The role of endomycorrhizal fungi in iron uptake by Hilariajamesii

Abstract

The semiarid warm season grass galleta [Hilaria jamesii (Torr.)] was used in a series of mycorrhizal experiments to determine the mechanism of enhanced iron (Fe) absorption under conditions of Fe deficiency.

Galleta was grown from seed in sterilized soil which had either been infested with mycorrhizal fungi or left uninfested. The four fungal species used to infest the soil were Glomus albidum, Glomus fasciculatum, Glomus macrocarpum, and Glomus mosseae. After 85 days of growth, the nonmycorrhizal and mycorrhizal plants were removed from the soil and placed in complete Hoagland's hydroponic nutrient solutions with phosphorus (P) at 1/5 the normal concentration. Galleta, grown hydroponically from seed, was used as a second nonmycorrhizal control. At the end of ten days of growth, the plants were transferred to Hoagland's nutrient solution at 1/5 the phosphorus concentration and without Fe. The plants were grown for twenty days in this solution; at the end of the growth period, all of the treatments exhibited marked Fe deficiency symptoms.

The initial rate uptake studies were run on excised roots for five minutes in 0.5 μM ⁵⁹FeHEDTA. The desorbed roots were weighed and counted to determine the amount of ⁵⁹Fe absorbed. Additional samples of the roots were assayed with the bacterial (Arthrobacter flavescens ATCC 25091) bioassay for Fe‐chelate. In all of the radioiron uptake studies, the mycorrhizal plants absorbed greater amounts of Fe than did either of the two controls. All of the mycorrhizal treatments assayed positive for siderophore (Fe‐chelate) activity. These results suggest that in the natural environment where Fe availability is limited, a major factor in the mycorrhizal plants’ capability to absorb Fe is its capacity to produce siderophores for the chelation and transport of Fe into its tissues.

Key words:

• Endomycorrhizae
• Mycorrhizae
• Iron uptake
• Hilaria jamesii
• Siderophore
• Arthrobacter flavescens
• Galleta