The effect of the dark interval in intermittent light on thylakoid development: photosynthetic unit formation and light harvesting protein accumulation

Abstract

Etiolated bean plants were grown in intermittent light with dark intervals of shorter or longer duration, to modulate the rate of chlorophyll accumulation, relative to that of the other thylakoid components formed. We thus produced conditions under which chlorophyll becomes more or less a limiting factor. We then tested whether LHC complexes can be incorporated in the thylakoid. It was found that an equal amount of chlorophyll, formed under the same total irradiation received, may be used for the stabilization of few and large-in-size PS units containing LHC components (short dark-interval intermittent light), or for the stabilization of many and small-in-size PS units with no LHC components (long dark-interval intermittent light). The size of the PS units diminishes as the dark-interval duration is increased, with no further change after 98 minutes. The PSII/cytf ratio remains constant throughout development in intermittent light and equal to that of mature chloroplasts (PSII/cytf = 1) except in the case of very long dark-interval regimes, where about half PSII units per cytf are present. The PSII/PSI ratio was found to be correlated with the PSII unit size (the larger the size, the lower the ratio). The number of PSI units operating on the same electron transfer chain varied depending on the size of the PSII unit (the larger the PSII unit size, the more the PSI units per chain). The results suggest that it is not the chlorophyll content per se which regulates the stabilization of LHC in developing thylakoids and consequently the size of the PS units, but rather the rate by which it is accumulated, relative to that of the other thylakoid components.

Two routes of chlorophyllide synthesis that are differentially regulated by light in barley (Hordeum vulgare L.).

“…The formation of light-harvesting structures is disturbed in these plants while the Chl-containing core complexes of photosystems I and II appear to assemble normally (N. Lebedev and KA., unpublished work). A similar phenomenon has been observed in intermittent-lighttreated seedlings (34) that are also likely to suffer from a POR-A deficiency. While these results support the view that the functions of POR-A and POR-B during chloroplast formation are distinct, other explanations of these observations cannot yet be excluded.…”

Chloramphenicol‐induced stabilization of light‐harvesting complexes in thylakoids during development

“…It is interesting to note that the PS II/PS I ratio in CAP-treated ImL leaves is lower than for untreated controls. It has been reported [4,11] that during development the PS II/PS I ratio is correlated with the PS II unit size, viz. the larger the size the lower the ratio.…”

“…PS I and PS II activities were monitored as in [ 11 ]. Low-temperature fluorescence spectra were recorded in a fluorometer set-up according to [11]. SDS-PAGE of thylakoid polypeptides was performed as described [11], after thorough washing of thylakoids with 0.05 M Tricine, pH 7.2.…”

“…Chl was extracted from leaves as in [1] and determined according to [13]. PS I and PS II activities were monitored as in [ 11 ]. Low-temperature fluorescence spectra were recorded in a fluorometer set-up according to [11].…”

“…Low-temperature fluorescence spectra were recorded in a fluorometer set-up according to [11]. SDS-PAGE of thylakoid polypeptides was performed as described [11], after thorough washing of thylakoids with 0.05 M Tricine, pH 7.2. All determinations in 18 h CL leaves were made after immersing the leaves in H20 and drying as above.…”