Nitrogen Assimilation in Barley (Hordeum vulgare L. cv. Mazurka) in Response to Nitrate and Ammonium Nutrition

Barley plants (Hordeum vulgare L. cv. Mazurka) were grown inaerated solution cultures with 2 mM or 8 mM inorganic nitrogensupplied as nitrate alone, ammonium alone or 1:1 nitrate+ammonium.Activities of the principal inorganic nitrogen assimilatoryenzymes and nitrogen transport were measured. Activities ofnitrate and nitrite reductases, glutamine synthetase and glutamatesynthase were greater in leaves than in roots but glutamatedehydrogenase was most active in roots. Only nitrate and nitritereductases changed notably (4–10 times) in response tothe different nitrogen treatments. Nitrate reductase appearedto be rate-limiting for nitrate assimilation to glutamate inroots and also in leaves, where its total in vitro activitywas closely related to nitrate flux in the xylem sap and wasslightly in excess of that needed to reduce the transportednitrate. Xylem nitrate concentration was 13 times greater thanthat in the nutrient solution. Ammonium nitrogen was assimilatedalmost completely in the roots and the small amount releasedinto the xylem sap was similar for the nitrate and the ammoniumtreatments. The presence of ammonium in the nutrient decreasedboth export of nitrate to the xylem and its accumulation inleaves and roots. Nitrate was stored in stem bases and was releasedto the xylem and thence to the leaves during nitrogen starvation.In these experiments, ammonium was assimilated principally inthe roots and nitrate in the leaves. Any advantage of this divisionof function may depend partly on total conversion of inorganicnitrogen to amino acids when nitrate and ammonium are givenin optimal concentrations. Hordeum vulgare L., barley, nitrate, ammonium, nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, nitrogen transport     

Tentoxin effects on infrastructure and greening of ivyleaf morningglory (Ipomoea hederacea var. hederacea) cotyledons

The effects of 20 μM tentoxin on mesophyll chloroplast ultra-structural development, chlorophyll organization and accumulation, and pigment transformations in cotyledons of dark-grown, 4-day-old ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. var. hederacea]were monitored. After 6 h of white light (200 μEm^?2T.s^?1), many plastids of tentoxin-treated tissues contained prolamellar bodies or inconsistent internal membrane orientation in contrast to the uniform internal membrane orientation and absence of prolamellar bodies in controls. Grana stacking did not progress beyond three to four disc loculi in tentoxin-treatments, and fret membranes were usually discontinuous and reduced. Cylindrical or cupped grana appeared in many chloroplasts after 3 days of light, while other chloroplasts in which disruption was more pronounced had few grana except for remnants, but usually did possess vesicles or structures resembling prolamellar bodies. Tentoxin had no apparent effect on stroma density or plastoglobuli size and number. No starch grains appeared in any of the tentoxin treatments, whereas they appeared after 24 h in controls. Initial protochlorophyllide content and its photoconversion to chlorophyllide and subsequent Shibata shift were not affected by tentoxin. Chlorophyll accumulation rates in tentoxin-treated cotyledons were about 10% of control rates during the first 24 h of greening and about 20% of controls from 48 to 72 h of greening. Chlorophyll alb ratio and PSU size (total Chl/P700) were not significantly affected by tentoxin.     

Analysis of growth during light-induced hook opening in cress

Abstract. Growth in various regions of the hypocotyls of dark-grown cress seedlings before and after exposure lo continuous white light has been analysed by time-lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle.     

The adaptive significance of amphistomatic leaves

Abstract A clear correlation between the presence of stomata on both surfaces and factors such as habitat, growth form, and physiology has yet to emerge in the literature. However, certain loose trends with these factors are evident, and these are reviewed along with evidence for hypostomaty as the primitive form. It is proposed that the effect of developing stomata on the upper surface as well as the lower is to increase maximum leaf conductance to CO₂. Plants with a high photosynthetic capacity, living in full-sun environments, and experiencing rapidly fluctuating or continuously available soil water (as opposed to seasonal or long-term soil water depletion), are identified as deriving an adaptive advantage from a high maximum leaf conductance. The correlation between groups of plants fitting the above conditions and those noted to be amphistomatic is remarkable. Plants not fitting the conditions are found to be largely hypostomatic.     

The Importance of the History of Science to the American Society of Zoologists

As the history of science has developed as a professional intellectualdiscipline, it has had and will continue to have an importantrole in defining science and its place in our culture. Suchdefinitions should be based on as much information as possible.Scientists can help supply some of this information throughparticipation in symposia on the history of science. In addition,scientists can learn much about the nature of their disciplineby becoming aware of the concepts of science which are derivedfrom the careful analysis of its history. Efforts should bemade to bring historians of science and scientists togetherfor their mutual benefit.     

Fatty Acid and Chlorophyll Levels of Coastal Bermudagrass during the Day and during Maturation

Lipids were extracted from fresh, field-grown coastal bermudagrass (Cynodon dactylon (L.) Pers.) and the fatty acids determined by gas chromatography. Total fatty acid levels (dry weight basis) increased during the day and reached a single maximum at sunset in 2-week-old grass; whereas, in older grass, the fluctuations in fatty acid levels showed two maxima. The first maximum occurred 4 h after sunrise and the second maximum occurred at sunset. Total fatty acid levels, based on dry weight, decreased during the first 6 weeks of growth and changed very little after an additional 4 weeks' growth in bermudagrass leaf blades. Chlorophyll levels (dry weight basis) continuously decreased during the entire growth period (10 weeks). Chlorophyll alb ratios increased at sunset in 2- and 6-week-old grass, but this ratio did not change during the day in subsequent growth stages. The results of these experiments show that stages of maturity affected fatty acid fluctuations during the day as well as total fatty acid and chlorophyll levels in Coastal bermudagrass leaf blades. Chlorophyll alb ratios varied independently of fatty acid levels.     

The Electrical Potential Difference Across the Tonoplast of Root Cells

Changes in electrical potential, measured as a microelectrodewas advanced into epidermal cells and from cell to cell in rootsof Lolium multiflorum and Zea mays, are described. The recordingssuggest that the electrical potential difference between thecytoplasm and vacuole, E_vc is of the order of a few millivolts,the vacuole tending to be the more positive. E_vc appeared tobe approximately the same for epidermal, cortical, endodermal,and pericycle cells.     

Role of the Vegetal Body in the Regulation of Development in Bithynia tentaculata (Prosobranchia, Gastropoda)

In the first polar lobe of the egg of Bithyma tentaculata thereis a cup-shaped mass of small vesicles rich in RNA, called thevegetal body. It is passed to the CD blastomere with the polarlobe and then its contents are distributed to C and D. Whenthe polar lobe is removed, embryos form neither mesentoblastnor mesoderm bands. They fail to establish bilateral symmetryor to form eyes, foot, operculum and shell. AB half embryosdevelop only the structures found in lobeless embryos, whileCD halves develop lobe dependent adult structures such as eyes,foot and shell. AD- and BC-2/4-embryos develop similarly andboth have lobe dependent structures. Three quarter embryos developas in other molluscs except that ABD (–C) develops poorlyand ABC (–D) develops all lobe-dependent structures. Thus,all evidence available indicates that C receives cytoplasm usuallyrestricted to D in molluscs and therefore has the capacity toexert a similar morphogenetic influence on development.     

Algal nitrogen fixation in Californian streams: diel cycles and nocturnal fixation

Thirty-six hour diurnal studies of Ng-fixation by Nostoc in a rocky-bedded stream were carried out during the peak of the seasonal cycle of growth on clear and cloudy days in 1971 and 1972. On both occasions an unexpected pattern of N₂-fixation occurred with maximum fixation rates in the light but also in the dark portion of the day, with lowest fixation periods in the early evening. I postulate that competition for reductant between nitrogenase and other processes, especially photorespiration, controls this unusual diel cycle rather than variations in the intracellular N-pool. N₂-fixation rates on a cloudless May day in 1971 ranged from 0.2 to 4.8 nmoles C₂H₄ cm⁻² h⁻¹ and from 0.3 to 3.3 nmoles C₂H₄ mg⁻¹ h⁻¹ dry weight of Nostoc, depending on time of day and favourableness of site. On the same site on a cloudy, rainy May day in 1972 fixation ranged from 0.5 to 3.1 nmoles C₂H₄ mg⁻¹ h⁻¹ dry weight, and from 1 to 4.5 nmoles C2H4 mg⁻¹ h⁻¹ ash-free dry weight of Nostoc. Since Nostoc is most abundant in unshaded areas, and since one-third of each day's nitrogen i s fixed in the dark, future studies should take dark fixation into account.