Arbuscular mycorrhizae and nitrogen assimilation in maize after drought and recovery

Abstract

In a greenhouse experiment, the effect of arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) colonization on N assimilation in maize (Zea mays L.) was examined after well‐watered, drought and recovery periods. Seeds of selection cycles C0 (drought‐sensitive) and C8 (drought‐resistant) of the tropical maize cultivar Tuxpeño sequía were used for this study. Maize plants were exposed or not to drought stress for 3 weeks (45‐65 days after sowing, DAS) followed by 3 weeks of recovery (66‐86 DAS) at the preflowering stage. Root and shoot samples harvested at the end of the drought or well‐watered and recovery periods were determined for key enzymes involved in N assimilation (NR, nitrate reductase; NiR, nitrite reductase; GS, glutamine synthetase; GOGAT, glutamate synthase), protein and amino acid concentrations, and total N contents. Drought stress significantly (P ≤ 0.01 or P ≤ 0.001) decreased all the enzyme activities except NiR in the roots and shoots of both cultivars. After 3 weeks of drought, the AM roots of both cultivars had higher activities of NR (C0, 45%; C8, 26%), GS (C0, 76%; C8, 33%) and GOGAT (C0, 41%; C8, 53%) than non‐AM roots and were comparable to well‐watered plants. These enzyme activities were also enhanced in drought‐stressed AM shoots of C0 and C8. Total amino acid concentrations in AM plants of C0 were 4.6 and 1.6 times higher in roots and shoots, respectively, compared to non‐AM plants. The predominant amino acids detected were Ala, Arg, Asn, Asp, Gln and Glu which constituted approximately 56 and 75% of the total pool in roots and shoots, respectively. Soluble proteins and total N contents were also higher in AM plants than non‐AM plants under drought conditions. The enhancement of N‐assimilating enzymes and nitrogenous compounds in maize may indicate a transfer of NO3− through the extraradical mycelium or increased N assimilation due to the AM symbiosis. Our overall results suggest that AM association plays an important role in enhancing N assimilation or N nutritional status which enables the host plant to withstand drought conditions and recover after stress is relieved.

Arbuscular Mycorrhizal Fungus Inoculation on Antioxidant Enzyme Activities in Maize Plants at Different Levels of Fe and Zn Fertilization

“…The increase in soluble protein concentrations in mycorrhizal inoculated maize plants corresponded with earlier reports (Mathur and Vyas, 1996;Subramanian and Charest, 1998). Arines et al, (1993) also detected two to six fold increases in soluble proteins in mycorrhizal clover roots.…”

Effects of AM colonization on “wild tobacco” plants grown in zinc-contaminated soil

“…Arbuscular mycorrhizal (AM) symbiosis is a very ancient interaction between plant roots and zygomycetes fungi (Morton & Benny 1990). It is believed that AM symbiosis occurs in over 90% of terrestrial plants; it significantly increases tolerance to drought, nutrient deficiency, cold or warm temperature, and, in some cases, heavy metal contamination , Davies et al 2001, Paradis et al 1995, Subramanian et al 1997, Subramanian & Charest, 1998. Recent phytoremediation studies that incorporated the AM-variable have had mixed findings.…”

Arbuscular mycorrhizae and soil/plant water relations

“…AM symbiosis can also alter plant water relations and responses to drought (Augé 2001). In many instances these AM-induced changes have been interpreted as improved drought resistance (e.g., Davies et al 1993;Ruiz-Lozano and Azcón 1995;Subramanian and Charest 1998;Porcel et al 2003).…”

“…AM symbiosis can also alter plant water relations and responses to drought (Augé 2001). In many instances these AM-induced changes have been interpreted as improved drought resistance (e.g., Davies et al 1993;Ruiz-Lozano and Azcón 1995;Subramanian and Charest 1998;Porcel et al 2003).Studies of mycorrhizal water relations have almost always focused on how AM fungi affect the plant. There is growing interest in the effects of AM fungi on the soil itself, and we have begun testing the possibility that "mycorrhizal soil" may somehow directly influence plant physiology, regardless of whether the plant itself is mycorrhizal.…”