How drone flies (Eristalis tenax L., Syrphidae,Diptera) use floral guides to locate food sources

In this study we show how inexperienced syrphid flies, Eristalis tenax, orient on artificial flowers by means of floral guides. To test the effect of floral guides such as line and ring markings on the probability and speed of the location of a potential food source, we exploited the spontaneous proboscis reaction triggered by yellow colour stimuli. We tested whether and how fast the flies, when placed on the edge of a circular dummy flower, found a small central yellow spot and touched it with the proboscis extended. The flies found the central yellow spot more often and faster if guide lines from the margin to the yellow spot were present. The effect of guide lines was dependent on the colour of the dummy flower, and independent of the colour of the guide lines, except for yellow guide lines releasing the proboscis reaction. The effect of guide lines was stronger if the yellow spot was hidden in a 2 mm deep depression and thus not as easily visible to the flies. Ring guides had a significant effect on performance only when the intensity of the central yellow spot was low.     

Colour perception of single and mixed monochromatic lights in the blowfly Lucilia cuprina

Colour perception of spectral lights and mixtures of two monochromatic lights of blue and yellow wavelengths was studied in the blowfly Lucilia cuprina by using a generalization test in which the fly had to compare these lights in memory with coloured papers (blue, green, yellow and red) represented in the test array. Flies trained to a monochromatic light in the wavelength range of 429–491 nm responded to blue; those trained to 502–511 nm to green; and those trained to 522–582 nm to yellow. The maximal generalization for blue was found at 429 nm and that for yellow at 543 nm. Flies trained to the mixtures responded neither to blue, green nor yellow, when the blue component was mixed with the yellow component in a ratio of approximately 1 3. It seems that the fly perceives the mixtures as a neutral or an achromatic light. Colour loci of coloured papers, spectral lights and mixtures of two monochromatic lights used formed blue, yellow and neutral clusters in a colour triangle with respect to generalization responses to test colours.     

Bumblebees require visual pollen stimuli to initiate and multimodal stimuli to complete a full behavioral sequence in close‐range flower orientation

Flower visits are complex encounters, in which animals are attracted by floral signals, guided toward the site of the first physical contact with a flower, land, and finally take up floral rewards. At close range, signals of stamens and pollen play an important role to facilitate flower handling in bees, yet the pollen stimuli eliciting behavioral responses are poorly known. In this study, we test the response of flower‐naive bumblebees (Bombus terrestris) toward single and multimodal pollen stimuli as compared to natural dandelion pollen. As artificial pollen stimuli, we used the yellow flavonoid pigment quercetin, the scent compound eugenol, the amino acid proline, the monosaccharide glucose, and the texture of pollen‐grain‐sized glass pellets as a tactile stimulus. Three test stimuli, dandelion pollen, one out of various uni‐ and multimodal stimulus combinations, and a solvent control were presented simultaneously to individual bumblebees, whose response was recorded. The results indicate that bumblebees respond in an irreversible sequence of behavioral reactions. Bumblebees approached the visual stimulus quercetin as often as natural dandelion pollen. An additional olfactory stimulus resulted in slightly more frequent landings. The multimodal stimulus combinations including visual, olfactory, gustatory, and tactile stimuli elicited approaches, antennal contacts, and landings as often as natural pollen. Subsequent reactions like proboscis extension, mandible biting, and buzzing were more often but not regularly observed at dandelion pollen. Our study shows that visual signals of pollen are sufficient to trigger initial responses of bumblebees, whereas multimodal pollen stimuli elicit full behavioral response as compared to natural pollen. Our results suggest a major role of pollen cues for the attraction of bees toward flowers and also explain, why many floral guides mimic the visual signals of pollen and anthers, that is, the yellow and UV‐absorbing color, to direct bumblebees toward the site where they access the floral rewards.     

Phytochrome action in light-grown mustard: kinetics,fluence-rate compensation and ecological significance

Internode extension in young, light-grown mustard plants was measured continuously to a high degree of resolution using linear voltage displacement transducers. Plants were grown in background white light (WL) and the first internode was irradiated with supplementary far-red (FR) from fibre-optic light guides, depressing the Pfr/P (ratio of FR-absorbing form of phytochrome to total spectrophotometrically assayable phytochrome) within the internode and causing an acceleration of extension rate. The internode was sensitive to periods of FR as brief as 1 min, with a sharp increase in extension rate occurring after the return to background WL only. The mean latent period of the response to FR was approx. 10 min. Periods of FR longer than approx. 35 min caused an apparently biphasic growth response, with an initial sharp acceleration in extension rate (Phase 1) being followed by a brief deceleration and a further acceleration to a more-or-less steady elevated rate, somewhat less than the first peak (Phase 2). With such longer-term FR, extension rate decelerated upon FR switch-off after a mean lag of approx. 6 min, achieving the prestimulation extension rate within 16 min. The magnitude of the FR-induced increase in extension rate, expressed as a percentage of the rate in WL alone, was an inverse, linear function of the phytochrome photoequilibrium (i.e. Pfr/P, measured in etiolated test material irradiated under the same geometry) over the range 0.17 to 0.63. This relationship was not significantly affected by variations in backround WL fluence rate over the range 50–150 mol·m^-2·s^-1 and was held both for Phase 1 and Phase 2 of the response. The data provide evidence for rapid coupling/uncoupling between phytochrome and its transduction chain in the light-grown plant and for fluence-rate compensation of the regulation of extension rate. The extensive linearity of the relationship between phytochrome photoequilibrium and proportional extension rate increment allows for fine tuning in shade avoidance. The results are discussed with respect to recent evidence on the nature of phytochrome in light-grown plants and in relation to the function of phytochrome in plants growing in the natural environment.Abbreviations FR far-red light - LVDT linear voltage displacement transducer - P total spectrophotometrically assayable phytochrome - PAR photosynthetically active radiation (400–700 nm) - Pfr FR-absorbing form of phytochrome - Pr R-absorbing form of phytochrome - R red light - WL white light     

Effects of light quality on the chloroplastic ultrastructure and photosynthetic characteristics of cucumber seedlings

To understand how light quality influences plant photosynthesis, we investigated chloroplastic ultrastructure, chlorophyll fluorescence and photosynthetic parameters, Rubisco and chlorophyll content and photosynthesis-related genes expression in cucumber seedlings exposed to different light qualities: white, red, blue, yellow and green lights with the same photosynthetic photon flux density of 100 μmol m^?2 s^?1. The results revealed that plant growth, CO₂ assimilation rate and chlorophyll content were significantly reduced in the seedlings grown under red, blue, yellow and green lights as compared with those grown under white light, but each monochromatic light played its special role in regulating plant morphogenesis and photosynthesis. Seedling leaves were thickened and slightly curled; Rubisco biosynthesis, expression of the rca, rbcS and rbcL, the maximal photochemical efficiency of PSII (Fv/Fm) and quantum yield of PSII electron transport (Ф_PSII) were all increased in seedlings grown under blue light as compared with those grown under white light. Furthermore, the photosynthetic rate of seedlings grown under blue light was significantly increased, and leaf number and chlorophyll content of seedlings grown under red light were increased as compared with those exposed to other monochromatic lights. On the contrary, the seedlings grown under yellow and green lights were dwarf with the new leaves etiolated. Moreover, photosynthesis, Rubisco biosynthesis and relative gene expression were greatly decreased in seedlings grown under yellow and green light, but chloroplast structural features were less influenced. Interestingly, the Fv/Fm, Ф_PSII value and chlorophyll content of the seedlings grown under green light were much higher than those grown under yellow light.     

Spectral sensitivity of the photonegative reaction of the blood-sucking bug Triatoma infestans (Heteroptera: Reduviidae)

We studied the spectral sensitivity of the visual system of the blood-sucking bug Triatoma infestans, one of the main vectors of Chagas Disease in South America. We quantified the photonegative reaction of this insect in a rectangular arena, half of which was kept dark and the other half illuminated with various intensities of different monochromatic lights (or broadband stimuli for λ>665 nm). As a behavioral parameter of the photonegative response, we measured the time each insect spent in the dark half of the arena. We found that low intensity levels (under 0.06 μW/cm²) of monochromatic lights of 397, 458, 499, and 555 nm evoked a statistically significant (i.e., different from that of control groups) photonegative reaction. Insects were less sensitive to monochromatic lights of 357 nm (UV) and 621 nm (dark orange), and to broadband stimuli in the red part of the spectrum (665–695 nm). These findings indicate that the visual system of T. infestans is sensitive to broader regions of the spectrum than those previously reported.     

Acclimation of Arabidopsis thaliana to the light environment: Changes in composition of the photosynthetic apparatus

Acclimation to changes in the light environment was investigated in Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta. Plants grown under four light regimes showed differences in their development, morphology, photosynthetic performance and in the composition of the photosynthetic apparatus. Plants grown under high light showed higher maximum rates of oxygen evolution and lower levels of light-harvesting complexes than their low light-grown counterparts; plants transferred to low light showed rapid changes in maximum photosynthetic rate and chlorophyll-a/b ratio as they became acclimated to the new environment. In contrast, plants grown under lights of differing spectral quality showed significant differences in the ratio of photosystem II to photosystem I. These changes are consistent with a model in which photosynthetic metabolism provides signals which regulate the composition of the thylakoid membrane.Abbreviations Aac1 gene encoding actin - Chl chlorophyll - F far-red-enriched light (R:FR = 0.72) - FR far-red light - H high light (400 mol · m^–2 · s^–1) - L low light (100 ml · m^–2 · s^–1) - LHCII light-harvesting complex of PSII - Lhcb genes encoding the proteins of LHCII - R red light - Rbcs genes encoding the small subunit of Rubisco - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - W white light (R:FR = 1.40) This work was supported by Natural Environment Research Council Grant No. GR3/7571A. We would like to thank H. Smith (Botany Department, University of Leicester) and E. Murchie (University of Sheffield) for helpful discussions.     

Are carotenoids the blue-light photoreceptor in the photoinduction of protoperithecia in Neurospora crassa?

A triple albino mutant of Neurospora crassa with a measured content of carotenoids absorbing at 470 nm less than 0.5% of that of the wild type (calculated value less than 8·10^-4%) had the same threshold for photoinduction of protoperithecia as the wild type when illuminated with monochromatic light at 471 nm. This is strong evidence against the hypothesis that the bulk of carotenoids are the blue-light photoreceptor for this phenomenon. However, it is impossible to exclude traces of carotenoids acting as the photoreceptor at less than 3·10^-12 M in a very efficient sensory transduction chain.Abbreviations A absorbance - al albino mutant - WT wild type     

Blue light promotes ionic current influx at the growing apex ofVaucheria terrestris

Irradiation of the growing apex of the algaVaucheria terrestris Götz var.terrestris with blue light (BL), which causes a transient acceleration of growth, also causes a large transient increase in inwardly directed current, which was monitored with a vibrating probe. The growing apex is normally the site of an inward current, and the surface of the non-growing, basal part of the coenocytic cell the site of an outward current. Irradiation of the apex causes only a slight increase in current efflux at the basal part of the cell. The BL-promoted current influx at the apex (BLCI) usually starts within 10 s after the onset of irradiation, preceding the light-growth response. With BL pulses shorter than 3 min, the BLCI reaches a maximum in about 3 min, and then declines to its original value over the next 3 min. If the BL pulse is longer than 3 min, the BLCI continues until the light is turned off. The threshold energy of the BLCI with broad-band BL is 2–5 J·m^-2, i.e. smaller than for both the light-growth response and phototropic response. The maximum BLCI reaches a value of approx. 5 A·cm^-2, equivalent to an influx of 50 pmol·cm^-2·s^-1 of monovalent cations. The effect of red light (RL) is completely different from that of BL: it either causes increases in the inward current of less than 0.3 A·cm^-2, or a transient decrease of current. Furthermore, the direction of the RL-induced change is always the same at the apex and trunk, indicating the participation of photosynthesis. Our results indicate that the BLCI is kinetically and spatially related to the light-growth response and the phototropic bending ofVaucheria. It seems to be a necessary step for the phototropic bending.Abbreviations APW artificial pond water - BL blue light - BLCI blue-light-induced current influx - LGR light-growth response - RL red light     

Photomorphogenesis in Chenopodium album. Effects of supplementary far-red light on the kinetics of stem extension

The effects of far-red light given against a background of white light on the stem-extension kinetics of three-week-old, light-grown Chenopodium album seedlings were investigated. Under white light alone, the stems (cotyledon-to-apex) extended almost exactly logarithmically with time. Under these conditions the increase in log [stem length in mm] per hour was approx. 3.7·10^-3, equivalent to about 1% per h during both skoto-and photoperiods. Supplementary far-red given throughout each photoperiod massively stimulated extension. The calculated logarithmic extension rate, however, slowly returned to that of the controls, following an initial large increase. This is predicted by a model in which far-red light linearly increases the extension rate of individual internodes which arise at an exponentially increasing rate. The behaviour of the model is also consistent with critical experiments in which far-red was given as a pre-treatment or transiently, as well as with other published data. Far-red stimulation of logarithmic extension rate in successive photoperiods was closely and linearly correlated with calculated phytochrome photoequilibrium. Daily short periods of supplementary far-red were especially potent in accelerating extension; the plants seemed least responsive at the end of the photoperiod.Abbreviations FR supplementary far-red light - I stem length (mm) - LSER logarithmic stem extension rate - Pfr far-red absorbing form of phytochrome - R:FR red:far-red fluence rate ratio - WL white light - _c calculated phytochrome photoequilibrium     

Visual detection of diminutive floral guides in the bumblebee <Emphasis Type="Italic">Bombus terrestris</Emphasis> and in the honeybee <Emphasis Type="Italic">Apis mellifera</Emphasis>

Many flowers display colour patterns comprising a large peripheral colour area that serves to attract flower visitors from some distance, and a small central, contrastingly coloured area made up by stamens or floral guides. In this study, we scaled down the size of floral guides to detect the minimal size bumblebees (Bombus terrestris) and honeybees (Apis mellifera) require for guidance. We analyzed the approach and the precise contact of the antennal tips with the floral guide of artificial flowers which precedes landing and inspection. Both bumblebees and honeybees were able to make antennal contact with circular floral guides which were 2 mm in diameter; bumblebees performed better than honeybees and antennated also at floral guides smaller than 2 mm. In discrimination experiments with bumblebees, a minimum floral guide size of 2 mm was required for discrimination between artificial flowers with and without floral guides. With increasing experience bumblebees targeted close to the site of reward instead of making antennal contact with the floral guide, whereas honeybees did not alter their initial behaviour with growing experience. Bumblebees and honeybees spontaneously target diminutive floral guides to achieve physical contact with flowers by means of their antennae which helps them to inspect flowers.     

The eye of the blue acara (Aequidens pulcher, Cichlidae) grows to compensate for defocus due to chromatic aberration

By rearing fish in various monochromatic illuminations we investigated (1) the potential for compensation of refractive error due to chromatic aberration, (2) the contributions of the chromatic channels to emmetropization, and (3) the role of color cues in the control of eye growth. Cichlid fish (Aequidens pulcher) were reared for 6 months (12 h light/12 h dark) in monochromatic lights (623.5, 534.1, 485.0 nm; spectral purity 5–10 nm). Light levels were isoirradiant at 1.1·10¹² quanta/s/cm². Two control groups were reared in white light with down-welling illuminances of 0.2 and 33 lx. Nasotemporal diameters (NTDs) of the eyes were measured in relation to lens size. Due to the oblique axis of highest acuity vision in cichlids, NTD is considered to be a more important dimension than axial length. Variances in NTD were equally small in all rearing groups. NTDs were enlarged with increasing wavelengths of the rearing lights with highly significant values over controls in the red-light group. The wavelength-dependent size of the eyes matched the changes in focal length due to longitudinal chromatic aberration. Complete recovery from eye enlargement was observed after fish reared in red light were exposed to a white light regime for 5 weeks. Small variances in NTD in all groups indicated stringent control of eye growth in the absence of color cues. The reversibility of the increase in NTD in fish reared in red light suggests that the eyes were emmetropized by visually guided mechanisms. Eye size in fish reared in white light was intermediate between the values expected if only blue-sensitive single or the red- and green-sensitive double cones contributed to the control of eye growth. This suggests that all chromatic channels participate in emmetropizing the fish eye.     

Colour choices of naive bumble bees and their implications for colour perception

The innate preferences of inexperienced bumble bees, Bombus terrestris, for floral colour stimuli were studied using artificial flowers. The artificial flowers provided a colour pattern and consisted of a star-shaped corolla and of central colour patches similar to the nectar guide of natural flowers. The innate choice behaviour was assessed in terms of the number of approach flights from some distance towards the artificial flowers and the percentage of approach flights terminating in antennal contact with the floral guide. The colours of the floral guide, the corolla and the background were varied. It was shown that the innate flower colour preference in bumble bees has two components. 1. The frequency of approaches from a distance is correlated with the colour difference between the corolla and the background against which it is presented. If the corolla colour was constant but its background colour varied, the relative attractiveness of the corolla increased with its colour difference to the background. The colour difference assessment underlying this behaviour on a perceptual basis can be attained by means of colour opponent coding, a system well-established in Hymenoptera. 2. The frequency of antennal contacts with the floral guides relative to that of approach flights cannot be accounted for by colour opponent coding alone. Whether the approach flights are interrupted, or whether they end in an antennal contact with the nectar guide is strongly dependent on the direction (sign) of the colour difference, not only its magnitude. The choice behaviour requires a unique perceptual dimension, possibly that of colour saturation or that of hue perception comparable to components of colour perception in humans.     

Acclimation of Arabidopsis thaliana to the light environment: changes in photosynthetic function

Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta was grown under light regimes of differing spectral qualities, which results in differences in the stoichiometries of the two photosynthetic reaction centres. The acclimative value of these changes was investigated by assessing photosynthetic function in these plants when exposed to two spectrally distinct actinic lights. Plants grown in an environment enriched in far-red light were better able to make efficient use of non-saturating levels of actinic light enriched in long-wavelength red light. Simultaneous measurements of chlorophyll fluorescence and absorption changes at 820 nm indicated that differences between plants grown under alternative light regimes can be ascribed to imbalances in excitation of photosystems I and II (PSI, PSII). Measurements of chlorophyll fluorescence emission and excitation spectra at 77 K provided strong evidence that there was little or no difference in the composition or function of PSI or PSII between the two sets of plants, implying that changes in photosynthetic stoichiometry are primarily responsible for the observed differences in photosynthetic function.Abbreviations Chl chlorophyll - FR far-red light - HF highirradiance FR-enriched light (400 mol·m^–2·s^–1, RFR = 0.72) - HW high-irradiance white light (400 mol·m^–2 1·1 s^–1RFR = 1.40) - LHCI, LHCII light-harvesting complex of PSI, PSII - qO quenching of dark-level chlorophyll fluorescence - qN non-photochemical quenching of variable chlorophyll fluorescence - qP photochemical quenching of variable chlorophyll fluorescence - R red light - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase We thank Dr. Sasha Ruban for assistance with the 77 K fluorescence measurements and for helpful discussions. This work was supported by Natural Environment Research Council Grant GR3/7571A.     

The photokinesis of oriental fruit flies,Bactrocera dorsalis,to LED lights of various wavelengths

The oriental fruit fly, Bactrocera dorsalis Hendel (Diptera: Tephritidae), is an invasive pest of orchards around the world, particularly in Asian countries such as China. Light traps offer a potential means for pest monitoring and management. This study aimed to evaluate the sensitivity of the fly to light and investigate the impact of monochromatic light in the sensitivity spectrum on B. dorsalis. Six light wavelengths in LEDs – green (522 nm), yellow (596 nm), blue (450 nm), red (633 nm), purple (440 nm), and white (compound light) – were adapted to test responses of 5‐, 10‐, and 20‐day‐old B. dorsalis adults kept in laboratory conditions. We also tested the effects of green and red lights on pupal development and adults’ life activities. The results indicated a phototaxis preference rank in B. dorsalis adults to monochromatic LEDs with, in decreasing order, green, yellow, purple, blue, and red. Moreover, positive phototaxis significantly increased with age. Male adults are more sensitive than female adults to test lights, mainly at the age of 10 and 20 days. Emergence rates of pupae exposed to 12 and 24 h green light daily were 42 and 67%, respectively, whereas controls held in red light emerged at 33 and 37%, respectively. Furthermore, body weight, female fecundity, and mortality of B. dorsalis in night‐time exposure of green light (from 21:00 to 09:00 hours; during daytime flies were illuminated by white LED light) were significantly higher than in red‐light test groups and dark controls. In conclusion, B. dorsalis displayed preference toward green light, and fly age and gender seemed to significantly impact the phototactic behavior. Green LED light exposure during nighttime remarkably improved the emergence rates of B. dorsalis, and it enhanced growth, development, and ovipositing peak period, but decreased adult lifespan. This research lays a foundation for the development of new trap models, e.g., with green sticky cards or green light, for monitoring and control of B. dorsalis in the field.     

Evidence against the involvement of phytochrome in UVB-induced inhibition of stem growth in green tomato plants

The effects of UVB on the kinetics of stem elongation of wild type (WT) and photomorphogenic mutants of tomato were studied by using linear voltage transducers connected to a computer. Twenty-one or twenty-six-day-old plants, grown in 12 h white light (150 μmol m⁻² s⁻¹ PAR)/12 h dark cycles, were first transferred to 200 μmol m⁻² s⁻¹ monochromatic yellow light for 12 h, then irradiated with 0.1 or 4.5 μmol m⁻² s⁻¹ UVB for 12 h and finally kept in darkness for another 24 h. The measurements of the kinetics of stem elongation started after 4 h under yellow light. Significant differences in stem growth during the irradiation with yellow light, as well as during the dark period, were found between the genotypes. In darkness, the magnitude of stem growth followed the order: tri > AC = fri > MMau > hp1. Two factors determined the large differences of growth in darkness: 1) the different stem elongation rate (SER) and 2) the different duration of the growing phase among the genotypes. In darkness the stem growth of au and hp1 mutants lasted for about 18 h, whereas it continued for the whole experimental period (36 h) in the other genotypes. UVB irradiation substantially reduced elongation growth of all genotypes (4.5 μmol m⁻² s⁻¹ being more effective than 0.1 μmol m⁻² s⁻¹). Both fluence rates of UVB induced a detectable reduction of SER already after 15 min of irradiation. Red light inhibited, while far red light promoted stem growth of all the genotypes tested. fri (phyA null), tri (phyB1 null), hp1 (exhibiting exaggerated phytochrome responses) mutants and WT tomato showed similar levels of UVB–induced inhibition of growth, while the aurea mutant showed the largest growth inhibition during the 12 h of irradiation. These results indicate that phytochrome is not directly involved in UVB control of stem elongation. The results of dichromatic irradiations UVB + red or UVB + far red indicate the presence of distinct and additive action of UVB photoreceptor and of the phytochrome system in the photoregulation of stem growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phototaxis in water fleas (Daphnia magna) is differently influenced by visible and UV light

The effects of vertical illumination with monochromatic lights on phototaxis of Daphnia magna in a test chamber were determined at five levels of equal quantal flux density (between 188 and 6.42 · 10⁻⁵ nEinstein). Visible adaptation light (500 nm) and subsequent spectral test light had the same quantal flux density. The animals reacted to ultraviolet light (260–380 nm) with negative phototaxis, whereas visible light (420–600 nm) caused positive phototaxis. Action spectra were determined, based on the evaluation of different parameters of phototactic behavior. The maximum spectral sensitivity in the ultraviolet was found at 340 nm. The maximum spectral efficiency in the visible varied in dependence on light intensity. Ecological consequences of the results are discussed. Accepted: 3 August 1998     

Changes in gene expression in the leaf of Lolium temulentum L. Ceres during the photoperiodic induction of flowering

Unifoliated plants of Lolium temulentum L. Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 mol photons·m^–2·s^–1, fluorescence + incandescence) with incandescence at 10–15 mol photonsm ^–2·s^–1. The polyadenylated-RNA complement of leaf blade tissues was analysed at 4-h intervals during the photoperiod extension in LD vs. SD, by using two-dimensional polyacrylamide gel electrophoresis to resolve in-vitro-translated products. Of the 991 spots that were analysed, none appeared or disappeared during the inductive cycle, i.e. no qualitative effect of floral induction was detected, at any time. Sixty-eight spots were found whose intensity was influenced by lengthening of the photoperiod; 50 of them, i.e. ca. 5% of the population analysed, were affected before the end of the extension period and were thus potentially related to floral induction. Many of these RNAs were not quantitatively constant during a 24-h cycle in SD. Seven of them oscillated according to the light-on and the light-off signals, among which three seemed to be controlled by phytochrome since their relative amount increased under the standard light conditions but decreased under incandescence even faster than in darkness. The large majority of other RNAs varied with a timing that was not clearly driven by the alternation of light and darkness, indicating that genes related to the biological clock may be especially sensitive to the lengthening of the photoperiod. Furthermore, seven spots were observed that underwent a phase-shift in LD, which consisted, for six of them, of a phase advance of 4–8 h. The steady-state level of CAB mRNA was analysed because the CAB gene family (encoding the chlorophyll a/b-binding proteins of the light-harvesting complexes) is known to be controlled both by the biological clock and phytochrome. In SD, the level was high in the light and low in darkness; the fluctuation was conducted by a circadian rhythm. When plants were exposed to the inductive LD, the peak of mRNA accumulation that was expected according to the endogenous rhythmicity was abolished, possibly because of the change in light quality during the LD extension.Abbreviations CAB chlorophyll a/b-binding proteins of the light-harvesting complexes - 2D two-dimensional - LD(s) longday(s) - LDP(s) long day plant(s) - SD(s) short day(s) - SDP(s) short day plant(s) This work was supported by the University of Liège through the Action de Recherche Concertée (# 88/93-129). Some analyses were performed with the collaboration of Dr. H. Ougham, Institute of Grassland and Environmental Research, Aberystwyth, UK. The authors also want to thank Dr. F. Cremer (Max Planck Institute for Plant Breeding, Köln, Germany) for critical discussion of the results.     

Associative visual learning, color discrimination, and chromatic adaptation in the harnessed honeybee Apis mellifera L.

We studied associative visual learning in harnessed honeybees trained with monochromatic lights associated with a reward of sucrose solution delivered to the antennae and proboscis, to elicit the proboscis extension reflex (PER). We demonstrated five properties of visual learning under these conditions. First, antennae deprivation significantly increased visual acquisition, suggesting that sensory input from the antennae interferes with visual learning. Second, covering the compound eyes with silver paste significantly decreased visual acquisition, while covering the ocelli did not. Third, there was no significant difference in the visual acquisition between nurse bees, guard bees, and foragers. Fourth, bees conditioned with a 540-nm light stimulus exhibited light-induced PER with a 618-nm, but not with a 439-nm light stimulus. Finally, bees conditioned with a 540-nm light stimulus exhibited PER immediately after the 439-nm light was turned off, suggesting that the bees reacted to an afterimage induced by prior adaptation to the 439-nm light that might be similar to the 540-nm light.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Analyzing photosynthetic activity and growth of Solanum lycopersicum seedlings exposed to different light qualities

To investigate how light quality influences tomato (Solanum lycopersicum L) seedlings, we examined changes in plant growth, chloroplast ultrastructure, photosynthetic parameters and some photosynthesis-related genes expression levels. For this, tomato plants were grown under different light qualities with the same photosynthetic photon flux density: red (R), blue (B), yellow (Y), green (G) and white (W) lights. Our results revealed that, compared with plants grown under W light, the growth of plants grown under monochromatic lights was inhibited with the growth reduction being more significant in the plants grown under Y and G lights. However, the monochromatic lights had their own effects on the growth and photosynthetic function of tomato seedlings. The plant height was reduced under blue light, but expression of rbcS, rbcL, psbA, psbB genes was up-regulated, and the ΦPSII and electron transport rate (ETR) values were enhanced. More starch grains were accumulated in chloroplasts. The root elongation, net photosynthetic rate (Pn), NPQ and rbcS and psbA genes expression were promoted under red light. Yellow light- and green light-illuminated plants grew badly with their lower Rubisco content and Pn value observed, and less starch grains accumulated in chloroplast. However, less influence was noted of light quality on chloroplast structure. Compared with yellow light, the values of ΦPSII, ETR, qP and NPQ of plants exposed to green light were significantly increased, suggesting that green light was beneficial to both the development of photosynthetic apparatus to some extent.