Effects of red and far-red light on cell division in the shoot apex ofSilene coeli-rosa L.

Summary 28-day-old plant ofSilene coeli-rosa were exposed at 1,700 hours to 5 or 10 minutes red light, 5 or 10 minutes far-red light, red followed by far-red, far-red followed by red or maintained in darkness. Measurements of the proportions of cells with the 2 C and 4 C amounts of DNA in the shoot apex of the plants, sampled at 2,000 hours, showed that far-red light promoted an increase in the G2 proportion whereas red light resulted in an increase in the G1 proportion of the cell cycle, relative to the dark controls. Moreover these changes were red, far-red reversible. All light treatments resulted in increases in the mitotic index in the apex compared with the dark controls, suggesting increases in the growth rate. The data implicate phytochrome in a low energy response and suggest that, in the shoot apex, G1 is shortened markedly following exposure to farred light, whilst G2 is shortened the most following exposure to red light. The results are discussed in relation to flower-initiation.     

Perithecial formation in Gelasinospora reticulispora

When hyphae in the basal region of 72-hold, dark-grown mycelium of G. reticulispora (Greis et Greis-Dengler) C. et M. Moreau (Sordariaceae) were exposed to a microbeam of monochromatic blue light, perithecial initials were induced only in hyphae located within or in the vicinity of the light spot. The average distance from the periphery of the microbeam spot to perithecial initials produced outside the spots was 100–200 m, regardless of the beam diameter or the incident light energy. The maximum distance of a perithecium formed outside a microbeam spot was ca. 700 m. The inductive effect of blue light became detectable at 100 J m^-2 and reached a maximum at 1000 J m^-2, regardless of beam diameter. A microphotographic examination showed that the microbeam irradiation was effective only in hyphae rich in protoplasm.V=Inoue and Furuya, 1975 b     

Phytochrome-mediated polarotropism of Adiantum capillus-veneris L. protonemata as analyzed by microbeam irradiation with polarized light

Summary Perception of polarized light inducing phytochrome-mediated polarotropism in protonemata of the fern Adiantum capillus-veneris L. was analyzed using brief microbeam irradiation with polarized red (R) or far-red light (FR). The polarotropic response inducible by irradiation of the subapical 10–30-m part with polarized R vibrating parallel to the cell axis was nullified by subsequently giving R at the apical 0–2.5-m region. This inhibitory effect of R showed an action dichroism, that is, polarized R vibrating normal to the cell axis was effective but the parallel-vibrating R was not. On the other hand, FR irradiation of the extreme tip after irradiation of the whole cell with depolarized R effectively induced a tropic response. This FR effect also showed action dichroism, with parallel-vibrating polarized FR being more effective than FR vibrating normal to the cell axis. When the apical-dome region and the adjacent subapical 10–20-m region were sequentially irradiated with polarized R vibrating obliquely in different directions, polarotropism took place depending on the vibrating direction of the light given to the apical-dome region. Obliquely vibrating polarized FR given to the apical dome after irradiation of the whole cell with depolarized R also induced polarotropism. Thus, the difference in amount (or percent) of the far-redabsorbing form of phytochrome (Pfr) between the extreme tip and the subapical region appears to be crucial in regulating the direction of apical growth; the difference in Pfr level between the two sides of the protonemal apex may occur mainly at the apical dome. Furthermore, the transition moments of the red-absorbing form of phytochrome (Pr) and Pfr seem to be aligned parallel and normal, respectively, to the cell surface at the periphery of the apical hemisphere.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light     

Blue- and red-light action in photoorientation of chloroplasts in Adiantum protonemata

An action spectrum for the low-fluencerate response of chloroplast movement in protonemata of the fern Adiantum capillus-veneris L. was determined using polarized light vibrating perpendicularly to the protonema axis. The spectrum had several peaks in the blue region around 450 nm and one in the red region at 680 nm, the blue peaks being higher than the red one. The red-light action was suppressed by nonpolarized far-red light given simultaneously or alternately, whereas the bluelight action was not. Chloroplast movement was also induced by a local irradiation with a narrow beam of monochromatic light. A beam of blue light at low energy fluence rates (7.3·10^-3-1.0 W m^-2) caused movement of the chloroplasts to the beam area (positive response), while one at high fluence rates (10 W m^-2 and higher) caused movement to outside of the beam area (negative response). A red beam caused a positive response at fluence rates up to 100 W m^-2, but a negative response at very high fluence rates (230 and 470 W m^-2). When a far-red beam was combined with total background irradiation with red light at fluence rates causing a low-fluence-rate response in whole cells, chloroplasts moved out of the beam area. When blue light was used as background irradiation, however, a narrow far-red beam had no effect on chloroplast distribution. These results indicate that the light-oriented movement of Adiantum chloroplasts is caused by red and blue light, mediated by phytochrome and another, unidentified photoreceptor(s), respectively. This movement depends on a local gradient of the far-red-absorbing form of phytochrome or of a photoexcited blue-light photoreceptor, and it includes positive and negative responses for both red and blue light.Abbreviations BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light - UV ultraviolet     

Light-induced changes in the photoresponses of plant stems the loss of a high irradiance response to far-red light

De-etiolation results in phytochrome destruction, greening, and the loss of the far-red high irradiance responses (HIR). Evidence is presented against the hypothesis that the loss of the far-red HIR is a direct consequence of phytochrome destruction. Loss of the far-red HIR for the inhibition of elongation in hypocotyls of Raphanus sativus involves two different, but linked, actions of phytochrome. An induction reaction requires the far-red absorbing form of phytochrome for about 20 min after which accumulation of its product depends only on time. A second reaction requires continuous light or frequent short irradiations and involves cycling of the phytochrome system. This acts on the product of the induction reaction. It is proposed that in green plants an important mode of operation of phytochrome in the light depends on pigment cycling, and that during de-etiolation this system is established under phytochrome control.Abbreviations HIR high irradiance response - R red - FR farred light - P_tot phytochrome, P_r its red absorbing form, P_fr its far-red absorbing form A.M. Jose was the holder of Ministry of Agriculture, Fisheries and Food award AE 6819     

Effects of blue and red light on unrolling of rice leaves

Unrolling of the second leaf of 8-day-old rice (Oryza sativa L.) seedlings was promoted by weak blue light (B), but not by red light (R). The effect of B was counteracted by irradiation with R just before or after the B. The counteracting effect of R was reversed by subsequent irradiation with far-red light but not by B, even if B was applied for 10 h. The B was effective when the region 0.5–2 cm from the tip of the leaf was irradiated. These results indicate that in rice photoreceptors for blue light located in the region 0.5–2 cm from the tip of the leaf play a key role in leaf unrolling and that a B-absorbing pigment and phytochrome participate in leaf unrolling in a closely related manner.Abbreviations B blue light - R red light - FR far-red light - W white light - D dark This work was presented at the Annual Meeting of the Japanese Society of Plant Physiologists on April 4, 1978, in Hiroshima     

Cell division in caffeine-induced binucleate protonemal cells ofAdiantum. II. Formation of the preprophase band and cell division in centrifuged and non-centrifuged cells

Organization of microtubules (MTs) in relation to the behavior of nuclei was examined in dividing binucleate cells ofAdiantum capillus-veneris L. To induce binucleate cells, caffeine, an inhibitor of formation of the cell plate, was applied at 4 mM to synchronously dividing protonemal cells during cytokinesis (Murata and Wada 1993). Formation of the preprophase band (PPB) during the next cell cycle was examined in non-centrifuged and centrifuged cells. The two nuclei were separated or associated with one another in both non-centrifuged and centrifuged cells, although the location of the nuclei in the cylindrical protonemal cells was different (Murata and Wada 1993). Irrespective of centrifugation, a single PPB was formed around the nuclei in cells with associated nuclei. Two PPBs were formed in cells with separated nuclei in centrifuged cells. Patterns of mitosis and cytokinesis varied, depending on the location of the PPB and the distribution of the nuclei. The role of the nucleus in formation of the PPB is discussed.     

Effect of light and gibberellic acid on cell division in the first foliage leaf of durum wheat (Triticum durum Desf.)

The present paper is part of a research program which aims at a quantitative analysis of the effects of light and gibberellic acid (GA₃) on growth of the first foliage leaf in durum wheat (Triticum durum Desf.). Since leaf growth is the combined result of the increase in cell number (cell division) and cell enlargement, the influence of light and GA₃ treatment on cell division in the basal meristem of the first leaf in two cultivars, Cappelli and Creso, was investigated. Creso is a short-strawed cultivar carrying the Gai 1 gene which influences both plant height and insensitivity to applied GA₃. Cell division, as measured by mitotic index, was similar in darkness, continuous red light and dichromatic irradiation (far-red plus red), while lower mitotic rates were observed under continuous far-red light: this indicates that the response of cell division is modulated by a high-irradiance reaction of phytochrome in both cultivars. The two cultivars showed different responses to blue light. In Cappelli, blue light and dichromatic irradiation (blue plus red) gave lower mitotic indices than the dark control, indicating the action of a specific blue-light-absorbing photoreceptor, whereas in Creso the response kinetics to all light regimes which included blue light were more complex. On the basis also of the results obtained with GA₃ application in Cappelli, it appears that (i) the hormonal treatment is able to change the pattern of mitotic index only in the presence of the action of a blue-light receptor and (ii) the different responses of the two cultivars could be the result of different endogenous hormonal levels. The importance of the observations in relation to the data for first-leaf longitudinal growth reported in a previous paper (Baroncelli et al. 1984, Planta 160, 298–304) is discussed.Abbreviations BL blue light - D darkness - FR far-red light - GA gibberellin - GA₃ gibberellic acid - m.i. mitotic index - Norflurazon 4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-totyl-3(2H)) pyridazinone - R red light - WL white light - phytochrome photoequilibrium     

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     

Elongation and cell division in Bdellovibrio bacteriovorus

Elongation and division of Bdellovibrio bacteriovorus were studied in axenic synchronous cultures. The cells elongate unidirectionally from one end attaining a length of several unit cells, and then divide into the corresponding number of cells. The length of the filament and, consequently, the progeny number, vary within the range of two to several dozen cells, according to the conditions used. A protein and a low molecular weight component are required for normal division.     

Fluence dependence of the ultraviolet-light-induced accumulation of chalcone synthase mRNA and effects of blue and far-red light in cultured parsley cells

The fluence dependence of the time course of accumulation of chalcone synthase mRNA in ultraviolet (UV)-light-irradiated cell suspension cultures of parsley (Petroselinum crispum) and the additional effects of blue and far-red light have been investigated. Variations of the UV fluence had no detectable influence on the initial rate of increase in mRNA amount or translational activity, nor on the preceding lag period of approximately 3 h, but strongly influenced the duration of the transient increase. The effects were the same whether the fluence rate or the time of irradiation was varied to obtain a given fluence. Blue-light pretreatment of the cells resulted in increased amounts of mRNA and abolished the apparent lag period. This effect remained cryptic without the subsequent UV-light treatment. Irradiation with long-wavelength far-red light following UV-light pulses shortened the duration of the mRNA accumulation period. This effect was not altered by a preceding blue-light treatment. Thus, three photoreceptors, a UV-B receptor, a blue-light receptor and phytochrome, participate in the regulation of chalcone synthase mRNA accumulation in this system.Abbreviations cDNA complementary DNA - UV ultraviolet - Pfr fai-red-absorbing form of phytochrome     

Floral initiation in sorghum hastened by gibberellic acid and far-red light

Combinations of far-red light (FR) (4 min) and gibberellic acid (GA₃), given at the beginning of a daily 12-h dark period in a growth room, were used to study floral induction in four maturity genotypes of the milo group of sorghum (Sorghum bicolor (L.) Moench). The 12-h dark period without GA₃ application or FR induced flowering in only the early genotype; FR hastened initiation in the early genotype, while GA₃ hastened floral initiation in the two intermidiate-flowering genotypes. GA₃ and FR together had a strong synergistic effect, hastening floral initiation by 30 to more than 80 d in the early and intermediate genotypes. Red light (R) did not hasten flowering; FR preceded by R gave the same effect as FR alone. GA₃ promoted stem elongation equally whether floral initiation occurred or not; thus, its effect on stem elongation was independent of floral initiation. The capacity of GA₃ to induce flowering in sorghum, a short-day plant, seems to be enhanced by phytochrome being in the P_R form at the beginning of the night when GA₃ was applied.Abbreviations FR far-red light - GA(s) gibberellin(s) - GA₃ gibberellic acid - R red light     

Control by light of hypocotyl growth in de-etiolated mustard seedlings

After sowing, mustard (Sinapis alba L.) seedlings were grown for 48 h in white light (25°C). These fully de-etiolated, green seedlings were used as experimental material between 48 and 72 (84) h after sowing. The question researched was to what extent control by light of hypocotyl elongation is due to phytochrome in these seedlings. It was found that the light effect on hypocotyl growth is very probably exerted through phytochrome only. In particular, we found no indication for the involvement of a specific blue light photoreceptor pigment.Abbreviations HIR high irradiance reaction - P_fr far-red absorbing, physiologically active form of phytochrome - P_r red absorbing, physiologically inactive form of phytochrome - Pot total phytochrome, i.e. [P_r]+[P_fr] - [P_fr]/[P_tot] - red red light - fr far-red light - wl white light - bl blue light - di dichromatic irradiation - l hypocotyl length     

The changes of nuclear position and distribution of circumferentially aligned cortical microtubules during the progression of cell cycle inAdiantum protonemata

The intracellular positions of the nucleus and of cortical, circumferentially aligned microtubules (CCAM) in filamentous, single-celled protonemata ofAdiantum capillus-veneris were determined throughout the cell cycle in the dark. When apical growth continued at G₁ phase, the nucleus migrated keeping a constant distance from the tip. When the apical growth stopped at late S or G₂ phase, the nucleus stopped moving forward and then slightly moved backward to the site of cytokinesis. The CCAM were found only in the dome of protonemal tip when growing under continuous red light; they increased in number after dark incubation for 12 hr and then decreased after 20th hr in the dark. The CCAM were usually observed in the region between the nucleus and the tip at 28 hr in the dark. They were located around the nuclear region at pre-prophase and prophase, but then totally disappeared at metaphase and thereafter.     

Effects of light on phytochrome in cauliflower curd

The effect of light on the phytochrome content of cauliflower (Brassica oleracea (L.) var. botrytis) curd was studied using in vivo spectrophotometry. It was found that light caused a rapid increase in phytochrome level whereas transfer to darkness caused a rapid loss, regardless of the amount of phytochrome initially present in the far red absorbing form. The amount of phytochrome detectable during continuous irradiation appears to be related to the photoequilibrium , and is thus controlled by phytochrome itself.Abbreviation Pr and Pfr red and far red absorbing forms of phytochrome, respectively     

Role of red light in hair-whorl formation induced by blue light in Acetabularia mediterranea

After a pre-treatment with red light, hair formation at the growing tip of the siphonaceous green alga Acetabularia mediterranea Lamour. (= A. acetabulum (L.) Silva) can be induced by a pulse of blue light. Red light is needed again after the inductive blue-light pulse if the new whorl of hairs is to develop within the next 24 h. In order to investigate the role of this red light, the duration of the red irradiation was varied and combined with periods of darkness. The response of hair-whorl formation was dependent on the total amount of red light, regardless of whether the red irradiation followed the blue pulse immediately or was separated from it by a period of darkness. Furthermore, periods of exposure to the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1-1dimethylurea had a similar effect to darkness. Both observations indicate that this red irradiation acts as a light source for photosynthesis. Whether or not the red light had an additional effect via phytochrome was tested in another type of experiment. The dependence of hair-whorl formation on red-light irradiance in the presence of simultaneous far-red irradiation was determined for the pre-irradiation period as well as for the irradiation period after the blue pulse. In both experiments, far-red light caused a small promotion of hair-whorl formation when low irradiances of red light were used. However, these differences were attributable to a low level of photosynthetic activity (which in fact was measurable) caused by red light reflected in the growth chamber. Furthermore, lowering the proportion of active phytochrome by far-red light would be expected to suppress hair-whorl formation. The influence of far-red light was also tested in a strain of Acetabularia mediterranea that developed hair whorls in about 20% of cells even when kept in complete darkness after the blue-light pulse. Far-red irradiation had no effect. These results strongly indicate that phytochrome is not involved in hair-whorl formation. Rather it is concluded that the effects of red light are caused by photosynthesis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

The effect of red and far-red light on proton secretion from mesophyll-cell protoplasts of Vicia faba L.

The influence of red and far-red irradiation on the transport of H⁺ and ⁸⁶Rb⁺ through the plasmalemma was studied using parenchymal protoplasts isolated from Vicia faba leaves. The results indicate that red light stimulates H⁺ secretion and the uptake of ⁸⁶Rb⁺. Moreover, it has been demonstrated that far-red irradiation acts antagonistically with respect to red light in both these processes.     

Effects of light on the cell cycle in the shoot apex ofSilene coeli-rosa L. on the first day of floral induction

Summary 28-day-old plants ofSilene coeli-rosa were exposed, at 1,700 hours, to 5 minutes far-red light, 5 minutes red, 5 minutes far-red followed by 5 minutes red light, or maintained in darkness (short day controls). All plants were exposed to tritiated (methyl-³H-)thymidine for 2 hours (1645–1845) and subsequently sampled at 2-hour intervals for 24 hours. The length of the cell cycle (pulse-label mitoses (PLM) method) and changes in cell number were measured in the shoot apical meristems. The cell cycle in the short day controls was 16–17 hours compared with a mean cell generation time of 18 hours. Exposing plants to far-red light resulted in a shortening of the cell cycle to 11 hours, red light resulted in a shortened cycle of 12 hours whilst far-red, red gave a value of 9 hours. Mean cell generation times following each light treatment were approximetely 2–5 hours longer than the corresponding cell cycle times, suggesting that the shortened cell cycles reverted to longer cycles over the experimental period. Measurements of the proportions of cells with the 2C and 4C amounts of DNA in the apical meristems of unlabeled plants indicated that G1 shortened but G2 lengthened in response to far-red light. A measurement of the labeling index also indicated that S-phase shortened in response to far-red. These data also suggested that red light caused G1 to shorten and G2 to lengthen although the corresponding PLM curve was consistent with a dramatic shortening of G2. Far-red followed by red resulted in decreases in the durations of both G2 and G1.     

Pole reversal and the development of cell asymmetry during division in cryptomonad flagellates

Summary A unique form of cell division is reported for the cellsKomma caudata andCryptomonas ovata (Cryptophyceae). During cytokinesis, the posterior tail-like region of each daughter cell develops from the anterior region of the parental cell. This process, termed pole reversal, involves a major realignment in overall cell polarity as well as alterations to cytoplasmic and surface components. Pole reversal may be a consequence of flagellar apparatus transformation and reorientation during division, and pole reversal may facilitate the development of the asymmetric cell shape in daughter cells.