Relationships Between Phenylalanine Ammonia-Lyase Activity and Physiological Responses of Soybean (Glycine max) Seedlings to Herbicides

Abstract

The effects of 16 herbicides from 14 different chemical classes on levels of soluble protein, hydroxyphenolics, anthocyanin, and chlorophyll were determined in light- and dark-grown soybean [Glycine max(L.) Merr. ‘Hill’] seedlings. Growth-reducing concentrations of the herbicides were supplied to 3-day-old dark-grown soybean seedlings in liquid culture. Soluble protein (per axis) was reduced by fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide}, and propanil (3′,4′-dichloropropionanilide) 24 or 48 h after treatment. In light-grown plants, soluble hydroxyphenolic compound levels were decreased on a per axis basis after 48 h by all chemical treatments except by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate}, DSMA (disodium methanearsonate), fluridone, MH (1,2-dihydro-3,6-pyridazinedione), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], TCA (trichloroacetic acid), and 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Total chlorophyll content in hypocotyls of these seedlings was decreased by fluridone, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one], norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone], paraquat, and 2,4-D, but others had no significant effect. Anthocyanin accumulation in hypocotyls of 48-h light-grown seedlings was decreased by atrazine, fenuron (1,1-dimethyl-3-phenylurea), metribuzin, norflurazon, paraquat, propanil, and propham (isopropyl carbanilate). Phenylalanine ammonia-lyase (PAL) activity (previously reported work) was positively correlated with anthocyanin levels in tissues after treatment with these 16 herbicides, but not with glyphosate [N-(phosphonomethyl)glycine]. There was, however, no correlation between extractable PAL activity and chlorophyll, soluble hydroxyphenolic compounds, or soluble protein content. These results indicated that extracted PAL activities usually reflect relative in vivo activities and that PAL activity is limiting to phenylpropanoid synthesis in vivo.

Enzyme Responses of Abutilon Theophrasti in an Enhanced Biocontrol System

“…In some plants, PAL activity was induced by glyphosate, possibly resulting from decreased feedback regulation (Duke and Hoagland, 1978;Hoagland and Duke 1983;Hoagland, 1989). However, the concentration of end products, such as anthocyanin and hydroxyphenol was significantly reduced by the treatment of glyphosate in spite of induction of PAL activity (Hoagland and Duke, 1983). In this study, glyphosate did not significantly affect either the efficacy of C. coccodes or the activities of PAL and peroxidase in A. theophrasti.…”

“…Interestingly, PAL activity in A. theophrasti was reduced when bentazon was applied and the efficacy of C. coccodes was significantly enhanced by the presence of bentazon. Atrazine, diuron, metribuzin, and paraquat, all herbicides that inhibit the photosynthetic electron transport system, reduce PAL activity, although the modes of action are unknown (Hoagland and Duke, 1983;Hoagland, 1989). While PAL indirectly influences structural defense responses early in secondary metabolism at the starting point of the phenylpropanoid pathway, peroxidase is a key enzyme in later stages of cell wall strengthening by polymerizing phenolic compounds.…”

“…Of the carbon fixed by photosynthetic plants, about 20% flows through this highly regulated pathway (Strack, 1997). In some plants, PAL activity was induced by glyphosate, possibly resulting from decreased feedback regulation (Duke and Hoagland, 1978;Hoagland and Duke 1983;Hoagland, 1989). However, the concentration of end products, such as anthocyanin and hydroxyphenol was significantly reduced by the treatment of glyphosate in spite of induction of PAL activity (Hoagland and Duke, 1983).…”

Direct and Indirect Effects of Invasive Plants on Soil Chemistry and Ecosystem Function

“…In a study of the effects of sixteen herbicides on soybean, Hoagland and Duke (1983) found that concentrations of hydroxyphenolics and anthocyanins were either increased or decreased, depending on the herbicide. Glyphosate inhibits the shikimic acid pathway, and thus accumulation of certain plant metabolites is characteristic of glyphosate exposure.…”

Interaction of Glufosinate and <i>Colletotrichum truncatum</i> on Ammonia Levels and Glutamine Synthetase Activity in Hemp Sesbania

“…Another product of PAL catalysis is ammonia. Furthermore, PAL was suggested as a target site for herbicides [59] and PAL activity was shown to be elevated or inhibited by various herbicides [60]. The fungal pathogen Alternaria cassiae, has bioherbicidal activity against sicklepod (Senna obtusifolia) [61] [62] [63], and alters phenylpropanoid metabolism in this weed [64].…”