Simultaneous quantification of salicylic acid and indole-3-acetic acid in strawberry plants inoculated with Azospirillum brasilense REC3

GUERRERO MOLINA, MARÍA F.; DIAZ RICCI, JUAN C.; PEDRAZA, RAÚL O.

La Falda

Workshop; II Workshop Latinoamericano sobre PGPR; 2014

Introduction Plant phytohormones are small molecules that regulate vital plant process and responses to biotic and abiotic stimulus. Salicylic acid (SA) is involved in the systemic acquired resistance (SAR) by which plants are provided with a systemic and long-lasting protection against a wide range of phytopathogens. PGPB colonization is often associated with the activation of an induced systemic resistance (ISR) in plants dependent of jasmonic acid and ethylene. Indole-3-acetic acid (IAA) is an auxin implicated in plant growth and development as well as in defence responses. The principal source of exogenous auxin comes from the rizhospheric microbiota. Some species, like Azospirillum brasilense are able to synthesize IAA by four different pathways highlighting the importance of it. The antagonistic or synergic relationships among hormone signalling allow plants to precisely regulate their response to a given stress. Thus, the objective of this work was to evaluate how Azospirillum brasilense REC3 modulates SA and IAA synthesis in strawberry plants.   Materials and Methods In-vitro micropropagated strawberry plants cv. `Camarosa¢¥ were axenically grown in hydroponic culture under controlled conditions (25¨¬C, 70% relative humidity and 16 h of photoperiod). The treatments were: non-inoculated control plants and plants inoculated with Azospirillum brasilense REC3 (106 CFU¡¤ml-1) with triplicates for each sampling time. The production of both phytohormones was quantified simultaneously by HPLC at different hours post-inoculation (hpi): 12, 24, 48, 72, 96 and 120. A C18 column (Prodigy 5 ODS-2, Phenomenex) was used in gradient with 0.1% CH3COOH and 100% CH3OH as mobile phases, monitoring the elution at two wave lengths: ¥ëAIA 280 nm and ¥ëAS 303 nm. SA and IAA content was expressed in ng¡¤mg-1 dry weight (DW). The rate of change was calculated as: (T2-T1/T1)¡¤100; being T1=control plants and T2=A. brasilense REC3-inoculated plants. Results The maximum relative level of SA in REC3-inoculated plants compared to non-inoculated controls was 107% higher at 24 hpi and a significantly decrease was observed after 72 hpi. The content of IAA in plants inoculated with REC3 showed an increasing trend from 12 hpi to 120 hpi. The relative level of IAA in inoculated plants was higher to control plants showing a maximum of 136% at 120 hpi. However, it was also observed a significantly increase of the relative levels of IAA at 12 hpi. Conclusions Salicylic acid content in plants inoculated with A. brasilense REC3 was higher than control plants during the first 48 hpi. SA synthesized by REC3 would have a dual function, acting as a siderophore to improve plant nutrition or activating plant defence via SAR. The quantification of indole-3-acetic acid showed an increasing trend from the first to the last essayed time, with higher values ​​in REC3-inoculated plants compared to control plants being the maximum at 120 hpi. According to these results, there would be a cross-talk between salicylic acid and indole-3-acetic acid pathways in strawberry plants inoculated with A. brasilense REC3.