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At least 19 recordsLinked to original sources
PubMed1987

Phototropism in Hypocotyls of Radish: IV. Flank Growth and Lateral Distribution of cis- and trans-Raphanusanins in the First Positive Phototropic Curvature.

The first positive phototropic curvature induced by a pulse of unilateral white irradiation (0.1 watt per square meter, 30 seconds) of etiolated and de-etiolated Sakurajima radish (Raphanus sativus var hortensis f. gigantissimus Makino) hypocotyls was analyzed in terms of differential growth and growth inhibitor contents of the hypocotyls. In both etiolated and de-etiolated hypocotyls, the growth rates at the lighted sides were suppressed whereas those at the shaded ones showed no change. De-etiolation treatment induced a larger difference between the growth rates at the lighted and shaded sides of the hypocotyls, resulting in a larger curvature of de-etiolated seedlings than of etiolated ones. The contents of growth inhibitors, cis- and trans-raphanusanins, increased in the lighted but not in the shaded halves of the hypocotyls of etiolated seedlings. In de-etiolated seedlings, the two inhibitors increased due to the de-etiolation treatment. When de-etiolated seedlings were exposed to a pulse of unilateral irradiation the level of the two inhibitors remained high along the lighted side for 1 h following the light pulse, whereas at the shaded side the contents of the inhibitors abruptly decreased upon transfer to the dark, the difference between their amounts in the lighted and shaded sides being larger than in etiolated seedlings. Another growth inhibitor, raphanusamide, did not respond to the phototropic stimulus, although its amounts increased by the de-etiolation treatment. These data suggest that cis- and trans-raphanusanins are involved in the first positive phototropic response of radish hypocotyls, and that de-etiolation magnifies the phototropic response through induction of a larger lateral gradient of the raphanusanins in the hypocotyls by the phototropic stimulus.

Journal Article↗
PubMed2000

Phototropic stimulation induces the conversion of glucosinolate to phototropism-regulating substances of radish hypocotyls.

The distribution of natural growth inhibitors, the raphanusanins (isomers of 3-(methylthio)methylene-2-pyrrolidinethione) and their precursors (4-methylthio-3-butenyl glucosinolate (MTBG) and 4-methylthio-3-butenyl isothiocyanate (MTBI), between illuminated and shaded halves of radish hypocotyls during phototropic curvature was analyzed using a physicochemical assay. Phototropic stimulation rapidly decreased MTBG content, and abruptly increased contents of MTBI and raphanusanins in the illuminated halves of radish hypocotyls within 30 min after the onset of unilateral illumination. Content in the shaded halves was similar to that in dark controls. When MTBG, MTBI, and raphanusanins at endogenous levels were applied unilaterally to etiolated hypocotyls, MTBI and raphanusanins caused hypocotyls to bend but MTBG showed no activity. Blue illumination promoted myrosinase (thioglucosidase) activity, which releases MTBI from MTBG, in hypocotyls after 10 min, although enzyme activity in dark controls did not change. These results suggest that phototropic stimulation promotes myrosinase activity in the illuminated side of radish hypocotyls, releasing bioactive MTBI from inactive MTBG and simultaneously producing bioactive raphanusanins.

Darkness↗
PubMed1997

Exposure of oat seedlings to blue light results in amplified phosphorylation of the putative photoreceptor for phototropism and in higher sensitivity of the plants to phototropic stimulation.

Dark recovery of blue light-induced in vitro phosphorylation in oat (Avena sativa L.) seedlings after in vivo preirradiation with blue light revealed different recovery kinetics for the coleoptile base and tip. Although, in both cases, maximum in vitro phosphorylation was observed 90 min after in vivo blue light treatment, the phosphorylation levels for the entire base were about 3-fold higher than those found in nonpreirradiated plants. The tip response only slightly exceeded that of the dark controls. The fluence applied during preirradiation determined the extent of the increase in phosphorylation. Consequently, unilateral irradiation and subsequent dark incubation resulted in a more pronounced increase in phosphorylation in the irradiated than in the shaded side of the coleoptile base. Furthermore, blue light-irradiation conditions, known to induce neither first- nor second-positive curvature in nonpreirradiated plants, stimulated both asymmetric distribution of protein phosphorylation and second-positive phototropic curvature in the coleoptile base when administered to blue light-pretreated plants. Based on these data, we conclude that photosensitivity of the coleoptile base increases upon exposure to blue light in a time-and fluence-dependent manner, providing an excellent explanation of the invalidity of the Bunsen-Roscoe reciprocity law for second-positive phototropism.

Avena↗
PubMed1966

Hormonal Relations in the Phototropic Response: III. The Movement of C-labeled and Endogenous Indoleacetic Acid in Phototropically Stimulated Zea Coleoptiles.

The effect of phototropic stimulation of Zea coleoptile tips on the distribution of both endogenous indoleacetic acid (IAA) and applied C(14)-labeled IAA was determined. The tips rested on bisected agar blocks. More IAA was found in the blocks under the shaded side of the coleoptile tips than those under the irradiated side. However, no significant difference was observed between the total amounts of IAA, endogenous or labeled, in the irradiated and shaded sides of the experimental system. In addition, less endogenous auxin was found in the shaded tissues than in their irradiated counterparts. It is suggested that phototropism following unilateral irradiation with first positive radiant densities might be a consequence of lateral inequalities in the ability of the irradiated and shaded tissues to transport auxin basipetally.

Journal Article↗
PubMed1987

Phototropism in Hypocotyls of Radish : III. Influence of Unilateral or Bilateral Illumination of Various Light Intensities on Phototropism and Distribution of cis- and trans-Raphanusanins and Raphanusamide.

When etiolated radish (Raphanus sativus var. hortensis f. gigantissimus Makino) hypocotyls were subjected to a continuous unilateral illumination with white fluorescent light at 0.05, 0.1, or 1 watt per square meter, the suppression of the growth rate on the lighted side depended on the light intensity. The growth rate at the shaded side was only a little affected by the illumination at 0.05 and 0.1 watt per square meter but considerably suppressed by that at 1 watt per square meter. Upon a continuous unequal bilateral illumination, the growth rate was more strongly suppressed on the side of the higher intensity than on the side of the lower one, resulting in phototropic curvature toward the light source of the higher intensity. It was calculated from correlation analysis of light intensity and growth rate that, on an average, 6.9% of the irradiation applied to one side reached the opposite side. The amounts of cis- and trans-raphanusanins and raphanusamide in hypocotyls subjected to unilateral or unequal bilateral illumination increased much more at the side of the lighted or the higher intensity than at the opposite side. The present study demonstrates that phototropism in radish hypocotyl is correlated with and we conclude caused by a gradient of growth inhibition in the hypocotyl, depending on irradiation-induced amounts of cis- and trans-raphanusanins and raphanusamide.

Journal Article↗
PubMed1986

Phototropism in Hypocotyls of Radish : I. Isolation and Identification of Growth Inhibitors, cis- and trans-Raphanusanins and Raphanusamide, Involved in Phototropism of Radish Hypocotyls.

Three growth inhibitors which might be involved in phototropism of Sakurajima radish (Raphanus sativus var. hortensis f. gigantissimus Makino) hypocotyls, were isolated as crystalline forms from light-exposed radish seedlings and identified as cis- and trans-raphanusanins and 6-methoxy-2,3,4,5-tetrahydro-1,3-oxazepin-2-one (designated raphanusamide). The cis- and trans-raphanusanins inhibited growth of etiolated radish hypocotyls at concentrations higher than 1.5 micromolar, raphanusamide at concentrations higher than 20 micromolar.

Journal Article↗
PubMed1986

Phototropism in Hypocotyls of Radish : II. Role of cis- and trans-Raphanusanins, and Raphanusamide in Phototropism of Radish Hypocotyls.

When etiolated radish (Raphanus sativus var. hortensis f. gigantissimus Makino) hypocotyls were subjected to a continuous unilateral illumination with white fluorescent light (0.1 watt per square meter), the growth rate at the lighted side was strongly inhibited for the first 2 hours, while that at the shaded side showed no change. After 2.5 hours growth on the lighted side recovered gradually, while that on the shaded side was slightly inhibited. The neutral growth inhibitors, cis- and trans-raphanusanins and raphanusamide, were determined in the lighted and shaded sides from 1 hour before until 2 hours after the start of unilateral illumination. In the lighted side, cis- and trans-raphanusanins increased by 0.5 hour after the start of illumination, reached 3 to 3.5-fold greater concentrations than in the shaded side after 1 hour, and then decreased gradually. Raphanusamide increased in the lighted side to a 3-fold greater concentration than that in the shaded one 2 hours after the start of the illumination. Unilateral applications of cis- and trans-raphanusanins and raphanusamide suppressed the growth of the hypocotyl on the applied side more than that on the opposite one, causing the hypocotyls to bend towards the site of application. The data suggest that phototropic curvature in radish is caused by the light-induced synthesis of growth-inhibiting cis- and trans-raphanusanins, and raphanusamide at the site of illumination.

Journal Article↗
PubMed1989

Mutants of Arabidopsis thaliana with altered phototropism.

Thirty five strains of Arabidopsis thaliana (L.) Heynh. have been identified with altered phototropic responses to 450-nm light. Four of these mutants have been more thoroughly characterized. Strain JK224 shows normal gravitropism and "second positive" phototropism. However, while the amplitude for "first positive" phototropism is the same as that in the wild-type, the threshold and fluence for the maximum response in "first positive" phototropism are shifted to higher fluence by a factor of 20-30. This mutant may represent an alteration in the photoreceptor pigment for phototropism. Strain JK218 exhibits no curvature to light at any fluence from 1 micromole m-2 to 2700 micromoles m-2, but shows normal gravitropism. Strain JK345 shows no "first positive" phototropism, and reduced gravitropism and "second positive" phototropism. Strain JK229 shows no measurable "first positive" phototropism, but normal gravitropism and "second positive" phototropism. Based on these data, it is suggested that: 1. gravitropism and phototropism contain at least one common element; 2. "first positive" and "second positive" phototropism contain at least one common element; and 3. "first positive" phototropism can be substantially altered without any apparent alteration of "second positive" phototropism.

Arabidopsis↗
PubMed2003

Phytochromes A and B mediate red-light-induced positive phototropism in roots.

The interaction of tropisms is important in determining the final growth form of the plant body. In roots, gravitropism is the predominant tropistic response, but phototropism also plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism that is mediated by the phototropin family of photoreceptors. In contrast, red light induces a positive phototropism in Arabidopsis roots. Because this red-light-induced response is weak relative to both gravitropism and negative phototropism, we used a novel device to study phototropism without the complications of a counteracting gravitational stimulus. This device is based on a computer-controlled system using real-time image analysis of root growth and a feedback-regulated rotatable stage. Our data show that this system is useful to study root phototropism in response to red light, because in wild-type roots, the maximal curvature detected with this apparatus is 30 degrees to 40 degrees, compared with 5 degrees to 10 degrees without the feedback system. In positive root phototropism, sensing of red light occurs in the root itself and is not dependent on shoot-derived signals resulting from light perception. Phytochrome (Phy)A and phyB were severely impaired in red-light-induced phototropism, whereas the phyD and phyE mutants were normal in this response. Thus, PHYA and PHYB play a key role in mediating red-light-dependent positive phototropism in roots. Although phytochrome has been shown to mediate phototropism in some lower plant groups, this is one of the few reports indicating a phytochrome-dependent phototropism in flowering plants.

Apoproteins↗
PubMed1999

Phytochrome-controlled phototropism of protonemata of the moss ceratodon purpureus: physiology of the wild type and class 2 ptr-mutants

Phototropism and polarotropism in protonemata of the moss Ceratodon purpureus are controlled by the photoreceptor phytochrome. One class of phototropism mutants is characterised by growing randomly when kept for a prolonged time (5 d or longer) in unilateral red light. It was found that a subclass of these mutants grows faster than the wild type, the rate of cell division and the length of the cells being increased. This difference is found for light-grown and dark-grown filaments. It is therefore suggested that the mutant phenotype neither results from a defect in phytochrome photoconversion nor from a defect in phytochrome-gradient formation. Instead, it is possible that a factor which is involved in both signal transduction of phototropism and regulation of cell size and cell division is deregulated. If dark-grown mutant filaments are phototropically stimulated for 24 h, they show a weak phototropic response. Phototropism and polarotropism fluence-rate effect curves for mutants were flattened and shifted to higher fluence rates compared with those for the wild type. With wild-type filaments, a previously unreported response was observed. At a low fluence rate, half of the filaments grew positively phototropically, while the other half grew negatively phototropically. It seems that under these conditions, a phytochrome gradient with two maxima for the far-red-absorbing form of phytochrome (Pfr) within the cross-section of the cell is displayed by the response of the filaments. At higher fluence rates, all filaments of the wild type grew towards the light. These data and results from microbeam irradiation experiments and from phototropism studies with filaments growing within agar, indicate that light refraction plays an important role in the formation of the Pfr gradient in phototropism of Ceratodon.

Journal Article↗
PubMed1996

Mutations of Arabidopsis in potential transduction and response components of the phototropic signaling pathway.

Four genetic loci were recently identified by mutations that affect phototropism in Arabidopsis thaliana (L.) Heyhn. seedlings. It was hypothesized that one of these loci, NPH1, encodes the apoprotein for a phototropic photoreceptor. All of the alleles at the other three mutant loci (nph2, nph3, and nph4) contained wild-type levels of the putative NPH1 protein and exhibited normal blue-light-dependent phosphorylation of the NPH1 protein. This indicated that the NPH2, NPH3, and NPH4 proteins likely function downstream of NPH1 photoactivation. We show here that, although the nph2, nph3, and nph4 mutants are all altered with respect to their phototropic responses, only the nph4 mutants are also altered in their gravitropic responsiveness. Thus, NPH2 and NPH3 appear to act as signal carriers in a phototropism-specific pathway, whereas NPH4 is required for both phototropism and gravitropism and thus may function directly in the differential growth response. Despite their altered phototropic responses in blue and green light as etiolated seedlings, the nph2 and nph4 mutants exhibited less dramatic mutant phenotypes as de-etiolated seedlings and when etiolated seedlings were irradiated with unilateral ultraviolet-A (UV-A) light. Examination of the phototropic responses of a mutant deficient in biologically active phytochromes, hy1-100, indicated that phytochrome transformation by UV-A light mediates an increase in phototropic responsiveness, accounting for the greater phototropic curvature of the nph2 and nph4 mutants to UV-A light than to blue light.

Apoproteins↗
PubMed1977

Specific inhibition of phototropism in corn seedlings.

Geotropism was used as a control for the specificity of potential inhibitors of phototropism by the coleoptiles of corn (Zea mays) seedlings. The compounds tested fall into three categories showing: (a) no inhibition of either phototropism or geotropism (KCl); (b) nonspecific inhibition of both phototropism and geotropism (KCN); and (c) specific inhibition of phototropism (KI, NaN(3), and phenylacetic acid). Simultaneous irradiation of coleoptiles with phototropically inert light in addition to the phototropically active blue light also results in an inhibition of phototropism. Since azide, iodide, and phenylacetic acid are known to interact with flavins while a simultaneous irradiation with a phototropically inert light may depopulate the first triplet state of flavins, these data support the hypothesis that the photoreceptor pigment for phototropism in corn is a flavin.

Journal Article↗
PubMed2004

Hypocotyl growth orientation in blue light is determined by phytochrome A inhibition of gravitropism and phototropin promotion of phototropism.

How developing seedlings integrate gravitropic and phototropic stimuli to determine their direction of growth is poorly understood. In this study we tested whether blue light influences hypocotyl gravitropism in Arabidopsis. Phototropin1 (phot1) triggers phototropism under low fluence rates of blue light but, at least in the dark, has no effect on gravitropism. By analyzing the growth orientation of phototropism-deficient seedlings in response to gravitropic and phototropic stimulations we show that blue light not only triggers phototropism but also represses hypocotyl gravitropism. At low fluence rates of blue light phot1 mutants were agravitropic. In contrast, phyAphot1 double mutants grew exclusively according to gravity demonstrating that phytochrome A (phyA) is necessary to inhibit gravitropism. Analyses of phot1cry1cry2 triple mutants indicate that cryptochromes play a minor role in this response. Thus the optimal growth orientation of hypocotyls is determined by the action of phyA-suppressing gravitropism and the phototropin-triggering phototropism. It has long been known that phytochromes promote phototropism but the mechanism involved is still unknown. Our data show that by inhibiting gravitropism phyA acts as a positive regulator of phototropism.

Arabidopsis↗
PubMed2001

Red-light-induced positive phototropism in Arabidopsis roots.

The interaction between light and gravity is critical in determining the final form of a plant. For example, the competing activities of gravitropism and phototropism can determine the final orientation of a stem or root. The results reported here indicate that, in addition to the previously described blue-light-dependent negative phototropic response in roots, roots of Arahidopsis thaliana (L.) Heynh. display a previously unknown red-light-dependent positive phototropic response. Both phototropic responses in roots are considerably weaker than the graviresponse, which often masks phototropic curvature. However, through the use of mutant strains with impaired gravitropism, we were able to identify a red-light-dependent positive phototropic response in Arabidopsis roots. The red-induced positive phototropic response is considerably weaker than the blue-light response and is barely detectable in plants with a normal gravitropic response.

Arabidopsis↗
PubMed2006

Negative phototropic response of rhizoid cells in the fern Adiantum capillus-veneris.

In general, phototropic responses in land plants are induced by blue light and mediated by blue light receptor phototropins. In many cryptogam plants including the fern Adiantum capillus-veneris, however, red as well as blue light effectively induces a positive phototropic response in protonemal cells. In A. capillus-veneris, the red light effect on the tropistic response is mediated by phytochrome 3 (phy3), a chimeric photoreceptor of phytochrome and full-length phototropin. Here, we report red and blue light-induced negative phototropism in A. capillus-veneris rhizoid cells. Mutants deficient for phy3 lacked red light-induced negative phototropism, indicating that under red light, phy3 mediates negative phototropism in rhizoid cells, contrasting with its role in regulating positive phototropism in protonemal cells. Mutants for phy3 were also partially deficient in rhizoid blue light-induced negative phototropism, suggesting that phy3, in conjunction with phototropins, redundantly mediates the blue light response.

Adiantum↗
PubMed2001

Phototropism in Arabidopsis roots is mediated by two sensory systems.

Phototropism has been well-characterized in stems and stem-like organs, but there have been relatively few studies of root phototropism. Our experiments suggest that there are two photosensory systems that elicit phototropic responses in roots of Arabidopsis thaliana: a previously identified blue-light photoreceptor system mediated by phototropin (=NPH1 protein) and a novel red-light-based mechanism. The phototropic responses in roots are much weaker than the graviresponse, which competes with and often masks the phototropic response. It was through the use of mutant plants with a weakened graviresponse that we were able to identify the activity of the red-light-dependent phototropic system. In addition, the red-light-based photoresponse in roots is even weaker compared to the blue-light response. Our results also suggest that phytochrome may be involved in mediating positive phototropism in roots.

Arabidopsis↗
PubMed2002

Spatial separation of light perception and growth response in maize root phototropism.

Although the effects of gravity on root growth are well known and interactions between light and gravity have been reported, details of root phototropic responses are less documented. We used high-resolution image analysis to study phototropism in primary roots of Zea mays L. Similar to the location of perception in gravitropism, the perception of light was localized in the root cap. Phototropic curvature away from the light, on the other hand, developed in the central elongation zone, more basal than the site of initiation of gravitropic curvature. The phototropic curvature saturated at approximately 10 micromoles m-2 s-1 blue light with a peak curvature of 29 +/- 4 degrees, in part due to induction of positive gravitropism following displacement of the root tip from vertical during negative phototropism. However, at higher fluence rates, development of phototropic curvature is arrested even if gravitropism is avoided by maintaining the root cap vertically using a rotating feedback system. Thus continuous illumination can cause adaptation in the signalling pathway of the phototropic response in roots.

Gravitropism↗