The Effects of Herbicides Targeting Aromatic and Branched Chain Amino Acid Biosynthesis Support the Presence of Functional Pathways in Broomrape

Abstract

It is not clear why herbicides targeting aromatic and branched-chain amino acid biosynthesis successfully control broomrapes—obligate parasitic plants that obtain all of their nutritional requirements, including amino acids, from the host. Our objective was to reveal the mode of action of imazapic and glyphosate in controlling the broomrape Phelipanche aegyptiaca and clarify if this obligatory parasite has its own machinery for the amino acids biosynthesis. P. aegyptiaca callus was studied to exclude the indirect influence of the herbicides on the parasite through the host plant. Using HRT – tomato plants resistant to imidazolinone herbicides, it was shown that imazapic is translocated from the foliage of treated plants to broomrape attachments on its roots and controls the parasite. Both herbicides inhibited P. aegyptiaca callus growth and altered the free amino acid content. Blasting of Arabidopsis thaliana 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and acetolactate synthase (ALS) cDNA against the genomic DNA of P. aegyptiaca yielded a single copy of each homolog in the latter, with about 78 and 75% similarity, respectively, to A. thaliana counterparts at the protein level. We also show for the first time that both EPSPS and ALS are active in P. aegyptiaca callus and flowering shoots and are inhibited by glyphosate and imazapic, respectively. Thus leading to deficiency of those amino acids in the parasite tissues and ultimately, death of the parasite, indicating the ability of P. aegyptiaca to synthesize branched-chain and aromatic amino acids through the activity of ALS and EPSPS, respectively.

Recent research progress in combatting root parasitic weeds

“…Dor et al [197] showed that the main mechanism by which ALS-inhibiting herbicides and glyphosate control P. aegyptiaca is direct inhibition of the enzymes ALS and EPSPS, which are present and active in the parasite tissues. Around the same time, a secondary effect of glyphosate action, inhibition of the translocation of phloemmobile solutes from the tomato to P. aegyptiaca, was indicated [198].…”

Identification of tolerance to metribuzin and imazethapyr herbicides in faba bean

“…Imazethapyr is a systemic herbicide that belongs to IMI class of herbicides (Imidazole) that control weeds by reducing the level of branched‐chain amino acids—isoleucine, leucine, and valine—through the inhibition of acetolactate synthase (ALS), an enzyme common to the biosynthesis of these amino acids. Imazethapyr can control broomrape (Dor et al., 2017; García‐Torres & López‐Granados, 1991; Rubiales & Fernández‐Aparicio, 2012; Tan et al., 2005) and annual weeds (Cantwell et al., 1989).…”

Modes of Herbicide Action

“…DOI: http://dx.doi.org/10.5772/intechopen.105356 herbicides include imazamox, imazapic, imazaquin, imazethapyr, nicosulfuron, metsulfuron, triasulfuron, chlorsulfuron, rimsulfuron, prosulfuron, pyroxsulam, diclosulam, and flumetsulam. In a study conducted by Dor [16], the tissue culture of broomrape was found to be more sensitive to imazapic in which a concentration of 0.05μM significantly decreased the biomass and a concentration of 10μM caused blackening of died callus, which suggests that free amino acid content increased with the increased in the concentration of imazapic as shown in Figure 2.…”