Regulation of Internodal Extension in Avena Shoots by the Inflorescence, Nodes, Leaves, and Intercalary Meristem

It has been found in recent studies that the inflorescence and nodes (node-pulvini) are the primary sources for native gibberellins in the Avena shoot, and that GA₃ is the predominant gibberellin in the inflorescence. In the present work, linear growth of next-to-last internode is drastically reduced by removal of the inflorescence and last leaf. This growth is completely abolished when the nodes are also excised. It is restored fully by the addition of GA₃ when the nodes are present, and restored only partially when the nodes are deleted. Internodal growth in Avena stem segments with basal node present is also restored by native GA₃-like substances extracted from Avena inflorescences and partially purified by silica gel partition column chromatography. Evidence from these studies, taken in toto, indicates that the inflorescence, nodes, and leaves supply gibberellins, leaves supply substrate, and nodes modulate the gibberellin growth response in next-to-last Avena internodes.     

Light Interception and Photosynthetic Efficiency in Some Glasshouse Crops

Productivity of glasshouse crops is strongly limited by lightreceipt, and efficient interception and use of light in photosynthesisis correspondingly important. Mature row crop canopies of cucumberand tomato intercepted about 76% of the light incident on theirupper surfaces; about 18% was lost through gaps between therows. Light transmitted through the entire depth of the canopywas reflected back by white plastic on the ground, so that thelower surface of the canopy received approximately 13% of thelight incident on the upper surface. The light flux incidenton the sides of these canopies (c. 2m tall and 6m x 16m in area)amounted to some 20–30% of that incident on the uppersurface. About 32% of daylight falling on the glasshouse (c.9m x 18m in area) was intercepted by the glasshouse structureand glazing; of the 68% entering the house, some fell on headlandsoccupying 35% of the glasshouse area. The loss of light to headlands,and the gain from canopy side-lighting, would be relativelysmaller for larger glasshouses. At near-ambient CO₂ concentrations, net photosynthetic ratesof the cucumber canopy were comparable to those of closed canopiesof other glasshouse and field crops which have maximum lightconversion efficiencies of 5–8µg CO₂ J^–1 at50–200 W m^–2 incident light flux density. Efficiencydecreases only slightly with stronger light. Glasshouse cropswith CO₂ enrichment to 1200 vpm achieve conversion efficienciesof 7–10µg CO₂ J^–1. Efficiencies of utilizationof intercepted light, on an energy basis, reach 6–10%in various field and glasshouse crops with near-ambient CO₂,and reached an exceptional 11% for the cucumber canopy. Glasshousecrops with CO₂ enrichment achieve maximum efficiency of lightenergy utilization between 12% and 13%. Key words: Glasshouse cucumber and tomato, light interception and utilization, photosynthetic efficiency, row crops     

Respiration and Circulation in Land Crabs: Novel Variations on the Marine Design

Both the "true" crabs (Brachyura) and hermit crabs (Anomura)include species that show numerous behavioral, morphological,and physiological specializations permitting terrestrial life.This paper examines respiratory and circulatory adaptationsfor air breathing in these land crabs. Respiratory specializationsinclude modification of gas exchange structures for air breathing(gills and elaborated branchial chamber linings), ventilatorymechanisms permitting effective air pumping, an elevated hemolymphoxygen capacity, and a primarily CO₂- rather than O₂- sensitiveventilatory control system. The qualitative aspects of hemolymphoxygen transport and metabolic rate are apparently unchangedfrom that of marine crabs. While the basic cardiovascular morphologyof land crabs appears similar to that of marine forms, thereis considerable elaboration of the vasculature of the branchialchamber lining, which in some species includes a unique doubleportal system. Cardiac output is lower in land crabs (probablyrelated to their higher hemolymph O₂ capacity), but insufficientdata on hemolymph pressures prevent comparisons with marineforms. In general, land crabs have modified (sometimes extensively)existing structures and processes found in their marine relativesrather than evolving structures for terrestrial life de novo.Accordingly, land crabs present a useful model for the evolutionof terrestriality, showing that even subtle anatomical changescan result in the large changes in physiological function necessaryfor the terrestrial invasion.     

Seasonal and diel periodicity in the drift of aquatic insects in a subtropical Florida stream

A study of insect drift was conducted in a small, subtropical Florida stream from December 1971 to December 1972 to describe the seasonal and diel periodicity and to determine factors influencing behavioural drift. Paired samples of 2 h duration beginning 15 min after sunset were taken biweekly, and hourly collections over a 24-h period were made quarterly. Benthic invertebrates were collected on each date from three habitats (riffle, pool and aquatic vegetation) and temperature, dissolved oxygen and current velocity were measured. Drift rates ranged from 100 to 2125 organisms/m². h (0·03 to 0·49 organisms/m³) and were greatest in winter and early spring; minimal rates occurred in the summer months. The following six taxa, in order of relative abundance, comprised 87% of the drift: Baetis intercalaris, Cheumatopsyche sp., Stenonema exiguum, Chironomidae, Stenelmis fuscata and Simulium sp. Total drift showed no significant correlation with temperature, dissolved oxygen or mean benthic abundance and only slight correlation with current velocity (r=0·34). Stepwise, multiple regression analyses indicated that riffle density and mean size of drifting organisms were important factors influencing the drift rates of B. intercalaris (R=0·67) and S. exiguum (R=0·82); mean size, riffle density and water temperature influenced the drift of Cheumatopsyche sp. (R=0·78). The other taxa of drifting insects showed no significant correlation with the variables measured. Diel (24 h) studies of the major taxa showed marked differences in the periodicity, both within and between taxa, indicating the need for long-term studies with frequent sample intervals in subtropical habitats. A new drift pattern for the family Chironomidae, alternans type, was observed for late instars of Polypedilum halterale.     

TRIANGULAR DIFFERENCE TESTING: REFINEMENTS TO SEQUENTIAL SENSITIVITY ANALYSIS FOR PREDICTIONS FOR INDIVIDUAL TRIADS

Using a model system of 3mM NaCl and purified water, predictions were made for subjects’ability to discriminate the odd sample in a set of nine triadic tasting sequences associated with the triangle test. With such individual triads rather than triangular testing protocols which involve more than one triad, it was found necessary to modify the regular Sequential Sensitivity Analysis. The modification required a consideration of sensory adaptation effects caused by repeated tasting of the same stimulus in some of the sequences. Further confirmation was also obtained for the order of magnitude of signal strengths of water and NaCl stimuli tasted after water or NaCl prerinses.     

Nuisance growth of Juncus bulbosus: the roles of genetics and environmental drivers tested in a large‐scale survey

1. Invasive species can transform aquatic ecosystems, and the nuisance growth of the freshwater macrophyte Juncus bulbosus has become a problem in many lakes and rivers in northern Europe. It affects biodiversity strongly and conflicts with human uses, not least compromising the generation of hydroelectricity. The causes of the proliferation of these massive stands of J. bulbosus are not finally resolved, however. 2. In this study, a wide range of catchment, lake and sediment parameters (n = 34) were assessed for 139 lakes in Southern Norway, with the aim of explaining the presence or absence of J. bulbosus and to assess potential drivers behind its prolific growth. 3. Juncus bulbosus was more often present in lakes with lower pH and phosphate concentrations, and a higher element ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (DIN : TotP). 4. Despite the many parameters measured across substantial environmental gradients, none explained nuisance growth. Genetic screening (amplified fragment length polymorphism fingerprinting) of plants from a subset of lakes and additional river sites also showed no genetic differences between the various growth forms. A macrophyte trophic index, however, suggested that the most problematic growth occurred in the most oligotrophic lakes. 5. The lack of consistent patterns may reflect either factors not assessed in our survey, or that the current extension of stands represents a gradual cumulative response over time, not characterised effectively in our snapshot survey. Nevertheless, we can now exclude some putative causes of nuisance growth, including in particular genetics and N‐deposition.     

Aspects of the Water Relations of Ileostylus micranthus (Hook. f.) Tieghem, a New Zealand Mistletoe

Leaf water potentials in the mistletoe, Ileostylus micranthusgrowing outdoors decreased rapidly during the early part ofthe day but remained relatively steady in the early afternoondespite increases in atmospheric vapour pressure deficit (vpd).Minimum water potentials of the mistletoe were relatively constant.They were held at values lower than those of hosts when thelatter maintained high water potentials but approached or evenexceeded those of hosts when they developed low water potentials.In contrast, cut shoots of Ileostylus usually maintained higherwater contents and leaf water potentials than those of its hostswhen both were desiccated separately in the laboratory. Pressure-volumeanalyses indicated that Ileostylus had lower water potentialat full turgor, a lower water potential but higher relativewater content at turgor loss, and a higher bulk modulus of elasticitythan the following four hosts: the native Kunzea ericoides andCoprosmapropinqua, and the introduced Ribes sanguineum and Teline monspessulana.Water potential at turgor loss (_tlp) was strongly correlatedwith the minimum field water potential of both mistletoes andhosts. When _tlpof mistletoe and host is similar (as on Kunzeaand Ribes) field water potentials are also similar, but when_tlpis lower in the mistletoe (as on Coprosma and Teline), thefield water potential of the mistletoe is lower than that ofits host. Consequently, I. micranthus is likely to be more frequenton hosts that maintain high field water potentials than on hoststhat develop low water potentials. Copyright 1999 Annals ofBotany Company Water relations, water potential, osmotic potential, pressure-volume, Ileostylus micranthus , mistletoe, New Zealand.