Phytochrome Participation in Induction of Haustoria in Cuscuta japonica, a Holoparasitic Flowering Plant

Seedlings of Cuscuta japonica pasted on an acrylic plate developedmany haustoria in response to far-red light after pre-irradiationwith white light. The effect of far-red light was cancelledcompletely by red light irradiated immediately after the far-redlight. In order to elucidate the photoreceptor(s) for photocontrolin the induction of haustoria, action spectra for the photo-inductionand its reversion were determined in the wavelength region from340 nm to 800 nm using the Okazaki Large Spectrograph. The action spectrum for the induction of haustoria had a pronouncedpeak at 740 nm and a small peak at 420 nm, while the actionspectrum for reversal of the induction had a pronounced peakat 660 nm and a small peak at 380 nm. These results indicatethat phytochrome is involved in the photocontrol of inductionof haustoria in Cuscuta japonica. Considering the far-red /redreversibility, it was suggested that phytochrome B is the photorecepter.This is the first reliable evidence of phytochome participationon development of haustoria in parasitic plants. ⁴Present address: Graduate School of Science Division of BiologicalScience, Nagoya University, Nagoya, 464-01 Japan.     

Development of the Casparian strip is delayed by blue light in pea stems

To understand the regulatory mechanisms involved in tissue development by light, the kinetics of regulation of Casparian strip (CS) development in garden pea stems was studied. We found that short-term irradiation with white light delayed the development of the CS and used this delay to assess the quantitative effect of light on CS development. We examined the effect of the duration and fluence rates of white light treatment on CS development and observed a significant relationship between fluence and the delay in CS development indicating that the Bunsen–Roscoe law of reciprocity holds for this response. The effect of white light irradiation was not inhibited in the presence of a photosynthetic inhibitor, DCMU, or a carotenoid biosynthesis inhibitor, Norflurazon, indicating that the delay in CS development by light is a photomorphogenetic response rather than a subsidiary effect mediated by photosynthetic activity. An action spectrum for the response displayed a major peak in the blue-light region, suggesting a dominant role for blue-light receptors. A minor peak in the red-light region also suggested the possible involvement of phytochromes. Although phytochromes are known to contribute to blue-light responses, phytochrome-deficient mutants showed a normal delay of CS development in response to blue light, indicating that the response is not mediated by phytochrome and suggesting a role for one or more specific blue-light receptors.     

Chloroplast DNA Variation in the genusSesamum

It is widely approved that comparing restriction profiles and maps of chloroplast DMA provides valuable information concerning inter-and/or intra-specific relationships among plant species. Such chloroplast DNA analysis was applied to species and strains inSesamum which is a genus of approximately 38 species and contains a large number of strains of the cultivated sesame,S. Indlcum. Our chloroplast DNA investigations of 22 species and strains showed that; (i) among four species (S. capense, S. radiatum, S. schinzianum andS. indicum), the chloroplast genome ofS. capense was most distantly related to that of the cultivated species,S. indicum, (ii) chloroplast DNA polymorphism was also recognized among eight cultivated stralns collected from various regions in the tropical zone, but not among eight different varieties grown in the temperate zone, and (iii) the chloroplast DNA alterations observed could be attributed to the site gains or losses with the exception of the alterartion detected within the inverted repeat sequences inS. capense chloroplast DNA. These results demonstrate the presence of chloroplast genome diversity amongSesamum species and strains, suggesting the usefulness of chloroplast DNA analysis for elucidating the species relationships in the genusSesamum and the origin and evolutionary process of the cultivated sesame species. The present paper is based on the contribution which was read in a symposium entitled “Organellar DNA Variations in Higher Plants and Their Taxonomic Significance”, at the 50th Annual Meeting of the Botanical Society of Japan in Shizuoka on October 2, 1990, under the auspices of the Japan Society of Plant Taxonomists.     

Haustoria of Cuscuta japonica, a Holoparasitic Flowering Plant, Are Induced by the Cooperative Effects of Far-Red Light and Tactile Stimuli

When seedlings of Cuscuta japonica were grown with Vigna radiata(the host plant) in a flower pot for 6 d under white light andthen irradiated with far-red or blue light (ca. 6 µmolphotons m^–2 s^–1), the seedlings parasitized V. radiata.However, no parasitism of the seedlings was observed under redor white light or in darkness. The parasitic behavior of seedlingsof C. japonica was observed even if an acrylic rod was usedas a substitute for the host plant. Upon incubation under far-redlight, the seedling twined tightly around the rod and developedhaustoria towards it. Haustoria also developed when apical andsubapical regions of seedlings were held between two glass platesthat were about 0.7 mm apart and were irradiated with far-redlight. However, no haustoria were induced by either the holdor irradiation alone. These results indicate that parasitismof Cuscuta japonica is controlled by the cooperative effectsof two physical signals, far-red light and appropriate tactilepressure. Our findings suggest that parasitism by the genusCuscuta involves a novel strategy. (Received April 10, 1996; Accepted August 21, 1996)     

Relationship between Germination and PFR Level in Spores of the Fern Lygodium japonicum

The relationship between germination and P_FR level in sporesof the fern Lygodium japonicum was investigated. Percent P_FRestimated from direct spectrophotometric measurement of sporesincreased with the logarithm of total fluence of 660 nm-light.The transformation from P_R to P_FR was saturated by giving ca.200 Jm^–2 of 660 nm-light and half-saturated by ca. 55J^–2 of 660 nm-light. Clear positive correlation was observedbetween % P_FR levels and germination rates in spores irradiatedwith 660 nm and/or 730 nm-light, or with 686 or 700 nm-light.The P_FR percentage in spores was raised to 16–34% by blue(415 nm) light irradiation. This P_FR level was enough to causesome germination when produced by monochromatic light of redto far-red region, but blue light did not cause any germination. After 660 nm-light irradiation, the P_FR level decreased graduallyin darkness (25±1°C) and P_FR completely disappearedin 8 h, but 730 nm-light given even 16 h after 660 nm-lightirradiation inhibited germination. ⁴Present address: Tropical Botanic Garden and Research Institute,Navaranga Road, Trivandrum 695 011, India. (Received March 15, 1983; Accepted June 4, 1983)     

Effects of Gibberellins and Their Methyl Esters on Dark Germination and Antheridium Formation in Lygodium japonicum and Anemia phyllitidis

The effects of GA₃, GA₄ and GA₉ and their methyl esters on darkspore germination and antheridium formation of the ferns Lygodiumjaponicum and Anemia phyllitidis were investigated. Althoughall induced both germination and antheridium formation in Lygodium,only the gibberellins induced these effects inAnemia. (Received August 28, 1986; Revision received November 14, 1986. )     

Action Spectrum in Ultraviolet and Blue Light Region for the Inhibition of Red-Light-Induced Spore Germination in Adiantum capillus-veneris L.

The action spectrum for the inhibition of red-light-inducedgermination of spores in the fern Adiantum capillus-veneriswas determined between 250 and 500 nm using the Okazaki largespectrograph. When monochromatic lights were given after red-lightirradiation, two prominent peaks for inhibition of spore germinationwere observed at 275 and 440 nm and a minor peak at ca. 390nm. ² Permanent address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan.     

Photo-Inhibition of Red-Light-Induced Spore Germination in Pteris vittata: Cyanide, Azide and Ethanol Counteracts Restorable Inhibitory Action of Near UV and Blue-light but not That of Far UV

In Pteris vittata, red-light-induction of spore germinationwas completely inhibited by subsequent irradiation with farUV (260 nm), near UV (380 nm) or blue (440 nm) monochromaticlight produced at the Okazaki Large Spectrograph. Germinationbut recovered from these photo-inhibition after less than 48h of darkness. Near UV- and blue-light-induced inhibition werestrongly counteracted by addition of 1 mM KCN, 1 RIM NaN₃ or100 mM ethanol. Far UV- and far red light-induced inhibition,however, was not influenced by these chemicals. Consequentlythe heights of peaks of action spectrum for this photo-inhibitionof spore germination was changed by addition of these chemicalsin the blue and near UV region but not at 260 nm. The resultssuggest that either or both of the photoreceptor system andthe signal transduction chain of the photo-inhibition are qualitativelydifferent between the shorter (i.e. far UV) and the longer (i.e.near UV and blue) wavelength regions. (Received August 31, 1989; Accepted February 19, 1990)     

Control by Ammonium Ion of the Change from Step-Up to Step-Down Photophobically Responding Cells in the Flagellate Alga Euglena gracilis

The regulation between step-down and step-up photophobic responses,resulting in photoaccumulation of the cells in an actinic lighttrap or cells' avoidance from an excessive illumination, iscrucially important for the survival of phototrophic organismssuch as Euglena gracilis. As for the factors involved in thisregulation in Euglena gracilis, we for the first time reporthere that ammonium ion specifically enhances step-down photophobicresponse, together with the effects of L-methionine-DL-sulfoximine(L-MSO), an inhibitor of ammonium assimilation, to specificallyenhance step-up photophobic response. The apparent positivecorrelation between the degree of greening and the step-downphotophobic response did not seem to reflect real causal relationshipin view of the results with effects of gabaculine, an inhibitorof -aminolaevulinic acid (-ALA) formation. The transmissionof stigma and step-down appearance did not show any correlationeither, in contrast to a previous assumption by other authors.Cycloheximide (CHX), an inhibitor of eukaryotic protein synthesis,suppressed step-down appearance and enhanced step-up appearance,probably suggesting an involvement of some (newly synthesized)protein(s) specifically in the step-down photosignal detectionand/or signal transduction process(es). (Received August 18, 1998; Accepted December 3, 1998)     

Effects of Anaerobiosis and Respiratory Inhibitors on Blue-Light Inhibition of Spore Germination in Pteris vittata

In a fern, Pteris vittata, inhibition by low-energy blue lightof phytochrome-dependent spore germination was counteractedby anerobiosis and respiratory inhibitors, such as KCN and NaN₃.A 50% inhibition of spore germination in a medium containing0.3 mM NaN₃ required about 8 times longer duration of blue lightirradiation compared with the control. The counteracting effectof NaN₃ continued for about 32 hr after withdrawal of the inhibitor.However, NaN₃ neither induced dark germination nor counteractedthe far-red light inhibition of spore germination. Reducingagents and uncouplers were tested and dithionite and arsenateslightly reversed the blue light inhibition of spore germination. (Received December 17, 1981; Accepted July 8, 1982)