Differential Effects of Nitrogen Limitation on Photosynthetic Efficiency of Photosystems I and II in Microalgae.

The effects of nitrogen starvation on photosynthetic efficiency were examined in three unicellular algae by measuring changes in the quantum yield of fluorescence with a pump-and-probe method and thermal efficiency (i.e. the percentage of trapped energy stored photochemically) with a pulsed photoacoustic method together with the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea to distinguish photosystems I and II (PSI and PSII). Measured at 620 nm, maximum thermal efficiency for both photosystems was 32% for the diatom Thalassiosira weissflogii (PSII:PSI ratio of 2:1), 39% for the green alga Dunaliella tertiolecta (PSII:PSI ratio of 1:1), and 29% for the cyanobacterium Synechococcus sp. PCC 7002 (PSII:PSI ratio of 1:2). Nitrogen starvation decreased total thermal efficiency by 56% for T. weissflogii and by 26% for D. tertiolecta but caused no change in Synechococcus. Decreases in the number of active PSII reaction centers (inferred from changes in variable fluorescence) were larger: 86% (T. weissflogii), 65% (D. tertiolecta), and 65% (Synechococcus). The selective inactivation of PSII under nitrogen starvation was confirmed by independent measurements of active PSII using oxygen flash yields and active PSI using P700 reduction. Relatively high thermal efficiencies were measured in all three species in the presence of the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, suggesting the potential for significant cyclic electron flow around PSI. Fluorescence or photoacoustic data agreed well; in T. weissflogii, the functional cross-sectional area of PSII at 620 nm was estimated to be the same using both methods (approximately 1.8 x 102 A2). The effects of nitrogen starvation occur mainly in PSII and are well represented by variable fluorescence measurements.

Sulfite inhibition of photochemical activity of intact pea leaves.

Sulfite treatment of pea leaf disks in light caused a significant decrease in the relative quantum yield of photosynthetic oxygen evolution and energy storage (ES) as measured by photoacoustic (PA) spectroscopy. The inhibition was concentration dependent and was less in darkness than in light, indicating light-dependent inhibitory site(s) on the photosynthetic electron transport chain. Further, in darksulfite-treated leaves, the energy storage was more affected than the relative quantum yield of oxygen evolution, suggesting that photophosphorylation and/or cyclic electron transport around PS I are sites of sulfite action in darkness. The Rfd values, the ratio of fluorescence decrease (fd) to the steady-state fluorescence (fs), decreased significantly in leaves treated with sulfite in light but were not affected in dark-treated ones, confirming the photoacoustic observations. Similarly, the ratio of variable fluorescence (Fv) to maximum fluorescence (Fm), a measure of PS II photochemical efficiency, was affected by sulfite treatment in light and not changed by treatment in darkness. An attempt was made to explain the mechanism of sulfite action on photosynthetic electron transport in light and in darkness.

Photoacoustic Study of Changes in the Energy Storage of Photosystems I and II during State 1-State 2 Transitions.

Using photoacoustic spectroscopy, state 1-state 2 transitions were demonstrated in vivo in intact sugar maple leaves (Acer saccharum Marsh.) by following the changes in energy storage of photosystems (PS) I and II. Energy storage measured with 650 nm modulated light (light 2) in the presence of background white light indicated the total energy stored by both photosystems (ES(t)), and in the presence of background far-red light showed the energy stored by PSI (ES(psi)). The difference between ES(t) and ES(psi) gave the energy stored by PSII (ES(psii)). While ES(t) remained nearly constant during state transitions, both ES(psi) and ES(psii) changed considerably. The ratio of ES(psii) to ES(psi), an indicator of the energy distribution between the two photosystems, decreased or increased during transition to state 2 or state 1, respectively. State transitions were completed in about 20 min and were fully reversible. During transition from state 1 to state 2, the fraction of excitation energy gained by PSI was nearly equal to that lost by PSII. This fraction of excitation energy transferred from PSII to PSI accounted for about 5% of the absorbed light (fluorescence is not considered), 19% of ES(t), 34% of ES(psii), and 43% of ES(psi) in state 2. NaF treatment inhibited the transition to state 1. Data in the present study confirm the concept of changes in absorption cross-section of photosystems during state transitions.

Photosynthetic energy storage of Photosystems I and II in the spectral range of photosynthetically active radiation in intact sugar maple leaves.

The relative activity of Photosystems (PS) I and II in the spectral range between 400 and 720 nm was studied by measuring photosynthetic energy storage (ES) of an intact sugar maple leaf using photoacoustic spectroscopy. ES, determined with a modulated (80 Hz) monochromatic light beam in the presence of saturating intensity of background non-modulated white light, indicated the total energy stored by both photosystems (EST). Using background far-red light, ES of PS I (ESPS I) was quantified. ESPS II was derived from EST-ESPS I. EST dependence on intensity and wavelength of modulated light was studied at 470, 560, 640 and 680 nm. EST was maximum in red light and minimum in blue light. It decreased with an increase in modulated light intensity. The ratio ESPS II/ESPS I, measured at 640 nm, remained nearly constant with an increase in modulated light intensity. The relative quantum yield of EST spectrum showed two peaks around 610 and 660 nm, and declined sharply after 680 nm, revealing a clear red drop. ESPS I spectrum presented peaks around 610 and 670 nm, and a minimum between 440 and 470 nm. ESPS I was observed beyond 700 nm up to 720 nm, indicating the energy stored by cyclic electron transport. ESPS II spectrum showed broad peaks, around 460, 490, 600 and 660 nm, and a shoulder between 530 and 560 nm. ESPS II was always higher than ESPS I between 400 and 690 nm and reached zero around 700 nm.

Effect of sulfur dioxide and sulfite on photochemical energy storage of isolated chloroplasts--a photoacoustic study.

Photoacoustic spectroscopy was used to study the effect of sulfite and SO(2) on isolated corn mesophyll chloroplasts by monitoring the photochemical energy storage. Sulfite incubation of isolated chloroplasts, either in light or in darkness, caused a decrease in photochemical energy storage. The more pronounced decrease in light indicates a light-dependent sulfite inhibitory site(s) in chloroplasts. Also diphenylcarbazide caused a partial recovery of energy storage in sulfite treated chloroplasts indicating a possible site of damage at the water oxidizing system. Although the chloroplast membranes were found to be insensitive to high concentrations of SO(2) for relatively short exposure periods (10 min) in light, exposure of chloroplasts to 28.5 ng cm(-3) SO(2) for 10 min caused a decrease in energy storage. An attempt was made to explain the mechanism of action of sulfite and SO(2) in chloroplasts.

The Traumatic Coma Data Bank: a nursing perspective, Part II.

The Traumatic Coma Data Bank (TCDB) was a collaborative project undertaken to study the nature and course of severe head injury. Evolution of nursing goals includes collection of data, communication, new clinical observations, designing future research projects, education and legislative impact. Management issues inherent in the collaborative research project are defining, collecting, entering, and analyzing and publishing results.

The Traumatic Coma Data Bank: a nursing perspective, Part I.

The Traumatic Coma Data Bank (TCDB) was a collaborative project undertaken to study the nature and causes of severe head injury, allowing patients similar in age, severity of insults and neurological and physical symptoms to be compared in terms of outcome. Systematic uniform data were collected during the prehospital, acute and rehabilitative phases on 581 patients from 6 centers during the pilot phase of the TCDB, June 1, 1979 through May 31, 1982. The pilot phase successfully determined that a collaborative approach to studying head injury was feasible and additional information gained was incorporated into the main phase April, 1983 through April, 1988. A description of the TCDB population as of this writing (730 patients) is included here.