Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: III. Effects of Concentration and Form of Nitrogen Supplied on Carbon Dioxide Compensation Point

Increasing the nitrate concentration in the nutrient media wasfound not to influence the carbon dioxide compensation point(). However, a higher value of was obtained in the presenceof ammonia nitrogen in the nutrient media. Increasing the nitrateconcentration in the media gave a higher activity of RuDP carboxylase,nitrate reductase, glycollate oxidase, and catalase. Similarlythe plants grown in ammonia nitrogen showed higher activitiesof RuDP carboxylase and catalase, and a considerably higherglycollate oxidase activity.     

An Investigation into the Effect of Varying Nitrogen Regimes on the Abundance of Peroxisomes and Activities of Nitrate Reductase and Catalase in Barley (Hordeum vulgare L.) and Maize (Zea mays L.)

Varying levels of nitrogen supplied as either nitrate or theammonium ion were shown to significantly affect the number ofperoxisomal profiles per cell section in both barley and thebundle sheath cells of maize. The enzyme activities of nitratereductase and catalase are also shown to be correlated withthe number of peroxisomal profiles. The implications of theserelationships are discussed.     

Alanine Aminotransferase and Aspartate Aminotransferase in Leishmania tarentolae1

SYNOPSIS. Culture stages (promastigotes) of Leishmania tarentolae were tested for alanine aminotransferase (E.C.2.6.1.2) and aspartate aminotransferase (E.C.2.6.1.1.). Neither enzyme was detected in crude cell extracts. After starch block electrophoresis, however, both transaminase activities were found in proteins migrating toward the anode. Only one species of each enzyme was found. Using coupled enzyme assay systems, the following physical and kinetic properties were seen: 1) aspartate aminotransferase was inhibited by α-ketoglutarate concentrations above 1.68 × 10^?2 M and alanine aminotransferase was inhibited by concentrations higher than 1.34 × 10^?2 M; 2) the Michaelis constant (Km[α-ketoglutarate]) was 5.4 × 10^?4 M for aspartate aminotransferase and 3.0 × 10^?4 M for alanine aminotransferase; 3) maximum activity was found at ?pH 8.5 (broad range between pH 7.75–9.0) for aspartate aminotransferase whereas maximum activity for alanine aminotransferase was ?pH 7.2 (range between pH 7.0–7.5); 4) both enzymes lost half of their activity after 4 days at 8 C; 5) aspartate aminotransferase was most active at 35 C and completely inactivated at 59.5 C, alanine aminotransferase exhibited maximum activity at 29.5 C and was completely inactivated at 61 C; and 6) neither enzyme showed enhanced activity with added pyridoxal phosphate.     

Sources of variation in haematocrit in birds

The validity of the haematocrit or packed cell volume as an indicator of condition in wild birds has recently been questioned. We reviewed over 300 published papers on haematocrit values for wild birds. These studies show that changes in haematocrit could be caused by a number of different natural factors that include age, sex, geographical elevation, energy expenditure, parasitism, nutrition and genetics. Haematocrit also increased with age from hatching, due to increased erythropoiesis, so that adult birds generally have greater haematocrit values than nestlings or juveniles. Haematocrit values were either independent of elevation or increased with elevation. A meta-analysis of 36 studies showed no difference in haematocrit between the sexes. Relationships between haematocrit value and both energy expenditure and parasitic infection vary between studies. In temperate climates, haematocrit tended to be higher in winter than in summer, which may be due to dehydration or increased oxygen demand caused by thermogenesis, moult or acquisition of reproductive status. Our review indicates that the use of haematocrit as a sole indicator of condition or health could lead to incorrect conclusions if natural factors that can affect haematocrit are not taken into consideration.     

Reproductive Advantages for Common Loons Using Rafts

Abstract: Artificial nesting islands, or rafts, are often deployed in common loon (Gavia immer) breeding territories to decrease negative impacts of mammalian predation and water-level fluctuations on nesting success. The management value of rafts has been demonstrated in other studies; however, no published studies have quantified the use or associated reproductive benefits of rafts on lakes exhibiting water-level fluctuations. These lakes constitute a major portion of loon nesting habitat in New England and the Midwest. We used long-term data sets from loon survey and raft management efforts on lakes with stable (SWL) and fluctuating water levels (FWL) in New Hampshire and Maine, USA, to compare raft-use patterns on both types of lakes. We then modeled the influence of percentage of nesting attempts on rafts, lake fluctuation type, and human development index on nesting success as a function of the number of nesting attempts. Loons used 76% of all rafts for nesting, and initial use patterns were similar between SWL and FWL lakes. Half (51%) of rafts used for nesting were first used during the initial year of deployment and 90% of those used were used by the third year. Based on our model, we would expect to see an 8.6% increase in nesting success associated with each successive categorical increase in raft use (0–33%, 33–60%, 60–100%). Nesting success varied with lake fluctuation type, increasing by 21.4% from FWL to SWL types. Our model estimated a 12.8% decrease in nesting success associated with an increasing human development index. Naturally nesting loons on FWL lakes are likely to display mean nesting success levels lower than those needed to sustain populations. We suggest that natural nesting habitat on lakes with fluctuating water levels during the loon nesting season may constitute an ecological trap warranting consideration of raft management. Findings in this study are germane for managing breeding loon populations, particularly those on reservoirs requiring permits from the Federal Energy Regulatory Commission.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: I. Effects of Light Period, Leaf Age, and Position, on Carbon Dioxide Compensation Point ({Gamma})

The carbon dioxide compensation point () was found to vary underconstant environmental conditions, as the duration of lighttreatment increased, and also with leaf age. The activitiesof RuDP carboxylase, catalase, glycollate oxidase, and nitratereductase were found to vary with duration of the light treatmentduring the course of a single day. RuDP carboxylase activity was found to exhibit a rhythmic fluctuationof activity with age, which had a frequency common to all theleaves examined. The activities of RuDP carboxylase, glycollateoxidase, and nitrate reductase in the leaves was found to increasewith ascending leaf position; the activities generally decreasedwith leaf age. The ratio of nitrate reductase activity to RuDPcarboxylase activity was found to give an excellent correlationwith measured T, and the value of nitrate reductase as an indirectmeasure of photorespiration and the relationship between nitrogenmetabolism and photorespiration is discussed.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: IV. The Effect of Light Intensity on the Carbon Dioxide Compensation Point

The carbon dioxide compensation point () was found to vary whenmeasured at increasing light intensities, in plants grown ata constant illumination. This response varied with the physiologicalage of the leaf. The also varied when measured at a constantillumination, with plants grown at different light intensities.The activity of the enzymes RuDP carboxylase, nitrate reductase,glycollate oxidase, and catalase was found to be influencedby the light intensity at which the plants were grown. A goodcorrelation was obtained between the measured and the ratioof nitrate reductase: RuDP carboxylase activities, suggestingthat nitrate reductase may be used as an indirect measure ofphotorespiration in plants receiving nitrate as the sole nitrogensource.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: II. Effects of External Concentrations of Carbon Dioxide and Oxygen

Plants grown in a high carbon dioxide environment (< 1 percent) were found to have increased levels of RuDP carboxylase,and suppressed activities of catalase, glycollate oxidase, andnitrate reductase, enzymes all associated with the peroxisome.Similarly, plants grown in low oxygen concentrations showedsuppressed activities of the peroxisomal enzymes. However, underthese conditions RuDP carboxylase activity was also suppressed.These results further suggest that nitrate reductase activityis associated with photorespiration.