Light regulation of photosynthetic membrane structure, organization, and function

Abstract

The light environment during plant growth determines the structural and functional properties of higher plant chloroplasts, thus revealing a dynamically regulated developmental system. Pisum sativum plants growing under intermittent illumination showed chloroplasts with fully functional photosystem (PS) II and PSI reaction centers that lacked the peripheral chlorophyll (Ch1) a/b and Ch1 a light-harvesting complexes (LHC), respectively. The results suggest a light flux differential threshold regulation in the biosynthesis of the photosystem core and peripheral antenna complexes. Sun-adapted species and plants growing under far-red-depleted illumination showed grana stacks composed of few (3-5) thylakoids connected with long intergrana (stroma) thylakoids. They had a PSII /PSI reaction center ratio in the range 1.3-1.9. Shade-adapted species and plants growing under far-red-enriched illumination showed large grana stacks composed of several thylakoids, often extending across the entire chloroplast body, and short intergrana stroma thylakoids. They had a higher PSII /PSI reaction center ratio, in the range of 2.2-4.0. Thus, the relative extent of grana and stroma thylakoid formation corresponds with the relative amounts of PSII and PSI in the chloroplast, respectively. The structural and functional adaptation of the photosynthetic membrane system in response to the quality of illumination involves mainly a control on the rate of PSII and PSI complex biosynthesis.

Photochemical Apparatus Organization in the Chloroplasts of Two Beta vulgaris Genotypes

“…The PSI antenna size (calculated from spectroscopic measurements) was also lower than other reported values, i.e. 144 molecules of Chl per PSI reaction center in the sugar beet hybrid compared to 195 in maize (11) and 209 to 222 in spinach and pea (17,18). PSII antenna sizes were comparable to those reported previously ( 17,18 (10,15,24).…”

“…The data obtained were compared with those of a standard Fl hybrid of the same species. The mutant was depleted in chlorophyll b relative to the hybrid and it had a higher photosystem II/photosystem I reaction center (Q/P7") (1,12,17,26).…”

“…The data obtained were compared with those of a standard Fl hybrid of the same species. The mutant was depleted in chlorophyll b relative to the hybrid and it had a higher photosystem II/photosystem I reaction center (Q/P7") (1,12,17,26).Investigation of the effects of mutations of genes coding for specific components of the thylakoid membrane permit greater precision in the interpretation of the structural/functional role of that component than would be possible for many environmental perturbations of thylakoid structure. In our laboratory (N. T.) we are studying currently a low Chl sugar beet mutant which exhibits high rates ofphotosynthesis and electron transport per unit Chl similar to those described by Miles (23): the mutation apparently affects some specific polypeptides of the LHCP.3 Here, we characterize the structural organization of thylakoid membranes of the low Chl mutant by combining spectroscopic analysis with gel electrophoresis.…”

“…In turn, such measurements enabled the estimation of the Chl antenna size of each PS in situ ( 18). Other (1,12,17,26).…”

“…Chl a molecules form the core antenna while the remainder is peripheral LHCP (17,28). On this basis, 54% of the total Chl is associated with the peripheral antenna ofthe hybrid as compared to 42% in the mutant while the proportion of total Chl in the PSII core was 16 and 29% in the hybrid and mutant, respectively.…”