Effects of repeated application of water stress on water status and growth of wheat

The effects on water status and growth of controlled cycles of water stress applied at various stages of development were studied on a semi-dwarf spring wheat (Triticum aestivum L.). The plants were grown in controlled environment chambers of the Duke University Phytetron at 24/18°C with a 12-h photo-period at about 600 μE m^?2 s^?1. Groups of plants were subjected to severe water stress by withholding irrigation, beginning at the 7th leaf, early anthesis, or early dough stages of development. A second cycle started 9 to 13 days after termination of the first cycle and maintained until the flag leaf water potential reached –25 bars at each of the growth stages. The lower leaves showed sign of wilting as indicated by curling in the first drying cycle at –7 bars and in the second cycle at –9 bars of leaf water potential during all stages of growth. Although these leaves recovered completely upon rewatering, onset of senescence was accelerated by three days in stressed plants. A preliminary drying cycle did not increase the ability of the plants to withstand subsequent stress because of severity of stress. Water stress of –25 bars at all three stages of growth reduced seed yield. The reduction was greater when a second stress cycle was also applied. Stress applied during early anthesis stage produced the smallest and the least number of seeds. The lack of osmotic adjustment probably was due to very rapid and severe development of water stress.     

Effects of ionic strength and relative humidity on the efflux of K+ (86Rb) and Ca2+ (45Ca) from roots of intact seedlings of cucumber, oat and wheat

Spring wheat (Triticum aestivum L. cv. Svenno), oat (Avena sativa L. cv. Brighton) and glasshouse cucumber (Cucumis sativus L. cv. Bestseller F1) were cultured for a week after germination on complete nutrient solutions of three different dilutions (1, 25 and 50% of the full strength medium). K⁺(⁸⁶Rb) and ⁴⁵Ca were present during the whole culture period. Relative humidity (RH) was 50% except during the last day, when half the material was transferred to 90% RH. Efflux of labelled ions was then followed during eight hours on unlabelled solutions of the same composition as before, and at both 50% and 90% RH in the atmosphere. – Uptake of K⁺(⁸⁶Rb) during growth tended to be saturated in the 25% medium. Contrariwise, the level of Ca²⁺ in the roots increased continuously with strength of the medium. At low concentrations cucumber roots were higher in Ca²⁺ than roots of oat or wheat, whereas all three species showed similar levels of Ca²⁺ in 50% medium. – At the lowest ionic strength, smooth efflux curves were obtained that could be resolved according to the three-compartment theory. At higher ionic strength, irregularities were observed, and more for Ca²⁺ than for K⁺; but for practical purposes compartment analysis with the same time constants could be applied as for the lowest concentration. – Discrimination between K⁺ and Rb⁺ differed between the roots, but not much between the shoots of different species. The roots of oat and wheat took up Rb⁺ preferentially over K⁺ in the 25% and 50% media; whereas K⁺ was preferred over Rb⁺ or little discrimination made in 1% medium and for cucumber. The shoots generally showed less discrimination than the roots. The main variability in discrimination between K⁺ and Rb⁺ thus appears to be localized in the tonoplasts of the roots cells. – Low RH around the shoots increased efflux of K⁺(⁸⁶Rb) from the cytoplasm and vacuoles of the root cells as compared to the efflux at high RH. DNP (2,4-dinitrophenol) in the medium had the same effect as high RH around the shoots. The signal system that must exist between shoots and roots is discussed as a response to “drought” conditions. In relation to investigations of others, it is assumed that the effect of DNP may indicate that part of the chain between roots and shoots consists of metabolically influenced sites, whose output is influenced by the rate of water transport.     

Late Ordovician-Early Silurian fluctuations in sea level from eastern Anticosti Island, Quebec

Over 1,000 m of Upper Ordovician to Lower Silurian mixed carbonate and clastic strata on Anticosti Island are nearly tectonically undisturbed, despite their proximity to the Northern Appalachians fronting Quebec's Gulf of St. Lawrence. Natural cliffs exposed along the coast and rivers in the eastern part of the island make a relatively conformable sequence belonging to the Ashgill and Llandovery Series. Fossil communities interpreted as depth-associated in life are especially repetitious in the Becscie, Gun River, Jupiter, and Chicotte Formations (Llandovery Series), and to a lesser degree in the Upper Vaureal and Ellis Bay Formations (Ashgill Series). Preliminary study of the pattern of changeovers in Eocoelia, Pentamerus and Stricklandia communities suggests that Anticosti seas deepened and shallowed three and a half times during the Early Silurian. High water peaks were reached during B₁-B₂, C₁-C₂ and C₄-C₅ times, with a final deepening trend beginning in late C₅ time. Age determinations of these events are based on the occurrence of graptolites (with some new records from Anticosti) keyed to the standard graptolite zones, and species of the Eocoelia lineage are also useful for correlation. The profile of the Anticosti sea-level curve compares well with other curves reconstructed from the Lower Silurian of New York, Michigan, and Iowa. Widespread synchronism in sea-level changes on the North American platform is thus corroborated.     

Taxonomic isolation and the accumulation of herbivorous insects: a comparison of introduced and native trees

Abstract.

• 1 Evidence from leaf-mining insects on Fagaceous hosts suggests that range expansions of insects onto introduced trees often involve species that feed on native hosts closely related to the introduced host.
• 2 An examination of the herbivorous entomofauna of British trees illustrates that the size of the entomofauna is partially determined by the taxonomic isolation of the host tree.

     

The Germination of Carrot (Daucus carota L.) Seed Harvested on Two Dates: A Physiological and Biochemical Study

The germination of two batches of carrot seed, harvested 44and 104 d after anthesis, was compared at 10 °C. Proteinand nucleic acid contents of the seeds were measured at intervals,together with fresh weight and respiration rate. The matureseed germinated 3.7 d earlier than the immature seed, with nodifference in percentage germination. The dry mature seed containedmore protein and nucleic acid per unit dry matter than did theimmature seed, and proportions of nucleic acid present as rRNAand poly(A)RNA were greater in the mature seed. The sequenceof metabolic reactivation was the same in both batches of seed,as were the relative rates of increase of each nucleic acidcomponent, fresh weight, and respiration rate. Differences inthe composition of the dry seed appear to be responsible forthe observed difference in rate of germination between the twoseed batches.     

Elevated concentrations of CO2 may double methane emissions from mires

The potential impact of an increase in methane emissions from natural wetlands on climate change models could be very large. We report a profound increase in methane emissions from cores of mire peat and vegetation as a direct result of increasing the CO₂ concentration from 355 to 550 μol mol^?1 (a 60% increase). Increased CH₄ fluxes were observed throughout the four month period of study. Seasonal variation in CH₄ flux, consistent with that seen in the field, was observed under both ambient and elevated CO₂. Under ambient CO₂, methane fluxes rose from 0.02 μol m_-2 s^?1 in May to 0.11 μol m^?2 s^?3 in July before declining again in August. Under elevated CO₂ methane fluxes were at least 100% greater throughout the experiment, rising from 0.05 μol m_-2 s^?1 in May to a peak of 0.27 μol m^?2 s^?1 in July. The stimulation of CO₄ emissions was accompanied by a 100% increase in rates of photosynthesis from 4.6 (± 0.3) under ambient CO₂ to 9.3 (± 0.7) μol m^?2 s^?1. Root and shoot biomass were unaffected.     

Relationships between nematodes, weevils, banana and plantain cultivars and damage

Infestation of banana and plantain suckers by nematodes (Pratylenchus good-eyi, Radopholus similis and Helicotylenchus multicinctus) and weevils (Cosmopolites sordidus) increased with time from establishment in a field of eight different cultivars. There was a strong association between nematode and weevil infestation; suckers infested with nematodes were more than four times more likely to be infected by weevil than suckers without nematodes. Weevil damage, measured by percentage coefficient of infestation (PCI) at harvest of the bunch, was higher on a plantain (cv. Gonja) and on an east African highland cooking banana (cv. Lusumba) than on the sweet and multi-purpose cultivars. There was a correlation between numbers of male weevils caught in a plot and the mean PCI measured in the plot, but no correlation with female numbers.     

Water Flow Through Vessel Perforation Plates--The Effects of Plate Angle and Thickness for Liriodendron tulipifera

The effects of scalariform perforation plate thickness and anglewithin vessel elements of Liriodendron tulipifera were studiedwith a computational fluid dynamical model. The pressure gradientand hence resistance to flow through the plate increased asthe perforation plate increased in thickness. Increasing theangle of the plate relative to the axis of the vessel (samenumber of pores) also increased the pressure gradient alongthe modelled cell. For the model matching the actual vesselelement, the plate contributed 8% to the flow resistance ofthe vessel element. This contribution increased only to 11%for doubled plate thickness, and to 14% for a plate at an angleof 60° to the vessel axis. The perforation plate alteredthe velocity profile across the vessel element, but to a differentextent depending on the angle of the plate. A plate at an acuteangle to the vessel axis has little effect on the paraboloidprofile as found upstream from the plate, while obtuse angleplates change the flow profile such that fluid through poresnear the wall is accelerated to a greater velocity than foundin the centre of the cell. Key words: Conductance, perforation plate, vessel, water flow     

Starch-degrading enzymes during the induction of CAM in Mesembryanthemum crystallinum

Mesembryanthemum crystallinum plants were irrigated with 400 mol m^?3 NaCl to induce CAM and levels of leaf starch, and activities of starch-degrading enzymes were measured. During Crassulacean acid metabolism (CAM) induction, daily starch turnover gradually became more pronounced and was three- to four-fold greater than in leaves of C₃ plants after 3 weeks. Activities of α- and β-amylase, D-enzyme and starch phosphorylase all increased 10- to 20-fold within 3 weeks of the start of salt treatment. Activities of α- and β-amylase increased more than fourfold within the first 24 h of salt treatment, which is the fastest increase in enzyme activities so far measured during the induction of CAM with salt solution in intact plants of this species. Most enzyme activities were partially chloroplastic; however, the principal starch-degrading activity was constituted by an extra-chloroplastic β-amylase. CAM starch-phosphorylase activity, which was mainly chloroplastic, exhibited a two- to three-fold diurnal change in parallel with starch content. CAM induction in M. crystallinum is clearly associated with greater starch turnover and enhanced starch-degrading enzyme activities, which as catalysts of the initial reaction to release carbon for synthesis of phosphoenolpyruvate (PEP) appear highly significant for the functioning of the CAM pathway. The diurnal rhythm of phosphorylase activity may be of particular significance.     

Effects of ultraviolet radiation on corals and other coral reef organisms

The discovery of the importance of solar ultraviolet radiation (UVR) as a factor affecting the biology of coral reefs dates only to about 1980. Interest has heightened during the past five years owing to the demonstration of loss of stratospheric ozone through human activities. We have only begun to document gross, qualitative effects of UVR on coral reef organisms, usually in experiments comparing the biological response to the presence or absence of UVR through the use of UV-cutoff filters, or to varying levels of UVR in transplantation studies. Most such studies have not distinguished between the effects of UVA (320–400 nm) and those of UVB (290–320 nm), although in the context of global change involving stratospheric ozone loss, it is the latter wavelengths that are relevant. To date we have been addressing physiological and ecological questions, not yet attempting to evaluate quantitatively the impact of forecast increases in solar UVB penetration. Interacting and synergistic effects of UVR with increased temperature, pollutants, sedimentation, visible light, etc. have scarcely been studied but will be essential to understanding and predicting the fate of coral reefs under conditions of global change. Here we comprehensively review the effects of UVR on corals and other reef macroorganisms, mindful that although much is known of proximal effects, little of this knowledge is directly useful in making long-term predictions regarding the health of coral reefs. We conclude that even small anthropogenic increases in UVB levels will have sublethal physiological manifestations in corals and other reef organisms, but that this will have relatively small impact on the distribution of reef corals and coral reefs, perhaps affecting their minimum depths of occurrence.