New natural hybrids of Convolvulus (Convolvulaceae) from Turkey

The present study introduces two new nothospecies from Turkey, Convolvulus×pseudocompactus C. Aykurt & Sümbül (C. oleifolius Desr. var. deserti Pamp.×C. compactus Boiss.) and Convolvulus×peshmenii C. Aykurt & Sümbül (C. holosericeus Bieb. subsp. macrocalycinus Hausskn. & Bornm.×C. compactus Boiss.). Morphological differences and similarities between the hybrids and their parents are discussed; in addition, habit and sepals are illustrated as diagnostic characters, and the geographic distribution of the hybrids and their parents are mapped. Pollen characteristics of Convolvulus×pseudocompactus, Convolvulus×peshmenii and their parents were examined by means of light microscopy and SEM. Detailed morphological and palynological investigations have been performed for hybrid individuals and parental species. As a result of the palynological investigations, the rate of dehydrated pollen grains was established as an important criterion to determine the hybrid status of Convolvulus taxa.     

Phytochrome Control of Another Phytochrome-mediated Process

The phytochrome-mediated attachment of root tips of mung bean (Phaseolus aureus) and barley (Hordeum vulgare) to glass is affected by the prior exposure of hydrated seeds or seedlings to red or far red radiation. Prior irradiation of seeds or seedlings of mung bean with red light promotes attachment, while far red light promotes detachment of root tips. Similar exposure of barley seeds and seedlings to red light accentuates detachment, while far red light accentuates attachment of root tips. Red-far red light reversibility of the pretreatments indicates phytochrome control.     

The role of phytochrome in the geotropic behavior of roots of Convolvulus arvensis

Summary Geotropic behavior in roots of Convolvulus arvensis is influenced by both gravity and light. In darkness, the roots grow horizontally; exposure to light induces a positive orthogeotropic response. The response is elicited by red light of narrow band width and is reversed by a far-red-light treatment following the red exposure. Phytochrome thus mediates this light response. Experiments with microbeam irradiation suggest that this pigment is located in the root apex, probably in the root cap. Statoliths are present and are shown to sediment upon reorientation of the root apex in both light-and dark-grown roots.Work supported in part by U.S. Public Health Service grant GM-16353 and submitted by D.A.T. to the Graduate School at the University of Oregon in partial fulfillment of the requirements for a M.S. degree.     

Inhibition of Etiolation in Spirogyra by Phytochrome

Cells of Spirogyra filaments grown in darkness become longer than light grown cells. This elongation can be prevented by a few minutes of red light given with intervals of 24 h under the dark period. Far-red light given after the red light pulse counteracts the red light effect. Cells which have finished their elongation in light do not elongate further in darkness. Along with the cell elongation the chloroplasts become less spirally wound and ultimately shortened to straight bands.     

Shoot phytochrome B modulates reactive oxygen species homeostasis in roots via abscisic acid signaling in Arabidopsis

Underground roots normally reside in darkness. However, they are often exposed to ambient light that penetrates through cracks in the soil layers which can occur due to wind, heavy rain or temperature extremes. In response to light exposure, roots produce reactive oxygen species (ROS) which promote root growth. It is known that ROS‐induced growth promotion facilitates rapid escape of the roots from non‐natural light. Meanwhile, long‐term exposure of the roots to light elicits a ROS burst, which causes oxidative damage to cellular components, necessitating that cellular levels of ROS should be tightly regulated in the roots. Here we demonstrate that the red/far‐red light photoreceptor phytochrome B (phyB) stimulates the biosynthesis of abscisic acid (ABA) in the shoots, and notably the shoot‐derived ABA signals induce a peroxidase‐mediated ROS detoxification reaction in the roots. Accordingly, while ROS accumulate in the roots of the phyb mutant that exhibits reduced primary root growth in the light, such an accumulation of ROS did not occur in the dark‐grown phyb roots that exhibited normal growth. These observations indicate that mobile shoot‐to‐root ABA signaling links shoot phyB‐mediated light perception with root ROS homeostasis to help roots adapt to unfavorable light exposure. We propose that ABA‐mediated shoot‐to‐root phyB signaling contributes to the synchronization of shoot and root growth for optimal propagation and performance in plants.     

COMPARATIVE ANATOMY OF ENDOGENOUS BUD AND LATERAL ROOT FORMATION IN CONVOLVULUS ARVENSIS ROOTS CULTURED IN VITRO

The anatomy of endogenous bud and lateral root formation was studied in Convolvulus arvensis roots cultured in vitro. Although early stages in the initiation of buds and roots were found to be identical, continued development of primordia into roots or buds was accompanied by differences in participating primary root tissues, in rates of development, and in orientation of cell divisions. Evidence for the existence of a primordium capable of developing into either a bud or root is discussed with reference to Convolvulus roots and other plant parts shown to have similar morphogenetic potentials.     

Light quality growth promotion of Spiraea nipponica: the influence of a low photon fluence rate and transfer time to a higher fluence rate

Combinations of different light quality and fluence exposure times were investigated for their effects on in vitro growth of the woody plant Spiraea nipponica. An interaction was demonstrated between different levels of benzyladenine (BA) used for in vitro propagation and the specific light regimes investigated. This relationship was affected by the length of exposure to either white or red/FR light and the time of transfer from one fluence rate to another. In all instances exposure to red/FR light resulted in more extensive growth than under white light. Thus explants cultured under 0.25 and 0.4 mg l^-1 of BA exhibited high shoot proliferation rates when transferred, after 4 weeks of low photon fluence red/FR light, to higher fluence white light for a further week. The proliferation rates obtained were higher than any white light treatment including that with the highest BA level of 0.5 mg l^-1. In addition, the combination of red/FR light exposure with a white light stage of higher fluence improved proliferation at lower exogenous BA levels.     

A phytochrome-mediated alteration from stem to rosette growth on chicory root explants in vitro

Chicory root explants (Cichorium intybus L. var. foliosum) of two cultivars, taken before and after hydroponic forcing, were cultured in vitro in complete darkness supplemented with red and far-red light treatments. Using 5 min red light per day, the strong stem elongation occurring in complete darkness was converted to rosette formation. This reaction was reversed to stem elongation (accompanied by leaf formation) adding 15 min far-red light after the red light. Fifteen min far-red light per day alone caused the same reaction as 5 min red/15 min far-red light. Far-red light followed by red light caused rosette formation. In stems, formed under complete darkness in vitro, the presence of phytochrome was shown. No phytochrome was detected in the root fragment itself.Abbreviations R red light - FR far-red light - GA gibberellinic acid - A absorbance - FW fresh weight     

AN INTERPRETATION OF DOSE-RESPONSE CURVES FOR LIGHT-INDUCED CELL ELONGATION IN FERN PROTONEMATA

Protonemata of Onoclea sensibilis and Diyopteris filix-mas elongate in response to both red and far-red light. The promotion caused by far-red is larger than that caused by red light. This phenomenon differs from a typical response to phytochrome, the photoreceptor pigment immediately suggested by the activity of red and far-red light. The phenomenon has been explained by two different hypotheses, one of which holds that phytochrome is solely responsible for the response, whereas the other postulates an interaction between phytochrome and P₅₈₀, a yellow-green light absorbing pigment, to account for the response. The hypothesis that phytochrome is the sole photoreceptor leads to some specific predictions concerning the shapes of the dose-response curves for light-induced protonema elongation. These predictions were tested with both continuous and short-term irradiation. In all instances saturating far-red light caused greater elongation than did saturating red light, and no dose of red light duplicated the activity of saturating far-red light. Other experiments tested the interactions of red and far-red light and the effects of different doses of yellow-green light on protonema elongation. The results of many of the experiments were not in agreement with the hypothesis that phytochrome is the sole photoreceptor, whereas they were in agreement with the assumption that filament elongation is controlled by both phytochrome and P₅₈₀.     

Light germination ofAnthoceros miyabeanus spores

The effects of light on the spore germination of a hornwort species,Anthoceros miyabeanus Steph., were investigated. Spores of this species were photoblastic, but their sensitivities to light quality were different. Under either continuous white, red or diffused daylight, more than 80% of the spores germinated, but under blue light none or a few of them germinated. Under continuous far-red light or in total darkness, the spores did not germinate at all.Anthoceros spores required red light irradiation for a very long duration, i.e., over 12–24 hr of red light for saturated germination. However, the spore germination showed clear photo-reversibility by repeated irradiation of red and far-red light. The germination pattern clearly varied with the light quality. There were two fundamental patterns; (1) cell mass type in white or blue light: spores divide before germination, and the sporelings divide frequently and form 1–2 rhizoids soon after germination, and (2) germ tube type in red light: spores germinate without cell division, and the single-cell sporelings elongate without cell division and rhizoid formation.     

Induction mechanism of adventitious root from leaf explants of <Emphasis Type="Italic">Morinda citrifolia</Emphasis> as affected by auxin and light quality

An efficient protocol for adventitious root induction from leaf explants of Morinda citrifolia treated with different concentrations of indole-3-butyric acid (IBA) and α-naphthaleneacetic acid (NAA) was established in relation to physiological process changes during adventitious root induction under different light sources (fluorescent, red, blue, red + blue, and far-red). Among the different concentrations of IBA and NAA, 1.0 mg l⁻¹ IBA was proven as the best auxin source for adventitious root induction under fluorescent light. Higher concentrations of IBA and NAA trigger callus formation in both light and dark conditions. Maximum numbers of adventitious roots were induced under red light (26) followed by blue light (22) and the lowest under far-red light (6). In contrast, numerous callus formations were induced by red + blue followed by red and blue, while the highest root length (1.66 cm) with negligible callusing was observed under fluorescent light. Catalase and guaicacol peroxidase activities were highest under red light followed by fluorescent light and the lowest under red + blue light, but superoxide dismutase activity was not significantly influenced by different light sources. Ascorbate peroxidase played an important role in detoxification of the harmful effects of hydrogen peroxide (H₂O₂). Under fluorescent light, significantly lower accumulation of H₂O₂ was observed. Accumulation of H₂O₂ in the induced root under different light showed a positive correlation with peroxidation of lipids and was observed higher under far-red followed by red + blue and blue light.     

Photomorphogenesis of the Gynophore, Pod and Embryo in Peanut, Arachis hypogaea L.

Darkened excized gynophores ceased to elongate after 8–10days in vitro and started to form a pod. Gynophore elongationwas inhibited to a greater extent in total darkness than underlow irradiance, while pod and embryo growth was stimulated indarkness only. Intact gynophores, enclosed in transparent vials containingglass beads, continued to elongate in both light and darkness.In light the elongating gynophores thickened as they penetratedbetween the glass beads, forming a seedless pod at the bottomof the vials. In the dark the elongating gynophores producedsmall pods in which the seeds had started to grow. Excized gynophores elongated in vitro under continuous whitelight at a rate similar to that of intact exposed gynophores.The rate of elongation in vitro, was lower under continuousblue or red-enriched light, than under white light, and wasfurther reduced under continuous far-red irradiation. Pods didnot form during any of the continuous irradiation treatmentsbut only after transfer to darkness, the largest pods formingafter continuous far-red irradiation. As little as 10 min daily exposure to red or far-red irradiancehad the same effect on gynophore elongation as continuous irradiation.Pods formed only when the daily periods of far-red irradiationwere 30 min or less. Reducing the daily exposures to 2 min decreasedthe time to onset of pod formation from 30 to 16 days. Far-redfollowing red irradiation was effective in inhibiting gynophoreelongation stimulated by red irradiation. Pod formation in red/far-redirradiation was only 50 per cent of that observed in far-redirradiation. The involvement of light in continual gynophoreelongation and in the concomitant inhibition of proembryo growthis discussed. Arachis hypogaea L., peanut, gynophore, photomorphogenesis, embryo development, pod development, proembryo     

Photoperceptive Site of the Photoinduction of Root Hairs in Lettuce (Lactuca sativa L. cv. Grand Rapids) Seedlings Under Low pH Conditions

Lactuca sativa L. cv. Grand Rapids) seedlings under acidic conditions by a phytochrome-mediated response. Microbeam irradiation of 1 mm root segments with the first (100 Jm⁻²) and second (1,000 Jm⁻²) maxima of the fluence response curve for red light induction of root hair initiation indicated that the ca. 5 mm apical portion of 12 mm long roots was the site of photoperception. The root hair-forming portion of the root was situated at a distance of 1.7 mm from the root tip at the time of red light irradiation and extended (at most 1.5 mm) towards the basal end at a later stage of development, irrespective of which portion of the root was irradiated with red light. Received 13 August 1999/ Accepted in revised form 22 December 1999     

CHANGES INDUCED BY WATER ON EUPHORBIA SUPINA SEED COAT STRUCTURES

Moisture applied to dry seeds of Euphorbia supina Raf. caused helices embedded in the seed coat to elongate. The helices consist initially of tightly coiled strands that loosen when moistened. The helices can repeatedly elongate and contract, but their configuration and expandability gradually changes as the strands coalesce to form thin plates. With prolonged exposure to moisture and drying, the plates, in turn, coalesce into an amorphous layer that covers the seed. Periodic Acid-Schiff test produced red coloration, which indicates the helices contain polysaccharides, probably mucilage.     

Non-photosynthetic effects of red and far-red light on root-nodule formation by leguminous plants

Summary Nodulation of pea and broad bean plants grown in the light was found to be reduced when the roots were exposed to far-red light for 5–15 minutes daily during 5 consecutive days following inoculation with nodule bacteria. Similar results were obtained following a single exposure to far-red light during a period of 15 minutes at the 3rd or 4th day after inoculation. When the roots were exposed to far-red light either before inoculation or during the first two days afterwards there were either no effects or only slight effects on nodulation The inhibitory effect of far-red light on nodulation was partly reduced by subsequent exposure to red light, provided that the same part of the plant was exposed to both red and far-red light,viz either the root or the shoot. When different parts of the plant were exposed to red and far-red light respectively, there was no interaction between the two kinds of light on nodulation. Plants whose roots were exposed to far-red light did not subsequently show stem elongation.Nodules were found to develop on the roots of pea plants grown in the dark, provided that the plants were kept at or below 22°C. At 25°C nodulation was almost absent. Nodulation was decreased by addition of kinetin and IAA. In contrast to plants grown in the light pea plants grown in the dark, inoculated with either an effective or ineffective strain of Rhizobium, developed equal numbers of nodules. Exposure to red light slightly increased the percentage of nodulated plants but decreased the number of nodules per plant. Exposure to far-red light slightly decreased both the percentage of nodulated plants and the number of nodules per plant. The effect of far-red light was counteracted by red light andvice versa.     

Gene profiling of the red light signalling pathways in roots

Red light, acting through the phytochromes, controls numerousaspects of plant development. Many of the signal transductionelements downstream of the phytochromes have been identifiedin the aerial portions of the plant; however, very few elementsin red-light signalling have been identified specifically forroots. Gene profiling studies using microarrays and quantitativeReal-Time PCR were performed to characterize gene expressionchanges in roots of Arabidopsis seedlings exposed to 1 h ofred light. Several factors acting downstream of phytochromesin red-light signalling in roots were identified. Some of thegenes found to be differentially expressed in this study havealready been characterized in the red-light-signalling pathwayfor whole plants. For example, PHYTOCHROME KINASE 1 (PKS1),LONG HYPOCOTYL 5 (HY5), EARLY FLOWERING 4 (ELF4), and GIGANTEA(GI) were all significantly up-regulated in roots of seedlingsexposed to 1 h of red light. The up-regulation of SUPPRESSOROF PHYTOCHROME A RESPONSES 1 (SPA1) and CONSTITUTIVE PHOTOMORPHOGENIC1-like (COP1-like) genes suggests that the PHYA-mediated pathwaywas attenuated by red light. In addition, genes involved inlateral root and root hair formation, root plastid development,phenylpropanoid metabolism, and hormone signalling were alsoregulated by exposure to red light. Interestingly, members ofthe RPT2/NPH3 (ROOT PHOTOTROPIC 2/NON PHOTOTROPIC HYPOCOTYL3) family, which have been shown to mediate blue-light-inducedphototropism, were also differentially regulated in roots inred light. Therefore, these results suggest that red and bluelight pathways interact in roots of seedlings and that manyelements involved in red-light-signalling found in the aerialportions of the plant are differentially expressed in rootswithin 1 h of red light exposure. Key words: Arabidopsis, gene profiling, microarray, photomorphogenesis, red light, roots     

An investigation of the effects of light on basidiocarp formation of Coprinus domesticus

Coprinus domesticus, grown on a synthetic agar medium, failed to produce primordia and basidiocarps unless exposed to light. Lightdark cycles are not required for maturation of basidiocarps. Short exposure to white light induced primordia, but a longer exposure was necessary for primordia to develop into basidiocarps. The length of exposure to light was related inversely to the length the stipe finally attained. Young basidiocarps were phototropic, growing towards the light. The mycelium of cultures were dark brown following exposure to white and blue light, but the mycelium was light yellow in cultures grown in darkness. The blue end of the visible spectrum at intensities ranging from 1.5–3 × 10⁴ ergs/cm²/sec induced mature basidiocarps, whereas green, red and far red failed to induce basidiocarps and primordia.Department of Biology contribution no. 90     

Phytochrome Controlled Adhesion of Mung Bean Root Tips to Glass: A Detailed characterization of the Phenomenon

Various parameters of the Tanada effect (Proc. Natl. Acad. Sci. U.S. 59: 376–380. 1968) have been defined. This phenomenon, in which root tips of Phaseolus aureus L. adhere to a negatively charged glass surface when they are irradiated with 660 nm (red) light and release under 730 nm (far-red) light, has been characterized as follows. Secondary roots, whether etiolated or light grown exhibit photoreversible adhesion. Primary roots do not. Tips from 6–8 mm secondary roots exhibit the best response to red light, whereas tips from 3 mm roots respond best to far-red light. Red light saturetes the adhesion system at about 50 μ W/cm²xnm and far-red light, release system at about 150 ü W/cm² xnm. The adhesion effect begins to show escape from far-red reversibility within 60–90 seconds, an observation quite different from other “typical” long term de- etiolation effects. In addition, root tips irradiated with red light begin to release spontaneously in the dark after 10 min, and have nearly completed release after 50 min. Tips irradiated with continuous red light show gradual release after 15 minutes of exposure. Whether these data indicate an extremely rapid dark reversion of P_fr to P_r or decay of P_fr under continuous red light is not known at this time. In order to study tip adhesion and release, the glass beaker surface may be negatively charged with thiocyanate (SCN^-), nitrate (NO₃^-), sulfate (SO₄^2-), chloride (Cl^-), phosphate (PO₄^3-), citrate (C₆H₅O₇^3-), oxalate (C₂O₄^2-) or glutamine (C₅H₈NO₄^-). Benzoate (C₇H₅O₂^-) and acetate (CH₃COO^-) were found to be relatively ineffective for red light adhesion, however when citrate and oxalate were used release was inhibited. This was apparently due to a chelation of Ca²⁺since release began immediately as excess Ca⁺² was added to the bathing solution. Substitution of GTP, ITP, UTP, or CTP for ATP resulted in only 20 to 40% adhesion and release for GTP, ITP and UTP, CTP showed normal adhesion kinetics under red light but very slow release kinetics under far-red light. The effects of red and far-red light in the numbers of secondary roots are that red light inhibits root initiation while far-red light partially reverses the red light effect.     

Responses of Trachelospermum asiaticum (Apocynaceae) seedlings to growth in a light intensity gradient

We recorded the growth of 24 seedlings of Trachelospermum asiaticum, a root climber, placed between a light source and a wall. Shoot length of seedlings planted at the brightest points nearly matched the distance the shoot tips moved toward the wall surface. In contrast, although the seedlings planted at the darkest points did elongate, the tips moved an average distance of only 0.4 cm. Creeping shoots of T. asiaticum planted in brighter environments exhibit negative phototropism, which encourages them to grow rapidly toward dark places, allowing them to reach supporting hosts faster than those that germinate close to the host.