Influence of Ammonium on the Growth and Development of Suspension Cultures of Pauľs Scarlet Rose

In this work as in previous studies from this laboratory it was demonstrated that the presence of a trace amount of NH₄⁺ (72.8 μmol) stimulated the growth of Pau?s Scarlet Rose on a defined medium containing NO₃^? (1920 μmol) as the only other source of nitrogen. A kinetic analysis of several growth parameters showed that the rate of increase of dry weight, fresh weight, cell number, and cell volume were greater during early stages of growth (days 0–8) when NH₄⁺ was provided. During later stages (days 8–14) this relationship between the two cultures did not hold. The cells provided NH₄⁺ continued to increase in fresh weight and cell volume, but the cells which were not provided NH₄⁺ had a greater rate of dry weight and cell number increase. These differences led to 14-day-old cultures which were approximately equal in dry weight and cell number but differed by a factor of 2 in fresh weight. The presence of NH₄⁺ speeded up the development and growth of the cells.     

Observations and experiments on the use of an avirulent mutant strain of tobacco mosaic virus as a means of controlling tomato mosaic

In 1973 tobacco mosaic virus (TMV) strain M II-16 was successfully used by growers in the United Kingdom to protect commercial tomato crops against the severe effects of naturally occurring strains of TMV. However, plants in many crops had mosaic leaf symptoms which were occasionally severe, so possible reasons for symptom appearance were examined. The concentration of the mutant strain in commercially produced inocula (assessed by infectivity and spectrophotometry) ranged from 28 to 1220 μg virus/ml; nevertheless all samples contained sufficient virus to infect a high percentage of inoculated tomato seedlings. Increasing the distance between the plants and the spray gun used for inoculation from 5 to 15 cm resulted in a significant decrease in the number of tomato seedlings infected. When M II-16 infected tomato plants were subsequently inoculated with each of fifty-three different isolates of TMV, none showed severe symptoms of the challenging isolates within 4 wk, although some isolates of strain o induced atypically mild leaf symptoms. In a further experiment, M II-16 infected plants showed conspicuous leaf symptoms only 7 wk after inoculation with a virulent TMV isolate. M II-16 multiplied more slowly in tomato plants and had a lower specific infectivity than a naturally occurring strain of TMV. More than 50% of plants in crops inoculated with strain M II-16 which subsequently showed conspicuous leaf mosaic contained TMV strain 1 or a form intermediate between strains o and 1. It is suggested that the production of TMV symptoms in commercial crops previously inoculated with strain M II-16 may result from an initially low level of infection, due to inefficient inoculation, which allows subsequent infection of unprotected plants by virulent strains. Incomplete protection by strain M II-16 against all naturally occurring strains may also be an important factor.     

Estimating and Correcting for Bias in Population Assessments of Sooty Shearwaters

Abstract: We investigated the precision and accuracy of an infrared burrowscope for detecting sooty shearwater (Pufffinus griseus) chicks at 13 plots from 3 islands in southern New Zealand in 2003. We partially excavated burrows systems to reveal the entire burrow contents after 2 teams of observers had prospected all burrow entrances. Accuracy was similar between islands and observer teams at approximately 85%. The majority of the inaccuracy stemmed from failure to detect some chicks. Logistic regression modeling identified 4 burrow characteristics occurring between the entrance and the nest-site that influenced detection of burrow occupants. Detection was lower at nest-sites further from burrow entrances, in burrows with a high rate of burrow division, and in burrows with a high level of curvature. There was a positive relationship between the interaction of rate of division and curvature and detection of chicks. Distance from the burrow entrance was the only parameter that could be reliably used as a predictor of detection rate, so a reduced model containing only this variable was constructed to correct for burrowscope bias. The correction factor performed well on The Snares and Bench Island where predicted bias was very similar to observed levels (within 5%), but bias was overestimated on Putauhinu by up to 19.1%. Consistent bias, lack of damage to burrows from excavation, and the successful application of a correction factor all indicate the value of further testing burrowscope accuracy on other burrow-nesting seabird species.     

Growth of Tiller Buds in Barley: Effects of Shade Treatment and Mineral Nutrition

Examination of the stem apex of Proctor barley showed that thebud of the coleoptile tiller, Tc, is probably present in thedry grain and that the bud, TI, carried in the axil of the firstleaf is present at or soon after 24 h from planting. Subsequentlytiller buds are initiated with a plastochron of about 4 days,this being rather longer than that for the foliar primordia.During the initial phase of bud growth vascular connectionsare established with the leaf above, but not to the subtendingleaf. At some time after these vascular connections are formedand when it has a dry weight of 4–7 µg the bud entersa phase of rapid, exponential growth in dry weight. Shading the first leaf delays the onset of rapid growth forboth Tc and Ti, but after a lag period rapid growth commences;this is coincident with development of the second leaf as anorgan exporting assimilated carbon. The phase of rapid growth of tiller buds is delayed when applicationof either nitrogenous or nonnitrogenous minerals is delayed.Ammonium was found to be less satisfactory as a nitrogen sourcethan nitrate, probably because of toxicity effects. Slight growthof Tc and T1 occurs in presence of nonnitrogenous minerals andabsence of nitrogen but growth is greater when nitrogen is suppliedin absence of the other minerals, although such growth is substantiallyless than that found when all nutrients are supplied. The interactionbetween nitrogen and non-nitrogenous minerals which controlsbud growth was not found to affect growth of the parent plantwhich is, as previously shown, controlled by timing of the nitrogensupply. AnotheT distinction is that higher concentrations ofnitrogen and the other minerals are required for maximum growthof the bud than for that of the plant. Tiller bud growth is interpreted as occurring in two phases.In the first, initiation, phase there is a close associationwith the subtending leaf, and nutritionally bud and leaf arelinked. This phase is followed by one in which the bud is directlyconnected by vascular traces to the leaf above, which becauseof this controls bud growth by modulating supply of assimilatedcarbon and nitrogen, and other minerals to it.