Influence of phosphate rock sources and rates on rice and common bean production in an Oxisol

A field experiment was conducted for five consecutive years to determine upland rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.) response to eight P sources at three P rates in an Oxisol of Central Brazil. The P sources tested were triple superphosphate (TSP), Arafertil phosphate partially acidulated (APPA), phosphate of Patos partially acidulated (PPPA), phosphate of Araxa concentrated (PAC), phosphate of Catalao (PC), phosphate of Jacupiranga (PJ), phosphate of Patos de Minas (PPM), and phosphate of Abaete (PA). All phosphate rock sources were of Brazilian origin. The P rates used were 87, 174 and 262 kg P ha^-1. Yield response to P sources and rates varied from crop to crop. Rice and bean yields were significantly correlated with Bray 1 P, but not Mehlich 1 P. In the first year, TSP and the two partially acidulated phosphate rocks (APPA, PPPA) produced higher grain yields. In the second year and all remaining years of the experiment, the efficiency of phosphate rock sources as measured by grain yield was equivalent to TSP or partially acidulated P sources. The results suggest that these phosphate rock sources could be used in rice-bean rotations on Brazilian Oxisols. Yield losses in the first year could be partially offset by the addition of a small amount of soluble P.     

Calcium (45Ca) accumulation and transport in chicory (Cichorium intybus L.) root during bud development (forcing)

The lower part (4 cm) of the witloof chicory tap-root (15 cm) was immersed in a complete nutrient solution for 21 days, in the darkness at 18°C and at high RH. This process of forcing which leads to the emergence of an etiolated bud (chicon) was associated with a decrease in root dry weight. Although the amount of calcium in the root and the root cationic exchange capacity remained constant during forcing, the net uptake of calcium, negligible at the onset of forcing, progressively increased to a rate after ten days of 45 mol day^–1. Absorption of ⁴⁵Ca remained at a constant high rate, while the initially low upward migration of ⁴⁵Ca within the root and the chicon accelerated markedly. This upward migration was associated with a progressive decline in the release of newly absorbed ⁴⁵Ca. The data support the hypothesis that calcium acquisition by witloof chicory root is predominantly determined by calcium efflux. As the forcing progressed, the influx remained almost constant while a large decrease in the efflux led to a net uptake of calcium. Upward translocation was probably linked to the formation of new negative exchange sites within the growing chicon. The hypothesis that calcium movement occurred along a preferential pathway (xylem vessels) or involved a mass movement through the root is discussed.     

Role of magnesium in combination with liming in alleviating acid-soil stress with the aluminium-sensitive sorghum genotype CV323

An experiment to study the effects of Mg nutrition on root and shoot development of the Al-sensitive sorghum (Sorghum bicolor (L.) Moench) genotype CV323 grown in pots of sandy loam under different acid soil stress is reported. This experiment had a factorial design: four rates of liming were combined with four rates of Mg fertilization. When no Mg was added, the pH of the soil solutions (collected in ceramic cups) increased from 4.0 (unlimed) to 4.2, 4.7 and 5.9 at the increasing rates of liming. After 30 days of growth dry matter yields of the limed treatments were 40%, 115% and 199% higher than that of the unlimed treatment. Without liming and at the highest liming rate, adding Mg did not affect plant biomass significantly. At the two intermediate levels of liming, however, 11.3 mg extra Mg per kg soil increased dry matter yield to the same levels as found at the highest liming rate. Concentrations of Mg in the soil solution rose after Mg was added and fell when lime was added, but adding both Mg and lime increased Mg concentrations in the plant shoots. In plants of the limed treatments, dry matter yield was correlated closely with the Mg concentration in the shoot. This was not so in the unlimed treatment. Furthermore, in the unlimed treatments root development was inhibited, but reduced Mg uptake by the plants resulted mainly from the direct effect of Al- (or H-) ions in the soil solution rather than from impaired root development. It is concluded that Mg fertilization counteracted the interfering effects of Al- and H ions on Mg uptake.     

A genetically related response to iron deficiency stress in muskmelon

A mutant muskmelon (Cucumis melo L.) with characteristic Fe-deficiency chlorosis symptoms was compared to related cultivars in its ability to obtain Fe via the widely known Fe-stress response mechanisms of dicotyledonous plants. The three cultivars (fefe, the Fe-inefficient mutant; Mainstream and Edisto, both Fe efficient plants) were grown in nutrient solution in either 0 or 3.5 mg L^-1 Fe as FeCl₃. None of the three cultivars released reductants or phytosiderophores, but both Edisto and Mainstream produced massive amounts of H+ ions to reduce and maintain the pH of nutrient solutions below pH 4.0. The roots of these two Fe-efficient cultivars were also capable of reducing Fe³⁺ to Fe²⁺. These responses maintained green plants, resulted in high leaf Fe in both Edisto and Mainstream, and produced Mn toxicity in Mainstream. The lack of Fe-deficiency stress response in fefe not only affected leaf Fe concentration and chlorosis, but also resulted in reduced uptake of Mn. The importance of reduced Fe (Fe²⁺) to the Fe-efficient cultivars was confirmed by growing the cultivars with BPDS (4, 7-diphenyl-1, 10-phenanthroline disulfonic acid, a ferrous chelator) and EDDHA [ethylene-diamine di (0-hydroxphenylacetic acid)] (a ferric chelator), and observing increased chlorosis and reduced Fe uptake in BPDS grown plants. The Fe-deficiency response observed in these cultivars points out the diversity of responses to Fe deficiency stress in plants. The fefe mutant has a limited ability to absorb Fe and Mn and perhaps could be used to better understand Mn uptake in plants.     

The pH profile for acid-induced elongation of coleoptile and epicotyl sections is consistent with the acid-growth theory

The acid-growth theory predicts that a solution with a pH identical to that of the apoplast of auxintreated tissues (4.5–5.0) should induce elongation at a rate comparable to that of auxin. Different pH profiles for elongation have been obtained, however, depending on the type of pretreatment between harvest of the sections and the start of the pH-incubations. To determine the acid sensitivity under in vivo conditions, oat (Avena sativa L.) coleoptile, maize (Zea mays L.) coleoptile and pea (Pisum sativum L.) epicotyl sections were abraded so that exogenous buffers could penetrate the free space, and placed in buffered solutions of pH 3.5–6.5 without any preincubation. The extension, without auxin, was measured over the first 3 h. Experiments conducted in three laboratories produced similar results. For all three species, sections placed in buffer without pretreatment elongated at least threefold faster at pH 5.0 than at 6.0 or 6.5, and the rate elongation at pH 5.0 was comparable to that induced by auxin. Pretreatment of abraded sections with pH-6.5 buffer or distilled water adjusted to pH 6.5 or above gave similar results. We conclude that the pH present in the apoplast of auxin-treated coleoptile and stems is sufficiently low to account for the initial growth response to auxin.Abbreviations FS free space - IAA indole-3-acetic acid This research was supported by a grant from the National Adonautics and space Administration (NASA), NAGW 1394 to R.E.C., NASA grant NAGW-297 to M.L.E., and NASA grant NAG 1849 to D.L.R.     

Photomovement in Dunaliella salina: Fluence rate-response curves and action spectra

We determined the action spectra of the photophobic responses as well as the phototactic response in Dunaliella salina (Volvocales) using both single cells and populations. The action spectra of the photophobic responses have maxima at 510 nm, the spectrum for phototaxis has a maximum at 450–460 nm. These action spectra are not compatible with the hypothesis that flavoproteins are the photoreceptor pigments, and we suggest that carotenoproteins or rhodopsins act as the photoreceptor pigments. We also conclude that the phototactic response in Dunaliella is an elementary response, quite independent of the step-up and step-down photophobic responses. We also determined the action spectra of the photoaccumulation response in populations of cells adapted to two different salt conditions. Both action spectra have a peak a 490 nm. The photoaccumulation response may be a complex response composed of the phototactic and photophobic responses. Blue or blue-green light does not elicit a photokinetic response in Dunaliella.Diagrams of the optical set-ups used for measuring the responses at the single-cell level and of the plans for building the phototaxometer described in this paper are available to the interested readerWe thank Mr. M. Kubota for a tremendous amount of technical assistance and Mr. R. Nagy for building the phototaxometer. We thank T. Kondo, Professor H. Imaseki and the members of the Laboratory of Biological Regulation, NIBB, for their help and support in various aspects of this research. This research was supported, in part, from grants from the Okazaki Large Spectrograph (Project Nos. 86-535, 87-518, 88-523), the Japanese Society for the Promotion of Science, and the College of Agriculture and Life Sciences at Cornell University to R. W.     

Induction of transverse polarity by blue light: An all-or-none response

Phototropic stimulation induces a spatial memory. This was inferred from experiments with maize (Zea mays L.) coleoptiles involving opposing blue-light pulses, separated by variable time intervals, and rotation on a horizontal clinostat (Nick and Schafer, 1988b, Planta 175, 380-388). In those experiments, individual seedlings either curved towards the first or towards the second pulse, or they remained straight. Bending, if it occurred, seemed to be an all-or-none response. Intermediates, i.e. plants, bending only weakly, were not observed. In the first part of the present study it was attempted to create such intermediates. For this purpose the strength of the first, inducing, and the second, opposing, pulse was varied. The result was complex: (i) Individual seedlings maintained the all-or-none expression of spatial memory. (ii) However, on the level of the whole population, the time intervals at which a given response type dominated depended on the fluence ratio. (iii) Furthermore, the final curvature was determined by the fluence ratio. These results are discussed in terms of a blue-light-induced transverse polarity. This polarity initiates from a labile precursor, which can be reoriented by an opposing stimulation (indicated by the strong bending towards the second pulse). The strong curvatures towards the first pulse over long time intervals reveal that, eventually, the blue-light-induced transverse polarity becomes stabilised and thus immune to the counterpulse. In the second part of the study, the relation between phototropic transduction and transverse polarity was characterised by a phenomenological approach involving the following points: (i) Sensory adaptation for induction of transverse polarity disappears with a time course similar to that for phototropic sensory adaptatation. (ii) The fluence response for induction of transverse polarity is a saturation curve and not bell-shaped like the curve for phototropism (iii) For strong counterpulses and long time intervals the clinostat-elicited nastic response (Nick and Schafer 1989, Planta 179, 123-131) becomes manifest and causes an "aiming error" towards the caryopsis. (iv) Temperature-sensitivity of polarity induction was high in the first 20 min after induction, then dropped sharply and rose again with the approach of polarity fixation. (v) Stimulus-summation experiments indicated that, for different inducing fluences, the actual fixation of polarity happened at about 2 h after induction. These experiments point towards an early separation of the transduction chains mediating phototropism and transverse polarity, possibly before phototrophic asymmetry is formed.     

Distribution and immunolocalization of stachyose synthase in Cucumis melo L.

Indirect evidence for the site of stachyose biosynthesis has been provided by determining the occurrence and distribution of stachyose, raffinose and galactinol, the donor of the galactosyl moiety for stachyose synthesis, in Cucumis melo L. cv. Ranjadew. Studies of enzyme activities for the synthesis of these sugars and their distribution in different plant organs and isolates has led to the conclusion that stachyose is synthesized mainly in mature leaves and seeds. Nevertheless, stachyose-synthase activity varied with leaf age, the developmental stage of a plant, the growing season and the plant cultivar used. No stachyose or stachyose-synthase activity could be detected in isolated mesophyll protoplasts and chloroplasts, whereas both were found in a minor-vein-enriched fraction isolated from mature leaves. The conclusion that stachyose biosynthesis is associated with minor veins was confirmed by immunolocalization of the enzyme. Positive specific immunoreactivity of stachyose synthase with polyclonal anti-stachyose-synthase antibodies, labeled with protein A-gold, was detected in intermediary cells of leaf minor veins. The implication of this local synthesis of the main transport sugar for phloem loading in mature leaves of Cucumis melo is discussed.Abbreviation RUBPCase ribulose-1,5-bisphosphate carboxylase This work was supported by Deutsche Forschungsgemeinschaft. The excellent assistance of Ms. B. Müller in preparing the samples for electron microscopy is gratefully acknowledged. The authors thank Professor H.J. Schneider-Poetsch for anti-RuBPCase antibodies.