Phototropic Reactions Research Articles

Is the Responsiveness to Light Related to the Differences in Stem Straightness among Populations of Pinus pinaster?

Stem straightness is related to wood quality and yield. Although important genetic differences in stem straightness among the natural populations of Pinus pinaster are well established, the main drivers of these differences are not well known. Since the responses of trees to light are key ecological features that induce stem curvature, we hypothesized that populations with better straightness should exhibit lower photomorphogenetic and phototropic sensitivity. We compared three populations to identify the main processes driven by primary and secondary growth that explain their differences in response to light. One-year-old seedlings were grown under two treatments—direct sunlight and lateral light plus shade—for a period of 5 months. The length and the leaning of the stems were measured weekly. The asymmetry of radial growth and compression wood (CW) formation were analyzed in cross-sections. We found differences among the populations in photomorphogenetic and phototropic reactions. However, the population with straighter stems was not characterized by reduced sensitivity to light. Photo(gravi)tropic responses driven by primary growth and gravitropic responses driven by secondary growth explained the kinetics of the stem leaning and CW pattern. Asymmetric radial growth and CW formation did not contribute to the phototropic reactions.

Tissue-specific and subcellular localization of phototropin determined by immuno-blotting

Phototropin (phot) is a UV/blue- light receptor mediating phototropic reactions of plants as a response to unilateral irradiation. Using an antiserum directed against the N-terminal part of Arabidopsis phot1, we show here cross-reaction with phototropin from Avena sativa, Eruca sativa, Glycine max, Lepidium sativum, Lycopersicon esculentum, Pisum sativum, Sinapis alba, and Zea mays. In all investigated plants, blue light irradiation led to a gel mobility shift of phototropin corresponding to an apparent increase in size of 2-3 kDa. This increase is transient: the apparent size of the phototropin band reverted back to the original size in the dark within 60-90 min. The capacity for in vitro phosphorylation increased to 350% ( A. sativa) and 200% ( L. sativum) at 90 min after a blue light pulse without an increase in the amount of phototropin protein. Starting from coleoptile tips of monocots that contained the highest concentration of phototropin, we found an exponential decrease in basipetal sections of equal size while a linear decrease was determined for dicots in basipetal sections starting from the section below the hypocotyl hook. We confirmed the membrane association of all phototropin in dark-grown seedlings; after a 2-min blue light pulse, however, 20% of phototropin was found in the cytosolic fraction and only 80% in the membrane fraction. Both fractions showed the gel mobility shift indicating light-dependent autophosphorylation. Detergent-free solubilization of phototropin with chaotropic reagents was investigated with etiolated A. sativa seedlings. Up to 95% of phototropin was solubilized with a mixture of sodium bromide and sodium diphosphate, and subsequently subjected to affinity purification using Cibachron Blue 3GA-agarose as a dinucleotide analogue. Immediately after solubilization, soluble phototropin still showed blue-light-dependent autophosphorylation but lost its activity within less than 1 h.

Evaluation of planting surfaces for crop production in microgravity

In microgravity, plants can be cultivated on curvilinear domed (convex) surfaces, e.g. cylindrical, spherical, and thoroidal, with light sources arrayed evenly along a concave surface above the crop surface. In this case, the plant stems align along the normals to the crop surface with crowns moving apart as plants grow owing to phototropic reactions. Analyses showed that, compared with crops raised on flat surfaces, the curvilinear crop surfaces carry the promise of significantly increasing the specific productivity of crops both per unit internal growth chamber volume and per unit energy required by plants. The highest effectiveness of volume and power utilization was demonstrated by the spherical crop surface and the least by the cylindrical one. The thoroidal crop surface has an effectiveness between the two. The cylindrical surface of the laboratory model, PHYTOCYCLE, had a specific productivity of 30 g of fresh Pekinese cabbage biomass per kWh which is 28% higher than what has been harvested from a flat crop surface under comparable conditions. PHYTOCYCLE plant growing chamber volume was 40% less than the volume of a flat crop surface growing chamber.

Biodiversity of bryophilous ascomycetes

Up to now, about 300 species of ascomycetes are known to grow obligately on the gametophytes of mosses or hepatics; these belong to more than 80 ascomycete genera, some of them unknown elsewhere, and at least nine orders. They vary greatly in relation to the mode of nutrition (necrotrophic, biotrophic and gall-inducing parasites), the host organs infected, host specificity, and geographical distribution. Diversity of these fungi is illustrated by spore outlines of 36 species. Hyphae growing superficially, inter- or intracellularly, and various types of appressoria and haustoria are illustrated. Adaptations to the unique substratum, such as the formation of minute reduced ascomata containing gelatinous material, a preference for moist microhabitats such as the interlamellar spaces of leaves in Polytrichales, and phototropic reactions are discussed. Convergent evolution leading to similar morphological features is rather common. The colonization of mosses and hepatics by ascomycetes is a very frequent though generally neglected phenomenon. Some bryophytes seem to grow always with their specific parasites. It is supposed that species diversity among the bryophilous ascomycetes is as high as among the lichenicolous ones. Numerous new taxa remain to be described, but only a small fraction of bryophytes has been proved to be infected so far.

Immunological estimation of growth regulator distribution in phototropically reacting sunflower seedlings

The distribution of immunoassayable xanthoxin (XA), abscisic acid (ABA) and indole‐3‐acetic acid (IAA) in all parts of sunflower (Helianthus annuus L.) seedlings was determined. During the course of phototropic curvature, including the lag phase (5 min), the distribution of these growth regulators was analyzed in the illuminated and shaded side of the hypocotyl, as well as in the peripheral and central tissues. All three growth regulators showed no detectable asymmetries between the illuminated and shaded hypocotyl halves during the lag phase and early phototropic curvature. Also, no indication for an exchange of XA, ABA or IAA between the peripheral and central tissues was observed. Partial removal of the peripheral cell layers revealed that changes in the growth properties of this tissue, preferentially at the illuminated side of the hypocotyl, are required for the phototropic reaction. Complete removal of the peripheral cell layers abolishes the phototropic response. In dark‐incubated, green sunflower seedlings, the loss of sensitivity to phototropic stimulation is correlated with decreasing levels of IAA immunoreactivity, whereas no changes in the levels of ABA‐ and XA immunoreactivity were recorded. The findings are discussed with respect to the involvement of ABA, XA and IAA in phototropic reactions of green dicotyledonous shoots.

An automatic device to record the force necessary to compensate plant movements

A device, which automatically and continuously keeps moving plants in fixed positions, has been constructed. The apparatus is based on optical detection of any movements of the plant organ under study. The plant organ is kept in the desired position by means of wires, and the force necessary to apply to the wires to achieve this is recorded. The force reflects any tendency of the plant organ to move. The system is controlled by an Apple II computer. The device can work in one or two dimensions and record compensation forces in a wide range. In the experiments mentioned below, the magnitude of the forces necessary to keep the plants in a fixed position was of the order of 10‐4N.Circadian leaf movements of Oxalis regnellii Mig. were studied in the device. The leaf rhythm continued, although the leaflets were clamped and the light input on the leaf therefore constant. Circumnutation of hypocotyls of Helianthus annus L. cv. Californicus were drastically reduced in amplitude when the hypocotyls were kept in vertical position by the wires. Since the gravitropic input signal to this system was zeroed by the equipment, the results demonstrated that in the absence of gravitropic inputs the circumnutation reactions drastically diminish. This confirmed that circumnutations of these hypocotyls are influenced by gravity. Finally, the apparatus was used to study phototropic reactions: By clamping phototropically stimulated coleoptiles of Avena sativa L. cv. Seger no gravitational stimulations were involved and the phototropic reaction without interference from gravity could be studied.

Ethologie du stade infestant du cop�pode ascidicole Notodelphyidae Pachypygus gibber. I. R�actions � la lumi�re au cours de la vie larvaire p�lagique

The phototropic reactions of pelagic larvae of Pachypygus gibber (Thorell) under laboratory conditions change according to their stage and their age. The behaviour of these larvae is described by 4 experimental parameters: threshold of the reaction, orientation towards the light or the opposite, speed and form of motility. Specimens were tested under different conditions of illumination. In the nauplii, the threshold reaction to light is higher than that in Copepodids 1 and 2. In the early planktonic stages (nauplii, Copepodids 1 and young Copepodids 2, from emergence to 3 days), most specimens respond positively to light, however the response is negative in older Copepodids 2 (4 to 10 days). There is a parallel evolution between the development of P. gibber and the change from positive to negative phototropism. The inversion of this response occurs in the developmental period between the 3-day old Copepodids 2 and the Copepodids 2 of 4 to 6 days of age. This reversal in vitro could correspond to the moment of penetration into the host. The average swimming speed is fastest in the positive phase of Copepodids 1, and is very slow in the older Copepodids 2. The form of the motility, rectilinear for most Copepodids 1, becomes increasingly winding as the Copepodids 2 grow. This random “exploration” of the environment would increase the possibility of finding the host. The evolution of phototropism is apparently related to the search for the host and its infestation.

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

SUMMARY 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.

Die phototropische Reaktion der Zoide von Bugula avicularia L.

1. In diluted seawater (density 1.017) Bugula-zooids grow uniserially instead of biserially. Phototropic growth reactions have been measured with uniserially grown zooids (see section C, 1). 2. Under the influence of light the path taken by the spherical cells along the cupula of the bud is the arc of the phototropic inclination. The length of the path is proportional to the illumination time and a function of the light intensity (see section D, 6, 7). 3. The phototropic bending at first increases with the logarithm of the intensity; at 100 lux it drops to 1/3 of the former maximum and continues to drop with higher intensities (see section C, 2). 4. The threshold intensity (with 15 min illumination) where there is no longer a phototropic reaction is in the order of 10−12 watts/mm2 at 506 mμ. Each spherical cell receives approximately 400 quanta per second (see section D, 9). 5. The action spectrum of the phototropic reaction has its maximum at approximately 500 mμ, a minimum at 400 mμ, and rises again with shorter wavelengths. At 686 mμ the curve's amplitude is very low. The shape of the spectral efficiency curve is similar to curves of retinin-opsin compounds (see section C, 4 and D, 3). 6. Absorption measurements of whole, living zooids show a gradual rise towards shorter wavelengths (see section C. 5). 7. Superimposed on the phototropic bendings are morphogenetically fixed bendings which also occur in darkness. These, as well as irregular, light-independent bendings cause the great variance in the data (see section C 6, 7 and D, 4). 8. The extent of the morphogenetically fixed bendings is dependent on the wavelength. This dependence differs from the action spectrum of the phototropic bendings (see section C 6, 7 and D, 4). 9. The light-directed movement of the spherical cells begins between 5 and 30 min after the onset of the light stimulus. Similar reaction times are observed when the incidence of light is changed 180°. Latency accounts for the main part of the reaction time. Ten to 30 min after the end of a longer light stimulus, the cells begin to deviate from the former direction of movement (see section C, 8 and D, 5). 10. A 180°-change in the direction of movement takes between 9 and 18 min, both in the dark as well as after a directional light stimulus (see section C, 8 and D, 5). 11. The cells may move up to two hours with approximately constant speed (2–3 μ/10 min) under the influence of light (see section C, 8 and D 6, 7). 12. Sometimes spherical cells rhythmically separate and close together. No influence of the light stimulus on this “pulsation” was observed (see section C, 9 and D, 8). 13. If we assume that the spherical cells secrete wall material, they are bound to make movements relative to the cuticle, because the wall material flows out of range of the cell plate. These relative movements are discussed in connection with the pulsations and the phototropic movements of the cells (see section 0, 10 and D, 8). 14. Some observations indicate that the single spherical cell is capable of light directed movement. However, the following considerations are also valid in principle, even if only the cell plate react phototropically as a whole (see section D, 2). 15. The spherical cells have a higher refractive index than the surrounding medium and they focus the light. This effect probably serves to produce the intracellular intensity gradient necessary for orientation (see section D, 2). 16. It is necessary to postulate the presence of intracellular receptive units which are able to transform the intensity pattern of the cell's interior into a corresponding excitation pattern by translating local intensities independently of each other into physiological values (local excitations) (see section D 1, 2). 17. Directed reaction is the result of a comparison of local responses or of processes dependent on them. This comparison could be understood as a vectorial sum formed by the difference in the values of opposing vectors (see section D, 2). 18. The measured reaction itself could be the result of a mathematical difference between partial reactions. Under two other very probable assumptions the partial reactions would have a sigmoid dependence on light intensity. This dependence could be calculated through integration of the measured reaction curve In this case the drop in the phototropic reaction at high intensities could be explained by an increased saturation of the partial reactions (see section C, 2 and D, 2). 19. The main possible ways of detecting the directions of the light source are enumerated (see section D, 1).

FACTORS INFLUENCING METAMORPHOSIS OF BUGULA LARVAE

1. In calcium-free van't Hoff's solution and both Na-free and K-free mixtures having the other ions in the same proportion as in sea water at a pH of 7.1-8.0, the larvae of Bugula flabellata behaved exactly like those in sea water containing an excess of MgCl2. Phototropic reactions were lost, ciliated tissue was shed as material migrated basally from the pallial furrow and metamorphosis did not occur.2. In isotonic Mg-free solutions (pH = 8.0) metamorphosis was greatly accelerated, fixation occurring within 30 minutes to 3 hours in the majority of larvae; these organisms developed well-formed zooids in 10 hours. (Normally only about 77% of the larvae metamorphose by 12 hours.)3. Neutral red, methylene blue and, to a lesser extent, eosin accelerated metamorphosis. Neutral red, the most potent of the three, was effective in concentrations of 1:1,000,000 parts of sea water; methylene blue caused acceleration in concentrations of 1:500,000 parts. At a concentration of 1:100,000 parts of neutral red the average duration of the natatory period was about an hour.4. Metamorphosis failed to occur in Ca-free, Na-free and K-free media to which neutral red had been added in proportions of 1:100,000 parts. The same concentration of neutral red in isotonic Mg-free media (pH = 8.0) had a greater accelerating effect than when the dye was added to sea water in the same proportions. A reduction of temperature to 4° C. to 12° C. of sea water containing neutral red in parts of 1:100,000 antagonized the accelerating effects of neutral red. The staining reactions of neutral red and the problems involved in the study of metamorphosis are also discussed.

The Effect of Temperature on the Reaction ofGlossina morsitansWestw. to Light

In the course of studies of the behaviour of the tsetse-fly,Glossina morsitans, certain facts of considerable interest concerning its phototropic reactions have been established.

REACTIONS OF LIMULUS TO ILLUMINATED FIELDS OF DIFFERENT AREA AND FLICKER FREQUENCY

In phototropic tests with young Limulus, the phototropic reactions to flickering fields were studied. If the two fields are equal in area and brightness but different in flicker frequency, the number of animals going to the two fields is proportional to their flicker frequencies. Equal stimulating effects of two fields differing in flicker frequency are obtained by reduction of the area of the faster flickering field. The areas for equal effect must be inversely proportional to their flicker frequencies. It seems that equal effects are dependent upon equality of the number of active excitation elements per unit of time.