Nitrogen Uptake from Amino Acids in Maize through Arbuscular Mycorrhizal Symbiosis

Maize plants are well colonized with arbuscular mycorrhizal fungi (AMF), which contribute mineral nutrients absorption from soil. However little is known about their role in nitrogen (N) absorption especially from amino acids, which reach a considerable quantity in soils. This experiment was conducted to investigate N acquisition from amino acids through AMF symbiosis. AMF inoculation clearly increased the N content of maize supplied with amino acids (Glu, Ala and Pro). Further study of xylem sap revealed that the composition of amino acids was changed by AMF inoculation. These results indicate that AMF contribute N from amino acids, and may affect the nitrogen assimilation of host plants.

Effects of flooding on arbuscular mycorrhizal colonization and root-nodule formation in different roots of soybeans

In several countries in monsoon Asia, soybean crops are cultivated in upland fields converted from paddies. In such fields, excess soil water often induces extensive damage followed by lower nutrient uptake by this crop. In this study, the effects of flooding during the early growth stage of pot-grown soybeans on arbuscular mycorrhizal (AM) colonization and root nodule formation were investigated. Twenty days after sowing cv. Fukuyutaka, half of the pots were flooded (flooding) and the other half were left unflooded (irrigation). The plants were sampled after 39 days of flooding. Typical morphological alterations to flooding were found, including an enlarged hypocotyl diameter and partial cracking of the surface tissues, and adventitious roots developed on the soil surface. The primary and lateral roots were shorter and the adventitious roots were longer in flooding than in irrigation. In flooding, the ratio of the aerenchyma area to the stele area was 82.5% in adventitious roots. The AM colonization ratio in flooding was significantly lower than in irrigation. The ratio in flooding was markedly low in the primary and lateral roots, but it was not necessarily low in the adventitious roots. Root nodules were formed on the adventitious roots but not on the primary and lateral roots, especially in flooding. These results showing different rates of AM colonization and root nodule formation between the two different types of roots improve the understanding of responses of soybeans grown in paddy-rotated upland fields.

Effect of inoculation with arbuscular mycorrhizal fungi on growth, nutrient uptake and curcumin production of turmeric (<i>Curcuma longa </i>L.)

Profitable turmeric (Curcuma longa L.) production requires adequate nutrients. We have investigated the effect of inoculation with arbus cular mycorrhizal fungi (AMF) on growth, nutrient uptake, yield and curcumin production of turmeric under field and glasshouse conditions. Although AMF inoculation slightly increased plant height, leaf number and shoot N content, no statistical differences were observed in vegetative growth parameters, biomass production, nutrient uptake and curcumin content compared to control plants under field conditions. It was difficult to determine the exact effect of inoculated AMF on turmeric growth because of indigenous AMF. On the other hand, turmeric showed better response to AMF inoculation under greenhouse conditions. AMF inoculation resulted in higher biomass production and nutrient uptake of turmeric. Moreover the concen tration of curcumin, contained in the rhizome of turmeric, increased in AMF treatment. These results indicate that AMF inoculation has beneficial effects on turmeric growth and curcumin production. AMF inoculation to turmeric field would be effective when indigenous soil populations of AMF are low or native AMF are no longer effective.