Copper and herbivory lead to priming and synergism in phytohormones and plant volatiles in the absence of salicylate-jasmonate antagonism

Abiotic stress factors can interfere with the emission of herbivore-induced plant volatile organic compounds (VOCs) and thus disrupt chemical communication channels between plants and other organisms. We investigated whether copper (Cu) stress alone or in conjunction with insect damage modifies the kinetics of (1) VOCs, (2) the VOC-inducing phytohormone jasmonic acid (JA) and (3) its putative antagonist salicylic acid (SA). Hydroponically grown Zea mays exposed to 10 and 80 µM of Cu showed no increases in JA or VOC levels in the absence of herbivory. However when challenged by herbivores, Cu (80 µM) caused ROS generation in root tissues and primed for increased JA accumulation and VOC emission in leaves. SA synthesis was equally primed but higher concentrations were also apparent before insects started feeding. In contrast, plants grown at 10 µM Cu did not differ from controls. These results show that abiotic and biotic stresses result in concentration-dependent, non-additive defense responses. Further support is given to the notion that JA-SA antagonism is absent in Z. mays.     

The Role of Free Indole-3-acetic Acid (IAA) Levels, IAA Transport, and Sucrose Transport in the High Temperature Inhibition of Primary Root Development in Pea (Pisum sativum L. cv. Alaska)

apd: 15 September 2000     

Is there a relationship between branched amino acid pool size and cell cycle inhibition in roots treated with imidazolinone herbicides?

Excised pea root tips were cultured in White's medium for 24 h and then treated for 12 h with one of the imidazolinone herbicides at 0.2, 2, 20, or 200 μM. Pursuit and Assert were almost ineffective in inhibiting the mitotic index (MI), except at the highest concentrations. Arsenal (ARS) and Scepter both showed good inhibition with 20 μM by 8 h. Adding all three branched amino acids (BAA) (VAL, ILE, and LEU) at 0.1 mM blocked herbicide action. Treatment with the BAAs singly had no protective effect. Experiments were performed to determine the BAA pool size and MI after an 8-h treatment with ARS at 2 and 200 μM and Chlorsulfuron (CS), a sulfonylurea herbicide, at 28 nM. Both CS and ARS at 200 μM inhibited the MI to almost 0 by 8 h. ARS at 2 μM inhibited the MI by about 40%. The BAA pool size in all three treatments was reduced by approximately 50%, whether the MI was totally blocked or not. The 1-mm root tips had a greater amount of VAL than did the mature portions of the roots, whereas ILE and LEU were slightly less in the root tip. Other soluble amino acids did not show consistent differences between herbicide-treated roots and controls. The implications of the pool size reduction, in instances where the MI was not totally inhibited, is discussed in light of new data from other laboratories on the mode of action of the imidazolinone herbicides.