Tuberization and abscisic acid content inSolanum tuberosum as affected by nitrogen nutrition

Summary Potato plants (Solanum tuberosum L.) were grown under constant climatic conditions in water culture with continuous and discontinuous nitrogen supply. The effect of N nutrition on tuberization and abscicic acid (ABA) content in various parts of the plants was investigated. With the exception of the stolons, interrupting the N supply caused an increase in the ABA content. After renewed N supply the ABA content dropped within 3 days to the original level. With continuous N supply the ABA content varied only to a limited extent. The ABA content of the stolons was not affected by the mode of N nutrition and remained at an almost constant level despite the fact that exogenous ABA was translocated within the stolon acropetally and accumulated in the tip. After tuberization the ABA content of the stolons and tubers rose considerably. The increase in ABA content in roots. exudate, and shoot after N withdrawal was accompanied by the initiation of tuberization in ‘physiologically old’ plants but not in “physiologically young’ plants of the same age. It is postulated that although ABA is involved in the regulation of tuberization, it is the balance between ‘promoting’ hormones such as ABA and ‘inhibiting’ hormones such as gibberellic acid which is the controlling factor.

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Zusammenfassung In Wasserkulturversuchen wurde der Einfluss von kontinuierlicher und diskontinuierlicher N-Ern?hrung auf das Wachstum. die Knollenbildung sowie den Gehalt an Abscisins?ure (ABA) in verschiedenen Teilen der Kartoffelpflanze untersucht. Die Pflanzen wuchsen unter konstanten Klimabedingungen (20 C, 12 h Tagesl?nge). Diskontinuierliche N-Ern?hrung bedeutet eine Unterbrechung des N-Angebotes für 7 Tage mit nachfolgendem erneuten N-Angebot. W?hrend einer N-Entzugsphase und der nachfolgenden N-Aufnahmephase wurden Pflanzen im Abstand von 2–3 Tagen geerntet und auf den ABA-Gehalt im Spross. Exsudat, Wurzel und den Stolonen untersucht. Parallel dazu wurden gleich alte, kontinuierlich mit N ern?hrte Pflanzen geerntet und analysiert. ABA wurde gaschromatographisch bestimmt. Kontinuierliche N-Ern?hrung bewirkte ein stetes Spross-und Wurzelwachstum, Knolleninduktion trat nicht ein. Unterbrechung des N-Angebotes (diskon.-N) beeintr?chtigte sowohl das Spross-als auch das Wurzelwachstum (Abb. 1). Zwei Tage nach Beginn der N-Entzugsphase wurden Knollen induziert. Der ABA-Gehalt schwankt bei kontinuierlich-N w?hrend der gew?hlten Versuchsdauer unregelm?ssig. Dagegen steigt der ABA-Gehalt nach Unterbrechung des N-Angebotes an, und zwar im Spross um das Doppelte, in der Wurzel und im Exsudat um das 10-bzw. 20-fache. Wird danach erneut N angeboten. verringert sich der ABA-Gehalt innerhalb von 3 Tagen auf das Ausgangsniveau (Abb. 2). Diese Beziehung ist unabh?ngig vom physiologischen Alter der Pflanzen und wird auch bei nicht induzierten physiologisch jungen Pflanzen gefunden (Tab. 1). Der ABA-Gehalt der Stolonen wird offensichtlich nicht von der N-Ern?hrung beeinflusst. Er bleibt nahezu konstant und steigt erst nach der Induktion mit zunehmendem Knollenwachstum an (Abb. 2). Die fehlende Beziehung zwischen N-Ern?hrung und ABA-Gehalt der Stolonen kann nicht auf eine mangelnde ABA-Verlagerung zurückgeführt werden, denn ABA (als 2-¹⁴C-ABA angeboten) wird in der wachsenden Stolone akropetal verlagert und in der Spitze akkumuliert (Abb. 3). Reguliert wird die Knollenbildung wahrscheinlich vom Gleichgewicht die Induktion ‘f?rdernder’ wie ABA und ‘hemmender’ Wuchsstoffe Ist der Gehalt an ‘hemmenden’ Wuchsstoffen niedrig, kann durch Erh?hung des ABA-Gehaltes. z.B. nach Unterbrechung des N-Angebotes, die Knollenbildung induziert werden. Die Erh?hung des ABA-Gehaltes reicht jedoch offensichtlich nicht aus, um den wahrscheinlich sehr hohen Gehalt an ‘hemmenden’ Wuchsstoffen in physiologisch jungen Pflanzen zu kompensieren und die Knollenbildung zu induzieren (Tab. 1).

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Résumé L'influence d'une nutrition en azote continue et discontinue sur la croissance, la formation des tubercules et la teneur en acide abscissique (ABA) de diverses parties de la plane de pomme de terre a été étudiée dans des essais en hydroponie. Les conditions de croissance ont été maintenues constantes (20°C, longueur du jour 12 h). Une nutrition discontinue d'azote signifie une interruption de 7 jours dans l'apport d'azote. Les plantes ont été récoltées tous les 2 à 3 jours pendant la période sans azote ainsi que pendant la période consécutive. La teneur en ABA a été analysée dans les tiges, exsudat, racines et stolons. Des plantes d'un même age, mais alimentées en azote de manière continue ont été récoltées et analysées en parallèle. L'ABA a été déterminé par chromatographie en phase gazeuse. Une alimentation ininterrompue d'azote a pour effet une croissance constante de la tige et des racines: la formation des tubercules n'est pas induite. L'interruption de l'apport d'azote (procédé discontinu) entrave aussi bien la croissance de la tige que celle des racines (fig. 1). La tubérisation commence 2 jours après le début de la phase de suppression d'azote. La teneur en ABA varie irrégulièrement dans le procédé N-continu pendant la durée de l'essai. Dans le procédé N-discontinu, le taux d'ABA double dans la tige et augmente de 10 à 20 fois dans les racines et l'exsudat. Lorsque l'apport d'azote est à nouveau garanti, la teneur en ABA rejoint son niveau initial après 3 jours (fig. 2). Cette relation est indépendante de l'age physiologique de la plante; on la trouve également sur des plantes physiologiquement jeunes dont la tubérisation n'est pas induite (tab. 1). La teneur en ABA des stolons ne semble pas être influencée par la nutrition azotée. Elle demeure pratiquement constante et n'augmente qu'après l'induction. avec le développement des tubercules (fig. 2). La relatin inexistante entre la nutrition azotée et la teneur en ABA dans les stolons ne peut être attribuée à une translocation insuffisante de l'ABA, car l'ABA (incorporé sous forme de 2-¹⁴C-ABA) se déplace acropétalement dans les stolons en croissance pour s'accumuler dans la pointe (fig. 3). La tubérisation est probablement contr?lée par l'équilibre entre les substances de croissance ‘favorisant’ (tel l'ABA) et ‘inhibant’ l'induction. Si la teneur en substances ‘inhibant’ l'induction est basse, une augmentation de la teneur en ABA, par interruption de l'apport d'azote par exemple, peut induire la formation des tubercules. L'augmentation de la teneur en ABA ne suffit pas à compenser la teneur, probablement très élevée, en substances ‘inhibant’ l'induction, chez des plantes physiologiquement jeunes et à induire par là, la formation des tubercules.

     

Quantification of anthropogenic lead in Slovak forest and arable soils along a deposition gradient with stable lead isotope ratios

Isotope ratios of Pb may provide the opportunity to determine the contribution of Pb from a point source to Pb concentrations in soil. Our objective was to quantify the contribution of anthropogenic Pb to total Pb and chemical Pb fractions in contaminated soil profiles with the help of ²⁰⁶Pb/²⁰⁷Pb isotope ratios. We sampled 5 forest and 5 arable Cambisols along a transect from a Cu smelter and determined Pb concentrations and ²⁰⁶Pb/²⁰⁷Pb isotope ratios in total digests of all horizons and in 7 chemical fractions of the A horizons. In the organic layer under forest, Pb concentrations decreased from 2155 mg kg^—1 at 1.1 km distance from the smelter to 402 mg kg^—1 at 8 km distance; in the Ap horizons, it decreased from 126 to 72 mg kg^—1. In the total digests, ²⁰⁶Pb/²⁰⁷Pb isotope ratios could be explained by simple mixing of smelter‐ and background‐Pb as indicated by the correlation between the inverse of the Pb concentration and the ²⁰⁶Pb/²⁰⁷Pb ratio (r = 0.93). The mean proportion of smelter‐Pb in soil horizons decreased with depth from 87% (Oi) to 21% (C) under forest and from 64% (A) to 30% (B) in the arable soils. The smelter‐Pb proportions in the B horizons ranged from 6 to 66% and were independent of the distance from the smelter indicating variable leaching rates. The ²⁰⁶Pb/²⁰⁷Pb ratios in the chemical fractions could not be explained by a simple mixing model. Thus, the ²⁰⁶Pb/²⁰⁷Pb ratios may be used to determine the contribution of anthropogenic Pb in total digests but not in chemical Pb fractions.     

Predicting heavy metal transfer from soil to plant: potential use of Freundlich‐type functions

Soil‐plant transfer of metals is a nonlinear process. We therefore aimed at evaluating the potential of Freundlich‐type functions (c_Plant = b × c_Soil^a) to predict Cd, Cu, Pb, and Zn concentrations in wheat (Triticum aestivum L.) grain and leaf (c_Plant) from soil concentrations (c_Soil). Wheat plants and soil A horizons, mainly developed from Holocene sediments, were sampled at 54 agricultural sites in Slovakia. Metals were extracted from soils with 0.025 M EDTA at pH 4.6 and concentrated HNO₃/HClO₄ (3:1); plant samples were digested with concentrated HNO₃. Total metal concentrations of soil samples were 0.07—25 mg Cd kg^—1, 9.3—220 mg Cu kg^—1, 14—1827 mg Pb kg^—1, and 34—1454 mg Zn kg^—1. On average, between 20 % (Zn) and 80 % (Cd) of the total concentrations were EDTA‐extractable. The total metal concentrations of grain samples were < 0.01—1.3 mg Cd kg^—1, 1.3—6.6 mg Cu kg^—1, < 0.05—0.30 mg Pb kg^—1, and 8—104 mg Zn kg^—1. The leaves contained up to 3.2 mg Cd kg^—1, 111 mg Cu kg^—1, 4.3 mg Pb kg^—1, and 177 mg Zn kg^—1. Linear regression without data transformation was precluded because of the nonnormal data distribution. The Freundlich‐type function was suitable to predict Cd (grain: r = 0.71, leaf: 0.86 for the log‐transformed data) and Zn concentrations (grain: 0.69, leaf: 0.68) in wheat grain and leaf from the EDTA‐extractable metal concentrations. The prediction of Cu and Pb concentrations in grain (Cu: r = 0.44, Pb: 0.41) was poorer and in leaf only possible for Pb (0.50). We suggest to use the Freundlich‐type function for defining threshold values instead of linear regression because it is more appropriate to simulate the nonlinear uptake processes and because it offers interpretation potential. The results suggest that the coefficient b of the Freundlich‐type function depends on the intensity of metal uptake, while the coefficient a reflects the plants' capability to control the heavy metal uptake. The latter is also sensitive to metal translocation in plants and atmospheric deposition.<?show $6#>     

Age estimates of globular clusters in the Milky Way: constraints on cosmology

Recent observations of stellar globular clusters in the Milky Way Galaxy, combined with revised ranges of parameters in stellar evolution codes and new estimates of the earliest epoch of globular cluster formation, result in a 95% confidence level lower limit on the age of the Universe of 11.2 billion years. This age is inconsistent with the expansion age for a flat Universe for the currently allowed range of the Hubble constant, unless the cosmic equation of state is dominated by a component that violates the strong energy condition. This means that the three fundamental observables in cosmology-the age of the Universe, the distance-redshift relation, and the geometry of the Universe-now independently support the case for a dark energy-dominated Universe.     

Rehabilitation of diseased cacao fields in Peru through shade regulation and timing of biocontrol measures

The objective of this case study was to test the effectiveness of biocontrol for the rehabilitation of abandoned, diseased (moniliasis, witches' broom and black pod) cocoa and to develop testable hypotheses regarding the effect of shade and biocontrol timing. Three trial fields differed in their shade regimes. Biocontrol was administered starting either at flowering or pod filling. Disease incidence and yield were compared with cultural control alone. Biocontrol reduced moniliasis from 49% to 25%, independent of the shading regime and application time. Witches' broom was most severe without shade and unaffected by biocontrol. No significant effects on black pod were observed. Although biocontrol increased percentage healthy fruit independent of shading and timing, only the shaded plot with biocontrol from flowering onwards responded with increased yield. Our hypothesis is: 'In the rehabilitation of abandoned cacao, only fields under sustainable shade management and early onset of biocontrol can realise their production potential.' This revised version was published online in June 2006 with corrections to the Cover Date.     

Concentrations and forms of heavy metals in Slovak soils

The risk assessment of heavy‐metal contamination in soils requires knowledge of the controls of metal concentrations and speciation. We tested the relationship between soil properties (pH, CEC, C_org, oxide concentrations, texture) and land use (forest, grassland, arable) and the partitioning of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn among the seven fractions of a sequential extraction procedure in 146 A horizons from Slovakia. Using a cluster analysis, we identified 92 soils as representing background metal concentrations while the remaining 54 soils showed anthropogenic contamination. Among the background soils, forest soils had the lowest heavy‐metal concentrations except for Pb (highest), because of the shielding effect of the organic layer. Arable soils had the highest Cr, Cu, and Ni concentrations suggesting metal input with agrochemicals. Grassland soils had the highest Cd and Zn concentrations probably for geogenic reasons. Besides the parent material (highest metal concentrations in soils from carbonatic rock, lowest in quartz‐rich soils with sandy texture), pedogenic eluviation processes controlled metal concentrations with podzols showing depletion of most metals in E horizons. Partitioning among the seven fractions of the sequential extraction procedure was element‐specific. The pH was the overwhelming control of the contributions of the bioavailable fractions (fractions 1–4) of all metals and even influenced the contributions of Fe oxide‐associated metals (fractions 5 and 6) to total metal concentrations. For fractions 5 and 6, Fe concentrations in oxides were the most important control of contributions to total metal concentrations. After statistically separating the pH from land use, we found that the contributions of Cu in fractions 1–4 and of NH₄NO₃‐extractable Al, Cd, Pb, and Zn to total metal concentrations were significantly higher under forest than under grassland and in some cases arable use. Our results confirm that metal speciation in soils is mainly controlled by the pH. Furthermore, land use has a significant effect.     

Landscape occupancy and local population size depends on host plant distribution in the butterfly Cupido minimus

We tested whether the landscape occupancy and local population size of the monophagous butterfly Cupido minimus can be predicted by patch size and isolation of its host plant or by other habitat characteristics. C. minimus and its larval food plant Anthyllis vulneraria are classified as rare and endangered in northern Germany. Adults of C. minimus are ranked as the most sedentary butterfly species in northern Europe.Around the city of Göttingen (Germany), we checked all known locations of A. vulneraria (n=70) in June 2002 for butterfly eggs (in blooming flowerheads) and adult butterflies (within 20-min transects).We found eggs of C. minimus or a high number of adults (>7) in all habitats with A. vulneraria (which are calcareous grasslands) even when isolated up to 2-4 km. In multiple regression analyses, local population size of adult butterflies was positively related to the cover of its larval food plant A. vulneraria explaining 65% of variance. Cover of A. vulneraria increased with increasing habitat area and increasing cover of plant species in flower and decreased with increasing cover of shrub layer. Habitat isolation and further factors describing habitat quality were not related to C. minimus population size or cover of its larval food plant.The results suggest that dispersal ability of C. minimus is greater than expected and that management should focus to increase A. vulneraria patches. For conservation, low impact grazing once a year and removing of excessive shrubs in winter seems to be the most appropriate strategies.