Variations in the geotropic sensitivity of germinating Funaria spores in response to some external influences

Experiments on the germination of the spores of Funaria have established the following.

• 1. 

  Some growth substances such as vitamins slightly promote the geotropic response of germinating spores in darkness.
• 2. 

  Glucose, even in concentrations as low as 10 mg./L, strongly stimulates the geotropic response.
• 3. 

  Light (at an intensity of 1000 lux and more) strongly inhibits the geotropic response. This effect is probably phototonic and can be partly counteracted by glucose.
• 4. 

  The nature of the phototropic and geotropic reactions of chloronema is variable, and depends to a certain extent on environmental influences.

     

Trifluralin herbicide-induced resistance of melon to fusarium wilt involves expression of stress- and defence-related genes

To identify genes involved in trifluralin herbicide-induced resistance of melon to Fusarium oxysporum f. sp. melonis , suppression subtractive hybridization (SSH) and cDNA-amplified fragment-length polymorphism (cDNA-AFLP) were used. A total of 123 clones—60 of which have never been isolated from melon—were isolated, sequenced and annotated. A significant proportion (35%) of the total 123 clones exhibited similarity to genes that have been formerly described as stress- or defence-related. Thirty-two selected clones were subjected to a detailed expression analysis, one-third of which were found to be up-regulated in response to trifluralin treatment and/or fusarium inoculation. The putative roles of seven of these clones in stress are discussed. Furthermore, the expression of four stress-related and up-regulated genes was enhanced when the plants were subjected to salinity stress, suggesting that trifluralin induces a general stress response which protects the plant against fusarium wilt.     

Visual fields in the Black-crowned Night Heron Nycticorax nycticorax: nocturnality does not result in owl-like features

Compared with diurnally active species, the eyes of nocturnally active herons (Ardeidae) are relatively larger and more widely separated. These features are found in comparisons between the nocturnally foraging Black-crowned Night Heron Nycticorax nycticorax and the diurnally active Cattle Egret Bubulcus ibis. Casual viewing of the Black-crowned Night Heron gives the impression of a somewhat owl-like appearance, with an apparently wide degree of binocular overlap. Visual fields and eye movements were determined in two alert, restrained Black-crowned Night Herons with the use of an ophthalmoscopic technique. A wide degree of binocular overlap was not confirmed, and the Black-crowned Night Heron's visual field closely resembles those of diurnally foraging herons (Western Reef Heron Egretta gularis schistacea , Squacco Heron Ardeola ralloides , Cattle Egret). The Black-crowned Night Heron's binocular field is vertically long and narrow (maximum width 22̀), with the bill placed approximately at the centre. Monocular and cyclopean field widths in the horizontal plane equal 171̀ and 320̀, respectively. Retinal binocular overlap can be abolished by eye movements. There is a blind sector (10–13̀ wide) at the margin of each eye's optical field, and this results in the functional retinal binocular field being much narrower than the optical binocular fields. It is these blind sectors which give rise to the appearance of a much wider binocular field. The visual field characteristics of this heron species may be best understood in relation to the foraging technique of capturing agile, evasive prey directly in the bill. The comparatively large size of the Black-crowned Night Herons' eyes may be associated with activity over a wide range of natural light levels but does not give rise to binocular fields larger than those of diurnal heron species.     

Phytochrome Pelletability in Barley

Phytochrome pelletability in the 1000 g and 20,000 g pellet from crude homogenates of etiolated Hordeum vulgare L. cv. Ark Royal primary leaves is enhanced by red light in vivo and in vitro. Red enhanced phytochrome pelletability appears different in the 1000 g and 20,000 g pellets after red light in vivo, being irreversible by subsequent far red light in the latter. Mg²⁺ concentration in the range 1–20 mM has no effect on red enhanced phytochrome pelletability. The enhancement of pelletability is reduced by low pH and high 2-mercaptoethanol concentration, conditions which lead to a high level of pelletability of the far red absorbing form of phytochrome. Washing these pellets at high pH or low 2-mercaptoethanol concentration reveals the red enhancement of pelletability. The results are discussed in terms of a possible two point attachment of phytochrome to membranes.     

Visual fields in the Stone-curlew Burhinus oedicnemus

The Stone-curlew Burhinus oedicnemus is a short-billed terrestrial wading bird (Burhinidae; Charadriiformes) which forages primarily for surface living invertebrates in open, sparsely vegetated habitats during twilight and nighttime. Visual field topography in restrained alert birds was investigated using an ophthalmoscopic reflex technique. The visual fields have the following features: (1) Eye movements of significant amplitude appear to be absent. (2) The retinal binocular field is relatively small, with the bill placed near its centre. It extends vertically through 80° in the median sagittal plane with a maximum width of 18° occurring 5° above the bill. (3) With the head in a typical posture (eye-bill-tip angle approximately 15° below the horizontal), the binocular field stretches from 60° below to 20° above the horizontal. (4) The blind area behind the head is relatively narrow (15° at the horizontal), giving the bird near panoramic vision in the horizontal plane, but the widest blind area (32°) occurs directly above the head. (5) Monocular retinal fields in the horizontal plane are 182° wide and are asymmetric about the optic axis. (6) There is a blind sector of 7–12° at the margin of the optical fields, indicating that binocular field widths are not maximized. Interspecific comparisons of these visual field features suggest that the foraging of Stone-curlews is guided primarily by visual cues.     

Orthophosphate Absorption by the Sporophyte of Funaria Hygrometrica During Maturation

The absorption of phosphate by the sporophyte of Funaria hygrometrica,during its maturation, has been studied using ³²P. More radioactivitywas found in the capsule when the absorption occured throughthe seta alone than when it look place through the leaves ofthe gametophyte. Each stage of capsule development studied isdescribed from transverse sections and electron micrographs.Phosphate is accumulated very actively by the capsule in theyoungest stage when the spores are being formed. The exchangesbetween the capsular tissues and the spores are low.     

Salinity Stress and the Content of Proline in Roots of Pisum sativum and Tamarix tetragyna

Amino acid composition of the free amino acid pool and the TCA-insolubleprotein fraction were investigated in root tips of pea and Tamarixtetragyna plants grown at various levels of NaCl salinity. Salinitystress induced an increase of proline content, mainly in thefree amino acid pool in both plants, and of proline or hydroxyprolinecontent in the protein. Externally-supplied proline was absorbedand incorporated into protein, by pea roots, more effectivelythan by Tamarix roots. Salinity stress, apparently, stimulatedthe metabolism of externally-supplied labelled proline. Pearoots have a very large pool of free glutamic acid; however,70 per cent of the ¹⁴C from externally-supplied ¹⁴C-U-glutamicacid was released as CO₂. Very small amounts of it were incorporatedinto protein. No measurable amount of radioactivity could bedetected in any one of the individual amino acids, either ofprotein hydrolysate or the free amino acid pool. Proline very effectively counteracted the inhibitory effectof NaCl on pea seed germination and root growth. A similar effectbut to a lesser degree was achieved with phenylalanine and asparticacid. The feasibility of proline being a cytoplasmic osmoticumis discussed.     

Histochemical Localization of Citral Accumulation in Lemongrass Leaves (Cymbopogon citratus(DC.) Stapf., Poaceae)

Lemongrasses (Cymbopogonspp., Poaceae) are a group of commerciallyimportant C₄tropical grasses. Their leaves contain up to 1.5%(d.wt) essential oils with a typical lemon-like aroma, consistingmainly of citral (a mixture of the isomeric acyclic monoterpenealdehydes geranial and neral). To specifically locate the sitesof citral accumulation in lemongrass we employed Schiff's reagent,which reacts with aldehydes and gives a purple-red colorationwith citral. Using this technique, single oil-accumulating cellswere detected in the adaxial side of leaf mesophyll, commonlyadjacent to non-photosynthetic tissue, and between vascularbundles. Cell walls of these oil cells are lignified. Our resultssuggest that citral accumulation takes place in individual oilcells within the leaf tissues.Copyright 1998 Annals of BotanyCompany Lemongrass;Cymbopogon citratus; Poaceae; oil cells; histochemistry; citral; aldehydes; Schiff's-reagent.