Kazuomi Kadoya

Growth stimulatory substances for vesicular-arbuscular mycorrhizal fungi in Bahia grass (Paspalum notatum Flügge.) roots

Three kinds of the growth stimulatory substances for vesicular-arbuscular mycorrhizal (VAM) fungi were isolated from the 25% methyl alcohol (MeOH) eluates of Bahia grass roots fractionated by flash chromatography. One of them was identified as eupalitin (3,5-dihydroxy-6,7-dimethoxy-4’-hydroxy flavone). At 10 ppm, this compound significantly stimulated the in vitro hyphal growth of a VAM fungus, Gigaspora ramisporophora Spain. The others were not identified. These results suggest that the flavonoids such as eupalitin, and the unidentified compounds may act as signal molecules in VAM symbiosis.

Effects of arbuscular mycorrhizal fungi on tree growth, leaf water potential, and levels of 1-aminocyclopropane-1-carboxylic acid and ethylene in the roots of papaya under water-stress conditions.

Abstract Seedlings of papaya (Carica papaya L. var. Solo) were transplanted to pots with or without an arbuscular mycorrhizal (AM) fungus (Gigaspora margarita Becker and Hall). After 3 months, half the plants were subjected to water stress by withdrawing irrigation. The leaf water potential (LWP) was measured during 20 days of water-stress treatment and then the plants were harvested. Root ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations were measured and plant fresh weight determined. The LWP decreased during the water-stress treatment and this decrease was more severe in the non-AM plants. Plant fresh weight was higher for AM than non-AM plants under both conditions. Under well-irrigated conditions, the ethylene concentration in the roots was increased by the presence of AM, although there was no significant difference between AM and non-AM roots in ACC levels. ACC increased in both AM and non-AM roots under water-stress conditions. The water-stress treatment resulted in a marked increase in ethylene concentration in non-AM roots but the concentration in AM roots was slightly lower than under normal conditions.

Effect of root-zone flooding on mycorrhizal and non-mycorrhizal peach (Prunus persica Batsch) seedlings.

The effect of root-zone flooding on mycorrhizal and non-mycorrhizal peach seedlings growing in a low P medium was examined. Mycorrhizal seedlings showed relatively faster development prior to flooding and recorded significantly higher concentrations of shoot P, K and Zn and biomass yield. Ethanol accumulation was significantly higher in the taproots of non-mycorrhizal as compared to mycorrhizal plants after 3 days of flooding. A more rapid decline in plant health was also observed in non-mycorrhizal as compared to mycorrhizal seedlings. The presence or absence of the fungal partner led to significant difference in the ratio of roots that remained viable after extended flooding. Therefore, it is clear that arbuscular mycorrhizal (AM) infection confers limited tolerance to flooding on peach seedlings. This could be due to improved plant nutrition, the suppression of ethanol accumulation in roots and the extension of the duration of root activity in a flooded environment.

Continuous measurement of oxygen concentration in citrus soil by means of a waterproof zirconia oxygen sensor

A limiting-current type of zirconia oxygen sensor has been developed and its efficiency was tested for the determination of oxygen in soil air. This oxygen sensor is waterproof and has a very short response time. By the use of the sensor, changes in soil oxygen concentration, due to undecomposed organic material and waterlogging, were observed. The sensor was found to be highly stable in the soil and suitable for continuous oxygen monitoring in the field.

Cyanide metabolism linked with ethylene biosynthesis in ripening processes of climacteric and non-climacteric fruits

Abstract The cyanide metabolism linked with the ethylene biosynthesis was compared with fruits of apple (climacteric type), satsuma mandarin (non-climacteric type) and grape (non-climacteric type) during their development and in storage after harvest. In apple, the rate of ethylene production and β-cyanoalanine synthase activity were very low in young immature fruit, but increased markedly with the onset of ripening. At the same time corresponding increases in the ACC content were observed, whereas the cyanide content was slightly increased. In satsuma mandarin and grape, ethylene production was low during development and maturation, but increased slightly during senescing processes. The β-cyanoalanine synthase activities were extremely low compared with that of apple, although slight increases were observed during maturation through senescing processes. It seems that no bulk induction of β-cyanoalanine synthase is needed for non-climacteric fruits with the onset of ripening. The ACC content in grape was consistently higher than in apple, although the rate of ethylene production was quite low. The cyanide content in grape considerably increased during maturation and ripening processes. The causes of these specificities of grape are not clear at present.

Effects of ethylene and hydrogen cyanide on β-cyanoalanine synthase activity in satsuma mandarin (Citrus unshiu Marc.) fruit

Abstract Exogenous ethylene increased β-cyanoalanine synthase activity in satsuma mandarin fruit. An inward decreasing gradient in the activity was found in ethylene-treated fruit; the highest activity was in the flavedo and the lowest in the juice sacs. β-Cyanoalanine synthase activity in the peel (flavedo and albedo) increased in parallel with increasing ethylene concentrations up to 500 ppm and then leveled off. Green mature fruit were less responsive to ethylene in the induction of β-cyanoalanine synthase activity than more mature fruit. Regardless of ripening stage, the latter group of fruit responded to ethylene to reach similar maximum enzyme activities, which were approximately two-fold greater than those of green mature fruit. 2,5-Norbornadiene, a specific inhibitor of ethylene action, repressed the ethylene-induced increase in β-cyanoalanine synthase activity. Hydrogen cyanide did not induce β-cyanoalanine synthase but rather reduced the activity at high concentrations.

EVALUATION OF THE MYCELIAL NETWORK FORMED BY ARBUSCULAR MYCORRHIZAL HYPHAE IN THE RHIZOSPHERE OF PAPAYA AND OTHER PLANTS UNDER INTERCROPPING SYSTEM

Um experimento foi conduzido em casa-de-vegetacao para observar a distribuicao de hifas de fungos micorrizicos arbusculares (FMA), na rizosfera do mamoeiro intercalado com outras plantas. Para isto foram construidos vasos de acrilico divididos em tres compartimentos. Mudas de mamoeiro (Carica papaya L.) foram transplantadas para um dos compartimentos laterais em todos os vasos, enquanto que mudas de grama batatais (Paspalum notatum Flugge) e milheto (Pennisetum glaucum L. R. Br.) foram separadamente transplantadas para o outro compartimento situado na outra extremidade. Um outro tratamento foi constituido de mudas de mamoeiro em um compartimento e 25% de extrato metanolico de raizes de grama batatais (BRE) ou de milheto (MRE), fracionados em cromatografo de coluna. Um vaso com apenas mudas de mamoeiro foi preparado como testemunha. O compartimento central foi inoculado com o fungo Gigaspora margarita. A densidade de hifas, a percentagem de infeccao micorrizica e o numero de esporos nos compartimentos com grama batatais e milheto foram maiores do que naqueles com mamoeiro. Nos compartimentos com BRE e MRE e algumas hifas e esporos foram observados nestes compartimentos. Naqueles sem planta, foram observadas poucas hifas ou esporos.

Cyanide metabolism linked with ethylene biosynthesis in satsuma mandarin (Citrus unshiu Marc.) fruit

Abstract The cyanide metabolism linked with ethylene biosynthesis was examined with detached satsuma mandarin fruit at different stages of ontogeny. Young immature fruit showed a rapid rise in ethylene production after detaching. Concomitant increases were observed in the β-cyanoalanine synthase activity, ACC and cyanide content with the rise of ethylene production. Moreover, partially yellowing, abscising young fruit on the tree also showed an increased rate of ethylene production, as well as high ACC content and β-cyanoalanine synthase activity. However, the conspicuous increase in ethylene production disappeared as the fruit became larger. Similarly, there was no marked increase in β-cyanoalanine synthase activity. The mechanism of how citrus fruit lose the ability to produce ethylene as they develop remains to be elucidated.