Growth analysis of wild-type and photomorphogenic-mutant tomato plants

A custom designed growth-measuring apparatus, controlled by a microcomputer has been used to study extension growth kinetics of wild-type and photomorphogenic-mutant tomato ( Lycopersicon esculentum Mill.) plants with and without end-of-day farred light (EODFR). The following photomorphogenic mutants were used. Far-red insensitive ( fri ^.1): deficient in phytochrome A (phyA); temporarily red light-insensitive ( tri ^.3): deficient in phytochrome Bl (phyB1), and their isogenic wild type (WT) cv. MoneyMaker. aurea (au) : deficient in phytochrome chromophore biosynthesis; high-pigment-1 ( hp-1 ): exhibiting exaggerated phytochrome responses, and their isogenic WT cv. Ailsa Craig. The stem elongation rate (SER) during a 24-h period of all the genotypes studied shows a similar pattern, having two dramatic transients, one shortly after the onset of the light period (a sharp decline in SER) and another shortly after the start of the dark period (a sharp increase in SER). These transients are probably associated with water relations as a consequence of opening and closure of the stomata. The fastest SER occurs during the dramatic oscillations early in the dark period. Between the genotypes there are large quantitative differences in SER. All the genotypes tested exhibited a strong EODFR response, resulting in a relative promotion of SER during the first period after the start of EODFR and in the subsequent light and dark periods. These results indicate that phyA, absent in the fri ^.1 mutant, does not play a major role in SER of light-grown tomato plants, whereas phyB 1, absent in the tri ^.3 mutant, is partly responsible for the compact stature of WT plants. An additional phytochrome other than phy A and phy B1 must therefore be capable of eliciting the EODFR response.     

Stem extension-growth responses to blue light require Pfr in tomato seedlings but are not reduced by the low phytochrome levels of the aurea mutant

The effects of blue light (B) on stem extension growth were investigated in wild-type (WT) and aurea (au ) mutant seedlings of tomato. The au mutant has reduced phytochrome levels. Etiolated seedlings were grown under background red light (R) or far-red light (FR) with or without B. Hypocotyl growth was inhibited by B added to R but not by B added to FR, both in WT and au seedlings. The levels of B and/or R reaching the stem of fully de-etiolated seedlings grown in a glasshouse were reduced by means of collars around it. Both in WT and au -mutant seedlings the responses to B were larger at high than at low R/FR quantum ratios. In etiolated and light-grown au seedlings, changing the levels of phytochrome-absorbable radiation did not cause the same effect as changing B levels, indicating the action of specific BL/UV-A photoreceptor(s) (BAP). The responses to B are reduced by the low calculated levels of Pfr established by light treatments but not by the low levels of phytochrome present in the au mutant. The au mutant appears to be deficient in a phytochrome pool that is not essential for the interdependent co-action observed between phytochrome and BAP in the control of stem extension growth in tomato.     

The joint action of phytochrome and alternating temperatures in the control of seed germination in Dactylis glomerata

The promoting effect of light and alternating temperatures on the germination of seeds of three contrasting populations of Dactylis glomerata L. was studied. Irradiation treatments using broad band low irradiance light sources resulted in red/far-red reversible effects, demonstrating the involvement of phytochrome in germination control. Reduction of germination by far-red below the level of a dark control indicated the presence of high pre-existing levels of the active form of phytochrome (P_fr) in some individuals. The capacity for dark germination at 21/11°C (12 h/12 h) was shown to be dependent on P_fr. Although some individuals were capable of germination at constant temperatures following red irradiation, in most seeds germination was dependent on the presence of P_fr and alternating temperatures. Some individuals responded to a single red irradiation, although a large proportion of seeds required high levels of P_fr to be maintained for long periods. Previously published dose response curves for alternating temperatures and a measured dark reversion time of 48 h for P_fr established by a single 60 min red irradiation, provided firm evidence of a direct correlation between the requirements for repeated irradiation and number of alternating temperature cycles.     

Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. I. The photoreceptor

Broad-band UV-B radiation inhibited hypocotyl elongation in etiolated tomato ( Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by < 3 μmol m⁻² s⁻¹ of UV-B radiation provided against a background of white light (> 620 μmol m⁻² s⁻¹ between 320 and 800 nm), and was similar in wild-type and phytochrome-1-deficient aurea mutant seedlings. These observations suggest that the effect of UV-B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m⁻² s⁻¹ of monochromatic UV radiation against a while light background (63 μmol m⁻² s⁻¹ showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV-B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN, and phenylacetic acid) largely abolished the inhibitor) effect of broad-hand UV-B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10⁻⁴ M , which have been shown in vitro to be effective in quenching the triplet excited stales of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV-A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation evened by UV-B. Kl applied after UV-B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system invoked in UV-B perception by tomato seedlings during de-etiolation may be a flavin.     

Phytochrome control of skotodormancy release in Grand Rapids lettuce achenes

Light-requiring Grand Rapids lettuce ( Lactuca sativa L.) achenes develop skotodormancy when imbibed in darkness for 7 days at 25°C. Redried skotodormant achenes maintain this type of dormancy upon subsequent rehydration. At 25°C full germination of skotodormant achenes can be induced by continuous and intermittent red light illumination as well as by several brief red irradiations given daily. One brief (10 min) red light irradiation can partly break skotodormancy at 20°C, while at lower temperatures the same treatment results in full induction of germination. Phytochrome control of the release from skotodormancy is proven by a) the dependence of the germination response on the relative sequence of red and far-red light in cyclic irradiations, and b) the reversion of red action by subsequent far-red irradiation. The time course of germination of skotodormant achenes treated with intermittent red light depends upon the length of dark interval between the light pulses. Germination is considerably delayed compared to that of non-skotodormant ones, induced by a single brief red light treatment. This fact in combination with the requirement, over a long period of time, of P_fr action for full manifestation of germination, indicates that skotodormancy is a deeper form of dormancy. It is concluded that the germination of lettuce achenes may always be subjected to phytochrome control.     

Genetic analysis of the roles of phytochromes A and B1 in the reversed gravitropic response of the lz-2 tomato mutant

The lz-2 mutation in tomato ( Lycopersicon esculentum ) causes conditional reversal of shoot gravitropism by light. This response is mediated by phytochrome. To further elicit the mechanism by which phytochrome regulates the lz-2 phenotype, phytochrome-deficient lz-2 plants were generated. Introduction of au alleles, which severely block chromophore biosynthesis, eliminated the reversal of hypocotyl gravitropism in continuous red and far-red light. The fri ¹ and tri ¹ alleles were introduced to specifically deplete phytochromes A and B1, respectively. In dark-grown seedlings, phytochrome A was necessary for response to high-irradiance far-red light, a complete response to low fluence red light, and also mediated the effects of blue light in a far-red reversible manner. Loss of phytochrome B1 alone did not significantly affect the behaviour of lz-2 plants under any light treatment tested. However, dark-grown lz-2 plants lacking both phytochrome A and B1 exhibited reduced responses to continuous red and were less responsive to low fluence red light and high fluence blue light than plants that were deficient for phytochrome A alone. In high light, full spectrum greenhouse conditions, lz-2 plants grew downward regardless of the phytochrome deficiency. These results indicate that phytochromes A and B1 play significant roles in mediating the lz-2 phenotype and that at least one additional phytochrome is involved in reversing shoot gravitropism in this mutant.     

The effect of SAN 9789 and light on the germination of seeds from Taraxacum vulgare

Photoblastic seeds (achenes) of Taraxacum vulgare coll. were treated with a water solution of SAN 9789, 4-chloro-5 (methylamino) -2- (α,α,α-trifluoro- m -tolyl) -3(2H) pyridazinone. SAN-treatment increased the germination in darkness from 0 to 12%. An irradiation for 5 min with red light, giving a germination of 12% for seeds in water only, gave together with SAN treatment a germination of 60%. In both water and SAN, the effect of red irradiation could be reversed by a short irradiation (15 min) of far-red light. If far-red light was repeatedly given (5 min per h) it had hardly any effect on germination in water (4% germination), but for seeds in SAN solution, intermittent far-red light had a stimulating effect (63% germination). If far-red light was given continuously for 96 h, the germination in water was 1% and in SAN solution 17%. The results in the present paper indicate that SAN may broaden the concentration interval of P_fr for which germination is high.     

Photoperiod and light quality effects on rate of dark respiration and on photosynthetic capacity in developing seedlings of Chenopodium rubrum

Development and acclimation of energy transduction were studied in seedlings of Chenopodium rubrum L. ecotype selection 184 (50° 10' N; 105° 35' W) in response to photomorphogenic and photoperiodic treatments. Dark respiration and photosynthetic capacity [nmol O₂ (pair of cotyledons)⁻¹ h⁻¹] were measured with an oxygen electrode. Changes in chloroplast ultrastructure were analyzed concomitantly. After germination, seedlings were grown at constant temperature either in darkness or in continuous light (white, red, far-red and blue) or were subjected to diurnal cycles of light/dark or changes in light quality. Dark respiration was low in far-red light treated seedlings. In red light treated seedlings dark respiration was high and the mean value did not depend on fluence rate or photoperiod. Blue light stimulated transitorily and modulated dark respiration in photoperiodic cycles. Photosynthetic capacity was reduced by far-red light and increased by red light. In response to blue light photosynthetic capacity increased, with indications of a requirement for continuous energy input. Phytochrome and a separate blue light receptor seemed to be involved. In continuous red light a clear cut circadian rhythm of dark respiration was observed. Blue light had a specific effect on chloroplast structure.     

Effect of riboflavie and cyanide on blue light induction of betacyanin formation in Amamnthus caudatus seedlings

The role of phyto chrome and flavins in blue light induction of betacyanin formation was studied in etiolated, three-day-old Amaranthus caudatus L. seedlings, using the criterion of far-red reversibility and exogenously applied riboflavin and KCN. The effect of riboflavin was studied using high fluence rate blue light (42.7 :nmol m⁻²s⁻¹nm⁻¹ at 450 nm). When present in the incubation medium during illumination, riboflavin promoted the far-red reversibility with short light treatments and suppressed the inductive action of continuous illumiaation. If added after light treatments, it promoted betacyanin formation. The filtration of blue light through the riboflavin solution caused profound changes in light quality without affecting the far-red reversibility after 30 mm illumination. The effect of 1 mM KCN was tested with 70'% lower fluence of blue light. Cyanide caused the suppression of the inductive effect with 5 min blue light, which was accompanied by an enhancement of betacyanin induction by the terminal far-red light pulse. With 30 min blue light, however, it caused the appearance of far-red reversibility. The inductive effect of continuous blue illumination was slightly promoted by this Inhibitor. These results demonstrate that the effect of blue light on the pbyto chrome system is complex, whereas the physiological (inductive) action of the flavin triplet state is limited to low fluence, short blue light treatments.     

PHOTOMORPHOGENESIS IN PTERIS VITTATA: I. PHYTOCHROME-MEDIATED SPORE GERMINATION AND BLUE LIGHT INTERACTION

1. Spores of the fern Pteris vittata did not germinate under totaldark conditions, while an exposure of the spores to continuouswhite light brought about germination. The germination was mosteffectively induced by red light and somewhat by green and far-red,but not at all by blue light. The sensitivity of spores to redlight increased and leveled off about 4 days after sowing at27–28. The promoting effect of red light could be broughtabout by a single exposure of low intensity. Far-red light givenimmediately after red light almost completely reversed the redlight effect, and the photoresponse to red and far-red lightwas repeatedly reversible. The photoreversibility was lost duringan intervening darkness between red and far-red irradiations,and 50% of the initial reversibility was lost after about 6hr of darkness at 27–28. These observations suggest thatthe phytochrome system controls the germination of the fernspore.
2. When the imbibed spores were briefly exposed to a low-energyblue light immediately before or after red irradiation, theirgermination was completely inhibited. The blue light-inducedinhibition was never reversed by brief red irradiation givenimmediately after the blue light. The escape reaction of redlight-induced germination as indicated by blue light given aftervarious periods of intervening darkness was also observed, andits rate was very similar to that determined by using far-redlight. Spores exposed to blue light required 3 days' incubationin darkness at 27–28 to recover their sensitivity tored light. The recovery in darkness of this red sensitivitywas temperature-dependent. It is thus suggested that an unknownbluelight absorbing pigment may be involved in the inhibitionof phytochrome-mediated spore germination.

(Received August 21, 1967; )     

Retention of Photoinduction of Cytosolic Enzymes in aurea Mutant of Tomato (Lycopersicon esculentum)

The tomato (Lycopersicon esculentum Mill.) aurea (au) mutant has been characterized as a phytochrome-deficient mutant lacking spectrally detectable phytochrome A in etiolated seedlings. Seedlings of au grown under red light (RL) lack phytochrome regulation of nuclear genes encoding plastidic proteins, possess ill-developed chloroplasts, and are slow to de-etiolate. In the present study, the effect of phytochrome deficiency on photoinduction of enzymes in etiolated au seedlings was investigated. The photoinduction of the cytosolic enzymes amylase and nitrate reductase (NR) and of the plastidic enzyme nitrite reductase (NiR) in au was compared with that in the isogenic wild-type (WT) tomato and the high-pigment (hp) mutant with exaggerated phytochrome response. In WT and hp, both brief RL pulses and continuous RL induced amylase, NR, and NiR activities, whereas in au no photoinduction of enzymes was observed with brief RL pulses, and continuous RL induced only amylase and NR activities. The time courses of photoinduction of NR and amylase in au under continuous RL followed patterns qualitatively similar to hp and WT. A blue-light pretreatment prior to continuous RL exposure was ineffective in inducing NiR activity in au. Only continuous white light could elicit a photoinduction of NiR in au seedlings. The norflurazon-triggered loss of photoinduction of NiR in WT and hp indicated that NiR photoinduction depended on chloroplast biogenesis. The results indicate that observed photoinduction of NR and amylase in au may be mediated by a residual phytochrome pool.     

Antagonistic action of low-fluence and high-irradiance modes of response of phytochrome on germination and beta-mannanase activity in Datura ferox seeds

Seed germination is often induced by a pulse of red light perceived by phytochrome and cancelled by a subsequent pulse of far-red light. When the pulse of red light is followed by several hours of darkness, a pulse of far-red light is no longer effective and prolonged far-red is necessary to block germination. The aim was to investigate whether the red light pulse and prolonged far-red light act on the same or different processes during germination of Datura ferox seeds. Forty-five hours after the inductive red light pulse, germination could not be blocked by one pulse or six hourly pulses of far-red light, but was significantly reduced by 6 h of continuous far-red light. The pulse of red light increased embryo growth potential and the activities of beta-mannanase and beta-mannosidase extracted from the micropylar region of the endosperm. Continuous far-red light had no effect on embryo growth potential or beta-mannosidase activity, but severely reduced the activity of beta-mannanase. The effect of far-red light had the features of a high-irradiance response of phytochrome. Both germination and beta-mannanase activity were restored by a pulse of red light given after the end of the continuous far-red treatment. It is concluded that the low-fluence response and the high-irradiance response modes of phytochrome have antagonistic effects on seed germination and that the control of beta-mannanase activity is one process where this antagonism is established.     

Photocontrol of spore germination in the fern Thelypteris kunthii

The light requirement for germination in spores of the fern Thelypteris kunthii (Desv.) Morton was fully satisfied by a long period of continuous red light or partially by intermittent, short periods of red light. Red light-potentiated spore germination was inhibited by brief far-red light irradiation, indicating phytochrome involvement. Repeated exposure of spores to prolonged red and short far-red irradiations, or exposure of red-potentiated spores to far-red light after an extended period in darkness, led to their escape from inhibition of germination by far-red light. Prolonged irradiation of spores with blue light before or after red light treatment partially antagonized the effect of red light.     

The characteristics of light in floral induction in vitro of Cichorium intybus. The possible role of phytochrome

The action of light in the initiation of floral buds in vitro has been studied using monochromatic light qualities on root explants of a long day plant, Cichorium intybus L. cv. Witloof. Red light (660 nm, 0.30 W m^-2) promotes flowering, while far-red (730 nm, 0.31 W m^-2) and irradiation with combined red + far-red (0.20 + 0.41 W m^-2) have no effect. In short day conditions floral response can be obtained in two ways: 1) by interrupting the dark period with 5 brief irradiations of red light (0.45 W m^-2, 12 min) at regular intervals, although these are counteracted by far-red irradiations of equal intensity and duration; 2) by interrupting the long night with 5 h red light applied during the second third of the night, while at the beginning or at the end it is ineffective. Red light efficiency appears to depend on the photosynthetic activity of the tissues, so that flowering increases with increasing intensity of white light and is suppressed if no white light is supplied. The reproductive development is determined by the coordination of proper irradiation conditions with sufficient sensitivity of the perceiving meristematic cells. The period of highest sensitivity to environmental light conditions in the life cycle of a Cichorium root explant occurs between the 8th and the 16th day after the start of the culture. The data strongly suggest that phytochrome is involved in flower induction of Cichorium in vitro.     

Synergism between gibberellic acid and low Pfr levels inducing germination of Kalanchoë seeds

Sown on water, seeds of Kalanchoëbiossfetdiana Poelln. cv. Feuerblute are absolutely light-requiring and show full red/far-red reversibility. In seeds, sown on 2 ×10^-3 M gibberellic acid, red/far-red reversibility disappears and both short red and far-red irradiations induce germination. Gibberellic acid alone does not induce germination, but it increases the physiological activity of P_fr to the extent, that the low P_fr level obtained by far-red irradiation becomes very effective. The synergism between gibberellic acid and far-red light appears after a two-day incubation; period. The nature of this lag phase was examined by measuring both germination and uptake of labelled gibberellic acid in intact seeds and seeds with a punctured seed coat. The lag phase was shown to be independent of the uptake kinetics of gibberellic acid and allows development to a specific stage, necessary for germination after phytochrome-phototransformation. The kinetics of the uptake of gibberellic acid by intact seeds and embryos of intact seeds are different. In intact seeds most of the gibberellic acid is retained in the seed coat; only a small fraction actually penetrates to the embryo where it can exert its physiological activity.     

Photocontrol of in vitro bud regeneration: A comparative study of the interaction between light and IAA in a wild type and an aurea mutant of Lycopersicon esculentum

In the presence of 0.2 μ M IAA both the wild type and the aurea mutant of Lycopersicon esculentum Mill, showed a low but significant percentage of bud formation in the dark, whereas no bud formation occurred in the dark when 20 μ M IAA was present in the medium. In both systems blue light always showed a strong promoting effect on bud regeneration, both as final percentage of regeneration and by shortening the initial lag period, suggesting the action of a specific blue light photoreceptor. Red and far-red light increased the percentage of bud differentiation in wild type explants, with both the IAA concentrations. In the aurea mutant only red at the lowest IAA concentration had such an effect. The final percentage of bud regeneration under red light was greater or equal to that found under blue light in the wild type as well as in the aurea mutant explants cultured in the presence of the lowest IAA concentration.     

Photoresponses of Light-Grown phyA Mutants of Arabidopsis (Phytochrome A Is Required for the Perception of Daylength Extensions)

Several aspects of the photophysiology of wild-type Arabidopsis thaliana seedlings were compared with those of a phytochrome A null mutant, phyA-1, and a mutant, fhy1, that is putatively involved in the transduction of light signals from phytochrome A. Although phyA seedlings display a near wild-type phenotype when grown in white light (W), they nevertheless display several photomorphogenic abnormalities. Thus, whereas the germination of wild-type and fhy1 seeds is almost fully promoted by a pulse of red light (R) or by continuous far-red light (FR), phyA seed germination is responsive only to R. Following growth under day/night cycles, but not under continuous W, the hypocotyls of light-grown phyA and fhy1 seedlings are more elongated than those of wild-type seedlings. For seedlings grown under low red/far-red (R/FR) ratio light conditions, phyA and fhy1 seedlings display a more marked promotion of hypocotyl elongation than wild-type seedlings. Similarly, seedlings that are doubly null for phytochrome A and phytochrome B(phyA phyB) also have more elongated hypocotyls under low R/FR ratio conditions than phyB seedlings. This indicates that phytochrome A action in light-grown seedlings is antagonistic to the action of phytochrome B. Although wild-type, fhy1, and phyA seedlings flower at essentially the same time under both short-day and long-day conditions, an obvious consequence of phytochrome A deficiency is a pronounced late flowering under conditions where a short day of 8 h of fluorescent W is extended by 8 h of low-fluence-rate incandescent light. The evidence thus indicates that phytochrome A plays a role in seed germination, in the control of elongation growth of light-grown seedlings, and in the perception of daylength.     

Effect of red, far-red radiations on germination of cotton seed

Seeds of two cultivars, H-14 and J-34 of Gossypium hirsutumL. soaked in the dark for durations of 8, 12 and 16 hr wereexposed to red and far-red radiations alone and in differentsuccessions. While cv. J-34 was unresponsive to all light treatments,seed germinaiton in cv.H-14 was promoted by darkness and byexposure to far-red radiation and was inhibited by red andwhitelight.Seed germination depended upon what treatment was given at theend. The effect ofred light was reversed by far-red and viceversa. Although instances of light inhibition of seed germinationare known, the authors are not aware of any clear cut instancein the literature on far-red promotion of seed germination (Received November 4, 1970; )     

Effect of light and temperature on the germination of lettuce seeds

A short period (15–30 min) at 30° C promotes germination of seeds of Lactuca sativa L. cv. Repolhuda in darkness. Far-red light reverses this stimulation, and the escape curves for phytochrome and high-temperature action are quite similar, indicating that the two factors act at a common point in the chain of events leading to germination. It is suggested that high temperature acts by decreasing the threshold of the active, far-red absorbing, form of phytochrome (Pfr) needed to promote germination.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light