The response of the photosynthetic apparatus in the green alga Dunaliella salina, to irradiance stress was investigated. Cells were grown under physiological conditions at 500 millimoles per square meter per second (control) and under irradiance-stress conditions at 1700 millimoles per square meter per second incident intensity (high light, HL). In control cells, the light-harvesting antenna of photosystem I (PSI) contained 210 chlorophyll a/b molecules. It was reduced to 105 chlorophyll a/b in HL-grown cells. In control cells, the dominant form of photosystem 11 (PSII) was PSll,(about 63% of the total PSII) containing >250 chlorophyll a/b molecules. The smaller antenna size PSIIcenters (about 37% of PSII) contained 135 ± 10 chlorophyll a/b molecules. In sharp contrast, the dominant form of PSII in HL-grown cells accounted for about 95% of all PSII centers and had an antenna size of only about 60 chlorophyll a molecules. This newly identified PSII unit is termed PSII. The HL-grown cells showed a substantially elevated PSII/PSI stoichiometry ratio in their thylakoid membranes (PSII/PSI = 3.0/1.0) compared to that of control cells (PSII/PSI = 1.4/1.0). The steady state irradiance stress created a chronic photoinhibition condition in which D. salina thylakoids accumulate an excess of photochemically inactive PSII units. These PSII units contain both the reaction center proteins and the core chlorophyllprotein antenna complex but cannot perform a photochemical charge separation. The results are discussed in terms of regulatory mechanism(s) in the plant cell whose function is to alleviate the adverse effect of irradiance stress.

The photochemical apparatus orgaization in the thylakoid membrane of Macrocystis pyrifera, the gt kelp, was investigated. Chloroplasts were isolated from surface and minus 20 meter blades. Photosynthetic electron-transport complex quantitation revealed ratios of photosystem (PS) II/cytochrome bh-J7PSI = 1. Macrocystis, the giant kelp, is economically and ecologically the most important algal species in the nearshore subtidal environment of the California coast (23). The macroscopic sporophyte stage serves not only as the physical structure of the kelp forest canopy, but also as the primary biotic structuring agent in terms of the composition of the algal understory community (26). Canopy blades can affect the photosynthesis of subcanopy blades by reducing light intensity (1 1). Studies ofthe light regime in the kelp forest have concentrated on the light intensity (photon flux density) gradient rather than on the light quality (spectral composition) to which various portions ofthe plant are exposed. Both of these factors influence the rate of photosynthesis and the composition of the photosynthetic apparatus (20).The nearshore marine habitat, like other aquatic systems, is exposed to a light environment that is enriched in blue and green wavelengths. Within 2 to 3 m of the surface, most of the red and yellow wavelengths are absorbed by the water, as well as the violet and ultraviolet components (6). At -20 m, under the kelp I Supported by National Science Foundation grant DMB-8400 169. canopy, total irradiance is 1% of that at the surface (11). The response and adaptation of the photosynthetic apparatus of mature Macrocystis blades to the substantially different spectral properties of surface and -20 m microhabitats is not known.Previous work with Macrocystis utilized pigment extraction (7), 02 evolution (30), and whole blade long-term fluorescence induction (5) techniques in the measurement of photosynthesis. Such previous investigations, however, did not address the question of the structural-functional organization of the electrontransport components in the thylakoid membrane of Macrocystis. In the present study, the organization ofthe integral thylakoid membrane complexes (PSII, Cyt b-fand PSI) in mature, vegetative surface blades of Macrocystis was compared to that of vegetative blades collected at -20 m. Additional measurements provided information about the absorption cross section of the antenna of PSI1 and PSI in thylakoids isolated from blades from these two light environments. Evaluation of the Chl a-core antenna of PSI and the association of the peripheral Chl a/cfucoxanthin light-harvesting-pigment complex with PSII and PSI is presented. MATERIALS AND METHODSMacrocystis sporophyte blades were collected approximately three times per month (June 1985 to November 1986) from one of two study sites in Monterey Bay, California. Healthy, fully expanded, vegetative surface blades were collected from each population growing in less than 10 m depth, such that no more than five blades from one stipe,...

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The vast majority of rural and remote nurses used at least one peripheral information source to inform their practice. Increasing the number of research sources used by these nurses requires attention to issues of information access in these areas, as well as issues of staff recruitment and retention of staff in under-serviced rural and remote regions.

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