Glomus intraradices causes differential changes in amino acid and starch concentrations of in vitro strawberry subjected to water stress

The effect of colonization of tissue-cultured strawberry (Fragaria x ananas sa Duch. cv. Kent) plantlets in vitro by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices on plantlet response to poly(ethylene glycol) (PE G)-8000-induced water stress was investigated. The plantlets were inoculate d axenically and co-cultured with the AMF for 4 wk, then transferred to 15% PEG-8000 solutions for 4, 8 and 12 h. Relative water content, water potent ial, osmotic potential, leaf conductance for water vapour diffusion and pho tosynthetic efficiency as estimated by chlorophyll a fluorescence were all affected by the PEG treatment and its duration but not by the presence of t he intraradical phase of the AMF. However, distinct differences in PEG-indu ced changes in amino acid content were observed between nonmycorrhizal and mycorrhizal plantlets. In the latter, the treatment with PEG caused a subst antial decrease in asparagine levels in leaves that was accompanied by a ma rked increase in asparagine concentration in roots. The opposite was observ ed in nonmycorrhizal plantlets. Furthermore, concentrations of aspartic aci d, serine, threonine, amino-N-butyric acid, alanine and starch increased in roots of mycorrhizal and decreased in nonmycorrhizal plantlets. Our result s suggest the presence of a mobile pool of asparagine that can be transloca ted from leaves to roots or vice versa in response to PEG-induced water str ess, depending on the mycorrhizal status of the plantlets. These opposite p atterns suggest different strategies of mycorrhizal and nonmycorrhizal plan tlets to water stress, which seem to involve different adjustments in nitro gen and carbon metabolism.