L'Azione dell'Ossigeno Liquido Sulla Germinabilità dei Semi Duri di Ginestrino (Lotus Corniculatus L.) e di Ladino (Trifolium Repens L.)

Abstract

Comparative researches on morphology and physiology of PICEA and LARIX. Fresh weight and chlorophyll content in seedlings kept at various light intensities. — The fresh weight and the chlorophyll content of lots of seedlings from Larix decidua and Picea excelsa grown on sand for 12 days in climatic cell at 25 [ddot]C with 86% relative humidity and a light intensity of 90, 250, 500, 1.000, 2.000 and 4.000 lux were determined.

The fresh weight of Picea seedlings is not significantly affected by all light intensities except for 4.000 lux, where it is 20% higher. Even in dim light (90 lux) the fresh weight of Picea seedlings is only 7% inferior to that of the lot kept at 2.000 lux.

The results obtained in Larix are remarkably different; its fresh weight is more influenced by the light intensity: at 4.000 lux, e. g., the fresh weight is considerably higher (more than 20%) than the arithmetical mean of all the lots, while at 90 lux it appears greatly inferior (30%) to the lot kept at 2.000 lux.

No correlation exhists between fresh weight and chlorophyll content variations.

In Larix only the difference between seedlings kept at 250 lux and 90 lux is very strong. In the latter the chlorophyll content for g. f. w. is 40% inferior to the average of all the lots. At the maxime intensities the chlorophyll content of Larix seedlings appears to be particularly increased, while that of Picea seedlings is slightly inferior to that observed at 2.000 lux.

These figures are in agreement with the special ecology of the two plants and particularly with the light need of Larix, as it is clearly demonstrated by the fresh weight and chlorophyll content per g. f. w. and by the different ratio in chlorophyll contents of the lots of seedlings kept at 2.000 and 4.000 lux.     

Light and Nitrate Requirements for Induction of Nitrate Reductase Activity in Hordeum vulgare

The importance of light to the induction of nitrate reductase activity in barley (Hordeum vulgare L.) was studied. Activity in etiolated leaves in darkness stayed at a low endogenous level even while large amounts of nitrate were actively accumulated. Light was required for any increase in activity, though the requirement may be satisfied to a limited extent before nitrate is available. Nitrate reductase activity was induced in the dark in green leaves which had not previously had nitrate but were supplied nitrate at the beginning of the dark period. If the nitrate then made available was sufficient, nitrate reductase activity increased until the effect of the previous light treatment was exhausted. Activity then decreased even though nitrate uptake continued. Upon returning the leaves to light, enzymatic activity increased again, as expected. Nitrate uptake was eliminated as an experimental variable by giving dark-grown plants nitrate, then detaching the leaves for induction studies. Under these conditions light saturation occurred between 3600 and 7700 lux at exemplary periods of illumination. At intensities of 3600 lux and above, activity increased sharply after a 6-hour lag period. As light intensity was decreased below 3600 lux the lag period became longer. Thus, when sufficient nitrate was available, the extent of induction of nitrate reductase activity was regulated by light.     

Effects of light and temperature on symptom development and virus content of tobacco leaves inoculated with potato mop-top virus

Necrotic spots or small rings develop after 3–4 days in leaves of Nicotiana tabacum cv. Xanthi-nc inoculated with potato mop-top virus and kept at 14 °C in continuous light (4320 lux); a series of concentric necrotic rings of increasing diameter then form at 2- to 3-day intervals around each initial lesion. Successive rings take longer to appear when either the light intensity or the photoperiod is decreased. Virus accumulation is much decreased and lesions rarely develop either at 14· in darkness or at 22° in light. Virus accumulates rapidly when plants are transferred from these conditions to 14° in light (4320 lux), and necrotic spots or rings develop whose size depends on the interval between inoculation and transfer, and on the conditions during this period. In such plants, necrosis seems to occur only when conditions become favourable for virus synthesis, it is confined to recently infected cells and it does not prevent virus spread to further healthy cells. From the sizes of the necrotic rings, the virus is estimated to invade tissue in light (4320 lux) at c. 38 μm/h at 22° and c. 16 μm/h at 14°. Invasion in darkness at either temperature is very slow. Necrotic rings develop, and the rate of virus accumulation increases when inoculated plants are transferred from 22° in light (4320 lux) to 14° in darkness, but no lesions appear when the order of the treatments is reversed. The process of lesion formation thus includes an early phase requiring light and a later phase requiring low temperature. The light-requiring phase takes about a day at 14° but less at 22°. The later phase takes about 2 days in light (4320 lux) or 3 days in darkness.     

Possible mechanisms of light-induced chlorophyll degradation in senescing leaves of Hydrilla verticillata

Light treatment markedly accelerated the chlorophyll loss in senescing leaves of Hydrilla verticillata [(L.f.) Royle] as compared to dark treatment, whereas such acceleration could not be observed in senescing spinach (Spinacia oleracea L.) leaves. The light-induced cholorophyll loss in Hydrilla was retarded slightly by chloramphenicol and markedly by cycloheximide. Catalase (EC 1.11.1.6) activity did not change appreciably in Hydrilla leaves either in light or in darkness, while in spinach it declined markedly in the dark, and light retarded such decline. Peroxidase activity in Hydrilla showed faster increase in light than in darkness, while in spinach it increased only in light during senescence. The activity of phenol(pyrogallol)-specific peroxidase increased markedly in light, and that of ascorbate-specific peroxidase decreased slightly both in light and darkness during senescence of Hydrilla leaves. This rise in phenolspecific peroxidase activity was prevented by cycloheximide treatment. Pretreatment of Hydrilla leaves with monophenol (2,4-dichlorophenol) and o-diphenol (hydroquinone) accelerated and retarded, respectively, the light-induced cholorophyll loss. Pretreatment of Hydrilla leaves with H₂O₂ augmented the chlorophyll loss more markedly in light than in darkness. The endogenous level of H₂O₂ increased more in light than in dark during senescence of Hydrilla leaves. Treatment of Hydrilla leaves with 3-(3.4-dichlorophenyl)-l,l-dimethylurea. a photosystem II inhibitor, prevented both light-induced rise in H₂O: level and chlorophyll loss, but it was without effect in the dark. Retardation of light-induced chlorophyll loss occurred during senescence of Hydrilla leaves when light was given in different photoperiods in a 24-h daily cycle for 6 days instead of as continuous irradiance. There was a negative correlation between the length of the photoperiod and the extent of cholorophyll loss.     

Metabolism of Oat Leaves during Senescence: V. Senescence in Light

A comparison has been made of the progress of senescence in the first leaf of 7-day-old oat plants (Avena sativa cv. Victory) in darkness and in white light. Light delays the senescence, and intensities not over 100 to 200 ft-c (1000-2000 lux) suffice for the maximum effect. In such intensities, chlorophyll loss and amino acid liberation still go on in detached leaves at one-third to one-half the rate observed in darkness; however, when the leaves are attached to the plant, the loss of chlorophyll in 5 days is barely detectable. Transfer of the leaves from 1 or 2 days in the low intensity light to darkness, or vice versa, shows no carryover of the effects of the preceding exposure, so that such treatment affords no evidence for the photoproduction of a stable substance, such as cytokinin, inhibiting senescence. Light causes a large increase in invertaselabile sugar and a smaller increase in glucose, and application of 100 to 300 mm glucose or sucrose in the dark maintains the chlorophyll, at least partially. Correspondingly, short exposure to high light intensity, which increased the sugar content, had a moderate effect in maintaining the chlorophyll. However, 3-(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU) completely prevents the increases in sugars and yet does not prevent the effect of light on senescence, whether determined by chlorophyll loss or by protein hydrolysis. Light causes a 300% increase in the respiration of detached oat leaves, and kinetin lowers that only partly, but unlike the increased respiration associated with senescence in the dark, the increase in the light is fully sensitive to dinitrophenol, and therefore cannot be ascribed to respiratory uncoupling. The increased respiration in light is prevented by DCMU, parallel with the prevention of sugar formation. It is therefore ascribed to the accumulation of soluble sugars, acting as respirable substrate. Also, l-serine does not antagonize the light effect. For all of these reasons, it is concluded that the action of light is not mediated by photosynthetic sugar formation, nor by photoproduction of a cytokinin. Instead, we propose that light exerts its effect by photoproduction of ATP. The action of sugars is ascribed to the same mechanism but by way of respiratory ATP. This hypothesis unifies most of the observed phenomena of the senescence process in oat leaves, and helps to explain some of the divergent findings of earlier workers.     

An Endogenous Rhythm in the Rate of CO2 Output of Bryophyllum: II. THE EFFECTS OF LIGHT AND DARKNESS ON THE PHASE AND PERIOD OF THE RHYTHM

The effects of light, darkness, and changes in light intensityon the phase and period of the endogenous rhythm in the rateof CO₂ output of excised leaves of Bryophyllum fedtschenkoihave been examined. The duration, intensity, and wavelength of a short light treatment,and the point in the cycle at which it is administered, determinethe degree of phase shift induced in a rhythm persisting indarkness. When light treatments of 3 and 6 hours' duration,at an intensity of 3,000 lux, are applied between the peaksthe phase is completely reset, the first post-treatment peakoccurring 18–19 hours after the end of the treatment.The degree of phase shift is therefore determined not by theduration of the treatment but by the time at which the treatmentterminates. One hour's illumination has little or no effect.The phase is unaffected when light treatments of up to 5 hours'duration at an intensity of 3,000 lux are applied at the crestof a peak. Over the range 8-3,000 lux the intensity of lightduring a 6-hour treatment applied between the peaks does notaffect the efficiency with which that treatment completely resetsthe phase. At an intensity of 2 lux, however, the phase delayis equal to the duration of the treatment. A 6-hour red-light treatment (850 ergs/cm.²/sec.) applied betweenthe peaks completely resets the phase whereas blue light (10,860ergs/cm.²/sec.) has no effect on the phase but induces a slightprotraction of the period. Moreover, continuous red light inhibitsthe rhythm, which recommences in blue light. A rhythm is induced in illuminated leaves when the light intensityis either gradually or suddenly reduced by at least 80 per cent.Whether a given intensity of illumination inhibits or permitsthe persistence of a rhythm depends upon the light intensityby which it is immediately preceded. A rhythm will persist in illuminated leaves for approximatelyas long as in leaves in darkness and the phase shows no correlationwith time of day. The period is unaffected by the intensityof white light (from 0-500 lux) to which the leaves are subjected.The duration of a short dark treatment, and the point in thecycle at which it is applied, determine the degree of phaseshift induced in a rhythm in illuminated leaves. The phase isreset when 3-, 6-, and 9-hour dark treatments are applied atthe crest of a peak, the amount of phase shift increasing toa maximum with 9 hours' darkness. The phase shift is not equalto the duration of the treatment. The phase is unaffected when3- and 6-hour dark treatments are applied between the peaks. The variation in the sensitivity of the phase of a rhythm persistingin darkness to short light treatments is in the opposite senseto that of a rhythm persisting in light to short dark treatments.The phase of a rhythm in illuminated leaves is completely resetwhen the leaves are transferred to continuous darkness commencingeither at the crest of, or between, the peaks. The results are discussed and compared with those of other authors.     

Nature of photooxidative events in leaves treated with chlorosis-inducing herbicides

Leaves of rye seedlings (Secale cereale L.) grown in the presence of four chlorosis-inducing herbicides under a low light intensity of 10 lux formed chlorophyll. When segments of such dim-light-grown leaves were exposed to 30,000 lux at either 0°C or 30°C, treatments with aminotriazole or haloxidine (group 1) showed no or only minor changes of their chlorophyll contents. In treatments with San 6706 or difunon (group 2), however, rapid photodestruction of chlorophyll occurred both at 0°C and at 30°C and was accompanied by an increase of malondialdehyde that was not seen in the presence of group 1 herbicides. Unlike the in vivo behavior, virtually equal rates of chlorophyll breakdown were observed for aminotriazole and San 6706 treatments in suspensions of isolated chloroplasts from 10 lux-grown leaves after exposure to strong light. The free radical scavengers p-benzoquinone and hydroquinone and the d-penicillamine copper complex exerting superoxide dismutating activity effectively prevented photooxidation of chlorophyll in 10 lux-grown herbicide-treated leaf segments or even restored an accumulation of chlorophyll at 30,000 lux. Ascorbate and several singlet oxygen or hydroxyl radical scavengers had no protective effects. Deuterium oxide and H₂O₂ did not enhance the degradation of chlorophyll. Superoxide dismutase activity was decreased in leaves bleached in the presence of group 2 herbicides.     

Effects of continuous light and darkness on the eyes of the troglobitic salamander Typhlotriton spelaeus

Larval Typhlotriton spelaeus collected from five caves in Pulaski Co., Missouri, were kept as larvae or induced to transform in darkness or continuous fluorescent illumination. Larvae maintained in darkness for 215 and 279 days had smaller eyes, smaller rod inner and outer segments, and fewer metaphase figures in the genninative zone of the neural retina than comparable larvae maintained in light (258 lux). Except for visual cell size, differences were small and for each characteristic exceptions were observed. One larva kept in light showed early retinal degeneration comparable to that in transformed adults of T. spelaeus. All larvae exhibited optomotor behavior both before and after the experiment. Among animals induced to transform by L-thyroxin and maintained in darkness 111 to 366 days, visual cell and pigment epithelium degeneration was more extensive and more frequent than in animals kept for the same length of time in light (237-298 lux). In darkness the frequency of animals with retinal degeneration increased between 111 and 366 days. In light some animals exhibited pigment epithelium reduction with normal visual cells, and others had free, pigmented cells in the subretinal space. These effects were not comparable to degeneration in darkness. Eyelids covered the eyes of only a few animals in both light and dark treatments. The extent of eyelid encroachment over the eye was greater in darkness than in light. Most animals exhibited optomotor responses after experiments, but responses of animals kept in darkness were impaired in comparison to those of animals kept in light.     

The interplay between cytokinins and light during senescence in detached Arabidopsis leaves

Light and cytokinins are known to be the key players in the regulation of plant senescence. In detached leaves, the retarding effect of light on senescence is well described; however, it is not clear to what extent is this effect connected with changes in endogenous cytokinin levels. We have performed a detailed analysis of changes in endogenous content of 29 cytokinin forms in detached leaves of Arabidopsis thaliana (wild‐type and 3 cytokinin receptor double mutants). Leaves were kept under different light conditions, and changes in cytokinin content were correlated with changes in chlorophyll content, efficiency of photosystem II photochemistry, and lipid peroxidation. In leaves kept in darkness, we have observed decreased content of the most abundant cytokinin free bases and ribosides, but the content of cis‐zeatin increased, which indicates the role of this cytokinin in the maintenance of basal leaf viability. Our findings underscore the importance of light conditions on the content of specific cytokinins, especially N⁶‐(Δ²‐isopentenyl)adenine. On the basis of our results, we present a scheme summarizing the contribution of the main active forms of cytokinins, cytokinin receptors, and light to senescence regulation. We conclude that light can compensate the disrupted cytokinin signalling in detached leaves.     

Oak seedlings grown in different light qualities

Oak seedlings (Quercus robur L.) were germinated in darkness for 3 weeks and then given continuous long wavelength far-red light (LFR; wavelengths longer than 700 nm). A control group of seedlings was kept in darkness. After 2 additional weeks the chlorophyll formation ability in red light was examined in the different seedlings. The stability of the protochlorophyll(ide) and chlorophyll(ide) forms to high intensity red irradiation was also measured. Oak seedlings grown in darkness accumulated protochlorophyll(ide) (6 μg per g fresh matter). Absorption spectra and fluorescence spectra indicated the presence of more protochlorophyll(ide)_628–632 than protochlorophyllide_650–657. The level of protochlorophyll(ide) was higher in leaves of plants cultivated in LFR light (13 μg per g fresh matter) than in leaves of dark grown plants. 12% of the protochlorophyll(ide) was esterified in both cases. The level of protochlorophyll(ide)_628–632 in LFR grown oaks varied with the age of the leaves, being higher in the older (basal) leaves, but also in the very youngest (top-most) leaves. The ability of the leaves to form photostable chlorophyll in red light showed a similar age dependence, being low in rather young and in older leaves. A low ability to form photostable chlorophyll thus appears to be correlated with a high content of protochlorophyll(ide)_628–632. Upon irradiation only the protochlorophyllide_650–657 was transformed to chlorophyllide. After this phototransformation the chlorophyllide peak at 684 nm shifted to 671 nm within about 30 min in darkness. This shift took place without any accompanying change in photostability of the chlorophyll(ide). Upon irradiation with strong red light a similar shift took place within one minute. This indicates that the chlorophyllide after phototransformation was rather loosely bound to the photoreducing enzyme. The development towards photostable chlorophyll forms consists of three phases and is discussed.     

Effect of different light intensities on growth,reproduction, amino acid synthesis,fat and sugar contents in ulva fasciata delile

Various physiological processes of Ulva fasciata were investigated in the laboratory under light intensities of 1500, 2500 and 3500 lux respectively.It was shown that there is a strong correlation between light intensity and growth rate, which increased with the increase in light intensity up till 2500 lux. Light intensities above 3000 lux resulted in bleaching of the algal thalli.In no instance there was any discharge of swarmers in total darkness nor at very reduced light intensities of about 100 lux.Zoospores were always negatively phototactic, while gametes were positively phototactic, appearing always on the well-illuminated sides of the culture bottles.The maximum yield of total nitrogen, dry weight, and amino acid content coincides with the optimum light intensity. Under such conditions leucine, valine, -alanine and glutamic acids are found in abundance, while phenyl alanine, -aminobutyric and glycine are moderately represented.The amount of total fat content increases with the increse in light intensity up till 3500 lux. This might refer to a strong correlation between the rate of photosynthesis and the fat synthesis.It was found that fructose and raffinose were present in negligible amounts under reduced light intensities (1500 lux), while sucrose was found in rather higher quantities. The quantity of glucose is higher than that of fructose and raffinose but much less than that of sucrose under the same light intensity.Alexandria UniversityKuwait UniversityKuwait University     

Effect of Light Intensity on the Phase and Period Response Curves in the Nocturnal Field Mouse Mus booduga

The effect of light intensity on the phase response curve (PRC) and the period response curve (τRC) of the nocturnal field mouse Mus booduga was studied. PRCs and τRCs were constructed by exposing animals free-running in constant darkness (DD), to fluorescent light pulses (LPs) of 100 lux and 1000 lux intensities for 15min duration. The waveform of the PRCs and τRCs evoked by high light intensity (1000 lux) stimuli was significantly different compared to those constructed using low light intensity (100 lux). Moreover, a weak but significant correlation was observed between phase shifts and period changes when light stimuli of 1000 lux intensity were used; however, the phase shifts and period changes in the 100 lux PRC and τRC were not correlated. This suggests that the intensity of light stimuli affects both phase and period responses in the locomotor activity rhythm of the nocturnal field mouse M. booduga. These results indicate that complex mechanisms are involved in entrainment of circadian clocks, even in nocturnal rodents, in which PRC, τRC, and dose responses play a significant role.     

Far-red induced changes of the protochlorophyllide components in wheat leaves

Biosynthesis of chlorophyll is partly controlled by the phytochrome system. In order to study the effects of an activated phytochrome system on the protochlorophyllide (PChlide) biosynthesis without accompanying phototransformation to chlorophyll, wheat seedlings (Triticum aestivum L. cv. Starke II Weibull) were irradiated with long wavelength far-red light of low intensity. Absorption spectra were measured in vivo after different times in the far-red light or in darkness. The relationship between the different PChlide forms, the absorbance ratio _{650nm636 nm} changed with age in darkness, and the change was more pronounced when the leaves were grown in far-red light. Absorption spectra of dark-grown leaves always showed a maximum in the red region at 650 nm. For leaves grown in far-red light the absorption at 636 nm was high, with a maximum at the 5 day stage where it exceeded the absorption at 650 nm. At the same time there was a maximum in the total amount of PChlide accumulated in the leaves, about 30% more than in leaves grown in darkness. But the amount of the directly phototransformable PChlide, mainly PChlide_650–657, was not increased. The amount of PChlide_628–632, or more probably the amount of (PChlide_628–632, + PChlide _636–657) was thus higher in young wheat leaves grown in far-red light than in those grown in darkness. After the 5 day stage the absorption at 636 nm relative to 650 nm decreased with age, and at the 8 day stage the spectra were almost the same in both types of leaves. Low temperature fluorescence spectra of the leaves also showed a change in the ratio between the different PChlide forms. The height of the fluorescence peak at 632 nm relative to the peak at 657 nm was higher in leaves grown in far-red light than in dark-grown leaves. – After exposure of the leaves to a light flash, the half time for the Shibata shift was measured. It increased with age both for leaves grown in darkness and in far-red light; but in older leaves grown in far-red light (7–8 days) the half time was slightly longer than in dark-grown leaves. – The chlorophyll accumulation in white light as well as the leaf unrolling were faster for leaves pre-irradiated with far-red light. The total length of the seedlings was equal or somewhat shorter in far-red light, but the length of the coleoptile was markedly reduced from 8.1 ± 0.1 cm for dark-grown seedlings to 5.2 ± 0.1 cm for seedlings grown in far-red light.     

Some factors affecting the chloroplast replication in the mossPlagiomnium trichomanes

Summary Some factors affecting the chloroplast replication were studied using the leaf cells of the mossPlagiomnium trichomanes. There was a significant positive correlation between chloroplast number per cell and cell volume in leaves of any developmental stage. However, when the detached leaves were cultured on nutrient agar, it was observed that the chloroplast replication occurred without cell enlargement regardless of the developmental stage of leaves. This implies that cell enlargement is not an essential factor for the chloroplast replication, but one of the environmental factors affecting it. Light is essential for the chloroplast replication which response to the light intensity. In the dark, there was little increase in chloroplast number per cell. With a light intensity of 50 lux, the increase rate of chloroplast number per cell was about half of that with 3,000 lux. Day length also affected significantly the chloroplast replication.     

Light acclimation maintains the redox state of the PS II electron acceptor Q2 within a narrow range over a broad range of light intensities

Chrysanthemum inducum-hybrid `Coral Charm', Hibiscus rosa-sinensis L. `Cairo Red' and Spathiphyllum wallisii Regel `Petit' were grown in natural light in a greenhouse at three levels of irradiance using permanent shade screens. Light acclimation of photosynthesis was characterized using modulated chlorophyll a fluorescence of intact leaves. A close correlation was found between the degree of reduction of the primary electron acceptor Q_A of Photosystem II (PS II) approximated as the fluorescence parameter 1−q_P, and light acclimation. The action range of 1−q_P was 0–0.4 from darkness to full irradiance around noon, within the respective light treatments in the greenhouse, indicating that most PS II reaction centres were kept open. In general, the index for electron transport (ETR) measured by chlorophyll fluorescence was higher for high-light (HL) than intermediate-(IL) and low-light (LL) grown plants. However, HL Chrysanthemum showed 40% higher ETR than HL Hibiscus at light saturation, despite identical redox states of Q_A. The light acclimation of the non-radiative dissipation of excess energy in the antenna, NPQ, varied considerably between the species. However, when normalized against q_P, a strong negative correlation was found between thermal dissipation and ETR measured by chlorophyll fluorescence. To be able to accommodate a high flux of electrons through PS II, the plants with the highest light-saturated ETR had the lowest NPQ/q_P. The possibility of using chlorophyll fluorescence for quantification of the energy balance between energy input and utilization in PS II in intact leaves is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

THE ROLE OF LIGHT IN HISTOGENESIS AND DIFFERENTIATION IN THE SHOOT OF PISUM SATIVUM. II. THE LEAF

Thomson , Betty F., and Pauline Monz Miller . (Connecticut Coll., New London.) The role of light in histogenesis and differentiation in the shoot of Pisum sativum, II. The leaf. Amer. Jour. Bot. 49(4): 383–387. Illus. 1962.—Development of the form and anatomy of leaves was studied in plants of Pisum sativum grown in vermiculite under constant conditions and exposed daily to red or white light or kept in continuous darkness. The red light used had an intensity in the morphogenetically active red region of the spectrum of 70–75% that of the white light. Light had no effect on the manner of initiation or early development of leaf primordia. Quantitative data from older leaves showed that light has no effect on the pattern of later development but does affect the rate and extent of development. Under all light conditions, the length of the leaflet is closely correlated with the state of its internal anatomy. “Mature” etiolated leaves duplicate young stages of light-grown leaves. Mature leaves grown in red light duplicate not-quite-mature leaves grown in white light. The difference between white-light and red-light leaves is attributed here to light intensity and resembles that between sun and shade leaves.     

Ricerche Comparate Sulla Morfologia e Sulla Fisiologia di Larix e di Picea

Abstract

Comparative researches on morphology and physiology of PICEA and LARIX. The chlorophyll content of seeds and seedlings during germinations in darkness. — Very different are the chlorophyll contents of the seeds and the seedlings of Picea excelsa and Larix decidua grown in darkness.

In Picea chlorophyll is abundantly synthetized in cotyledons in the passage from seed to seedling stages. In Larix however this synthesis is very poor. These differences are more evident after the outgrowth of cotyledons from the primary endosperm and its exhaustion.

If seedlings of both species are exposed to 3.000 lux of light intensity for 24 hours, after development in darkness, one can observe much stronger chlorophyll synthesis in Larix cotyledons than icea.

These figures quanti atively express the different light-dipendence of chlorophyll synthesis in these two plants and offer a more adherent interpretation of the different ecological behaviours that are caracteristic of these two plants.     

Light Scattering as an Indicator of the Energy State in Leaves of the Crassulacean Acid Metabolism Plant Kalanchoë pinnata

Both transmittance changes in a weak beam of green light (light scattering) and the slow decay of chlorophyll a fluorescence were used as indicators of the energy state of leaves of a Crassulacean acid metabolism plant, Kalanchoë pinnata, at frequent intervals during 12-hour light/12-hour dark cycles. To induce light scattering and fluorescence changes, leaves were exposed to red light for 6 minutes. When measurements were made during the light period, the leaves were kept in darkness for 6 minutes before illumination. In the middle of the light period, when malic acid decarboxylation was very active and stomatal conductance was low, light scattering changes were small and indicated that the energy state of leaves was low. This result was supported by determination of adenylate levels. Light scattering and ATP/ADP ratios increased during the late light period when the tissue was deacidified. Illumination produced maximum light scattering changes between the 2nd and 5th hour of the dark period, when rates of dark CO₂ fixation were highest. Light scattering and fluorescence measurements taken from leaves, which were illuminated with red or far-red light in the presence or absence of O₂ showed that, in addition to linear electron transport, K. pinnata has the potential for both cyclic and pseudocyclic electron transport. The results are relevant with regard to the high ATP demand during Crassulacean acid metabolism.     

CHLOROPHYLL AND CAROTENOID ACCUMULATION IN THREE CHLOROPHYLLOUS CALLUS PHENOTYPES OF GLYCINE MAX

Effects of exogenous carbohydrates and various medium supplements on chlorophyll and carotenoid accumulation in three chlorophyllous callus phenotypes of Glycine max (L.) Merrill were studied. Glucose (filtered), at 3%, supported the highest level of chlorophyll and carotenoids in the NG and Y phenotypes, while only moderate levels of chlorophyll accumulated in the LG phenotype. Sucrose (filtered and autoclaved), at 3%, supported phenotypical levels of chlorophyll and carotenoids for all phenotypes. Ascorbic acid, at 75 mg/l, stimulated chlorophyll-carotenoid accumulation for all phenotypes, while δ-aminolevulinic acid was slightly toxic for pigment biosynthesis in the NG and LG phenotypes. In contrast, δ-aminolevulinic acid supported chlorophyll-carotenoid accumulation in the Y phenotype. A negative correlation (r_XY) was evident between chlorophyll formation and callus growth for all phenotypes. Light intensity of 3,000 lux suppressed chlorophyll accumulation in the Y callus phenotype while an increase in pigment formation occurred in the NG and LG callus phenotypes. In comparison, light intensity of 700 lux supported chlorophyll accumulation in the Y callus phenotype. Carotenoid accumulation appeared to be coupled with chlorophyll formation in all callus phenotypes except for the Y callus phenotype when grown under the higher light intensity. All phenotypes accumulated chlorophylls a and b, α- and β-carotene, lutein plus zeaxanthin, violaxanthin and neoxanthin as indicated by their respective absorption maxima. Under cultural conditions, the genetic mutation (yll) in these soybean callus phenotypes appeared to regulate carotenoid formation which in turn influenced chlorophyll stability.     

Strong light elevates thermotolerance of photosynthetic apparatus and the content of membranes and polar lipids in wheat leaves

The influence of excess irradiance on resistance of wheat (Triticum aestivum L.) photosynthetic apparatus to heating in darkness and in the light was investigated and compared with changes in leaf cell ultra-structure and composition of cell lipids and fatty acids. The leaves of 14- to 16-day-old plants grown at low irradiance (about 20 W/m²) were exposed for 1 h to irradiance of 370 or 600 W/m² PAR. Using infrared gas analysis, we found that the preexposure of leaves to excess irradiation elevated resistance of apparent photosynthesis to 10-min heat treatment at 40–45°C. The rate of Hill reaction (reduction of 2,6-dichlorophenolindophenol by isolated chloroplasts) was higher for leaves heated at high irradiance than for leaves heated in darkness. During illumination of leaves with strong light, mesophyll cells became more abundant in mitochondria and peroxysomes, as well as in cisternae of endoplasmic reticulum and Golgi complex. The chloroplast thylakoids and grana became more extensive and numerous. At the same time, the leaf content of main classes of membrane glycerolipids increased in parallel with the increase in the phospholipid/glycolipid and lipid/chlorophyll ratios. The unsaturation index of fatty acids of membrane lipids increased because of the elevated content of linolenic acid. Thus, excessive light (not fully utilized in photosynthesis) induced in wheat leaves a series of nonspecific adaptive changes that were similar to those occurring under the action of other environmental factors, such as heat shock, cooling, salinity, and osmotic stresses.