Changes in Free Sugar Contents through Arbuscular Mycorrhizal Fungus Symbiosis in Tomato Seedlings Raised in a Greenhouse.

Abstract

To estimate the relationship between free sugar contents and growth enhancement through symbiosis of arbuscular mycorrhizal (AM) fungi (Glomus fasciculatum and Gigaspora margarita), we investigated the changes in free sugar contents through AM fungus symbiosis in tomato (Licopersicon esculentum Mill., cv. Momotaro-T 93) seedlings.Five weeks after inoculation, AM fungus infection level in a whole root system reached 17.6% in Glomus fasciculatum, while in Gigaspora margarita, 24.2%, although no major difference between noninoculated and inoculated plants appeared in the plant growth. Regardless of fungus species, total free sugar contents showed greater values in shoots, tap roots and branched roots of AM fungus-infected plants than in noninoculated ones; trehalose was detected in roots of plants infected with each fungus species. Twelve weeks after inoculation, exceeding noninoculated plants, AM fungus-infected plants gave greater values of plant height, proximal diameter of shoots, and dry weight of both shoots and roots, regardless of fungus species. Water contents of both shoots and roots showed similar levels among the treatments. AM fungus infection level showed 25.8% in Glomus fasciculatum, 38.2% in Gigaspora margarita. Total free sugar contents increased in shoots and tap roots of infected plants in both fungus species; the effect was pronounced more in Glomus fasciculatum than in Gigaspora margarita. Free sugar, which caused the increase in total free sugar contents, differed among the parts of the plants. Trehalose was detected in shoots and branched roots in Glomus fasciculatum-infected plants. These results suggest that increase of free sugar contents are closely associated with plant growth enhancement through AM fungus symbiosis in tomato seedlings.