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A laser system emitting 60–80 J pulses of (2–5) 10−11 sec duration was developed. Determinations were made of the energy densities corresponding to the threshold of the surface and internal damage of active elements by pulses of various durations. A multipass amplifier characterized by a gain up to 103 was constructed. This made it possible to use a low-power master oscillator and to amplify its output. In this way, 0.6 J pulses of (5–10) 10−12 sec duration were generated. The directionality of these pulses was close to the diffraction limit. Further amplification of the light pulses made it possible to increase the output energy to 40 J, which corresponded to an irradiance of (4–5) 1019 W sr−1 cm−2 in the diffraction angle and to an irradiance of over 1020 W sr−1 cm−2 along the axis.

The effect of high irradiance levels (approaching saturation) upon the shape of atomic fluorescence analytical curves is considered theoretically for both line and continuum sources. The linear range of the analytical curve may be greatly extended over that obtained with normal (low irradiance) sources, as is experimentally verified using a pulsed dye laser as an excitation source.

Temperature affects the total amount, the time course, and the red/far-red effectiveness ratio of light-dependent anthocyanin production in Brassica oleracea L. seedlings. Some of the effects of temperature on anthocyanin production in cabbage are in agreement with the predictions of a model proposed by JK Wall and CB Johnson (1983 Planta 159: 387-397) for the effects of temperature on the state of phytochrome and on the expression of phytochrome-mediated high irradiance responses, but others are not. The lack of a complete agreement between experimental results and model predictions might be due to factors related to the experimental system used or to limitations of the model or both.

Dependence of the growth of this alga culture on temperature displays a wide interval of temperatures (from 4 °C to 30 °C) and the dependence of the sexual reproduction only a narrow one (from 18 °C to 25 °C). The optimum temperatures for both the processes are not so different (round 23 °C). Dependence of both the processes on irradiance displays a wide interval of irradiances in both eases (from 4 W mt-2 to 80 W mt-2 PhAR and higher). The optimum irradiances for these processes are very different (approx. 50 W mt-2 PhAR for the growth and approx. 10 W mt-2 PhAR for the sexual reproduction) under the experimental conditions used.

With increasing altitude, the concentrations of chlorophyll (chl), carotenoids and phenolics decreased but the chla :b ratio increased in the fourArtemisia species grown at four altitudes. The increase in chla : b ratio was due to a reduction in chlb content. The changes in anthocyanin content were irregular. Thus phenolics and anthocyanin pools may be differently regulated along an altitudinal gradient.

An “action spectrum” between 400 and 620 nm for the radiation-induced phytochrome increase was obtained with mung bean hooks. A broad band between 410 and 480 nm was found to induce significant increases in phytochrome content. Radiation from 500 to 620 nm failed to promote any significant increase. Red irradiation immediately following far-red treatment showed no reversal. These results and an earlier finding that far-red irradiation promotes phytochrome increase suggest that the photoreceptor for the radiation-induced increase is probably not phytochrome, but could be a related pigment if the phenomenon is due to one photoreceptor. The blue light-induced increase in phytochrome content increases the possibility of the participation of phytochrome in blue light-mediated high irradiance responses of plants.

The photoelectrochemical etching of n-MoSe2 was investigated. The photocurrent of a regenerative photoelectrochemical cell comprising the above material in polyiodide solution is improved quite significantly following that treatment. Best results were obtained when the photoelectrode was photoetched under short circuit conditions and high irradiance. As was previously observed, for other layered compounds, very few etch pits are produced. This is rather surprising in view of the morphology of photoetched CdSe and the like. We discuss this point in detail and give first hints to explain this difference.

Exposure of leaves to light levels in excess of what can be utilized in photosynthesis often results in a decline in photosynthetic activity (1). This high-light effect is especially evident after return of the leaf to a low light level as a reduction in the photon yield of photosynthetic O2 evolution or CO2 uptake. In common usage the term photoinhibition includes any sustained reduction in photosynthetic activity induced by excessive light, irrespective of mechanistic considerations, but does not include transient reductions that are rapidly reversible and likely to reflect short-term regulation. In my talk today I will attempt to distinguish between two kinds of high-light-induced reduction in the efficiency of photochemistry of PSII: 1) an increase in the rate constant for dissipation of excitation energy in the antenna and 2) a decrease in the rate constant for the photochemistry of PSII which is likely to be caused by damage to the PSII reaction centers.

The effect of daylength and irradiance on the formation of gametangia in the male gametophyte of Sphacelaria rigidula Kutz (= S. furcigera Kutz [Prud'homme van Reine 19821) was investigated. Formation of gametangia was restricted to long-day conditions: In light-dark regimes with 12 h of light per day or less, no gametangia were formed. In long-day regimes high irradiances caused a suboptimal response, especially near the critical daylength. Interruption of a long dark period with a light break promoted gametangia formation. Light breaks were most effective when given at about the 6th hour of darkness. Nine inductive long-day cycles were required to induce the formation of gametangia, which appeared after ca. 15 d. The plants remained in the induced state only for a very short time. In regimes with very long days and at high irradiance the number of fertile plants decreased after some time, when vigorous vegetative growth started without any further formation of gametangia.

Uncoupled noncyclic electron flow in stacked (granal) chloroplasts with a lateral heterogeneity in the distribution of the two photosystems has been compared with that in unstacked (agranal) chloroplasts with a near-uniform distribution. Chloroplasts were maintained in either structural state in the same assay medium so as to equalize effects of ionic composition which may influence reaction rates. The assay medium, an ion-deficient solution, was capable of supporting high rates of electron flow from water to methyl viologen. At high irradiance, unstacked chloroplasts exhibited an uncoupled rate which was 30% (in chloroplasts isolated from lettuce grown in low light) or 55% (in chloroplasts isolated from lettuce grown in high light) higher than that of stacked chloroplasts; the percentage remained relatively constant in the temperature range 7 to 22 °C for both high-light and low-light chloroplasts. At low irradiance, stacked low-light chloroplasts, despite the spatial separation of the two photosystems, gave higher rates of electron flow than did unstacked low-light chloroplasts. The addition of MgCl 2 to stacked chloroplasts increased the uncoupled rate of noncyclic electron flow, but only at relatively high irradiances. The differences observed for stacked and unstacked chloroplasts, and for high-light and low-light chloroplasts are discussed. The approach taken in this work should be useful in other comparisons of stacked and unstacked chloroplasts.

The environment which supports and facilitates rooting of cuttings has a profound influence on the success or failure of the establishment of a new plant. The purpose of this chapter is to assess the types of variation in environment that are important. The intention is to focus on the entire process of adventitious rooting i.e. to include the preceding pre-cutting period, hereafter designated stock plant, as well as the subsequent post-rooting period which will be called establishment. These two marginal periods have all too often been neglected in the literature concerned with the effects of environmental conditions on adventitious rooting and the effects of various hormonal treatments on this process. Frequently there is a lack of concern for the environmental conditions of stock plants. Also many physiologically oriented papers neglect the fact that adventitious rooting is a means of propagation i.e. the establishment of a new plant. The environment which has received the most attention, judging from the number of research papers, is the rooting period itself. It is also the period where changes in environment have the most pronounced effect on the percentage of cuttings that succesfully form a root system and on the number and mass of roots formed. These effects are, however, greatly influenced by the physiological condition of the stock plant and this in turn affects the extent to which cuttings respond to their immediate environment. The latter defines the ‘quality’ of the cutting.

Superpulsed carbon dioxide lasers emit a controlled train of short duration, high-power pulses which minimize the protein coagulation effects of the laser. Very high irradiances can be used with superb control of vaporization without significant peripheral heating. In incisional work, superpulsing permits the surgeon to advance the hand piece as slowly and as accurately as desired, while experiencing a fraction of the necrosis attendant to conventional continuous-wave lasers. In va-porizational applications, target tissue volumes are flash vaporized before significant heat can be transferred to surrounding tissue, promoting faster wound healing and reduced scarring. The superpulse feature may significantly change the way in which the carbon dioxide laser is used in cutaneous surgery.

Induction by light of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) and of anthocyanin in cotyledons of the mustard (Sinapis alba L.) seedling is strongly affected by a light pretreatment which operates through phytochrome. If PAL or anthocyanin is induced by a light pulse, the effectiveness of phytochrome (Pfr) is strongly increased by a light pretreatment; however, if the increase of the PAL level or synthesis of anthocyanin is elicited by continuous far-red light (operating via phytochrome in the ‘High Irradiance Response’), effectiveness of light is strongly reduced by the same light pretreatment. This reduction of effectiveness is correlated with a decrease of total phytochrome (Ptot) caused by the light pretreatment. It is argued that the observations are compatible only with the ‘open phytochrome-receptor model’ as suggested by Schafer (J. Mathem. Biol. 2, 41–56, 1975). The peaks of the time courses of the PAL levels under continous far-red light are located at 48 h after sowing and do not depend on the original level of phytochrome. The decrease of the PAL levels beyond 48 h after sowing takes place independently of phytochrome and of the actual level of PAL.

Pulsed lasers such as Er:YAG and Ho:YAG with outputs at mid-infrared wavelengths emit radiation which may be transmitted by fibre to a treatment site. The thickness of soft-tissue damage beneath excisions made by these lasers is predicted using an extension to a model previously devised for CO2 laser radiation. The minimum achievable thickness occurs at a water absorption peak and at such high irradiance that heat cannot diffuse significantly compared with the radiation penetration depth. This minimum thickness is estimated to be in the order of 10 microns for the Er:YAG laser.

Using a model based on spectrophotometric measurements of the phytochrome of Sinapis alba L. seedlings we have used the published rate constants for the component reactions of this system to calculate the behaviour of the far-red absorbing form of phytochrome (Pfr), and other parameters, over a period of continuous irradiation. We have then analysed two of the most intensively studied photomorphogenetic responses, hypocotyl extension and anthocyanin synthesis, of these seedlings in terms of various parameters of the model. The results show that many of the main features of the high-irradiance response are correlated with Pfr level. However, a more detailed analysis leads to the conclusion that Pfr alone cannot account for some critical aspects of the response. In particular, it is necessary to hypothesize an additional ‘active’ component which is a function of the rate of photoconversion.

Previous reports indicate that ribulose 1,5-bisphosphate (RuBP) binds very tightly to inactive ribulose bisphosphate carboxylase (rubisco) in vitro. Therefore, we decided to investigate whether there was evidence for tight binding of RuBP associated with deactivation of rubisco in vivo. We modified a technique for rapidly separating `free9 metabolites from those bound to high molecular compounds. Arabidopsis thaliana plants were illuminated at various irradiances before freezing the leaves in liquid N 2 and assaying rubisco activity and RuBP. The percentage activation of rubisco varied from 37% at low irradiance (45 micromoles quanta per square meter per second) to 100% at high irradiance (800 micromoles quanta per square meter per second). The total amount of RuBP did not vary much with irradiance, but bound RuBP changed from 36% of the total at low irradiance to none at high irradiance. Bound RuBP was significantly correlated with the estimated number of inactive rubisco sites, with a ratio of about 1:1. After a step increase in irradiance, rubisco activation increased and total RuBP increased transiently, but steady levels of both occurred by 10 minutes. The amount of bound RuBP decreased with a similar time course to the estimated decrease in inactive rubisco sites. After a step decrease in irradiance, rubisco deactivated slowly for at least 25 minutes. Bound RuBP increased gradually but did so more slowly than the estimated increase in inactive rubisco sites.

When grown with adequate water and nitrogen (12 mM NO 3 - ) four clones of Solanum dulcamara from sun or shade habitats in Europe showed similar potential for acclimation of photosynthesis to irradiance level during growth. When grown with limiting nitrogen (0.6 mM NO 3 - ) all clones showed a low potential for acclimation of photosynthesis to irradiance during growth. If limiting nitrogen was accompanied by water stress at high irradiance, the initial slope of the irradiance response curve, and the irradiance saturated rate of photosynthesis were depressed, especially in a clone from a shaded habitat. These interactions are discussed in terms of earlier reports on the sunshade responses and sun-shade ecotypic differentiation in this species.

This is a basic problem from a theoretical as well as from a practical point of view. It implies the question of how phytochrome may function under natural conditions of illumination.

— Spectral sensitivities for C16 rranshexadecenoic acid accumulation in etiolated leaves of Vigna sinensis L. show two maxima, one in the blue and one in the far red, indicating a control by the high irradiance reaction. Spectral sensitivities are different for rranshexadecenoic acid and chlorophyll accumulation indicating that the biosynthesis of these compounds must not be obligatory linked.

The digital photometer system developed earlier has been upgraded by incorporating a microprocessor-based system with it. The optical response of the system is uniform in the detection range of 250-1100 nm. The associated non-linearity of measurements of high irradiance has also been removed by suitable circuit modifications. The system is now capable of storing time profiles of photometric data and has enhanced user-friendly options.

Ethylene production was induced in sections of dark-grown Sorghum vulgare L. seedlings by treatment with light in the blue and far red regions of the light spectrum. The action spectrum closely resembled the previously reported spectra for high irradiance response; thus, light-induced ethylene production is probably a high irradiance response with phytochrome as the initial photoreceptor.

Subterranean clover communities were grown at 12, 16, 20 and 24°C in naturally lit temperature- controlled glasshouses. Rates of net CO2 exchange of communities varying in leaf area index (LAI) from 1 to 8 were determined at several levels of irradiance at the temperature at which the plants were grown and at other measurement temperatures. When measured at each of the four growth temperatures and at an irradiance of 250 W m-2, the net CO2 exchange rate increased with increase in LAI up to 3. Higher values of LAI affected the rate only slightly. At each growth temperature and an irradiance of only 50 W m-3, net CO2 exchange decreased with increase in LA1 over the range 2-8. Net CO2 exchange rate followed a hyperbolic curve with increase in irradiance at all LAI values, the asymptote being largely independent of temperature and of LAI within the range 3-8. The net CO2 exchange rates of a community, determined at different measurement temperatures, were also directly related to measurement temperature at high irradiance but, owing to increased respiration rate at high temperature, inversely related to temperature at low irradiance. Differences in net CO2 exchange rates of a community at high irradiance due to different measurement temperatures were greater than the differences due to different growth temperatures.

Flowering can be induced in the long-day plant Sinapis alba in 8-h photoperiods provided that the irradiance is close to that at which leaf photosynthesis is light-saturated (e.g. 96 J m-2 s-1). Three such 8-h cycles result in 10% flowering and six are required for full flowering, whereas only one long-day cycle of 16-20 h duration at a much lower irradiance (25 J m-2 s-1) is required for full flowering. High irradiance during the single long day promotes flowering when given for the first 8 h of a 16-h photoperiod, but is inhibitory over the last 8 h. Photosynthetic CO2 uptake is crucial for this response to high irradiance, as both its inhibitory and promotive effects on flowering are reversed by the removal of atmospheric CO2 during the period of high irradiance. Compared with plants kept in short days (8-h photoperiod), export of 14C-labelled assimilates from the leaf during a 24-h period was only 50-60% greater in plants exposed to a long day (20-h photoperiod), because plants in short days compensated to a degree for their shorter photosynthetic period by mobilizing leaf reserves during darkness. However, flowering can occur with no evident enhancement of supply of assimilate to the shoot apex, for example following dis- placement of the short day or on removal of atmospheric CO2 during the last 12 h of exposure to a 20-h long day. Also, the flowering response to radiant flux density during the second half of a long day shows an optimum between 15 and 70 J m-2 s-1, with reduced flowering both above and below this irradiance. Thus, although there is no absolute requirement for long days to induce flowering in S. alba, light reactions cther than photosynthesis probably contribute to photoperiodic induction in this species.