Roger C. Fites

Foliar sensitivity of soybeans to ozone as related to several leaf parameters

The development of the first trifoliate leaf of soybean (Glycine max (L.) Merr.) was followed to determine the relationship between foliar sensitivity to ozone and leaf growth, stomatal resistance, and selected soluble metabolites. Maximum foliar sensitivity to ozone occurred during the latter stage of rapid leaf expansion. At this time relative stomatal resistance was low; levels of protein, amino acids, total soluble sugars, sucrose and starch were decreasing and reducing sugar levels were increasing. As foliar injury subsided, metabolite levels remained low except for total soluble sugars and reducing sugars. Trends in metabolite levels relative to increased foliar sensitivity to ozone were different from trends reported for other species. Results suggest that metabolite pools do not directly relate to foliar sensitivity.

Stress modification of allelopathy ofHelianthus annuus L. debris on seedling biomass production ofAmaranthus retroflexus L.

When added to soil,Helianthus annuus debris from plants grown under various nutrient stresses in the greenhouse and field had a significant negative effect onAmaranthus retroflexus seedling dry weight production. The regression models for dry weight versus total phenolic compounds and the variation in N, P, and K contents of theHelianthus debris were significant. It was possible to partially simulate debris inhibition ofA. retroflexus seedling dry weight production when chlorogenic acid alone was added to the soil instead ofHelianthus debris. The inhibition ofAmaranthus growth byHelianthus debris and chlorogenic acid was not evident when nutrient solution was applied to the soil.

Effects of multiple O3 exposures on carbohydrate and mineral contents of ladino clover

Abstract Ladino clover plants of various ages were exposed for 5 consecutive days for 6 hr/day to either carbon-filtered air or 0.1 ppm O 3 during one of two growth periods (August or April). The plants were grown during June–August and during January–April. Plants were harvested 1 week after receiving the final O 3 exposure. Ozone reduced root, shoot and plant dry weights and total non-structural carbohydrate (TNC, mg/g). Root TNC was not modified by O 3 . When O 3 induced reductions were expressed on a per cent basis, the reductions were identical for the two experimental growth periods. Plant size and TNC content were greater for plants grown during the January–April growth period whereas mineral content (% or ppm) was greater plants from June to August. When mineral content was altered by O 3 (and this varied with growth period), O 3 increased mineral content except for reductions in plant Na (during June–August growth period) and shoot S (determined only for January–April growth period). The potential effects of multiple O 3 exposures on forage quality and quantity are discussed.

Mapping and expression of a bifunctional thymidylate synthase, dihydrofolate reductase gene from maize.

A bifunctional gene (ZmDHFR-TS) encoding dihydrofolate reductase (DHFR) and thymidylate synthase (TS) was cloned from a Zea mays cDNA library. Both of these enzymes are involved in nucleotide biosynthesis, specifically in the formation of thymidine monophosphate (TMP). Comparison of the deduced amino acid sequence with DHFR-TS sequences from three other plant sources revealed over 75% similarity and motifs typical of DHFR-TS proteins. Two copies of the gene were mapped to chromosomes 2 and 4. This represents the first DHFR-TS gene cloned from a monocotyledonous plant. Expression of ZmDHFR-TS was examined in developing kernels and various tissues of maize by RNA gel blot hybridization analysis in order to determine the relationship between expression of this gene and DNA synthesis. RNA transcripts for ZmDHFR-TS accumulated to high levels in developing maize kernels when endosperm cells were undergoing endoreduplication and cell division. Meristematic maize tissues had high levels of ZmDHFR-TS mRNA, but transcripts were barely detectable in RNA isolated from the root elongation zone and from mature leaf tissues.

The appearance of pyrimidine nucleoside and deoxynucleoside kinase activities in peanut axes.

Abstract The appearance of pyrimidine nucleoside and deoxynucleoside kinase activities in peanut axes was followed during the first 96 hr of germination. The activation or synthesis of these enzymes preceded increases in RNA, DNA and fresh weight. The incorporation of DNA precursors into DNA occurred only after the formation of the pyrimidine deoxynucleoside kinases.

Thymidine kinase from peanut seedlings

Abstract Thymidine kinase (ATP:thymidine 5′-phosphotransferase, EC 2.7.1.21) from the hypocotyls of germinating peanuts ( Arachis hypogaea var. N.C.2) required the presence of a divalent cation and a phosphate donor (ATP) for the production of thymidine 5′-monophosphate. The divalent cation requirement could be fulfilled by Mg 2+ , Mn 2+ , Ca 2+ , Cu 2+ and Zn 2+ . Thymidylate phosphatase activity was present in all of the enzyme preparations despite attempts to inhibit this action. The kinase was relatively heat stable up to 60°; further temperature elevation resulted in complete inactivation. The production of TMP was optimal over a pH range of 7·5–9·0. The rate of thymidine phosphorylation was affected by uridine, deoxyuridine, cytidine and deoxycytidine. Partially purified extracts (15–20-fold) of thymidine kinase also phosphorylated the above pyrimidine nucleosides and deoxynucleosides.

Association of thymidine and uridine kinase activities with changes in nucleic acid levels during peanut fruit ontogeny

Abstract Various stages of pegs, cotyledons and embryonic axes from maturing peanut fruits were examined for their ability to phosphorylate thymidine and uridine. Highest specific activities during peg elongation were found just prior to increases in endosperm nuclei and embryo cell numbers. In the developing cotyledons and axes, the net kinase activities of crude extracts reached a maximum 1–2 weeks before maximal RNA and DNA contents were attained. An exception was the apparent lack of any relationship between uridine kinase activities and RNA levels in developing embryonic axes. The present results support the observation that peanut axes are devoid of thymidine and uridine kinases during the first 24 hr of germination, as fully developed fruits had very low specific activities for both of these phosphate transferases.

PYRITHIAMIN IS A COMPETITIVE INHIBITOR OF ATP: THIAMIN PYROPHOSPHOTRANSFERASE (EC 2.7.6.2) FROM DARK-GROWN SOYBEAN GLYCINE MAX (L.) MERR., CV. RANSOM II SEEDLING AXES

Abstract ATP:thiamin pyrophosphotransferase (TPT, EC 2.7.6.2) activity from dark-grown soybean [Glycine max (L.) Merr., cv. Ransom II] cotyledons and embryonic axes was monitored at 24-h intervals from initial water imbibition to 96 h post imbibition. TPT activity increased to a maximum by 48 h in both axes and cotyledons, but was consistently higher in axes. The specific activity of TPT isolated from light-greened axes was approximately 65% above dark-grown controls. No difference was detected between similarly treated cotyledons. TPT purified 132-fold from 48 h dark-grown axes had apparent Km values of 10−6 and 10−5 M for thiamin and GTP, respectively, while apparent Km values for ATP, UTP and CTP were 10−2 M. Pyrithiamin was a competitive inhibitor of soybean TPT with a Ki equivalent to the apparent Km for thiamin.

Thiamin stabilization of thiamin pyrophosphotransferase against in activation by thermal and low pH treatments

Summary Soybean seedling extracts were incubated at temperatures between 27 and 52°C for 10 min prior to determining thiamin pyrophosphotransferase activity. The activity of this enzyme was progressively decreased by increasing incubation temperatures. The addition of 8.2 mM thiamin during incubation prevented enzyme inactivation. Exogenous thiamin also stabilized the soybean enzyme during short term incubation at high H+ ion concentration (pH 4.0) before assay. The presence of 8.2 mM thiamin during incubation of the thiamin pyrophosphotransferases from soybean, rat liver and yeast at 60°C for 10 min minimized inactivation of the enzyme from each of these sources.

Effects of irradiance on amino and organic acid levels in ladino clover

Abstract White clover ( Trifolium repens L. cv. Tillman) plants were grown in a controlled environment chamber with a photosynthetic photon flux density (PPFD) of 550 μmol m −2 sec −1 for 28 days. Second trifoliolate leaves, sampled hourly, displayed varying pool concentration patterns of glycine and serine over the 24 hr sampling period. The 1100–1130 hr time period which reflected high levels of these metabolites was used in subsequent experiments. Plants 28 days old were randomly selected, divided and transferred to Continuous Stirred Tank Reactors (CSTR) gas exposure chambers with PPFD of 285 μmol m −2 sec −1 , or left in the original chamber. Metabolites from the glycolate, glycolytic and the oxidative pentose phosphate pathways were monitored every 24 hr up to 168 hr in each chamber type. The pool concentrations of all metabolites changed within 24 hr following transfer to the lower level of irradiance. Pool concentrations of glycine and serine at low irradiance were always lower than those at the higher irradiance, whereas 6-phosphogluconic acid first increased and then decreased, stabilizing 96 hr after transfer to levels below plants remaining in the controlled environment chamber. The data demonstrated that when plants are grown in one environment and then transferred to another for experimental purposes which include measurement of metabolite levels, adequate acclimation to the second environment is essential before treatments are imposed.