R. E. Wilkinson

Sorghum seedling root growth as influenced by H+, CA++, and MN++ concentrations 1

Abstract Root response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP140, SC599, TAM428, SC283, and SC574) were grown in white quartz flintshot sand and watered with 0.01M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 and Ca++ (0, 10, 100 mgl‐1 as CaCl2) or Mn++ (0, 1.4, or 140.0 mgl‐1 as HnCl2). At the acid soil tolerance impact response phase (< 10 days old), Ca++ did not influence initial root growth. Increased H+ concentration inhibited juvenile root growth equivalently in all six cultivars. This inhibition was reversed by exogenous GA3 in Funks G522DR but not in SC283 or SC574. Excess Mn++ (140 mgl‐1) further decreased root growth. Induction of an auxinase inhibitor by GA3 would support a hypothesis of H+ concentration influence on IAA transport and/or availability. Root growth matched IAA water partitioning and exogenous IAA (10‐10 and 10‐9 M) reversed the H+ concentration influence on root growth of SC...

H+, Ca++, and Mn++ influence on sorghum seedling shoot growth

Plant response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP 140, SC 599, TAM 428, SC 283, and SC 574) were grown in white quartz flintshot sand and watered with 0.01 M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 with concurrent treatments of Ca++ (0, 10, 100 mgl‐1 as CaCl2) or Mn++ (0, 1.4, 140.0 mgl‐1 as MnCl2). At the acid soil tolerance impact response phase (<10 days old), Ca++ or Mn++ did not influence seed germination (i.e., radicle exsertion). Ca++ did not influence initial shoot growth. Increased H+ concentration greatly inhibited juvenile shoot growth equivalently in all six cultivars. This inhibition was explicable as an influence of gibberellic acid (GA) availability to the aleurone layer and was explained as an accumulation (partitioning) of GA into lipid cellular constituents. Excess Mn++ further exacerbates this condition by limiting GA biosynthesis.

Sorghum cultivar variation in Ca2+ and aluminum influence on root curvature

Abstract Calcium (Ca2+) and aluminum induced unilateral root growth inhibitions (i.e. root curvature) when applied in agar to one side of sorghum [Sorghum bicolor (L.) Moench] roots. PCMBS (p‐chloromercuribenzenesulfonic acid) (10 mM) stopped the root growth inhibition (i.e. curvature) by aluminum in SC574 and SC283 (acid‐soil‐stress tolerant cultivars) but not in Funk G522DR (acid‐soil‐stress sensitive). PCMBS influenced Ca2+‐induced root growth inhibition (i.e. curvature) in Funk G522DR and SC283, but not in SC574.

Metolachlor influence on growth and terpenoid synthesis

Abstract Height and fresh weight of sorghum ( Sorghum bicolor L. var GA 522 DR) grown in sand were reduced by metolachlor (2-chloro- N -(2-ethyl-6-methylphenyl)- N -(2-methoxy-1-methylethyl) acetamide) (0, 0.125, 0.25, 0.5, or 1 ppmw) applied preemergence. Significantly different responses were obtained from plants grown at two light intensities (270 and 27 μein/m 2 /sec). When grown in nutrient solution containing 0, 0.0156, 0.0625, 0.25, 1, 16, or 64 ppmw metolachlor, shoot and root lengths were inhibited by metolachlor; fresh and dry weights of shoot, root, and total plant decreased as metolachlor concentration increased. Carotene content (micrograms per gram fresh weight) in sorghum leaves was decreased by metolachlor. Specific activity of carotene synthesized from [2- 14 C] mevalonic acid by carrot ( Daucus carota L.) disks was reduced 50% by 10 −5 and 10 −4 M metolachlor. Thus, terpenoid biosynthesis is influenced by metolachlor. Gibberellins are terminal products of plant terpenoid biosynthesis, and GA 3 reverses metolachlor inhibition of growth at specific ratios of GA 3 and metolachlor but not at other concentrations. Thus, one effect of metolachlor on plants may be an inhibition of GA synthesis that results in shoot and root growth reductions as metolachlor concentration increases. Other growth responses of plants to metolachlor are unexplained.

Nifedipine influence on calcium and aluminum absorption in roots of three sorghum cultivars

Abstract A 1,4‐dihydroxypyridine type of ion channel blocker, nifedipine [1,4‐dihydro‐2,6‐dimethyl‐4‐(2‐nitrophenyl)‐3,5‐pyridinedicarboxylate dimethyl ester], was tested on the root absorption of Al3+ and Ca2+ by sorghum [Sorghum bicolor (L.) Moench] cultivars with varying acid stress tolerance. In an acid stress sensitive cultivar, Funk G522DR, nifedipine (1 μM) influenced Ca2+ but not Al3+ absorption. In one acid stress tolerant cultivar, SC574, nifedipine (1 μM) influenced both Ca2+ and Al3+ absorption. In a second acid stress tolerant cultivar, SC283, nifedipine (1 μM) did not influence Ca2+ but did influence Al3+ absorption. Considerable genetic diversity is present in Ca2+ and Al3+ absorption between sorghum cultivars.

Quinone accumulation in S-ethyl dipropylthiocarbamate-treated wheat

Abstract Wheat ( Triticum aestivum L. cv Holley) was grown for 15 days in sand into which S -ethyl dipropylthiocarbamate (EPTC) (0, 15.6, 31.25, 62.5, or 125.0 μg/kg) had been incorporated. Growth was decreased more by EPTC under high light intensity (270 μein/m 2 /sec) than under low light (20 μein/m 2 /sec) intensity. Wheat grown in the dark did not respond to EPTC at these concentrations. In high light intensity, plastoquinone-9, plastohydroquinone-9, α-tocopheroquinone, and α-tocopherol contents (nanomoles per gram fresh weight) increased as EPTC concentration increased. Similar but less marked results occurred at the low light intensity. Plastohydroquinone-9/plastoquinone and α-tocopherol/α-tocopheroquinone ratios increased at both light intensities as EPTC concentration increased. This indicated an EPTC-induced inhibition of plastohydroquinone and α-tocopherol epoxidation. Chlorophyll a and b and total carotenoid contents increased as EPTC concentration increased in plants grown at high light intensities. Changes in the membrane electron carriers contents per unit of chlorophyll or carotenoid (micrograms per milligram of pigment) occurred. As a tentative hypothesis, it is suggested that transmembrane electron transport systems were inhibited, but growth in size (fresh weight per pot) was inhibited more than was synthesis of the various pigments and quinones. Thus, a separation of growth and metabolic response to EPTC was demonstrated.

Consequences of metolachlor induced inhibition of gibberellin biosynthesis in sorghum seedlings

Abstract Forage sorghum [Sorghum bicolor (L.) Moench] cultivars were field evaluated for response to seed protectants CGA 92194, CGA 133205, and flurazole for ability to reverse the activity of metolachlor (2.8 kg a.i./ha) and alachlor (3.36 kg a.i./ha). Funk “G102F” was “tolerant” to metolachlor and alachlor (∼17% decrease in forage production), R. C. Young “Red Top Kandy” was “intermediate” (37–50% inhibition), and AgraTech “GK 83S” was “susceptible” (60–65% inhibition). Average plant heights were decreased 0, 26, and 32% for “G102F,” “Red Top Kandy,” and “GK 83S,” respectively, while numbers of plants/4.57-m row were decreased 19, 70, and 90%, respectively. Resultant average individual plant fresh weights (g/plant) were 104, 200, and 410% of the untreated plants for G102F, Red Top Kandy, and GK 83S, respectively. Thus, metolachlor and alachlor lethal responses were exhibited at a very early stage of sorghum seedling development (

PHYSIOLOGICAL RESPONSE OF LIPID COMPONENTS TO THIOCARBAMATES AND ANTIDOTES

Thiocarbamate herbicide symptomology is consistent with a chronic loss of vital metabolic components on increasing toxicant concentration but not with acute blockage of a central reaction. S -Ethyl dipropylthiocarbamate (EPTC) activity is representative of the thiocarbamate herbicides. EPTC inhibits epicuticular wax synthesis, chloroplast fatty acid synthesis (FAS), “aged” tissue FAS and olelyl desaturase (DE) activity. These EPTC inhibitions of FAS and DE are reversed by 1, 8-naphthalic anhydride (N) and N , N -diallyl-2, 2-dichloroacetamide (R). Protein synthesis is not involved. EPTC-induced betacyanin efflux from “aged” red beet discs is time, temperature and concentration dependent and is reversed by N and R. Wheat root phospholipid content is decreased by EPTC and soybean leaf complex lipid class fatty acid contents are quantitatively and qualitatively altered by μM EPTC. The major response is a drastic decrease in linolenic acid (18:3) content. At high light intensities, wheat and corn growth is inhibited by EPTC. In darkness, neither crop is susceptible to EPTC at the same concentrations which induce growth reductions in the light. Differential penetration is not involved. EPTC inhibits wheat growth more than chlorophyll and carote-noid synthesis. Variation in wheat chloroplast electron carrier ratios indicates inhibition of epoxidation. Inhibition of polyphenol oxidase by EPTC is reversed by N and R. Thus, only the FAS portion of the total plant lipid synthesis is inhibited by the thiocarbamate herbicides. Mitochondrial phospholipid requirements for respiratory control and oxidative phosphorylation indicate that FAS inhibition is sufficient to explain thiocarbamate herbicide toxicity. However, the light intensity influence on plant responses to EPTC indicates the existence of more than one thiocarbamate herbicide mode of activity.

Composition of epicuticular wax on isocoma leaves

Isocoma coronopifolia and I. drumondii incorporated 14CO2 into epicuticular waxes in which free fatty acids and free fatty alcohols constituted 85%-90% of the total wax. Alkane (<5%), ester (<2%), and ketone (<3%) concentrations were low. Rates of synthesis of the major fractions by I. drummondii were uniform over a 24-h period, while 14CO2 recovery shifted from free fatty acids to alcohols in I. coronopifolia wax. Free fatty acids and free fatty alcohols consisted of short-chain alkyl moieties (<C20) with major constituents at C12. The predominance of short-chain, free fatty acids and alcohols suggests that the epicuticular waxes of these plants are relatively hydrophilic compared with other plants and partially explains the observed loss of epicuticular waxes in rainfall and variation in responses of these weedy shrubs to herbicide sprays.

Carotenogenic inhibition by norflurazon in wheat

Abstract Wheat ( Triticum aestivum L. cv Holley) seedlings were exposed to [ N - 14 CH 3 ]norflurazon in nutrient solution studies. The 14 CH 3 group was incorporated into a compound eluting on GLC at a relative retention temperature R f equivalent to n -C 21 H 36 and mass spectrometry validated a 295 MW. The concentration of [ N - 14 CH 3 ]norflurazon and/or R l [ 14 C]norflurazon which resulted in carotenogenesis inhibition was 0.07 μ M in the water contained in the leaves. The concentration of norflurazon required for phytoene accumulation as a mode-of-action was ca. 140 × the concentration of norflurazon required for geranylgeraniol accumulation. Geranylgeraniol accumulated at 1 ppbw (3.2 n M ) norflurazon and phytofluene accumulated throughout the norflurazon concentration series (1 to 1000 ppbw). Carotene content was increased by 1 to 16 ppbw norflurazon but was decreased by 64 ppbw norflurazon. Thus, two modes-of-activity for norflurazon are documented that depend upon concentration of the toxicant in the tissue. Norflurazon demethylation in prephytoenepyrophosphate synthesis resulted in a C 21 conjugate and increased concentrations of GGPP and phytoene in the tissue. At approximately 31 ppbw norflurazon, an inhibition of phytoene dehydrogenation occurred and phytoene accumulated. At 62 ppbw norflurazon, phytofluene hydrogenation inhibition occurred and phytofluene accumulated while β-carotene synthesis was inhibited. These inhibitions may possibly be reversible when substrate concentrations are in excess.