Amounts of extractable phenylalanine ammonia-lyase (PAL; E.C. 4.3.1.5) activity increased in the axes of 3-day-old, dark-grown soybean seedlings IGlyeine max (L.) Merr.] shortly after the seedlings were transferred to glyphosate IAf-(phosphonomethyl)-glychie] solutions. The stimulation of PAL activity in herbicide-treated tissue (as compared to control tissue) was detectable as early as 12 h after treatment, whereas growth inhibition (length, fresh weight and dry weight) was not significantly affected until 24 h on a fresh-weight basis and at 48 h on a dry-weight basis. PAL activity increased with time (12-72 h) in herbicide-treated axes when expressed as activity per gram fresh weight, specific activity, and on a per axis basis. PAL activity stimulation correlated positively with glyphosate concentration from 10"* to 10~' M. PAL activity in control tissues remained nearly constant over the sampling period (12-72 h). Total alcohol-soluble hydroxyphenolic compound levels in treated axes were not significantly different from the control at any sampling period. The total soluble amino acid pool showed a general decrease with time in glyphosate-treated tissues. The phenylalanine pool was lowered with treatment time and the ammonia concentration (per g fr. wt, basis) was increased after treatment. No significant differences were noted in the concentration of soluble protein of glyphosate-treated tissue when compared to controls. Visual effects {stunting, lack of secondary root formation, and necrotic areas) of glyphosate were more obvious in the root than in the hypocotyl. Analysis of various chemical constituents substantiated that other glyphosate effects were more clearly demonstrable in the root than in the hypocotyl or in the intact axis. On a per root basis glyphosate markedly increased PAL activity while reducing free phenylalanine, free tyrosine, soluble hydroxyphenolics, total free amino acids and ammonia content. The effect of glyphosate in the root was greatest on phenyl-' Mississippi Agricultural and Forestry Experiment Station »operating. alanine content, reducing it five-fold. The results indicate that glyphosate could exert its effect through either induction of PAL activity and/or inhibition of aromatic amino acid synthesis.Recently, we postulated that glyphosate might reduce growth in maize {Zea mays L.) by inducing phenylalanine 0031-9317/79/080357-10803,00/0 © 1979 Physiologia Plantarum

Greenhouse and laboratory studies were conducted to evaluate responses of ivyleaf morningglory, pitted morningglory, palmleaf morningglory, and smallflower morningglory to several herbicides in relation to leaf structure, epicuticular wax, and spray droplet behavior. Two- to four-leaf stage plants of each species were highly susceptible to acifluorfen, bentazon, bromoxynil, glufosinate, and glyphosate. However, at the five- to eight-leaf stage, these species were less susceptible, and control was herbicide specific. Spray droplets of these five herbicides had a higher contact angle on ivyleaf morningglory than the other three species with a few exceptions. Stomata and glands were present on both adaxial and abaxial leaf surfaces of all species, and palmleaf morningglory and smallflower morningglory had more of these than did the other two species. Trichomes were present on all species except palmleaf morningglory. Epicuticular wax mass was highest in ivyleaf morningglory (57 μg cm−2) and lowest in smallflower morningglory (14 μg cm−2). Wax consisted of homologous short-chain (< C18) or long-chain (> C20) hydrocarbons, alcohols, acids, and triterpenes. Smallflower morningglory waxes lacked short-chain length components. Triterpenes were absent in palmleaf morningglory and smallflower morningglory epicuticular waxes. Untriacontane (C31 hydrocarbon) and tridecanol (C30 alcohol) were common major long-chain components in waxes of all four species. Heptadecane (C17 hydrocarbon) and octanoic acid (C18) were common major short-chain length wax components in pitted, ivyleaf, and palmleaf morningglory. In spite of some differences in leaf surface structures, wax mass, and wax components among the four species, there was no clear relationship between these parameters and herbicide efficacy.

Laboratory and greenhouse studies were conducted on redvine and trumpetcreeper to characterize leaf surface and wax composition, determine responses of these weeds to glyphosate, characterize the nature of interactions between glyphosate and several selective postemergence herbicides (e.g., acifluorfen, bentazon, chlorimuron, imazaquin, and pyrithiobac) used in soybean and cotton, and determine the effects of various adjuvants on glyphosate activity on both species. Trumpetcreeper was consistently more susceptible to glyphosate than redvine. Glyphosate spray solution droplets had lower contact angle in trumpetcreeper than in redvine. Micro-roughness of the trumpetcreeper adaxial leaf surface was greater due to trichomes and glands compared to that of redvine, which had no trichomes or glands. Stomata or crystal wax deposition on the adaxial leaf surface were not observed in either species. The wax mass per unit area (22 to 37 µg cm−2) was similar regardless of the leaf age in both species. Epicuticular wax consisted of hydrocarbons, alcohols, acids, and triterpenes. Wax composition of young leaves of redvine was relatively hydrophilic (72% alcohols and acids, 24% hydrocarbons) compared to the hydrophobic components (23% alcohols and acids, 49% hydrocarbons) of old leaves. In contrast, wax of trumpetcreeper young leaves was relatively hydrophobic (9% alcohols and acids, 29% hydrocarbons), whereas old leaves had similar levels of hydrophilic and hydrophobic components (28% alcohols and acids, 31% hydrocarbons). Glyphosate mixed with selective postemergence herbicides were antagonistic when applied to redvine and trumpetcreeper, except acifluorfen. Various adjuvants did not increase glyphosate efficacy except ammonium sulfate, which increased glyphosate efficacy when applied alone to trumpetcreeper. These results showed that lower glyphosate efficacy was related to the more hydrophobic nature of redvine epicuticular waxes compared to that of trumpetcreeper.

Soybeans [Glycine max(L.) Merr.] were planted in an untilled, stale seedbed and conventionally tilled seedbed of Sharkey clay (Vertic Haplaquept) at Stoneville, Mississippi, in 1979 and 1980 to determine the feasibility of the stale -seedbed approach for soybean production in the Mississippi River Delta. Chemical weed control included applications of preplant, preemergence, and postemergence herbicides. Prickly sida (Sida spinosaL.) was the dominant weed in all tillage and weed-control systems. Perennial species were observed at harvest mostly in the stale - seedbed plots. Preemergence herbicides reduced the total weight of weeds per plot. Conventional seedbed preparation caused delays in planting of 3 weeks or more. In the presence of adequate soil moisture, yields of ‘Bedford,’ ‘Tracy’, and ‘Bragg’ cultivars from the stale - seedbed planting and areas that had been treated preemergence were always equal to or greater than yields from the tilled - seedbed plantings and areas that had been treated postemergence. In 1980, the hot, dry conditions of the growing season apparently negated any effect from either earlier planting or preemergence vs. post-emergence weed control.

Light enhanced the inhibiting effect of root-fed glyphosate (5 x l'0~* M) on dry weight accumulation of soybean [Glycine max, (L.) Merr.l seedling axes. Inhibition of growth by iight 'was greatest in hypocotyls, whereas by glyphosate it was greatest in roots. A synergistic effect of light and glyphosate on stimulation of phenylalanine ammonia-lyase (PAL, B.C. 4.3.1.5) activity was also demonstrated. In continuous white light PAL activity increased linearly for 4 days in axes of seedlings exposed to glyphosate. Evidence of phytochrome involvement in the light effect was shown. The stimulatory effect of glyphosate on PAL activity was greater in roots than in hypocotyls., Solable hydroxyphenolic compound levels were reduced by glyphosate bot were increased by light on a per axis basis. On a fresh weight basis, hydroxyphenolics were more concentrated in glyphosate-treated than in control tissues in the light. When compared to other amino acids, disproportionate decreases in free pools of phenylalanine and tyrosine occorred in axes of seedlings treated with giyphosate and iight. The effect of light on all measured parameters was mainly in the hypocotyl, while that of glyphosate was primarily in the root. In the light, glyphosate caused increases in levels of giutamine and other amino acids that may be the result of amination reactions, protecting from excess ammonia ,generated by enhanced PAL activity. These results suggest that PAL has a strong influence on its substrate levels in this system and/or that glyphosate inhibits synthesis of aromatic amino acids. 0031-9317/79/080307-11 S03.00/0

C4plants account for a small fraction of the total number of plant species (fewer than 1000 out of 250 000). A larger proportion of the world's weed species possess C4physiology. There are 2000 species in 500 genera and 125 families of flowering plants listed in the WSSA composite list of weeds. of that number, 146 species in 53 genera and 10 families exhibit the C4syndrome. This, as a percentage, is 17-fold greater than the percentage of C4plants in the total world plant population. In this report, we have listed the C4-weed species and provide specific information concerning various aspects of their Kranz anatomy and C4physiology.

Field studies were conducted from 1987 through 1990 on Sharkey clay to determine effect of weed control treatment (WTRT) on yield and net return from soybean grown with no irrigation (NI) or irrigation (I) during reproductive development. Weed control treatments were: 1) PRE glyphosate plus metribuzin plus metolachlor or pendimethalin, followed by POST bentazon plus acifluorfen or 2,4-DB plus linuron (high WTRT); 2) PRE glyphosate at a rate to kill existing weeds at planting (medium WTRT); or 3) PRE paraquat at a rate to desiccate but not necessarily kill existing weeds at planting (low WTRT). POST cultivation was used in all treatments. Weed ground cover in the high, medium, and low WTRT's was composed of annual grass and moderately competitive broadleaf species, and averaged 7, 25, and 49%, respectively, at harvest in 1990. Yield declined with decreasing weed control in the I treatment after the first year, but average net returns from the high and medium WTRT's were not different, and both exceeded average returns from the low WTRT. Yields from the high and medium WTRT's in the NI treatment were not different, and both exceeded yield from the low WTRT. Average net returns from the medium WTRT were greater than those from the high and low WTRT's in all years. Yield increase from irrigation and difference in average net returns between I and NI declined with decreasing weed control.

ABSTRACrThe phenylalanine ammonia-lyase (PAL) inhibitor L-a-aminooxy-fiphenylpropionkc acid (AOPP) was root-fed to Ught-exposed soybean seedUlngs alone or with glyphosate IN-(phosphonomethyl)glycinel to test further the hypothesis that PAL activity is involved in the mode of action of glyphosate. Extractable PAL activity was increased by 0.01 and 0.1 millimolar AOPP. AOPP reduced total soluble hydroxyphenolic compound levels and increased phenylalanine and tyrosine levels, indicating that in vivo PAL activity was inhibited by AOPP. The increase in extractable PAL caused by AOPP may be a result of decreased feedback inhibition of PAL synthesis by cinnamic acid and/or its derivatives. AOPP alone had no effect on growth (fresh weight and elongation) at either concentration, but at 0.1 mifllmolar it slightly alleviated growth (fresh weight) inhibition caused by 0.5 milimolar glyphosate after 4 days. Reduction of the free pool of phenylalanine by glyphosate was reversed by AOPP. These results indicate that glyphosate exerts some of its effects through reduction of aromatic amino acid pools through increases in PAL activity and that not all growth effects of glyphosate are due to reductions of aromatic amino acids.After the molecular mode ofaction ofthe nonselective herbicide glyphosate2 was proposed to be through inhibition of aromatic amino acid synthesis (21) data from other laboratories gave inconsistent support for this hypothesis (8,10,14). The hypothesis was based upon partial reversal of glyphosate's growth-inhibiting effects on duckweed and Rhizobium japonicum by exogenous aromatic amino acids. In seedlings or tissue cultures of higher terrestrial plants, others have found that glyphosate treatment does not always lower levels of free aromatic amino acids (14) and that feeding aromatic amino acids does not always reverse growth inhibition caused by glyphosate (8, 10). Also, Roisch and Lingens (25) found no in vitro effect of glyphosate on the enzymes (chorismate mutase and prephenate dehydrogenase) involved in aromatic amino acid synthesis that Jaworski (21) (11,16,17). In glyphosate-treated plants we and others have found increases in either ammonia or in free amino acids that are early amination products (11,16,17,23). However, we have found that glyphosate caused a decrease in both concentration (per g fresh weight) and content (per plant) of total alcoholsoluble hydroxyphenolic compounds (as assayed with a phosphomolybdic-phosphotungstic reagent) in tissues most affected by glyphosate (11,16,17). Bases for several equivocations that may be made regarding these findings are: (a) reliability of the assay used with qualitative changes in hydroxyphenolic compounds; (b) levels of insoluble and undetected hydroxyphenolic compounds; (c) turnover of hydroxyphenolic compounds. Consequently, our findings do not unequivocally support Jaworski's (21) or our (10,11,16,17) hypothesis.We have sought to clarify this situation by examination of the effects of a PAL inhibitor on glyphosate-caused effects, reasoning that,...