affected by the elevated CO2 concentration and strikingly affected by nitrogen supply. Chloroplast diameter (cross-sectional length) was slightly, but not significantly, greater in HC than AC treatments within an N treatment, but was smaller in LN than HN; chloroplast cross-sectional area also increased with HC in both N treatments, but only significantly so in LN. Elevated CO2 reduced the proportion of total thylakoids (significant at 5% and 0.1% in HN and LN, respectively) due to decreased granal thylakoids, but the proportion of inter-granal (stromal) thylakoid membranes was not affected compared to chloroplasts from plants grown with ambient CO2. Chloroplast stroma increased as a proportion of chloroplast volume with elevated compared to ambient CO2 with HN but not LN. Starch inclusions were not significantly different with elevated compared to ambient CO2 at HN, but the proportion of starch increased considerably at elevated compared to ambient C02 at LN, indicating an over-production of assimilates. Plastoglobuli in chloroplasts increased with deficient N, but decreased with elevated CO2. Larger chloroplasts with a greater proportion of stroma, but a smaller proportion of granal thylakoids, suggest increased CO2 assimilating capacity and decreased light harvesting/PSII capacity with elevated CO2. Chloroplast, ultrastructure, elevated CO2 concentration, nitrogen deficiency, sugar beet, Beta vulgaris This content is only available as a PDF. © Oxford University Press

Fischer,, Andreas;Brouquisse,, Renaud;Raymond,, Philippe

doi: 10.1093/jxb/46.12.1803pmid: N/A

Abstract Purple nutsedge is a perennial weed propagating vegetatively by an extended network of rhizomes and tubers. Large quantities of starch are stored in the tubers, but the properties of nitrogen reserves and their importance for early plant growth have received little attention in the past. Organic nitrogen compounds were studied in mature tubers by protein determination, SDS-PAGE and amino acid quantification and separation using reversed-phase HPLC. Changes in these compounds were followed in sprouting tuber pieces fed with a complete nutrient solution (containing nitrate, control) or with a nutrient solution without nitrogen source. As judged by gel electrophoresis or direct protein quantification, some net protein degradation occurred after 2–4 weeks of sprouting in the presence or absence of exogenous N. Amino acids decreased much faster, especially during the first 2 weeks. The major amino acids were arginine and asparagine, which together accounted for 70% of total amino acids at day 0, and which had almost disappeared after 4 weeks of sprouting. Sprout growth depended strongly on the availability of exogenous nitrogen during the second week. The results indicate that amino acids are the main N storage form of purple nutsedge tubers and, essentially, that no storage proteins are present. Future investigations on the N metabolism of sprouting nutsedge should focus on arginine and asparagine metabolism and eventually on nitrogen assimilation, which becomes important in an early phase of plant growth. Cyperus rotundus L., arginine, asparagine, nitrogen assimilation, storage proteins This content is only available as a PDF. © Oxford University Press

Romanov,, V.I.;Gordon,, A.J.;Minchin,, F.R.;Witty,, J.F.;Skøt,, L.;James,, C.L.;Borisov,, A.Y.;Tikhonovich,, I.A.

doi: 10.1093/jxb/46.12.1809pmid: N/A

Abstract A plant-determined pea mutant Sprint-2 Fix− and the parental line Sprint-2 were compared for selected physiological and biochemical parameters. The Fix− mutation prevented differentiation of Rhizobium leguminosarum bacteria into bacteroids and produced large, white, non-fixing nodules. These lacked nitrogenase-linked respiration, but had a background rate of CO2 evolution similar to the normal Fix+ nodules. The cortical structure of the ineffective nodules suggests the existence of an oxygen diffusion barrier and this was supported by a low oxygen concentration in the central region (0.5–3.0%), measured using an O2 sensitive micro-electrode. Sucrose and starch contents were similar in normal and ineffective nodules while ononitol content was about 15 times lower in the Fix− nodules. The distribution of starch was also different in the two nodule types. The activities of glutamine synthetase (GS), sucrose synthase (SS), phosphoenolpyruvate carboxylase (PEPC) and alanine pyruvate aminotransferase (APAT) were markedly higher in Fix+ nodules while the activities of pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) and glutamate dehydrogenase (GDH) were higher in Fix− nodules. The data from immunodetection of host nodule proteins confirmed the reduced levels of sucrose synthase and the almost complete absence of glutamine synthetase and leghaemoglobin in mutant nodules. There was no significant difference in the amount of nitrogenase component 1 extracted from the microsymbiont of normal and ineffective nodules, but component 2 was hardly detectable in the Fix− mutant. Pisum sativum, Fix− mutant, nodules This content is only available as a PDF. © Oxford University Press

Gurney, Anita, L.;Press, Malcolm, C.;Ransom, Joel, K.

doi: 10.1093/jxb/46.12.1817pmid: N/A

Abstract Two cultivars of sorghum (CK60 and Ochuti) and one cultivar of maize (H511) were grown in field plots in western Kenya in the presence or absence of the parasitic angiosperm Striga hermonthica, with or without a single addition of nitrogen fertilizer (150 kg N ha−1) using a factorial design. A progressive decline in rates of photosynthesis of Striga-infected plants were observed for the sorghum cultivar CK60 from 30 d after planting (DAP) and for maize from 40 DAP, until measurements ended 63 DAP. At this time photosynthetic rates were 46% and 31% lower in the Striga-infected sorghum and maize cultivars, respectively, compared to uninfected control plants. No decline in photosynthesis was observed in the second sorghum cultivar studied, Ochuti, a local land race reported to show some tolerance to the parasite. The trends in photosynthesis reflected stunting of the cereals, as determined by the height of the youngest emerged ligule, however, only the grain yield of the sorghum cultivar CK60 was significantly reduced by the presence of the parasite. The nitrogen application influenced neither the growth nor the photosynthetic parameters measured, and possible explanations for the absence of responses are discussed. It is concluded that S. hermonthica can reduce photosynthetic rates of field-grown sorghum and maize, and suggest that an ability to maintain high rates of photosynthesis whilst infected may be an important correlate of tolerance to the parasite. Parasitic angiosperm, photosynthesis, nitrogen, tropical weeds, tropical agriculture This content is only available as a PDF. © Oxford University Press

Kyparissis,, A.;Petropoulou,, Y.;Manetas,, Y.

doi: 10.1093/jxb/46.12.1825pmid: N/A

Abstract Photosynthetic pigments and relative water content of young leaves of P. fruticosa decreased considerably with the onset of the summer dry period and stabilized at low values for the last two summer months, while leaf growth was arrested. Corresponding decreases in photochemical efficiency of photosystem II, as judged by chlorophyll fluorescence measurements of predarkened leaves, were, however, negligible. Following the first autumn heavy rains, growth was restored and photosynthetic pigments and relative water content increased to the pre-drought values. The results indicate that the reduction of chlorophylls does not result from severe photoinhibitory damage but, instead, it may be an adaptive response against the adverse conditions of the Mediterranean summer. Some photosynthetic and photoprotective characteristics of P. fruticosa leaves at two stages of their development, i.e. at the severely dehydrated state with arrested growth during late summer and after their revival following the first heavy autumn rains were compared. Apart from the chlorophyll loss, the photon yield of O2 evolution and the photosynthetic capacity at saturated CO2 were considerably suppressed during the summer, indicating that the extremely low net photosynthetic rates observed in the field were the combined result of stomatal and mesophyll limitations. Epoxidation state was low at midday during the summer, indicating an active, photodissipative xanthophyll cycle. Although zeaxanthin content did not increase at midday after the rains, the potential of the cycle was maintained in the revived leaves, as judged by the high concentrations of the cycle components. After the rains, the activities of the anti-oxidant enzymes (superoxide dismutase, ascorbate peroxidase) remained relatively unchanged on a chlorophyll basis, but increased when expressed on a leaf surface area or protein basis. It may be concluded that P. fruticosa leaves avoid severe photoinhibitory and oxidative damage during the long, warm, dry and sunny Mediterranean summer by reducing light harvesting and electron flow capacity, whilst maintaining an adequate photoprotective ability. The preservation of a remarkable photodissipative and anti-oxidative potential after the rains may be related to the low predictability of precipitation even during the rainy winter. Chl loss, anti-oxidant enzymes, xanthophyll cycle, photosynthesis, water stress This content is only available as a PDF. © Oxford University Press

Premachandra, Gnanasiri, S.;Hahn, Daniel, T.;Rhodes,, David;Joly, Robert, J.

doi: 10.1093/jxb/46.12.1833pmid: N/A

Abstract A drought-tolerant grain sorghum line (K886) maintained significantly higher relative water content (RWC), osmotic potential at full turgor (ψx(100)) and turgor pressure (ψp) than did a drought-susceptible line (CS3541) when the two genotypes were grown in containers and subjected to severe water stress prior to anthesis. Leaf area expansion was inhibited to a greater extent by water deficit in line CS3541 than in K886. Both the basal ψx(100) and the capacity to accumulate solutes upon exposure to stress appear to play important roles in the measured genotypic differences in leaf water relations. Sap osmolarity was greater in line K886 than in CS3541 throughout the entire range of water potential induced. With the exception of proline, the baseline concentrations of each of eight solutes were higher in K886 than in CS3541. Further, when water deficit was imposed, K886 exhibited larger increases in sap osmolality than did CS3541. The concentrations of Kplus;, sugars, Cl− and P, predominant solutes contributing to osmotic adjustment, increased with increasing stress in K886, but essentially remained constant in CS3541. The two lines exhibited large differences in the relative contributions of individual solutes to osmotic adjustment, and these contributions changed markedly during stress development both within and between lines. The most notable differences between genotypes were with respect to the contributions of sugars and K+ ions. The capacity to accumulate K+ ions and to minimize stress-induced reductions in water content, turgor and leaf expansion appear to be useful traits for inclusion in germplasm screening programmes for improved drought tolerance in sorghum. Drought tolerance, glycinebetaine, osmotic adjustment, Sorghum bicolor, water stress This content is only available as a PDF. © Oxford University Press

Lutts,, S.;Kinet,, J.M.;Bouharmont,, J.

doi: 10.1093/jxb/46.12.1843pmid: N/A

Abstract The effects of NaCl stress on growth and development of rice {Oryza sativa L.) were studied and compared in varieties of various origins. During the vegetative stage, tall indica landraces (Nona Bokra, Buhra Rata, Panwell, and Pokkali) appeared to be resistant throughout while in japonica varieties (I Kong Pao (IKP) and Tainung 67) and elite breeding lines (IR 4630, IR 2153 and IR 31785), resistance fluctuated. Panwell, which was the only indica variety evaluated during the reproductive stage, also expressed salt resistance during booting, heading and grain maturation while varieties with the greatest variability in salt stress response during the vegetative phase (IR 4630, IR 31785 and IKP) also showed the greatest variability during reproductive development. Thus, varietal levels of resistance to salinity at different growth stages are not necessarily interdependent characteristics. Variability in salt resistance of different genotypes during the vegetative and reproductive phases of development was not correlated to their mean level of relative resistance. There was an ontogenic evolution of salt resistance and the young seedling stage appeared to be the most sensitive to NaCI during vegetative growth. Nevertheless, short- and middle term effects of stress have to be distinguished for each genotype since some varieties showed better growth during the second week of stress than during the first, whilst others showed an opposite trend. Moreover, even at specific stages of development, plant responses to NaCI were quite variable according to the criterion used to quantify salinity resistance. The identification of genotypes resistant to NaCI at specific developmental stages is essential to improve the understanding of the effects of salt stress upon phenology and to elaborate further breeding programmes. Rice, Oryza sativa L., salt resistance, NaCl, phenology This content is only available as a PDF. © Oxford University Press

García-Romera,, Inmaculada;Fry, Stephen, C.

doi: 10.1093/jxb/46.12.1853pmid: N/A

Abstract To study the metabolism of oligosaccharins, we monitored the fate of (6−14C)-labelled oligo-α-(1 →4)-D-galacturonides of degree of polymerization 8 and 9 (GalA8 and GalA9) when administered at ∽ 1 μM to cell suspension cultures of ‘Paul's Scarlet’ rose {Rosa sp.). Neither GalA8 nor GalA9, was appreciably taken up by or bound to the cells. Both GalA8 and GalA9 were rapidly hydrolysed by the culture (half-life 2–4 h). The products were smaller oligogalacturonides and galacturonic acid, indicating the action of exo-polygalacturonase. It is suggested that exo-polygalacturonase plays an important role in controlling the concentrations of biologically-active oligogalacturonides in uninfected plant tissues. Oligosaccharins, pectins, galacturonic acid, biological activity, exo-polygalacturonase, cell wall metabolism This content is only available as a PDF. Author notes 1Present address: Departamento de Microbiologla del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidin CSIC, Prof Albareda no. 1, 18008 Granada, Spain. © Oxford University Press

Farrar, J., F.;Minchin, P. E., H.;Thorpe, M., R.

doi: 10.1093/jxb/46.12.1859pmid: N/A

Abstract The import of photosynthate labelled with 11C from a source leaf into the two halves of a split root system of an intact barley plant was studied. When applied to one half of a split root system sugars that are absorbed and metabolized reduce subsequent import of 11C into that root half. The non-metabolized sugar analogue 3-O-methyl glucose has no effect on import, whilst mannose and 2–deoxyglucose inhibit both root elongation and import of 11C. EDTA, PCMBS, and apoplastic pH in the range 4–7, have little effect on partitioning. These results are interpreted in terms of a suggestion that phloem unloads directly into expanding cells in the elongation zone of root tips. Carbon partitioning, roots, 11C, sucrose, phloem, sugars, cell expansion This content is only available as a PDF. © Oxford University Press