A critical analysis of the causes of boron toxicity in plants

This study investigated the main factors contributing to boron toxicity in plants. Growth was rapidly inhibited by internal B concentrations in the range 1–5 m m across a range of plant types that included monocot, dicot and algal species. In contrast, mature cells were able to withstand up to 60 m m B for several days. In wheat, rapid inhibition of root growth occurred if high B was applied to the root tip, but not if high B was applied to mature sections of the root. In leaves, there were gradations in B concentrations that correlated with visible symptoms of toxicity. However, there was no evidence to support the hypothesis that toxicity in leaves is due to osmotic stress induced by the accumulation of B. Analysis of the sensitivity to B of a range of metabolic processes including photosynthesis, respiration and protein synthesis leads to the conclusion that growth is not restricted by effects of B on energy supply and not directly by inhibition of protein synthesis. At higher B concentrations, many cellular activities were found to be partially inhibited and the toxicity to mature tissues was therefore considered not to arise from the disruption of a single process, but from the accumulated retardation of many cellular processes, exacerbated in light by photo‐oxidative stress.     

Nest-site habitat selected by Short-toed Eagles Circaetus gallicus in Dadia Forest (northeastern Greece)

Data concerning habitat characteristics and general physiographic characteristics at 29 Short-toed Eagle Circaetus gallicus nest-sites (circular plot of 0.4 ha centred on the nest tree) were collected and compared with the same number of paired randomly selected plots in Dadia-Lefkimi-Soufli forest complex, northeast Greece. Short-toed Eagles used southern slopes for nesting and nest-sites were often located on the upper third of each slope. Nest trees were found significantly closer to rain water gullies, to the boundary of a different habitat type, and to the nearest forest opening greater than 0.5 ha than the randomly selected nest trees. Nest-sites had a significantly lower mean score of human disturbance than random sites and were found in mature pine forest associations, dominated by Calabrian Pine Pinus brutia or Black Pine P. nigra. The total tree density of Short-toed Eagle nest-sites was lower than random sites. Canopy cover in the dominant and intermediate tree layer at nest-sites was lower than at random sites. Short-toed Eagles tended to select sites for nesting that provided a combination of easy access and maximum shelter of the nest content from predators and inclement weather. The preservation of open structure of mature pine stands on south facing slopes near clearings may be critical for the continued conservation of the Short-toed Eagle in actively managed forests, such as the Dadia-Lefkimi-Soufli forest complex.     

Gibberellin-like Substances in the Sporophores of Agaricus bisporus (Lange) Imbach

Sporophores of cultivated Agaricus bisporus (Lange) Imbach,were shown to contain a gibberellin-like substance active inthe dwarf maize (d-5), -amylase and other bioassays. Ethyl-acetateextraction followed by paper, column, and thin-layer chromatographyrevealed the presence of one major active substance. Ficin hydrolysisof dried sporophore powder, after the complete removal of freesubstances, released more gibberellin-like substances, one ofwhich appeared identical to the free compound. The free substance was predominantly in the lamellae and residualpileus tissue. The major active substance released by ficinoccurred mostly in the lamellae but also in substantial equalamounts in both stipes and pilei. No activity was found in extractsof dikaryotic vegetative mycelium on malt agar. The level ofactivity in extracts from sporophores stored at – 20 °Cfell sharply after 7 d, and then remained constant over a periodof 6 weeks. The content of gibberellin-like substances in youngand old whole sporophores showed wide variation between experiments.In most cases young 2-d tissue had higher levels than old, 11-dtissue on a fresh-weight basis. Purified sporophore extractsand authentic gibberellins had no stimulating effect on growthof sporophores or of cultured vegetative mycelium. The inhibitorsof diterpene biosynthesis, CCC, and AMO-1618 induced a smallincrease in mycelial growth rate. Ethyl-acetate extraction ofhorse-straw compost prior to inoculation with Agaricus bisporusshowed the presence of gibberellin-like activity in significantamounts.     

Missing methane emissions from leaves of terrestrial plants

The controversial claim that attached leaves of terrestrial plants emit CH₄ aerobically remains to be corroborated. Here, we report CH₄ fluxes and CO₂ exchange rates for leaves of the C₄ species Zea mays using a high-accuracy traceable online analytical system. In contrast to earlier results for Z. mays , our measurements provide no evidence for substantial aerobic CH₄ emissions from photosynthesizing leaves illuminated with photosynthetically active radiation ( λ =400–700 nm), or from dark-respiring leaves. Preliminary measurements with the same system indicated a similar lack of aerobic CH₄ emissions in the light or dark from leaves of the C₃ species Nicotiana tabacum . These findings are supported by independent high-precision ¹³C-labeling studies that also failed to confirm substantial aerobic CH₄ emissions from plants. Nevertheless, we are not able to exclude the possibility that CH₄ emissions from plants may be linked to nonenzymatic processes with an action spectrum lying outside the wavelength range for photosynthesis.     

FUNCTIONAL MORPHOLOGY AND DESCRIPTION OF A NEW SPECIES OF AMYGDALUM (MYTILOIDEA) FROM THE OXYGEN MINIMUM ZONE OF THE ARABIAN SEA

A new species of Amygdalum (Amygdalum anoxicolum n. sp.) isdescribed living in the soft green muds of the oxygen minimumzone off the Oman margin in the northern Arabian Sea. It isdistinguished by both its shell and anatomical characters. Theanatomy is described and discussed in relation to the environment.The presence of haemoglobin is viewed as a direct adaptationto the low levels of oxygen found in its habitat. The observedwide size range of ingested food particles is discussed in relationto the low oxygen environment. The nest building habit is assumedto be a key adaptation to living in soft, high porosity mud.The distribution of the genus is examined in relation to thedistribution of known zones of hypoxia in the world9s oceans,but no relationship is evident. Amygdalum species are not indicatorsof low oxygen environments. (Received 17 August 2000; accepted 14 November 2000)     

Visual fields in Blue Ducks Hymenolaimus malacorhynchos and Pink-eared Ducks Malacorhynchus membranaceus: visual and tactile foraging

Blue Ducks Hymenolaimus malacorhynchos (Anatidae), an IUCN Red Listed Endangered species, reside in headwaters of New Zealand rivers and feed primarily on aquatic invertebrates. However, whether such food items are detected by tactile or visual cues is unknown. That Blue Ducks may use tactile cues when foraging is suggested by the presence of specialized flaps of thickened, keratinized epidermis containing Herbst's corpuscles along the ventral margins of the upper mandibles near the bill tip. Similar bill flaps are found only in one other duck species, Pink-eared Ducks Malacorhynchus membranaceus , that surface filter-feed on a range of planktonic organisms. Using an ophthalmoscopic reflex technique we determined the visual fields of both species. In Blue Ducks the eyes are frontally placed resulting in a relatively wide binocular field into which the narrow tapering bill intrudes. There is a large blind area to the rear of the head. This visual field topography is similar to that of other visually guided foragers including those that take mobile prey from the water column, e.g. penguins (Spheniscidae). By contrast, Pink-eared Duck visual fields show features found in other tactile feeding ducks: a narrow frontal binocular field with the bill falling at the periphery, and comprehensive visual coverage of the celestial hemisphere. We conclude that although Blue Ducks may take prey from rock surfaces they are primarily visual feeders of the water column and we suggest therefore that their foraging may be significantly disrupted by changes in water clarity. This introduces a previously unconsidered factor into the selection of sites for population enhancement or re-introductions, a current conservation focus.     

Phenotypic variation in colour pattern and seasonal plasticity in Eristalis hoverflies (Diptera: Syrphidae)

Abstract.

• 1 An examination of phenotypic variation in colour pattern was carried out on four Eristalis hoverfly species using museum material.
• 2 The amount of phenotypic variation varied substantially among the species with E.arbustorum being the most variable. The other species showed a wide colour pattern range but less variation within that range (E.abusivus and E.nemorum), or a narrow range of colour variation (E.horticola).
• 3 Sexual colour dimorphism was apparent in all four species, but most pronounced in E.abusivus and E.nemorum.
• 4 There were good phenotype-season relationships shown by both sexes in all species, except for female E.abusivus and E.nemorum, with paler insects being more abundant during the warmer summer months.
• 5 Female, but not male, E.arbustorum collected at inland sites were on average paler than those collected at coastal sites. This observation is considered with respect to temperature during the developmental stages.
• 6 The function of colour plasticity in hoverflies is discussed with reference to the need to maintain optimal thermal conditions for activity.

     

Cladistic analysis of the Lythraceae sensu lato based on morphological characters

GRAHAM, S. A., CRISCI, J. V. & HOCH, P. C, 1993. Cladistic analysis of the Lythraceae sensu lato based on morphological characters. The Lythraceae s. I. comprise 31 mostly highly distinctive genera distributed worldwide. Cladistic analyses of the family were undertaken using 26 characters from anatomy, floral morphology, pollen, and seed morphology. Of four outgroup hypotheses, the Onagraceae offered the best heuristic assessment, generating 3746 trees with a tree length of 83 and consistency index and (C.I.) of 0.41. A strict consensus tree from the 3746 trees produced a basal monophyletic group of five genera (Sonneratia, Duabanga, Punka, Lagerstroemia, Lawsonia) characterized by anthotelic (determinate) inflorescences and wet stigmas, and a second clade with blastotelic (indeterminate) inflorescences, dry stigmas, and reduced carpel number. Successive weighting with Onagraceae as outgroup generated five most parsimonious trees with a tree length of 164 and C.I. of 0.75. Internal branches are weakly supported by only seven non-homoplasious characters. Significant results of the analysis include: (1) recognition of the two major clades and a total of seven monophyletic groups within the family; (2) the paraphyly of subfamily Lythroideae (Lythraceae s. s .); and (3) indication that genera endemic to the New World have been derived from more than one ancient Old World evolutionary line. The current taxonomic classification of the family is not closely correlated with results of the cladistic analysis.     

Foraging movements of the Shy Albatross Diomedea cauta breeding in Australia; implications for interactions with longline fisheries

Satellite telemetry was used to identify the foraging zones of Shy Albatrosses Diomedea cauta breeding at two sites off Tasmania, Australia (Albatross Island in western Bass Strait and Pedra Branca to the south) to assess their level of interaction with longline fisheries. Adult birds from both colonies fed locally both in and outside the breeding season. Breeding birds from Albatross Island foraged over the Australian continental shelf or slope waters off northwest Tasmania, while those from Pedra Branca foraged between the colony and the southeastern edge of the continental shelf. The distances travelled by the birds and the duration of their foraging trips varied during the breeding cycle and tended to decrease as eggs approached hatching. Adults which were tracked near the end of the breeding season (March-April, n = 7 birds) deserted their chicks prematurely, and while dispersing further than incubating or brooding birds, they remained over the continental shelf and slope waters off southeast Australia. Home range analyses indicated 41% overlap between foraging zones of birds during successive breeding stages. Dispersal during the postbreeding period extended the foraging zones with less overlap between individuals (10% for Albatross Island and 19% for Pedra Branca). The recent contraction of the Japanese Southern Bluefin Tuna longline fishery to the south and east coasts of Tasmania has resulted in extensive overlap with adult Shy Albatrosses from Pedra Branca, but appears to pose a minimal threat to adult birds from Albatross Island. Coupled with the concomitant increase in the Australian domestic tuna longlining industry, adult Shy Albatrosses from southern Tasmania (Pedra Branca and the Mewstone) are vulnerable to incidental capture through out their annual cycle.     

Phytophthora cryptogea root rot of tomato in rock woo] nutrient culture. II. Effect of root zone temperature on infection, sporulation and symptom development

The effect of root-zone temperature on Phytophthora cryptogea root rot was studied in tomato cv. Counter grown under winter and summer conditions in rockwool culture. A nutrient temperature of 25°C resulted in increased root initiation and growth, higher in winter-grown than in summer-grown plants. Rhizosphere zoospore populations were greatly reduced at 25°C and above. Growth of P. cryptogea in vitro was optimal between 20°C and 25°C and completely suppressed at 30°C. Encystment was enhanced by increased temperatures above 20°C. Zoospore release in vitro occurred in cultures maintained at constant temperatures in the absence of the normal chilling stimulus. Optimal release was at 10°C; no zoospores were released at 30°C. Inoculated, winter-grown tomato plants maintained at 15°C developed acute aerial symptoms and died after 21 days. Comparable plants grown at a root-zone temperature of 25°C remained symptomless for the 3-months duration of the experiment. Summer-grown infected plants at the higher root temperature wilted but did not die. Enhanced temperature was ineffective as a curative treatment in summer-grown plants with established infection. Aerial symptoms of Phytophthora infection are seen as a function of the net amount of available healthy root. With high root zone temperatures this is determined by new root production and decreased inoculum and infection.