Biomedical subjects

C D Raper

Publications and source records attributed to C D Raper.

45 records · Page 3Linked to original sources

PubMed1984

Alterations in internal partitioning of carbon in soybean plants in response to nitrogen stress.

Alterations in internal partitioning of carbon were evaluated in plants exposed to limited nitrogen supply. Vegetative, nonnodulated soybean plants (Glycine max (L.) Merrill, 'Ransom') were grown for 21 days with 1.0 mM NO3- and then exposed to solutions containing 1.0, 0.1, or 0.0 mM NO3- for a 25-day treatment period. In nitrogen-limited plants, there were decreases in emergence of new leaves and in the expansion rate and final area at full expansion of individual leaves. As indicated by alterations in accumulation of dry weight, a larger proportion of available carbon in the plant was partitioned to the roots with decreased availability of nitrogen. Partitioning of reduced nitrogen to the root also was increased and, in plants devoid of an external supply, considerable redistribution of reduced nitrogen from leaves to the root occurred. The general decrease in growth potential and sink strength for nutrients in leaves of nitrogen-limited plants suggested that factors other than simply availability of nitrogen likely were involved in the restriction of growth in the leaf canopy and the associated increase in carbon allocation to the roots.

Ammonia↗

PubMed1982

Relative Content of NO(3) and Reduced N in Xylem Exudate as an Indicator of Root Reduction of Concurrently Absorbed NO(3).

It is unclear if the relative content of NO(3) (-) and reduced N in xylem exudate provides an accurate estimate of the percentage reduction of concurrently absorbed NO(3) (-) in the root. Experiments were conducted to determine whether NO(3) (-) and reduced N in xylem exudate of vegetative, nonnodulated soybean plants (Glycine max [L.] Merr., ;Ransom') originated from exogenous recently absorbed (15)NO(3) (-) or from endogenous (14)N pools. Plants either were decapitated and exposed to (15)NO(3) (-) solutions for 2 hours or were decapitated for the final 20 minutes of a 50-minute exposure to (15)NO(3) (-) in the dark and in the light. Considerable amounts of (14)NO(3) (-) and reduced (14)N were transported into the xylem, but almost all of the (15)N was present as (15)NO(3) (-). Dissimilar changes in transport of (14)NO(3) (-), reduced (14)N and (15)NO(3) (-) during the 2 hours of sap collection resulted in large variability over time in the percentage of total N in the exudate which was reduced N. Over a 20-minute period the rate of (15)N transport into the xylem of decapitated plants was only 21 to 36% of the (15)N delivered to the shoot of intact plants. Based on the proportion of total (15)N which was found as reduced (15)N in exudate and in intact plants in the dark, it was estimated that 5 to 17% of concurrently absorbed (15)NO(3) (-) was reduced in the root. This was much less than the 38 to 59% which would have been predicted from the relative content of total NO(3) (-) and total reduced N in the xylem exudate.

Journal Article↗

PubMed1982

Fatty Acid Composition and Nitrate Uptake of Soybean Roots during Acclimation to Low Temperature.

Fatty acid composition of old and new roots was determined for soybeans (Glycine max [L.] Merr. cv Ransom) at root-zone temperatures of 14, 18, and 22 degrees C during a 26-day period. New roots had a greater concentration of polyunsaturated fatty acids than old roots. The ratio of polyunsaturated to saturated fatty acid concentration in new roots exposed to 14 and 18 degrees C peaked at 16 days and declined, while the corresponding ratio in old roots increased throughout the treatment period. Apparently the response of fatty acid composition in old and new roots to low temperature was mediated by tissue aging or differentiation. These findings were contrary to the concept that modifications in fatty acid composition remain constant at lower temperatures.The function of root tissues exposed to lower temperature was evaluated with respect to the ability of the root systems to absorb NO(3) (-). Over the relatively long periods of exposure, the ability of whole root systems to absorb NO(3) (-) was similar at cool and warm temperatures. The effect of cool temperature on functioning of roots appeared to involve reductions in the rates of initiation and differentiation of young root tissues rather than changes in membrane permeability related to alteration of fatty acid composition.

Journal Article↗

PubMed1981

Nitrate Reduction in Roots as Affected by the Presence of Potassium and by Flux of Nitrate through the Roots.

Dark-grown, detopped corn seedlings (cv. Pioneer 3369A) were exposed to treatment solutions containing Ca(NO(3))(2), NaNO(3), or KNO(3); KNO(3) plus 50 or 100 millimolar sorbitol; and KNO(3) at root temperatures of 30, 22, or 16 C. In all experiments, the accelerated phase of NO(3) (-) transport had previously been induced by prior exposure to NO(3) (-) for 10 hours. The experimental system allowed direct measurements of net NO(3) (-) uptake and translocation, and calculation of NO(3) (-) reduction in the root. The presence of K(+) resulted in small increases in NO(3) (-) uptake, but appreciably stimulated NO(3) (-) translocation out of the root. Enhanced translocation was associated with a marked decrease in the proportion of absorbed NO(3) (-) that was reduced in the root. When translocation was slowed by osmoticum or by low root temperatures, a greater proportion of absorbed NO(3) (-) was reduced in the presence of K(+). Results support the proposition that NO(3) (-) reduction in the root is reciprocally related to the rate of NO(3) (-) transport through the root symplasm.

Journal Article↗

PubMed1979

Growth and Specific Nodule Activity of Soybean during Application and Recovery of a Leaf Moisture Stress.

Soybean plants growing at day/night temperatures of 30/18, 26/18, and 22/18 C were subjected to a single drying and recovery cycle during an 18- to 19-day period in the early to midpod development stage. Leaf total electrochemical water potential was reduced to about -24 bars during the 4-day drying cycle at all temperatures, but recovered to control levels upon rewatering. The changes in dry matter accumulation in whole plants and plant parts, specific activity of nodules as measured by acetylene reduction, and levels of adenosine phosphates in nodules were measured periodically during stress and recovery.Vegetative and reproductive growth were about equally suppressed by the leaf moisture stress. Both rate of appearance and number of pods were reduced. However, a similar average weight per pod for both stressed and control plants at the conclusion of the recovery period suggests that individual pod development is not irreversibly affected by a single stress cycle and that yield potential is restricted by a decrease in number of pods or seed. Dry matter accumulation in plants and pods was unaffected by temperature.Specific nodule activity and energy charge of nodules declined concurrently with leaf moisture potential. Recovery of specific nodule activity following rewatering lagged behind recovery of leaf moisture potential, but energy charge of nodules recovered as rapidly as leaf moisture potential upon rewatering. Thus, the delayed recovery of specific nodule activity does not appear to be related to recovery of energy charge of the nodules.

Journal Article↗

PubMedDate not supplied

Photoperiod regulation of floral initiation for soybean plants at different ages.

Soybean plants [Glycine max (L.) Merr.] of the determinate cultivar Ransom growing in controlled environments under 16-h photoperiods were exposed to 10, 12, 14, 15, and 16-h photoperiods upon expansion of either the two primaries or fifth trifoliolate leaf (V1 and V6 developmental stages, respectively) to determine the influence of plant size on sensitivity to photoperiod. Plants were sampled at 2 to 3-day intervals over a 21-day treatment period and examined microscopically for evidence of floral development. Time of floral initiation for plants exposed to photoperiod treatments at either V1 or V6 stage varied only by a few days among photoperiods, but the subsequent differentiation of floral primordia was much more rapid at shorter than at longer photoperiods. These results confirm previous observations for plants transferred upon expansion of the first trifoliolate leaf (V2 stage) and indicate that sensitivity of floral responsiveness to photoperiod changed little with plant size.

Environment, Controlled↗

PubMedDate not supplied

Dinitrogen fixation in soybean in response to leaf water stress and seed growth rate.

Late season declines in N2 fixation by soybeans [Glycine max (L.) Merr.] frequently are observed under field conditions but do not always occur under glasshouse and growth chamber culture where water stress is avoided and photoperiod is manipulated to alter rate of seed growth. To evaluate the effects of water stress and photoperiod during reproductive growth declines in N2-fixation, nodulated 'Ransom' soybeans dependent entirely on N2-fixation and growing under controlled environment conditions were divided into two groups at the beginning seed (R5) stage. At R5, photoperiod was utilized to experimentally alter the rate of seed growth as a sink for photosynthate and N by imposing a short-day photoperiod (SD) on half of the plants and a long-day photoperiod (LD) on the other half. Within each photoperiod treatment, half of the plants were subjected to a single episode of leaf water stress between -1.2 and -1.8 MPa at the full seed (R6) stage, and half served as nonstressed controls. Plants were sampled at 1- to 5-day intervals between R5 and full maturity (R8) stages and analyzed for N and total nonstructural carbohydrates (TNC). The rate of N accumulation from N2-fixation declined during reproductive growth for the stressed plants but not for the nonstressed plants. Thus, a water stress can actuate a late season decline in N2-fixation. When rate of seed growth was slowed under LD, N composition in leaves remained higher following water stress than when a faster rate of seed growth was promoted under SD. Dinitrogen-fixation activity and dry matter production recovered after rewatering for stressed plants under LD but not under SD. Concentration of TNC in leaflets was greater under LD for both stressed and nonstressed plants. Thus, concentration of TNC in leaflets does not appear to be as important in recovery from water stress as concentration of N.

Biomass↗

PubMedDate not supplied

Nitrogen nutrition and temporal effects of enhanced carbon dioxide on soybean growth.

Plants grown on porous media at elevated CO2 levels generally have low concentrations of tissue N and often appear to require increased levels of external N to maximize growth response. This study determines if soybean [Glycine max (L.) Merr. Ransom'] grown hydroponically at elevated CO2 requires increases in external NO3- concentrations beyond levels that are optimal at ambient CO2 to maintain tissue N concentrations and maximize the growth response. This study also investigates temporal influences of elevated CO2 on growth responses by soybean. Plants were grown vegetatively for 34 d in hydroponic culture at atmospheric CO2 concentrations of 400, 650, and 900 microliters L-1 and during the final 18 d at NO3- concentrations of 0.5, 1.0, 5.0 and 10.0 mM in the culture solution. At 650 and 900 microliters L-1 CO2, plants had maximum increases of 31 and 45% in dry weight during the experimental period. Plant growth at 900 microliters L-1 CO2 was stimulated earlier than at 650 microliters L-1. During the final 18 d of the experiment, the relative growth rates (RGR) of plants grown at elevated CO2 declined. Elevated CO2 caused increases in total N and total NO3(-)-N content and leaf area but not leaf number. Enhancing CO2 levels also caused a decrease in root:shoot ratios. Stomatal resistance increased by 2.1- and 2.8-fold for plants at the 650 and 900 microliters L-1 CO2, respectively. Nitrate level in the culture solutions had no effect on growth or on C:N ratios of tissues, nor did increases in CO2 levels cause a decrease in N concentration of plant tissues. Hence, increases in NO3- concentration of the hydroponic solution were not necessary to maintain the N status of the plants or to maximize the growth response to elevated CO2.

Biological Transport↗

PubMedDate not supplied

Chemical restrictions of roots in Ultisol subsoils lessened by long-term management.

Exchangeable Al in subsoils of Ultisols in the southeastern USA can restrict rooting depth. Downward movement of basic cations (Ca, Mg, and K), applied as lime and fertilizer, may diminish that restriction over time. Materials from the argillic horizon were collected from three paired sites, having managed (long-term cropping) and nonmanaged topsoils (Typic Paleudults and Hapludults). One managed site was cropped continuously for 15 yr while the others were cultivated for more than 30 yr. Concentrations of extractable cations and other nutrients from the paired sites were compared to determine the magnitude of change due to management. The ability of the subsoils to support plant growth was evaluated in a missing-nutrient greenhouse experiment with sorghum [Sorghum bicolor (L.) Moench]. Subsoils of managed sites had greater effective cation-exchange capacity (CEC) and base saturation than those of non-managed sites. While availabilities of Ca, Mg, and K in subsoils of nonmanaged sites were inadequate to support maximal plant growth, they were adequate in subsoils of managed sites. Compared with nonmanaged sites, KCl-exchangeable Al in subsoils of managed sites was 23% lower at the 15-yr location and 65 and 100% lower at the two other locations. In the absence of lime, sorghum growth was almost totally inhibited on nonmanaged subsoils amended with optimum nutrients. On the managed subsoils, where 100, 65, and 23% of the nonmanaged exchangeable Al had been neutralized by topsoil fertilization and liming, growth reductions under the same conditions were 0, 50, and 100%, respectively. Thus, relatively long-term management had improved these Ultisol subsoils for root growth and development.

Aluminum↗