Morphological functions of gibberellins in leptosporangiate fern gametophytes: insights into the evolution of form and gender expression

In addition to genetic load, the induction of maleness in leptosporangiate gametophytes by the pheromone antheridiogen may facilitate rates of outcrossing similar to those found in angiosperms. The antheridiogens that have been chemically identified are similar to gibberellins and probably evolved from this common plant hormone. The purposes of this study were to determine the functions of endogenous gibberellins in morphological development and gender expression in leptosporangiate fern gametophytes and to elucidate how antheridiogens may have evolved from gibberellin precursors. We grew gametophytes of Osmunda regalis and Athyrium filix‐femina on nutrient agar enriched with APOGEE, which blocks gibberellin synthesis. Osmunda regalis is a member of Osmundaceae, the only family in Osmundales, the sister group of all remaining extant leptosporangiate ferns. This family possesses a male‐first gender in isolation and lacks any known antheridiogen systems. In contrast, A. filix‐femina is a member of a derived family, Woodsiaceae, which possesses antheridiogen systems. Disruption of gibberellin synthesis retarded notch development and expression of both maleness and femaleness (i.e. gender status) in both species. On the basis of these results, we offer a simple model of gametophyte evolution driven by gender‐based fitness gain curves and the influence of exogenous gibberellins. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 599–615.     

Constitutive and induced resistance to pathogens in Arabidopsis thaliana depends on nitrogen supply

Knowledge about the induced pathogen resistance of plants is rapidly increasing, but little information exists on its dependence on abiotic growing conditions. Arabidopsis thaliana plants that had been cultivated under different nitrogen regimes were treated with BION^®, a chemical resistance elicitor. The activities of three enzyme classes functionally involved in resistance (chitinase, chitosanase and peroxidase) were quantified over 8 d following treatment as resistance markers. Constitutive levels of three markers and the induced level of peroxidase and chitinase activity were significantly lower under limiting nitrogen supply. Under such conditions the increase of chitosanase activity after resistance induction was severely delayed, although the induced maximum activity of chitosanase was not significantly affected. Total soluble protein content decreased during the first 12 h after resistance elicitation. Thereafter, the induced plants cultivated under high N conditions reached higher protein contents than controls, whereas N‐limited induced plants continuously had reduced protein contents. A plant's investment in resistance‐related compounds can be severely constrained under limiting nitrogen supply.     

The biology of Creatonotos (Lepidoptera: Arctiidae) with special reference to the androconial system

The reproductive biology of the arctiid moths Creatonotos transiens and C. gangis exhibits a novel ontogenetic phenomenon, the morphogenesis of male coremata size being directly controlled by the quantity of hostplant-derived pyrrolizidine alkaloids ingested by the larvae. In addition, the same alkaloids directly control the quantity of male pheromones synthesized and available for deployment by these scent organs. Reproduction in these insects thus shows striking linkages between ecological, behavioural, chemical and morphological features. This paper presents an account of the general biology of the moths, and reviews the literature on Creatonotos as a basis for reports on experimental work.     

Localization of Thermo-Osmotically Active Partitions in Young Leaves of Nuphar lutea

The submerged roots and rhizomes of the aquatic vascular macrophyteNuphar lutea (L.) Sm. are aerated, at least in part, by pressurizedventilation. Depending on temperature differences of up to 5K between the inside of young, just-emerged leaves and the surroundingair, pressure differences of 79 to 100 Pa higher than atmosphericare detectable inside the lacunuous spongy parenchyma of theleaf blades. The pressurization is a consequence of structuralfeatures of leaf tissues separating the air filled spaces ofthe spongy parenchyma from the atmosphere. These tissues areacting as thermo-osmotic partitions. Whereas the dimensionsof the stomatal openings (about 5·6 x 2·4 µm)and of the intercellular spaces of the palisade parenchyma (diametersabout 15 µm) are too large, those of the monolayers ofcells separating the palisade and the spongy parenchyma (diameters:0·7–1·2 µm) are small enough to impedefree gaseous diffusion. This inner non-homogeneous partitioninggives rise to the so-called Knudsen diffusion, a physical phenomenonleading to pressurization of the warmer air inside the spongyparenchyma. The rising pressure difference is strong enoughto establish an air flow through the aerenchyma of the wholeplant and out of the most porous older leaves in which a temperatureinduced pressurization is never detectable. These thermo-osmoticallyactive leaves enhance the influx of air to the rhizome and thediffusion path for oxygen to the roots is shortened to the distancebetween rhizome and root tips. Therefore, pressurized ventilationin Nuphar is seen to be of considerable ecological importancefor plant life in anaerobic environments. Key words: Aeration, leaf anatomy, thermo-osmosis of gases, Nuphar lutea     

Effects of flow and refugia on drift loss of benthic macroinvertebrates: implications for habitat restoration in lowland streams

• 1 Current stream restoration practices are rarely based on sufficient knowledge of the physical-habitat requirements of the biota. In this study the drift loss of two lowland stream benthic macroinvertebrates, Gammarus pulex (L.) (Amphipoda, Crustacea) and Ephemerella ignita (Poda) (Ephemeroptera, Insecta), was investigated over gradients of flow forces and abundance of woody debris in laboratory flume experiments.
• 2 The losses by drift of E. ignita and G. pulex increased significantly at median flume shear stresses of approximately 11 and 31 dyn cm^?2, respectively.
• 3 Above these critical shear-stress values the population losses of both species significantly decreased with increasing abundance of stationary woody debris.
• 4 Ephemerella ignita exhibited high population loss in the first period of hydraulic disturbance. Gammarus pulex was affected in a different way, showing an almost constant population loss over time. In contrast to E. ignita, G. pulex used the refugium ‘woody debris’ actively and more efficiently.
• 5 Restoration concepts of lowland running waters have to consider hydraulic disturbance by flow as a key element for potential benthic community recovery.
• 6 Woody debris in the baseflow channel of lowland streams appears to mitigate the impact of hydraulic disturbance to benthic macroinvertebrates caused by rising discharge.

     

Hemicellulosic Polysaccharides from the Xylopodium of Ocimum nudicaule: Changes in Composition in Dormancy and Sprouting

Changes in the yield and composition of hemicelluloses fromthe underground organs (xylopodia) of Ocimum nudicaule wereinvestigated. Hemicelluloses constituted about 12% of the delipidizedpowder in sprouting and about 30 % in dormant phases. Xyloseis the major component of hemicelluloses A and B (and is alsopresent in C), followed by arabinose, galactose, glucose, rhamnoseand mannose. The amounts of hemicellulose B decreased by sixtimes between dormancy and sprouting, whereas the yields ofhemicelluloses A and C remained constant. This, together withthe higher solubility of hemicellulose B and its higher susceptibilityto hemicellulase in sprouting indicates that this fraction constitutesa cell-wall bound storage polysaccharide, which may play a rolein the onset of xylopodia bud sprouting. Ocimum nudicaule, hemicelluloses, cell-wall storage polysaccharide     

Cytoplasmic Free Ca2+ in the Marine Alga Acetabularia: Measurement with Ca2+ -selective Microelectrodes and Kinetic Analysis

Neutral carrier–based Ca²⁺ –selective microelectrodeshave been examined for application in concentrated multi–ionsolutions. Calculations with data from the literature and ourcalibration series with Ca²⁺ –EGTA buffers (a convenientalgorithm for theircalculation is given) provide the physico–chemicalconditions for determination of submicromolar concentrationsof free Ca²⁺ in the cytoplasm (with about 400 mM K⁺ and 70 mMNa⁺) of the marine alga Acetabularia acetabulum. The experimentalresults give a cytoplasmic concentration of 560 nM free Ca²⁺corresponding to 140 nM activity. Recordings of cytoplasmicCa²⁺ uponremoval and re-addition of external (10 mM) Ca²⁺ showsteady–state changes by about 50 nM (following the directionof external Ca²⁺) which are preceded by transient over shoots.These kinetics are better described by damped oscillations ofa feedback control system than by two superimposed exponentials.Using the maximum rate of decrease of cytoplasmic Ca²⁺ uponremovalof external Ca²⁺, a unidirectional Ca²⁺ efflux of 0.3µmol m^–2 s^–1 is determined which is consideredto mark the steady–state turnover of Ca²⁺ at the plasmalemma.This high rate and the high electrochemical driving force forCa²⁺ (about – 580 mV)across the plasmalemma at a restingvoltage of about – 170 mV, point to a powerful Ca²⁺ transportsystem which cannot sufficiently be fuelled by ATP–hydrolysisbut requires additional energy Key words: Acetabularia, Ca²⁺–selective microelectrode, cytoplasmic free calcium, EGTA–buffer, homeostasis, plasmalemma