Solar UV-B radiation modulates phytohormone induction in soybean by insects of different feeding guilds: effects on plant defenses

DILLON, F; CHLUDIL, H; MITHOEFER, A; ZAVALA J.A.

Buenos Aires

Congreso; Fronteras en Biociencia 2; 2016

Max Planck

Although it is well known that solar ultraviolet-B radiation (UV-B) enhances plant defenses, there is less knowledge about the role the phytohormones in these interactions. Here we study in soybean the effects of solar UV-B on phytohormones and defensive traits, such as phenolic compounds and trypsin protease inhibitors (TPIs) induced by lepidopteran larvae (Anticarsia gemmatalis) and thrips (Caliotrhips phaseoli) damage. Two soybean cultivars (cv.) were grown in field conditions under two treatments generated by thick transparent plastics with different transmittance to UV-B: ambient UV-B and attenuated UV-B. Both, lepidopteran larvae and thrips induced jasmonates (JAs) independently of UV-B radiation. Thrips also induced salicylic acid (SA) and 12-oxophytodienoic acid (OPDA) in an UV-B independent-manner, but failed to induce ethylene (ET). Lepidopteran larvae induced ET and, solar UV-B radiation had synergistic effects on ET induction. As expected, flavonols where up regulated by UV-B radiation but herbivory did not affect flavonols production. On the opposite, while the phenolic compound galotannin was induced by herbivory, solar UV-B radiation did not affect the accumulation of this compound. Isoflavonoids and TPI activity were induced by A. gemmatalis damage and UV-B radiation increased their induction. Thrips damage induced TPI activity independently of UV-B, and was unable to increased isoflavonoids concentration. When the ethylene precursor (ACC) was applied exogenously to leaves isoflavonoids concentration increased in leaves, while SA and methyl jasmonate did not induce them. Our results show that ET is involved in the priming effect of UV-B radiation on induction of defenses, and that the application of a precursor of ET is enough to induce isoflavonoids. Based in our results phenolic compounds can be classified in three groups in function of their regulation: isoflavonoids (up-regulated by larvae herbivory, ethylene and UV-B), flavonols (up regulated by UV-B) and the galotannin (up regulated only by herbivory).