Conditions for rooting of leafy cuttings of Alnus incana

The rooting of softwood cuttings of Alnus incana (L.) Moench in nutrient solution was studied under controlled conditions. Cuttings consisting of one internode with the leaf and axillary bud attached rooted easily and more rapidly than shoot tip cuttings. Light was necessary for rooting but good rooting was obtained in photon flux densities of both 40 and 190 μmol m^-2s^-1. Root number and root length was reduced when light reached the base of the cuttings. Treatment with indolebutyric acid (10^-6–10^-4M) increased the number of roots but 10^-4M delayed rooting and decreased the root length. Debudded internode cuttings rooted as well as intact cuttings, and detached leaves also contained sufficient substances for rooting.     

Nitrogenase Activity in the Lichen Stereocaulon paschale: Recovery after Dry Storage

The effect of prolonged storage on nitrogenase activity in Stereocaulon paschale (L.) Fr. was studied. The thalli had a very low water content during the storage over silica gel at 4°C in the dark. For C₂H₂-reduction measurements the lichen samples were remoistened and held at 15°C in the light for 1–36 h before the addition of C₂H₂. With the longest pre-incubation time preceding the nitrogenase activity measurements there was no significant decrease in nitrogenase activity during 75 weeks of storage. The method of storage was simple and inexpensive and the nitrogenase activity characteristic of each lichen batch, due to seasonal variation, was well preserved during the storage.     

Day-to-day variation in nitrogenase activity of Alnus incana explained by weather variables: a multivariate time series analysis

A modelling system is described that indicates the extent to which day-to-day variations in nitrogenase activity in young Alnus incana (L.) Moench, grown in defined conditions in the field, may be affected by weather conditions both during and prior to the day of measurement. Nitrogenase activity (acetylene reduction activity, ARA) was measured weekly on intact field-grown grey alder (A. incana) plants, 0.15–0.42 m tall at planting, nodulated with Frankia. The measurements were done at noon on two groups of plants in 1987 and on two other groups in 1988. Each group was made up of five or six plants. Seven weather variables: daily sunshine hours, daily mean, maximum and minimum air temperature, daily mean and 1300 h relative humidity, and daily rainfall were used. The relation between log(ARA/leaf area) and the weather variables were analysed using a PLS model (partial least squares projection to latent structures). The advantage of PLS is that it can handle x-variables that are correlated. Data from 1987 were chosen as a training set. Multivariate PLS time series analysis was made by adding, in a stepwise manner, the weather data up to 5 d before the day of measurement. This procedure gave six models with n * 7 x-variables (n= 1–6). With the models from the time series analysis of 1987 data, true predictions of ARA per leaf area were made from weather data 1988 (test set 1) and from ‘early-season’ weather data from 1987 and 1988 (test set 2). The variation in ARA/leaf area could be predicted from the weather conditions. The predictions of the two test sets improved when the weather conditions one and two days before the day of measurements were added to the model. The further addition of weather data from 3 to 5 d before the day of measurement did not improve the model. The good predictions of ARA/leaf area show that the alders responded to the variable weather conditions in the same way in 1988 as in 1987, despite the ten-fold difference in size (leaf area) at the end of the growing season. Among the weather variables, air temperature and the daily sunshine hours were positively correlated to ARA, while relative air humidity and rainfall were negatively correlated to ARA. The daily minimum temperature and rainfall appeared to have least impact on ARA. By use of PLS, we could extract information out of a data set containing highly correlated x-variables, information that is non-accessible with conventional statistical tools such as multiple regression. When making measurements of nitrogenase activities under field conditions, we propose that attention should be paid to the weather conditions on the days preceding the day of measurement. The day-to-day variation in nitrogenase activity is discussed with reference to known effects of stress factors under controlled conditions.     

Nitrogenase Activity in Response to Darkening and Defoliation of Alnus incana

Huss-Danell, K. and Sellstedt, A. 1985. Nitrogenase activityin response to darkening and defoliation of Alnus incana. —J.exp. Bot. 36: 1352–1358 In the Alnus-Frankia symbiosis the nitrogen-fixing root nodulesare one of the sinks for carbon compounds newly formed in photosynthesisand exported from the leaves (source). The source-sink ratioof cloned plants of Alnus incana was reduced by darkening orby total or partial defoliation and the resulting nitrogenaseactivity (C₂H₂-reduction) was measured. Nitrogenase activityhad nearly ceased 5 h after total defoliation but not untilca. 5 d after total darkening. Most of the activity was lostduring the initial hours and days, respectively. When leaf areawas reduced approximately by half nitrogenase activity decreasedslightly less than by half. Removal of upper leaves seemed lessharmful than removal of lower leaves one day after defoliation.On the following 2 d the treatments appeared to be similar.Thus, nitrogenase activity was largely dependent on newly formedassimilates but could also depend on stored reserves that weremobilized. Measurements of in vitro nitrogenase activity inroot nodule homogenates from darkened plants indicated thatnitrogenase gradually became inactivated and/or depleted after1 and 2 d in darkness Key words: Carbon supply, Frankia, nitrogen fixation     

Respiration of Malate and Glutamate in Symbiotic Frankia Prepared from Alnus incana

Frankia vesicle clusters were prepared from root nodules ofAlnus incana (L.) Moench inoculated either with a local sourceof Frankia or with Frankia Cpll. The capacity of vesicle clustersto respire was investigated by respirometric and enzymologicalstudies. Simultaneous addition of malate, glutamate, and NAD⁺supported respiration in both types of Frankia, though at asmaller rate compared to the substrates NADH or 6-phosphogluconate.The saturating concentrations of malate and glutamate were alsomuch higher than with the other substrates. No respiration wassupported by succinate. Activity of the enzymes malate dehydrogenase(EC 1.1.1.37 [EC] ) and glutamate oxaloacetate transaminase (EC 2.6.1.1 [EC] )was demonstrated in crude extracts from both types of symbioticFrankia. Their maximum rates were high enough to account forthe respiration of malate and glutamate. This respiration wasinhibited by mersalylic acid, an inhibitor of the dicarboxylateshuttle in mitochondria, but it was shown that inhibition ofrespiration could be due to a direct effect on the enzymes.We conclude that respiration of malate and glutamate is mostlikely mediated by malate dehydrogenase and glutamate oxaloacetatetransaminase, but no explicit evidence for or against the presenceof a dicarboxylate carrier was found. The utilization of respiratorysubstrates was largely similar in the two types of Frankia,except for some differences in maximum rates and cofactor dependency. Key words: Actinorhizal symbioses, Alnus, dicarboxylate shuttle, Frankia, reducing power, respiration     

Nitrogenase Activity Measurements in Intact Plants of Alnus incana

A technique for C₂H₂-reduction assay on intact plants of Alnus incana (L.) Moench was evaluated. Cloned plants were grown, in pots, on fine gravel. During assay only the pot was inserted into a Perspex incubation chamber of simple construction. The incubation volume was rather small, plants with various shoot heights could be used, and the shoot was not exposed to the C₂H₄ produced. Intact plants showed high and constant C₂H₂-reduction rates during several hours of incubation. In comparison, excised nodulated roots conventionally incubated in test tubes showed low and decreasing rates, due to removal of the photo-synthesizing shoot and injury to the root nodules when drawn from the pot. Repeated nitrogenase activity assays on the same intact individual plants did not affect growth. The technique thus proved useful in studies. where repeated nitrogenase activity measurements are important.     

The Influence of Light and Oxygen on Nitrogenase Activity in the Lichen Stereocaulon paschale

Thalli of the lichen Slereocaulon paschale (L.) Fr. were prctreated in the light (light activated) or in the dark (dark starved). In short-time experiments with both light activated arid dark starved thalli, the nitrogenasc activity was higher in the light than in the dark, Light activated thalli had a very much higher rale of C₂H₂ reduction than dark starved thalli, both in the light and in the dark. The dark starved lhalli showed increasing nilrogenase activity when incubated in the light. Either light or oxygen was necessary for nitrogenase activity in light activated thalli. and up to about 10kPa oxygen they showed additive effects. Both in the light and in the dark the nitrogenase activity decreased when the oxygen partial pressure was lower than in normal air. The experimental data thus showed a short-term effect of light on nilrogenase activity by provision of ATP and reductant, and a long term effect probably by build up of reserves that were later utilized. Any immediate effect of photorespiration on nitrogenase activity could not be found in light activated thalli.