Tsuyoshi Horiguchi

MECHANISM OF MANGANESE TOXICITY AND TOLERANCE OF PLANTS : II. Deposition of Oxidized Manganese in Plant Tissues

Seedlings of rice (Oryza saliva L.), barley (Hordeum vulgare L.), alfalfa (Medicago sativa L.), cucumber (Cucumis sativus L.), pumpkin (Cucurbita moschata Duch), and tomato (Lycopersicon esculentum Mill.) were grown in culture solutions containing 0.3, 1.0, 3.2, 10, 32, and 100 ppm Mn for 19 days. After the treatment, Mn contents of the tops and the roots were determined. The presence of oxidized Mn on the roots and the leaves was demonstrated by the blue staining test with benzidine, the solubility and bleaching of oxidized Mn in the oxalic-sulfuric acid solution, and the absorption spectrum of manganipyrophosphate. Rice and pumpkin accumulated a higher amount of Mn in the tops than in the roots for all the levels of Mn tested in the culture solutions. Rice accumulated a remarkably high amount of Mn in the tops even at lower levels of Mn in the solution and the tops were able to tolerate a high Mn concentration in their tissues. On the other hand, Mn contents of alfalfa, tomato, and barley were higher in...

Responses of secondary metabolism in plants to nutrient deficiency

Since levels of some compounds related to secondary metabolism show a sensitive response to nutrient deficiency, we studied the relationship between nutrient deficiency and disorder of secondary metabolism to find a new method of deficiency diagnosis. Deficiencies of N, P and K stimulated phenolic metabolism in rice (Oryza sauva L.) plants. N-deficient plants showed the most sensitive response; levels of some phenolic acids increased in N-deficient plants. In particular, levels of p-coumaric acid and ferulic acid in tops increased noticeably under N deficiency. Addition of Si in the medium decreased sinapic acid level in barley (Hordeum vulgare L.) plants when other nutrient condition were normal. Addition of Si suppressed the increase of phenolic acid levels caused by Mn excess in barley plants. Phenolic acids were analysed in seed coats of (i) field-grown broad been (Vicia Java L.) considered Ca deficient and (ii) plants grown in nutrient solutions containing different Ca concentrations. Sinapic acid and caffeic acid in the seed coats of green seeds increased prior to visual appearance of the browning symptom. Level of p-coumaric acid in the seed coats of the plants grown in 0.5 mM Ca solution was markedly higher than in those grown in 2.0 mM Ca solution. The findings suggest that analysing compounds of secondary metabolism, such as phenolic acids, provides a method for diagnosing nutrient disorders prior to the appearance of visible symptoms.

Microbial Ecology in Tea Soils : I. Soil Properties and Microbial Populations

Abstract The soil chemical properties and microbial numbers in three volcanic ash soils and two non-volcanic ash soils, which had been continuously subjected to the same tea cultivation practices (21 y), were investigated. The results obtained were as follows. 1) pH values of all the soils gradually decreased from the original pH value (near neutral or mildly acid pH) to strongly acid values of about 4 or lower. In contrast, long-term tea cultivation practices resulted in the increase of the total C and N contents in the surface layers (0–20 cm) while the contents remained stable in the subsurface layers (20–40 cm). The increase in the organic matter content in non-volcanic ash soils was presumably due to the accumulation of microbial residues. The availability of P increased markedly. 2) Numbers of bacteria, actinomycetes, fungi, and denitrifiers were higher in volcanic ash soils than in non-volcanic ash soils, and also higher in surface layers than in subsurface layers. The results suggest that in spite...

Microbial ecology in tea soils: II. Soil protease activity

We determined the protease activity to analyze the mechanism of organic nitrogen decomposition (protein degradation) in tea soils. The hydrolyzing activities of N-benzoyl l-arginine amide (BAA), N-...

Studies on rice seed protease: VI. Metal Ion Activation of Rice Seed Peptidase*

Abstract Peptidase in rice seed was investigated with regard to metal ion activation. The embryo contained the highest activity of the peptidase which hydrolysed various synthetic peptldes (l-Leu-Gly-Gly, l-Leu-Gly, Gly-Gly, Gly-l-Leu, Gly-l-Phe, GlY-l-Met, etc.). The enzyme showed an optimum pH of 7.6 for the hydrolysis of Gly-Gly. The hydrolysis of the peptides by the peptidase was activated by metal ions (Mn2+, Co 2+) and inhibited by EDTA, except for the liberation of l-Len from l-Leu-Gly-Gly where Mn2+ was inactive and Co2+ was inhibitory. The metal ion effect was shown to involve activation of the enzyme rather than that of the substrate. The enzyme was activated by the activators for thlol groups and was sensitive to inhibition by the thiol reagents. It appeared probable that Mn2+ or Co2+ was bound through a thlol group at the active site of the enzyme.

Behaviour of fertilizer-N absorbed through root and fruit in peanut

A greenhouse experiment was conducted to study the uptake and translocation of N applied at different rates of15N fertilizer to the fruiting and rooting zones of peanut plants.Higher N level treatments in the fruiting zone resulted in higher N concentrations in the shell and gynophore with fruit and lower N concentration in the testa when compared with the results of lower level treatments in the fruiting zone. Regardless of N levels applied in both rooting and fruiting zones, about 60–65% of15N application to the rooting zone was absorbed through the root, of which 30–35% was found in the seed. With fertilizer application to the fruiting zone and regardless of levels applied to both zones, 35–40% of the15N supplied was absorbed through the shell, and 65% of this remained in the fruit parts while 35% of it was translocated to the vegetation and roots. The percentage of N in the vegetative and root parts, derived from the fertilizer-15N through the shell, was lower in the root and nodules than in the shoot and gynophore without fruit. The translocation of N, absorbed through the roots, to the fruit as well as the amount of symbiotically fixed N were decreased by additions of N to the fruiting zone.

Protein metabolism in rice seedling: I. Effect of the inhibitors of protein synthesis on the degradation of seed protein during germination*

Abstract The relationship between protein synthesis and degradation in germinating rice seed were studied with protein synthetic inhibitors. Both DNP and 8-AG inhibited the degradation of glutelin, the major storage protein in rice seed, while the inhibitors had no direct effect in the activity of rice seed proteinllse in vitro. The prevention can be partly ascribed to the Inhibition of proteinase synthesis because the inhibitors depressed the increase in proteinase activity during germination. When DNP treatment was started at the onset of germination, the degradation of glutelin in the endosperm was seriously inhibited and the endosperm remained rigid over 9 days of incubation at 30°C. In contrast, the inhibition was less efficient clent when the treatment was started in the later stage. It is suggested that the degradation of the storage protein in rice seed depends on the synthetic process of the hydrolytic enzymes which increase during germination. disintegrate the compartmentation of the endosperm a...