A new precipitation technique provides evidence for the permeability of Casparian bands to ions in young roots of corn (Zea mays L.) and rice (Oryza sativa L.)

Using an insoluble inorganic salt precipitation technique, the permeability of cell walls and especially of endodermal Casparian bands (CBs) for ions was tested in young roots of corn (Zea mays) and rice (Oryza sativa). The test was based on suction of either 100 µm CuSO₄ or 200 µm K₄[Fe(CN)₆] into the root from its medium using a pump (excised roots) or transpirational stream (intact seedlings), and subsequent perfusion of xylem of those root segments with the opposite salt component, which resulted in precipitation of insoluble brown crystals of copper ferrocyanide. Under suction, Cu²⁺ could cross the endodermis apoplastically in both plant species (although at low rates) developing brown salt precipitates in cell walls of early metaxylem and in the region between CBs and functioning metaxylem vessels. Hence, at least Cu²⁺ did cross the endodermis dragged along with the water. The results suggested that CBs were not perfect barriers to apoplastic ion fluxes. In contrast, ferrocyanide ions failed to cross the mature endodermis of both corn and rice at detectable amounts. The concentration limit of apoplastic copper was 0.8 µm at a perfusion with 200 µm K₄[Fe(CN)₆]. Asymmetric development of precipitates suggested that the cation, Cu²⁺, moved faster than the anion, [Fe(CN)₆]^4–, through cell walls including CBs. Using Chara cell wall preparations (‘ghosts’) as a model system, it was observed that, different from Cu²⁺, ferrocyanide ions remained inside wall-tubes suggesting a substantially lower permeability of the latter which agreed with the finding of an asymmetric development of precipitates. In both corn and rice roots, there was a significant apoplastic flux of ions in regions where laterals penetrated the endodermis. Overall, the results show that the permeability of CBs to ions is not zero. CBs do not represent a perfect barrier for ions, as is usually thought. The permeability of CBs may vary depending on growth conditions which are known to affect the intensity of formation of bands.     

Differences between Indica and Japonica rice varieties in CO2 exchange rates in response to leaf nitrogen and temperature

Four Indica and five Japonica varieties of rice (Oryza sativa L.) were examined to elucidate their differences in photosynthetic activity and dark respiratory rate as influenced by leaf nitrogen levels and temperatures. The photosynthetic rates of single leaf showed correlations with total nitrogen and soluble protein contents in the leaves. Respiratory rate was also positively correlated with the leaf nitrogen content. When compared at the same level of leaf nitrogen or soluble protein content, the four Indica varieties and one of Japonica varieties, Tainung 67, which have some Indica genes derived from one of its parents, showed higher photosynthetic rates than the remaining four Japonica varieties. At the same photosynthetic rate, the Indica varieties showed lower respiratory rate than Japonica varieties. When the leaf temperature rose from 20°C to 30°C, the photosynthetic rate increased by 18 to 41%, whereas the respiratory rate increased by 100 to 150%. These increasing rates in response to temperature were higher in the Japonica than in the Indica varieties. In this respect, Tainung 67 showed the same behavior as of the other four Japonica varieties.Abbreviations 30/20 ratios the ratios of photosynthetic and respiratory rates at 30°C to those at 20°C     

Distribution of zinc fractions and their transformation in submerged rice soils

Distribution of different forms of Zn in 16 acid alluvial rice growing soils of West Bengal (India) and their transformation on submergence were studied. The results showed that more than 84% of total Zn occurred in the relatively inactive clay lattice-bound form while a smaller fractionviz. 1.1, 1.6, 11.1 and 2.0 per cent of the total occurred as water-soluble plus exchangeable, organic complexed, amorphous sesquioxide-bound and crystalline sesquioxide bound forms, respectively. All these four Zn forms showed significant negative correlations with soil pH (r=−0.48^**, −0.39^*, −0.61^** and −0.67^**, respectively), while the latter two Zn forms showed significant positive correlations with Fe₂O₃ (0.68^** and 0.88^***) and Al₂O₃ (0.89^*** and 0.75^***) content of the soils. The different Zn forms were found to have positive and significant correlations amongst each other, suggesting the existence of a dynamic equilibrium of these forms in soil. Submergence caused an increase in the amorphous sesquioxide-bound form of Zn and a decrease in each of the other three forms. The magnitude of such decreases in water-soluble plus exchangeable and crystalline sesquioxide-bound forms was found to be correlated negatively with initial pH values of the soils and positively with the increase in the amorphous sesquioxide-bound form, indicating their adsorption on the surface of the freshly formed hydrated oxides of Fe, which view was supported by the existence of significant positive correlation between the increase in the amorphous sesquioxide-bound form of Zn and that in AlCl₃-extractable iron. The existence of a positive correlation between the decrease in crystalline sesquioxide-bound Zn and that in Fe₂O₃ content in soil suggested that on waterlogging the soil Zn occluded in the cry talline sesquioxide was released as a result of reduction of Fe₂O₃.     

A comparative study of the soil zinc fractions determined by chemical methods and electro-ultrafiltration (EUF) and their relations to zinc nutrition in rice

Rice (IR 42) was grown on two soils differing in zinc status for 30 days with and without Zn under submerged conditions in pots. The fate of soil zinc was characterized by extraction of the soil successively with copper acetate and sodium hypochlorite and by EUF extraction. Most of the applied zinc was extracted by copper acetate and represented as complexed fraction. There exists a close and significnat relation between Cu(OAc)₂-extractable zinc and Zn extracted by EUF for 5 minutes at 50 volts (r=0.98). The EUF-extractable zinc and Cu(OAc)₂-extractable zinc were significantly correlated with the zinc content in the plant (r=0.82). The data from this investigation suggest the possibility of Zn fractionation with the EUF technique and the fractions obtained agree closely to those determined by chemical methods. The results obtained indicate that Zn in soil is held by weak organic bonding and that the extractions by Cu(OAc)₂ and/or EUF-5 minutes serve as a useful basis for extimating zinc availability in rice soils.     

Effect of Hirschmanniella caudacrena on the Submersed Aquatic Plants Ceratophyllum demersum and Hydrilla verticillata

In vitro pathogenicity tests demonstrated that Hirschmanniella caudacrena is pathogenic to Ceratophyllum demersum (coontail). Symptoms were chlorotic tissue, deformed stems, and, finally, death of the plant. Inoculum densities of 500 nematodes per 5-cm-long cutting in a test tube containing 50 ml of water resulted in death and decay of some of the cuttings within 8 weeks; 100 nematodes killed the plants in 12 weeks, and 50 and 25 nematodes killed them in 16 weeks. The lowest inoculum level of 10 nematodes did not seriously affect the plants at 16 weeks when the experiment was terminated. A second test conducted outdoors in glass jars containing 3 liters of water and two cuttings weighing a total of 15 g fresh weight showed damage, but results were not statistically significant. Hydrilla verticillata inoculated with H. caudacrena was not affected seriously.     

Variation in feeding behaviour of Nilaparvata lugens on resistant and susceptible rice varieties

The feeding behaviour of Nilaparavata lugens was monitored on three rice varieties showing different levels of resistance in the Philippines, using a video-assisted observation method. N. lugens made more frequent, shorter probes on the moderately resistant IR46 and resistant IR62 rice varieties than on the susceptible IR22. Honeydew production was significantly lower on the resistant varieties though insect weight gains in 24 h were similar on IR46 and IR22, both being significantly greater than on the highly resistant variety.Population development, growth index and damage ratings were low on IR62 indicating antibiosis and/or non preference. When IR46 plants were infested as seedlings population increase, growth index and damage ratings were similar to those on the susceptible IR22. When infested at a later stage of plant growth the damage rating showed a moderate level of resistance though some population development was maintained, indicating antibiosis and tolerance. N. lugens started probing less frequently after surface exploration on both resistant varieties than on IR22 suggesting the presence of a resistance factor associated with the surface waxes of these varieties.

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Résumé Le comportement alimentaire de Nilaparvata lugens sur variétés de riz, sensible (IR22), partiellement résistante (IR46) et fortement résistante (IR62), a été contrôlé avec une méthode associant la vidéo à l'observation. N. lugens faisait des piqûres plus fréquentes et plus brèves sur IR46 et IR62, que sur la variété sensible. La production de miellat était significativement plus faible sur les variétés résistantes, bien que les gains de poids des insectes aient été les mêmes en 24 h sur IR46 et IR22, les deux étant significativement supérieurs à celui sur IR62.La croissance de la population, l'indice de croissance et le taux de dégâts étaient tous plus faibles sur IR62, ce qui révèle une antibiose et/ou une absence de préférence. Quand la contamination des IR46 a au lieu au stade semis, la croissance de population, l'indice de croissance et le taux de dégâts étaient semblables à ceux de la variété sensible IR22. Quand la contamination avait lieu à un stade ultérieur, le laux de dégâts révélait un niveau modéré de résistance bien qu'une certaine croissance de population se soit maintenue, ce qui révèle antibiose et tolérance.Après exploration de la surface des feuilles des deux variétés résistantes, N. lugens sondait moins fréquemment que sur IR22, ce qui laisse présumer un facteur de résistance associé aux cires superficielles de ces variétés.

     

The response ofAzolla pinnata R. Brown to the split application of phosphorus and the transfer of assimilated phosphorus to flooded rice plants

A field experiment was conducted at the Bangladesh Rice Research Institute, Joydebpur, Dhaka during the late wet season. Basal application of P at both 5 and 10 kg ha⁻¹ significantly increased total biomass production and nitrogen fixation byAzolla pinnata R. Brown (local strain). Addition of both 5 and 10 kg P ha⁻¹ in equal splits at inoculation and at six day intervals thereafter during growth periods of 12, 24 and 36 days increased biomass production and nitrogen fixation by Azolla over that attained with the basal application. Biomass and nitrogen fixation using a split application of 5 kg P ha⁻¹ exceeded that attained with basal application of 10 kg P ha⁻¹ and split application of 10 kg P ha⁻¹ resulted in 0.58, 11.2, and 18.3 t ha⁻¹ more biomass, and 0.47, 18.9, and 18.3 more kg fixed N ha⁻¹ at 12, 24 and 36 days, respectively, than the same amount applied as a basal application. Analyses indicated that the critical level of dry weight P in Azolla for sustained growth was in the range of 0.15–0.17%. Compared with the control, where no P was added, and additional 30 and 36 kg N ha⁻¹ were fixed after 24 and 36 days, respectively, when P was provided at 10 kg ha⁻¹ using a split application. A separate field study showed that flooded rice plants received P from incorporated Azolla with about 28% of the P present in the supplied Azolla being incorporated into the rice plants.     

Inducible nitrate reductase of rice plants as a possible indicator for nitrification in water-logged paddy soils

When following the pattern of the disappearance of NH ₄ ⁺ –N from ammonium sulfate applied to the flooded soil-rice plant system (field and greenhouse experiments) during a growing season, it was observed that the lowest NH ₄ ⁺ –N level coincided with the highest value of NR activity in the leaves. Nitrate was detected in both the root and shoot systems of the rice plants and autotrophic nitrifiers (Nitrosomonas and Nitrobacter) were particularly abundant. Since it was also demonstrated in this work that the NR activity of rice plants grown with nitrate fertilization (growth chamber culture experiments) was inducible by its substrate, it can be assumed that NH ₄ ⁺ –N oxidation takes place in the water-logged soil studied. Therefore, the occurrence of the nitrification process following NH ₄ ⁺ –N fertilizer application can be predicted by thein vitro orin situ evaluation of the NR activity of the rice leaf as an indicator.