Bruce N. Smith

Effect of Paclobutrazol on the Activities of some Enzymes of Activated Oxygen Metabolism and Lipid Peroxidation in Senescing Soybean Leaves

Summary Nineteen-day-old soybean [Glycine max (L.) Merr. cv. A 2] plants were treated with soil-applied paclobutrazol, an antigibberellin growth inhibitor, at the rate of 125 µg per 10 cm pot. The plants were then grown for 14 days under a 14 hr photoperiod after which they were transferred to the dark for senescence induction. At the end of the 14 day period in the light, treated plants exhibited higher chlorophyll (Chl) content and higher activities of catalase and glycolate oxidase compared to controls. In contrast, control leaves had higher activities of superoxide dismutase and a higher content of malondialdehyde (MDA), a product of lipid peroxidation. Upon transfer to dark, Chl and protein content declined in both control and treated plants, but the decline was much faster in controls. The activity of catalase declined markedly in controls while remaining constant in reated plants. Peroxidase and superoxide dismutase activities and MDA content increased in controls in the dark but remained relatively constant in treated plants. These results suggest that paclobutrazol delays dark-induced senescence in attached soybean leaves and that this delay is associated with the maintenance of catalase activity and the prevention of the senescence-linked rise in peroxidase activity and lipid peroxidation.

Carbon isotope ratios of soil organic matter and their use in assessing community composition changes in Curlew Valley, Utah

SummaryStable carbon isotope ratios of roots and soil organic matter were measured in Curlew Valley, Utah to determine if changes in the relative dominance of two shrub species had occurred in this salt-desert community. Measurements were made on soil cores along transects stretching from monospecific stands of Ceratoides lanata, a C3 shrub, to monospecific stands of Atriplex confertifolia, a C4 shrub. δ13C values of roots and soil organic matter under Ceratoides cover appeared to be in equilibrium with the current plant community. By contrast, δ13C values of roots and soils under Atriplex portions of the transects were more negative than would be expected for a C4-dominated community. These results indicate that a change in relative C3/C4 dominance has occurred, and suggest that the C4 shrub Atriplex confertifolia is increasing in importance in this salt-desert community.

A respiration based description of plant growth rate responses to temperature

Abstract. The temperature dependence of metabolic rates determines how plant growth rates vary with temperature. This paper shows that equations on physiological relations between respiration rates (i.e. rates of heat loss and CO2 evolution) and growth rates can be used to describe temperature effects on plant growth rate. Incorporating measured values of plant respiratory heat and CO2 rates at a few temperatures into the equations allows description of growth rates as a function of temperature and provides a physiological basis for understanding the effects of temperature on growth rate. The paper presents data on cabbage (Brassica oleracea L. Capitata) and tomato (Lycopersicon esculentum Miller cv. Ace) as model cool-climate and warm-climate cultivars to illustrate application of the methods in determining optimal growth climates for different cultivars, accessions, and ecotypes. The respiration-based calculations of growth rate vs. temperature yield curves for both species that are consistent with known temperature-growth requirements. We conclude that plant responses to temperature can be accurately predicted in detail from respiration rate measurements and the growth-respiration model. These studies demonstrate that the temperature dependence of growth rates is a function of the temperature dependencies of both metabolic rates and metabolic efficiency, which change continuously with temperature. The ultimate cause of high- and low-temperature growth limits is commonly not membrane phase transitions or enzyme denaturation as has been supposed, but is loss of substrate carbon conversion efficiency. The results show that “plant temperature stress” has been misunderstood and must be redefined because there is no “nonstressfull temperature”.

Natural Abundance of the Stable Isotopes of Carbon in Biological Systems

About 99% of all carbon is the 12C isotope while 1% is 13C. The other isotopes of carbon are, by comparison, extremely rare. For instance, only about one atom in every 1012 carbon atoms is 14C. The precise ratio of the isotopes will vary depending on the material analyzed. Limestones, atmospheric C02, marine algae, and land plants each possess characteristic 13C/12C ratios, differing slightly from one another. The lowest ratio so far observed is for carbon from ancient blue-green algal mats (Kaplan and Nissenbaum, 1966) and the highest for carbonate carbon from meteorites (Clayton, 1963). Fractionation of plant carbon is brought about primarily by carbon dioxide assimilation in photosynthesis and is due to preferential utilization of 12C and exclusion of 13C. Curiously enough, it has been found recently (Tregunna et al., 1970) that higher plants which fix carbon dioxide via the Calvin cycle pathway differ in 13C/12C ratios from plants which fix carbon dioxide via the C4-dicarboxylic acid pathway. Thus, it is now possible to determine whether a given sample of sucrose was synthesized in sugarcane or in sugar beet. While it is the aim of this paper to discuss a few recent studies on naturally-occurring 13C/12C ratios of biological materials, it is pertinent to note that the subject has been reviewed from a geochemical viewpoint (Bowen, 1966; Degens, 1969; Kroepelin, 1966; McMullen and Thode, 1963; Schwarcz, 1969). The various isotopic species of an element differ slightly in chemical properties from one another. Just as the chemical properties of different compounds determine their formation under various conditions, so the chemical properties of different isotopic species of the compounds will determine how the isotopic abundances distribute themselves in nature. Thus substitution

INTERACTIVE EFFECTS OF SODIUM CHLORIDE AND CALCIUM CHLORIDE ON THE ACCUMULATION OF PROLINE AND GLYCINEBETAINE IN PEANUT (ARACHIS HYPOGAEA L.)

Abstract Many plants, including peanut ( Arachis hypogaea L.), when exposed to salinity stress produce the osmoticants: proline and glycinebetaine. Calcium ions also play a role in osmoprotection. During germination of peanut seeds subjected to NaCl salinity stress, proline and glycinebetaine concentrations in the embryonic axis increased continuously. A further increase in glycinebetaine concentration was observed with the addition of calcium chloride to the sodium chloride. The effects of sodium and calcium are thus additive in causing accumulation of glycinebetaine. Calcium appears to confer greater osmoprotection to the seedling exposed to salinity in this way. Two enzymes play an important role in controlling the level of proline. Proline oxidase catalyzes the conversion of proline to glutamate, thus reducing the concentration of proline. Another enzyme, γ-glutamyl kinase, plays an important role in the synthesis of proline. Addition of calcium chloride to NaCl-stressed seedlings lowered the proline concentration by increasing the level of proline oxidase and decreasing γ-glutamyl kinase activities. Salinity stress, in the absence of calcium, increased proline due to reduced proline oxidase activity and increased γ-glutamyl kinase activity both in the cotyledons and embryonic axis of peanut seedlings. Thus calcium ions increase glycinebetaine production but decrease proline levels in NaCl stressed peanut seedlings.

Distribution of biomass of species differing in photosynthetic pathway along an altitudinal transect in southeastern Wyoming grassland.

SummaryBased on the physiological characteristics and responses of C3, C4, and CAM plants to environmental factors, it is generally predicted that C4 and CAM plants will become more abundant with increasing temperature and decreasing precipitation. To test this prediction, the relative contribution of each photosynthetic type to total plant community biomass was examined at seven study areas along an altitudinal transect in southeastern Wyoming grassland. In going from high (2,652 m) to low (1,405 m) elevation along this transect, mean annual temperature increased and annual precipitation decreased.The percentage of C4 biomass composing each study area decreased with increasing elevation, while the percentage of C3 biomass increased. All elevations had a significantly higher percentage of C4 biomass in August than in June, reflecting the warm season growth characteristic of C4 plants. Regressions of relative abundance of photosynthetic types on climatic variables showed that both mean annual temperature and annual precipitation were equally reliable as predictors of C3−C4 biomass, although we feel that temperature is of primary importance in explaining our observations. CAM species were present at all elevations, but showed no trends in biomass distribution with respect to elevation.

Insect herbivory on C3 and C4 grasses

SummaryThis study tested the hypothesis that grasses with the C4 photosynthetic pathway are avoided as a food source by insect herbivores in natural communities. Insects were sampled from ten pairs of C3−C4 grasses and their distributions analyzed by paired comparisons tests. Results showed no statistically significant differences in herbivore utilization of C3−C4 species. However, there was a trend towards heavier utilization of C3 species when means for both plant groups were compared. In particular, Homoptera and Diptera showed heavier usage of C3 plants. Significant correlations between insect abundances and plant protein levels suggest that herbivores respond to the higher protein content of C3 grasses. δ13C values for six of the most common grasshopper species in the study area indicated that three species fed on C3 plants, two species fed on C4 plants, and one species consumed a mixture of C3 and C4 tissue.

Vesicular-arbuscular mycorrhizae of weedy and colonizer plant species at disturbed sites in Utah

SummaryA survey was made of weedy plant species found on distubed sites in Utah. Of the 74 species sampled, 57% were found to contain VA mycorrhizae. Mycorrhizal and nonmycorrhizal species strictly followed taxonomic divisions, regardless of growth habit. Nonmycorrhizal species were members of the Amaranthaceae, Brassicaceae, Capparidaceae, Caryophyllaceae, Chenopodiaceae, Papaveraceae, Polygonaceae, Portulacaceae, Rubiaceae, and Zygophyllaceae.Cover data were obtained for all plant species, including nonweedy species, colonizing seven of the disturbed sites. Flat semiarid sites were dominated by nonmycorrhizal species. The proportion of mycorrhizal plant cover may be related to water availability. Rocky, sloping sites were dominated by mycorrhizal species. Disturbance by fire did not cause a significant change in the mycorrhizal component of the community.

Kinetics of plant growth and metabolism

Abstract Direct measurements of plant growth rates in terms of volume, length, net photosynthate, etc. provide little information concerning the mechanism of adaptation of metabolism to an environment. To derive the mechanism, metabolic properties must be measured as functions of environmental variables. Growth rates may be limited by the availability of nutrients including fixed carbon, by climate, by other environmental factors including toxins, or by the genetically determined properties of the plant. But in all cases, growth rate is equal to a function of respiration rate and efficiency. For a plant to thrive, its respiratory metabolism as well as its photosynthetic metabolism must be closely adapted to the seasonal and daily variations in the environment. Thus, measurement of respiratory properties is necessary for understanding plant adaptation. In terms of readily measurable respiratory variables, the rate law for growth driven by aerobic respiration is R SG =R CO 2 ϵ C 1−ϵ C =rR O 2 ϵ C 1−ϵ C =−R CO 2 Δ H CO 2 η H Δ H B = − Δ H CO 2 R CO 2 −R q Δ H B where RSG is the specific growth rate, RCO2 the specific rate of CO2 evolution, ϵC the fraction of substrate carbon converted into structural biomass or the substrate carbon conversion efficiency, r the respiratory quotient, RO2 the specific rate of O2 uptake, ΔHCO2 the enthalpy change for combustion of substrate per mole of CO2, ηH the fraction of enthalpy produced by oxidation of substrate that is conserved in the biomass synthesized through anabolism (i.e. the enthalpic efficiency), and ΔHB is the enthalpy change for conversion of substrate into structural biomass per C-mole. ΔHCO2 can be obtained from Thornton’s rule, and ΔHB from either heat of combustion or composition data or from growth measurements. Calorespirometric measurements can then be used to obtain values for ϵC and ηH. Measurements of RCO2(or of r and RO2) and the metabolic heat rate, Rq, as functions of environmental variables thus, can be used to rapidly ascertain the growth and metabolic responses of plants to environmental variables. This model and calorespirometric measurements are used to predict the responses of plant growth to differing climates, to predict the global gradient of plant species ranges and diversity, and to predict global treeline temperature conditions. Growth-season temperature and temperature variability are found to be major determinants of growth rates and distributions of plants. These findings may be useful in predicting the response of plants to climate changes.

Manganese accumulation along Utah roadways : a possible indication of motor vehicle exhaust pollution

Abstract An organic manganese compound is currently added to gasoline to replace tetraethyl lead as an antiknock fuel additive in the USA and Canada. Combustion exhaust gases contain manganese oxides. Manganese oxides are known to cause various deleterious health effects in experimental animals and humans. A field survey of roadside soil and plants in central Utah revealed that soil manganese concentrations in high traffic areas were up to 100-fold higher than historic lead levels. Soil manganese concentrations were highly correlated with distance from the roadway. Lead concentrations seem to have changed little from values reported twenty years ago but may have moved deeper into the soil profile. In addition, roadside aquatic plants were higher in leaf tissue manganese than herbs or grasses. Plant tissue manganese content was better correlated with plant type, traffic volume and microhabitat than with distance from the roadway. Submerged and emergent aquatic plants were sensitive bioindicators of manganese contamination. Roadside snow melt and water samples were low in manganese and lead content. We conclude that roadside soil and plants were apparently contaminated by manganese oxides from Mn-containing motor vehicle exhaust. Manganese concentrations in soil and in some plant species along impacted roadsides often exceeded levels known to cause toxicity.