INFLUENCE OF ARBUSCULAR MYCORRHIZAE ON THE METABOLISM OF MAIZE UNDER DROUGHT STRESS

A greenhouse experiment was carried out to investigate the influence of the arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck and Smith) on metabolic changes in tropical maize (Zea mays L.) under drought. Two cultivars, Tuxpeno sequia C0 (drought sensitive) and C8 (drought resistant), were subjected for 3 weeks to water stress following tasselling (75-95 days after sowing). Fully expanded 7th or 8th leaves were sampled and assessed for levels of chlorophyll, sugars, proteins, and amino acids. Chlorophyll content was not altered either by water stress or the presence of mycorrhizae. Mycorrhizal plants (M +) had higher total and reducing sugars than nonmycorrhizal plants (M -) at the end of 3 weeks of the drought cycle. An increase in protein content was observed with drought stress in MS plants of the cultivar C0. Most of the amino acids showed a linear increase during the period of water stress in M + and M - plants for both cultivars. Total amino acids increased by 40.6% and 43.7% in M - plants of C0 and C8, respectively. With the presence of AM fungus, amino acid levels increased by only 10.7% and 19.2% of leaf dry mass in C0 and C8, respectively. Alanine, asparagine, glutamine, and glycine accounted for 70% of the amino acid pool. Under drought, AM inoculation enabled the plants to retain considerable amounts of sugars and proteins, especially in the drought-sensitive cultivar C0. This may be of physiological importance in helping the plant to withstand moderate drought.