Kikuo Kumazawa

Incorporation of 15N into various nitrogenous compounds in intact soybean nodules after exposure to 15N2 gas

Abstract The intact nodules attached to the upper part of soybean roots were exposed to 15N2 and the incorporation of 15N into various soluble nitrogen constituents was investigated. Results indicated that ammonia, a primary product of N2 fixation, was located in more than two compartments. Ammonia reduced from N2 gas seemed to be incorporated firstly into glutamine especially amido-group nitrogen. Newly fixed nitrogen was secondly incorporated into glutamic acid and alanine in this sequence. These results suggested that fixed ammonia was assimilated by glutamine synthetase/glutamate synthase pathway. Turn-over rate of allantoin plus allantoic acid and serine was relatively high, although apparently these compounds were not primary products of newly fixed ammonia. 15N content of allantoin was always higher than that of allantoic acid. 15N incorporation to aspartic acid and asparagine was relatively slow, especially in early period. In bacteroid fraction there is much amount of ammonia comparing with other...

Nitrogen fertilization and nitrate pollution in groundwater in Japan: Present status and measures for sustainable agriculture

During the last two decades, nitrate nitrogen (NO3-N) concentrations in groundwater in Japan have increased steadily due to the development of intensive agriculture. In some areas, they have reached or even exceeded the unacceptable level for drinking water, 10 mg l−1. In 2000, the Environment Agency showed that 5.6% (173 of 3,374) tested wells and 4.7% (64 of 1,362) wells used for drinking water exceeded the standard level in 1999. The highest value of NO3-N in the wells was 100 mg l−1. Many researches have shown that NO3-N pollution of groundwater was widely observed in Japan, except the paddy field regions. Farming practices in Kagamigahara city of Gifu prefecture have been typical ones for reducing NO3-N pollution in groundwater. In the east district of the city, NO3-N concentration was low in 1966, but reached 27.5 mg l−1 in June, 1974. The farmers in this district began to reduce the nitrogen fertilizers in carrot cultivation, going from 256 kg N ha−1 in 1970 to 153 kg N ha−1 in 1991. The use of controlled release fertilizer increased fertilizer-nitrogen efficiency compared with common compound fertilizer and NO3-N concentration in the groundwater began to decrease steadily. It was discussed that in order to decrease the NO3-N pollution of groundwater, it is necessary to refocus not only agricultural technology but also agricultural policy, toward sustainable agriculture and rural development.

Assimilation and transport of nitrogenous compounds originated from 15N2 fixation and 15NO2 absorption

Abstract Nodulated leguminous plants utilize both combined nitrogen absorbed by roots and gaseous nitrogen fixed by root nodules. In order to elucidate the physiological role of N2 fixation compared with NO2 absorption, the assimilation and transport of nitrogenous compounds from these nitrogen sources were studied. One part of soybean plants was administered with labeled nitrogen gas and unlabeled nitrate, and another part with unlabeled nitrogen gas and labeled nitrate. After feeding of labeled compounds to roots, ammonia, nitrate, amino acids, amides and allantoin in nodules, roots and stems were separated, and 15N content of them were determined optically using JASCO NIA-l 15N-analyzer. In nodules supplied with 15N2, high 15N contents were found in glutamate, alanine, serine, γ-amino-butyrate, but in roots supplied with 15NO2, asparagine showed the highest 15N content after 8 hr 15N feeding. In stems, aIIantoin showed the highest 15N content in the case of 15N2 treatment, and the ratio (15N from 15N2/...

ANATOMICAL RESPONSES OF ROOT TIPS TO BORON DEFICIENCY : III. Effect of Boron Deficiency on Sub-Cellular Structure of Root Tips, Particularly on Morphology of Cell Wall and Its Related Organelles

Abstract Ultrastructural changes induced in young tomato root tip cells by the absence of boron from the nutrient solution were investigated with an electron microscope. Detailed observations of cortical cells revealed lome ultrastructural effects of boron deficiency as follows: 1) Lack of boron disordered the shape and arrangement of cortical cells. The abnormal accumulation of a “lipid-like substance” was observed. 2) In boron-deficient root tips, cell walls suffered an irregular thickening followed by a rugged or serrated structure. Occasionally, the disorganization of middle lamellae occurred and an accumulation of numerous vesicles was observed in the disorganized area. These cell wall alterations appeared most distinctly in the longitudinal walls. 3) Baron deficiency also caused an abnormal development of the Golgi apparatus. The number and size of secretory vesicles particularly increased in boron-deticient root tip cells. This abnormal development of the Golgi apparatus seemed to be related with t...

NITROGEN ASSIMILATION IN SOYBEAN NODULES : I. The Role of GS/GOGAT System in the Assimilation of Ammonia Produced by N_2-fixation

Abstract The ureides, allantoin and allantoic acid, have been found to exist in a wide variety of plant species usually in very small amounts, but in some species they play an important role in the storage and transport of nitrogen (19). In soybean plants, a very high content of allantoin has been demonstrated in the stems or shoots, only when the nodulation was well progressed (3, 8, 9, 11, 12, 18). This interesting phenomenon has been discussed in relation to various aspects of soybean physiology, especially the sites and pathways of allantoin synthesis (4, 5, 7, 10, 13–15, 18) and its roles in the vegetative and reproductive growth of soybean plants (6). Using 15N as a tracer, the present authors reported direct evidence that allantoin was vigorously synthesized in nodules, and that most of the allantoin in the shoots of well nodulated soybean plants was supplied from the nodules (14, 15, 18).

Behavior of zinc and copper in soil with long term application of sewage sludges

Abstract Two kinds of sewage sludge composts were applied separately to a crop field consisting of volcanic ash soil (Andosoil) twice a year at 10 t/ha for 12 years since 1978 and the changes in the concentrations of total and soluble Zn and Cu in the sewage sludge-treated soil were studied. The total amount of Zn in the surface soil of the sewage sludge-treated plots increased year by year. The total Zn concentration in the subsoil of these plots was higher than that of the non-treated plot after 12 years of application of the sewage sludge. Cu accumulated somewhat in the surface soil, but not in the subsoil during this period. These facts suggest that Zn moved down to about 20 cm in the Andosoil within 12 years. Sewage sludge application increased the ratio of soluble Zn to total Zn in both the surface soil and subsoil during a 9 year period.

Anatomical responses of root tips to boron deficiency I. Effects of boron deficiency on elongation of root tips and their morphological characteristics

Abstract Effects of boron deficiency on the elongation of root tips of tomato and sunflower seedlings were investigated and the morphological responses of root tips were discussed. The primary effect of boron deficiency was the rapid cessation of root elongation followed by browning and some morphological changes in the root tips, such as abnormal enlargement and dense appearance of lateral roots. Root elongation was extremely inhibited within 3 hr after the plants were placed in boron-free media and the lack of boron in the nutrient solution for 72 hr or more caused the root tips to suffer necrosis. The rapid cessation of root elongation was characteristic in boron deficiency and calcium deficiency among several essential element deficiencies which were tested. Differences between boron and calcium deficiency symptoms were discussed in relation to the morphological characteristics of the root tips.

Anatomical responses of root tips to boron deficiency II. Effect of boron deficiency on the cellular growth and development in root tips

Abstract Changes induced in the tissue structure and the cellular patterns of young tomato root tips by the absence of boron in the nutrient solution were investigated. Boron deficiency caused primarily the inhibition of cell division and cell elongation in root apices, and the cells of boron-deficient root tips were fully vacuolated. The cell wall in the apical region was thickened by boron deficiency and the intercellular spaces insufficiently developed. Boron deficiency also caused the radial enlargement of cortical cells, especially of endodermis, but this enlargement was not accompanied by an increase in water imbibition. In the advanced stage of boron deficiency, the disintegration of tissue structure had occurred. Primordia of lateral roots arose closely in root apices. Maturation of the vascular system, especially of the primary xylem, was exasperated abnormally, and frequently there occurred a differentiation of cambial layers close to the apical initials. Anatomical effects of boron deficiency a...

Nitrogen assimilation in soybean nodules. 2. 15N2 assimilation in bacteroid and cytosol fractions of soybean nodules.

15N assimilation was studied in bacteroid and cytosol fractions of soybean nodules. In the first experiment, after exposing the intact nodules to 15N2 for 5 min and 10 min, most of the fixed 15N was detected in cytosol fraction. In cytosol fraction, 15N content of glutamine was the highest and followed by glutamic acid, alanine, and allantoin in this sequence, whereas, in bacteroid fraction, glutamic acid showed the highest 15N content and alanine and glutamine followed. In the second experiment, 15N assimilation of various 15N-labeled compounds in the separated bacteroid and cytosol fractions was investigated. In the separated bacteroid fraction which was fed with 15NH4, 15N was incorporated very rapidly into glutamic acid, alanine, and aspartic acid, but very slowly into glutamine. From these results, it was suggested that most of the fixed ammonia was exported to cytosol and assimilated via glutamine synthetase to glutamine, then via glutamate synthase to glutamic acid, and from these compound...

Transport of fixed nitrogen from soybean nodules inoculated with H2-uptake positive and negative Rhizobium japonicum strains

Abstract The composition and the flow rate of xylem exudate were compared among 4 Rhizobium japonicum strains-H2-uptake positive and negative strains. The apparent rate of nitrogen transport from the nodulated roots formed with H2-uptake positive strains was bigher than that with Ha-uptake negative strains. Besides, the relative amount of asparagine-N in the xylem sap from the nodulated roots inoculated with H2-uptake positive strains was higher than that with H2-uptake negative strains though allantoin and allantoic acid were the principal forms of nitrogen in the xylem sap. It is suggested that the hydrogenase system affects the amount of fixed-N and the balance of carbon utilization in nodules and that a part of nitrogen assimilation system in the nodules may be altered.