Effects of oxygen level on metabolism and development of seedlings of Trapa natans and two ecologically related species

Seeds of the water plant Trapa natans L. (water chestnut) can germinate in strict anoxia. The seedlings show seminal roots growing upwards while shoot buds remain quiescent until O₂ becomes available. Trapa seedlings are highly tolerant to anoxia. The rate of ethanol fermentation was 21.2 μmol (g FW)⁻¹ h⁻¹, while production of lactate was negligible and lower than that of succinate. The seminal root of Trapa compares better to the rice coleoptile rather than to the rice root, both functionally and as to the metabolic response to anoxia. The anaerobic germination of Nuphar luteum L. and Scirpus mucronatus L. was also characterized by a limited developmental program.     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

Ultrastructural changes associated with June Yellows in strawberry and with leaf yellowing symptoms of viral and genetic origin in Fragaria, Rubus and Ribes

Light and electron microscopy was used to study the ultrastructural effects of June Yellows (JY) in leaves of strawberry. Four cultivars of strawberry, affected to different extents by JY, were compared with healthy (JY-free) cv. Cambridge Favourite and with strawberry infected with strawberry crinkle rhabdovirus, Fragaria vesca infected with strawberry mottle virus (SMotV), raspberry and black currant showing virus-induced yellowing and with strawberry and raspberry showing chaemeric yellow sectors in the leaves. Except for isometric virus-like particles detected in SMotV-infected F. vesca, no virus-like particles or structures of other pathogenic agents were found in any of the tissues examined. Leaf cells of JY-affected strawberry showed severe disruption of chloroplasts and plasmalemma, whorls of membranous vesicles and decreased vacuole size. The extent and severity of these abnormalities increased with increased severity of JY symptoms but, even in leaves with mild JY symptoms, chloroplast abnormalities were obvious. In the most severely affected leaves, the cells lacked discrete vacuoles and extensive hypertrophy was seen in other organelles such as nuclei and mitochondria. Few, if any, ultrastructural abnormalities were observed in virus-infected strawberry or F. vesca, or in chaemeric leaves of strawberry and raspberry. By contrast, in raspberry and black currant with yellowed leaves caused by virus infection, the cells showed enlarged chloroplasts, decreased vacuole size and vesicle formation. However, chloroplast enlargement and disruption in this material seemed due to increased size of starch grains which were largely absent from swollen chloroplasts of JY-affected strawberry. The ultrastructural abnormalities observed in JY-affected strawberry are, therefore, not inconsistent with the possibility that a pathogenic agent may be involved in the condition.     

Episodic exposure to acid and aluminium in soft water: survival and recovery of brown trout,Salmo trutta L.

Yolk-sac fry, swim-up fry and 1–2 yr juveniles of brown trout, Sulmo trutta L., were exposed to episodes of aluminium and low pH, maximum aluminium concentration 12 μmol l⁻¹ (323 μg l⁻¹), minimum pH 4.5, total duration up to 54 h (yolk-sac fry) or up to 78 h (swim-up fry and juveniles), in an artificial soft water medium, [Ca] 20 μmol l⁻¹ (0–8 mg l⁻¹) (nominal baseline: pH 5.6, zero aluminium concentration). Yolk-sac fry mortality was nil or very low. A marked increase in susceptibility, with high mortalities, occurred when the yolk was fully absorbed. Mortality of juveniles exposed to two successive episodes was lower than would have been expected on the basis of comparisons with mortalities in single episodes, and mortality declined as the interval between the two episodes was increased. Disturbance of sodium, potassium or calcium balance or gill damage in surviving yolk-sac fry or juveniles was still evident 5 to 6 days after the end of a single episode.     

Distribution of NO3− reduction between roots and shoots of peachtree seedlings as affected by NO3− uptake rate

The distribution of NO₃^? reduction between roots and shoots was studied in hydro-ponically-grown peach-tree seedlings (Prunus persica L.) during recovery from N starvation. Uptake, translocation and reduction of NO₃^?, together with transport through xylem and phloem of the newly reduced N were estimated, using ¹⁵N labellings, in intact plants supplied for 90 h with 0.5 mM NH₄⁺ and 0.5, 1.5 or 10 mM NO₃^?. Xylem transport of NO₃^? was further investigated by xylem sap analysis in a similar experiment. The roots were the main site of NO₃^? reduction at all 3 levels of NO₃^? nutrition. However, the contribution of the shoots to the whole plant NO₃^? reduction increased with increasing external NO₃^? availability. This contribution was estimated to be 20, 23 and 42% of the total assimilation at 0.5, 1.5 and 10 mM NO₃^?, respectively. Both ¹⁵N results and xylem sap analysis confirmed that this trend was due to an enhancement of NO₃^? translocation from roots to shoots. It is proposed that the lack of NO₃^? export to the shoots at low NO₃^? uptake rate resulted from a competition between NO₃^? reduction in the root epidermis/cortex and NO₃^? diffusion to the stele. On the other hand, net xylem transport of newly reduced N was very efficient since ca 70% of the amino acids synthesized in the roots were translocated to the shoots, regardless of the level of NO₃^? nutrition. This net xylem transport by far exceeded the net downward phloem transport of the reduced N assimilated in shoots. As a consequence, the reduced N resulting from NO₃^? assimilation, principally occurring in the roots, was mainly incorporated in the shoots.     

CALLING SONG DISPLACEMENT IN A ZONE OF OVERLAP AND HYBRIDIZATION

The ground crickets Allonemobius fasciatus and A. socius meet in a mosaic zone of overlap and hybridization stretching from the East Coast to at least Illinois. To test whether male calling song differences were enhanced in sympatry, we analyzed the songs of crickets from inside and outside the zone of overlap along two transects. No evidence of calling song displacement was found in A. socius males from populations within the zone of overlap. On the other hand, A. fasciatus displayed calling song displacement in three populations. Our results are consistent with the hypothesis that the selective pressure exerted by the challenge from a related species is frequency dependent. While not a conclusive demonstration, the observed shifts in calling song are strongly suggestive of reproductive character displacement.     

Influence of nicotianamine and iron supply on formation and elongation of adventitious roots in hypocotyl cuttings of the tomato mutant 'chloronerva' (Lycopersicon esculentum)

The influence of nicotianamine (NA) on formation and elongation of adventitious roots in hypocotyls of de-rooted NA-less mutant seedlings of Lycopersicon esculentum Mill, was examined in relation to the iron supply [ferric N-N'-ethylenediaminedi-(2-hydroxyphenylacetate) (FEDDHA), ferric ethylenediaminetetracetate (FeEDTA), ferric N-(2-hydroxyethyl)-ethylenediaminetriacetate (FeHEDTA, Fe-citrate and FeCl₃] in the nutrient solution. The initiation of root primordia in hypocotyl cuttings was independent of NA and occurred with about the same frequency in both, mutant and wild-type. In the mutant the development of primordia to adventitious roots was blocked at all iron sources used, except FeEDTA. Addition of NA (5x 10⁻⁶ to 2 × 10⁻⁵ M ) to the rooting medium resulted in a fast growth of adventitious roots in mutant cuttings with all iron sources tested. Rooting of wild-type cuttings was independent from NA application and iron sources. We suppose that NA is involved in the intracellular transport of iron. Its function is possibly linked with chelation of ferrous iron in the cell.     

Effect of salinisation of soil on growth and macro- and micro-nutrient accumulation in seedlings of Acacia catechu (Mimosaceae)

The effects of salinisation of soil on Acacia catechu (Mimosaceae) were studied by means of emergence and growth of seedlings and pattern of mineral accumulation. A mixture of chlorides and sulphates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.1, 6.3, 8.2,10.1 and 12.2 dSm⁻¹. A negative relationship between proportion of seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.1 dSm⁻¹. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.1 dSm⁻¹, which suggests that this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. Among the tissues, young roots and stem were most tolerant to salt stress and were followed by old roots and leaves, successively. Leaf tissue exhibited maximum reduction in dry mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated “fine root turnover”, is of importance to the mechanisms of salt tolerance. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K was affected in response to salinity; it rapidly decreased in root tissues with increased salinisation. Nitrogen content decreased in all tissues (leaf, stem and root) in response to low water treatment and salinisation of soil. Phosphorus content significantly decreased, while Ca increased in leaves as soil salinity increased. Changes in tissue and whole plant accumulation patterns of the other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species during salinisation, are discussed.     

Factors influencing the effectiveness of an attracticide formulation against the Oriental fruit moth, Grapholita molesta

An attracticide formulation, LastCall?OFM, was tested against the Oriental fruit moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae) in replicated small plot field trials in apple, Malus domestica (Borkhausen), orchards in South‐eastern Pennsylvania, USA. Attracticide treatments were applied using a calibrated hand pump, and treated plots were compared to similar untreated plots. Male moth activity was monitored using virgin female‐baited traps, and the potential for reduction in mating activity was assessed using sentinel virgin females. A comparison of application rates showed that 1500 droplets per ha of the attracticide formulation was as effective as 3000 droplets per ha, and both application rates reduced captures in synthetic pheromone‐baited traps for prolonged periods. Droplets placed either at high or low positions within the canopy significantly reduced trap capture and mating with sentinel females. In addition, the only sentinel females that mated in the treated plots were located in the untreated portion of the tree canopy. Mate finding behaviour was equally disrupted by formulations with and without insecticide. Therefore, under the test conditions, the mechanism by which the attracticide formulation worked was by disruption of male orientation, and not by the removal of males due to insecticide poisoning. Two field cage experiments tested the impact of population density on the competitiveness of the attracticide formulation compared to virgin females. A significant proportion of males were captured in female‐baited traps at the highest female‐to‐droplet ratio tested. Equal proportions of males were captured in attracticide‐baited traps at male moth densities of 10, 20, 40, and 80 males per cage. These results clarify some of the factors influencing the effectiveness and possible mechanisms of an attracticide management tactic against the Oriental fruit moth.