Responses of wild plants to nitrate availability

Summary Two annual species of Bromus, an invader (B. hordeaceus, ex B. mollis) and a non-invader (B. intermedius), were grown for 28 days in growth chambers, at 5 and 100 M NO ₃ ^- in flowing nutrient solution. No differences between the two species were observed at either NO ₃ ^- level, in terms of relative growth rate (RGR) or its components, dry matter partitioning, specific NO ₃ ^- absorption rate, nitrogen concentration, and other characteristics of NO ₃ ^- uptake and photosynthesis. The effects of decreasing NO ₃ ^- concentration in the solution were mainly to decrease the NO ₃ ^- concentration in the plants through decreased absorption rate, and to decrease the leaf area ratio through increased specific leaf mass and decreased leaf mass ratio. Organic nitrogen concentration varied little between the two treatments, which may be the reason why photosynthetic rates were not altered. Consequently, RGR was only slightly decreased in the 5-M treatment compared to the 100-M treatment. This is in contrast with other species, where growth is reduced at much higher NO ₃ ^- concentrations. These discrepancies may be related to differences in RGR, since a log-linear relationship was found between RGR and the NO ₃ ^- concentration at which growth is first reduced. In addition, a strong linear relationship was found between the RGR of these species and their maximum absorption rate for nitrate, suggesting that the growth of species with low maximum RGR may be partly regulated by nutrient uptake.     

Comparison of population dynamics between slow- and fast-growing strains of the rotifer Brachionus calyciflorus pallas in continuous culture

Summary The population dynamics of a slow- and a fast-growing strain of the rotifer Brachionus calyciflorus are compared. Rotifers were grown in steady-states, at various specific growth rates (), in both two-stage chemostat and turbidostat cultures on the green alga Chlorella pyrenoidosa. Population variables, including specific ingestion (I), loss (L) and filtration (F) rates, yield (Y), production (P) and half-saturation coefficient of growth (K _g), were calculated using a growth model based on saturation kinetics. I, L, F and K _g were shown to be higher and Y and P lower for the fast-growing strain. Differences between the two strains with regard to these variables may represent tradeoffs associated with the faster potential growth rate. Steady-state relationships between these values and for the fast-growing strain, however, deviated from model predictions which suggest a possible shift from carbon to non-carbon growth limitation.     

Effect of pod zone moisture content on reproductive growth in three cultivars of peanut (Arachis hypogaea)

Very little research has been done to investigate the effect of a dry podding zone on reproductive development in peanut plants that are otherwise well hydrated via subsoil moisture extraction. The influence of podding zone moisture content on reproductive development and growth of three peanut cultivars (McCubbin, Gajah and Robut 33-1) was investigated in pots grown in the glasshouse. In two cultivars (McCubbin and Gajah) seed yield was reduced in a dry (air-dry) compared to a wet (field capacity) podding zone. Seed yield of Robut 33-1 was unaffected by podding zone moisture content, indicating that cultivar variation in reproductive performance in response to podding zone moisture may exist.     

Role of protein and RNA synthesis in the initiation of auxin-mediated growth in coleoptiles of Zea mays L.

The kinetics of inhibition by protein- and RNA-synthesis inhibitors (cycloheximide and cordycepin, respectively) of indole-3-acetic acid (IAA)-induced elongation growth were investigated using abraded coleoptile segments of Zea mays L. Removal of the cuticle — a diffusion barrier for solutes — by mechanical abrasion of the outer epidermal cell wall increased the effectiveness of inhibitors tremendously. In an attempt to elucidate the role of growth-limiting protein(s) (GLP) in the growth mechanism the following results were obtained. The elongation induced by IAA was completely inhibited when cycloheximide (10 mol·l^-1) was applied to abraded coleoptile segments as shortly as 10 min before the onset of the growth response (=5 min after administration of IAA). However, when cycloheximide was applied after 60 min of IAA treatment (when a steady-state growth rate is reached), the time required for complete cessation of growth was much longer (about 40 min). Cycloheximide inhibited the incorporation of [³H]leucine into protein within about 5 min. Cordycepin (400 mol·l^-1) prevented IAA-induced growth when applied as shortly as 25 min before the onset of the growth response (=10 min before administration of IAA) but required more than 60 min for a full inhibition of steady-state growth. The incorporation of [³H]adenosine into RNA was inhibited by cordycepin within 10 min. It is concluded that, contrary to previous investigations with nonabraded organ segments, the initiation of growth by IAA depends directly on the synthesis of GLP. Moreover, the apparent lifetime of GLP is at least four times longer than the time required by cycloheximide to inhibit the initiation of growth by IAA. This is interpreted to mean that GLP is not present before IAA starts to act but is synthesized as a consequence of IAA action starting a few minutes before the initiation of growth. Interpreting the kinetics of growth inhibition by cordycepin in a similar way, we further conclude that GLP synthesis is mediated by IAA-induced synthesis of the corresponding mRNA which starts about 10 min before the onset of GLP synthesis. Inhibition by cycloheximide and cordycepin of IAA-induced growth cannot be alleviated by acidifying the cell wall to pH 4-5, indicating that these inhibitors do not act on growth via an inhibition of auxin-mediated proton excretion.Abbreviations CHI cycloheximide - COR cordycepin - GLP growth-dimiting protein(s) - IAA indole-3-acetic acid - mRNA_GLP mRNA coding for GLP     

Binding and internalization of gold-conjugated somatostatin and growth hormone-releasing hormone in cultured rat somatotropes

Summary The synthetic peptides somatostatin (SRIF) and growth hormone-releasing hormone (GRH) were coupled directly to colloidal gold of different particle sizes. Both conjugates were biologically active in displacing the corresponding radiolabeled hormones from high affinity binding sites in pituitary membranes. Release of growth hormone (GH) from cultured anterior pituitary cells was modulated by both conjugates alone or in combination. Ultrastructural studies were performed with cells incubated at 4° C (2 h) and 37° C (2 min-2 h) with one of the labeled peptides or their combination. Somatotropes were identified by immunostaining with anti-rGH followed by protein A-ferritin, thus obtaining a triple labeling. Both hormone conjugates were internalized in different vesicles in the beginning but accumulated during longer incubation times in the same compartment. The secretory vesicles and the nucleus were not labeled by any hormone conjugate. In contrast to SRIF-gold, the uptake of GRH-gold conjugate decreased with longer incubation times. This effect could be neutralized by simulatenous incubation of the somatotropes with both regulating hormones. Hence, whereas the binding and internalization of SRIF by somatotropes do not seem to be influenced by GRH, the corresponding processes for GRH are stimulated by the presence of SRIF.     

In vitro development of angiosperm floral buds and organs

In the last twenty-five years, young inflorescences, floral buds and individual floral organs of a number of species have been cultured in vitro. There is considerable variability in the requirement of plant growth regulators and nutritional factors for flower development of different species. This variability is compounded by the fact that the hormonal and nutritional requirements are different at various stages of organ and floral development. Experimental studies on normal and mutant flowers in vitro have provided insights into some of the regulatory processes in floral organogenesis. The potential use of the in vitro technique in elucidating the various mechanisms in flower development is stressed.     

Influence of 2-deoxy-D-glucose upon growth and invertase activity of carrot (Daucus carota L.) cell suspension cultures

Carrot (Daucus carota L.) cell suspension cultures grew well when provided with glucose, fructose, sucrose or raffinose. Galactose and melibiose supported less growth unless supplemented with glucose or fructose. In combination with ten different sugar mixtures, 2-deoxy-D-glucose (dGlc) inhibited culture growth. Inhibitory effects of dGlc were more marked with fructose, melibiose, raffinose or mixtures of these sugars in the culture medium. The presence of glucose or galactose reduced the inhibitory effects of dGlc on culture growth. Experiments with radioactive labelled sugars demonstrated that dGLc uptake was greater in the presence of fructose than glucose, and that growth inhibition of dGlc coincided with its uptake. Reduced protein content was also associated with the inhibitory effects of dGlc. Cultured cells contained lower levels of invertase (EC 3.2.1.26) activity during the active phase of culture growth (up to 25 days after subculture) than when growth had peaked and subsequently declined. Acid and alkaline invertase activities were not greatly reduced by exogenous hexoses. Invertase activity was greatest during periods of low protein content in all cultures and was inhibited by dGlc during the latter phases of the culture period. Free intracellular sugars throughout the culture period consisted mainly of glucose and fructose.     

Rats reproduce and rear litters during chronic exposure to 150-kV/m, 60-Hz electric fields

Mature female rats and their subsequent litters were exposed either to 112- or to 150-kV/m, 60-Hz electric fields or sham-exposed for 19 h daily through pre-breeding, breeding, and rearing periods of experimentation. Exposed females mated in equal percentages and reared litters of equal numbers, and mean body masses of pups were the same as those of sham-exposed animals. Thus, experiments to investigate electric-field effects on reproduction and development in rats are feasible at effective field strengths of 112 and 150 kV/m.