Changes in cutting composition during early stages of adventitious rooting of miniature rose altered by inoculation with arbuscular mycorrhizal fungi

Many changes in metabolism are known to occur during adventitious root formation, including changes in amino acids, proteins, and carbohydrates. The influence of arbuscular mycorrhizal fungi (AMF) on adventitious rooting of rose was tested by inoculating four cultivars with Glomus intraradices Schenck & Smith. Changes in cutting composition were measured during the initial stages of adventitious root formation. Although there were cultivar-specific differences in response, AMF inoculation generally increased the biomass and number of adventitious roots on cuttings before root colonization was detected. Application of rooting hormone increased this effect. Inoculation with AMF washings also increased the root biomass and number, but only when cuttings were treated with hormone. Changes in cutting composition in response to AMF were detected at 7 to 14 days. Differences in protein concentrations in response to AMF or hormone application were similar, while differences in amino acid and reducing sugar concentrations were not. Concentrations of proteins and amino acids in cuttings at the beginning of the experiment were positively correlated with adventitious rooting, while concentrations of reducing sugars and nonreducing sugars were not correlated with rooting. These results suggests that nitrogen-containing compounds play an important role in adventitious rooting, and that changes in amino acids associated with AMF inoculation were potentially different than those that occurred when cuttings were treated with rooting hormone alone. Carbohydrate concentrations in cuttings were not strongly related to initiation of adventitious roots, but reducing sugar may play a role in regulating part of the response of cuttings to AMF. The response of rose cuttings prior to colonization by G. intraradices suggests that AMF-plant signaling events occurred prior to rooting.