Chlorophyll-proteins from maize seedlings grown under intermittent light conditions

Abstract

Abstract.We studied the organization of the antenna system of maize (Zea mays L.) seedlings grown under intermittent light conditions for 11 d. These plants had a higher chlorophyll-a/b ratio, a higher ratio of carotenoids to chlorophyll and a lower ratio of chlorophyll to protein than plants grown in continuous light. We found all chlorophyll-protein complexes of maize to be present. However, the minor chlorophyll a/b-proteins CP29 and CP26, and to a greater extent CP24 and the major light-harvesting complex II were reduced relative to the photosystem (PS) II core-complex. Also the chlorophyll a/b-antennae of PSI were reduced relative to the reaction-centre polypeptides. When isolated by flatbed isoelectrofocussing, the chlorophyll-a/b complexes of PSII showed a higher chlorophyll-a/b ratio and a lower ratio of chlorophyll to protein than the same complexes from continuous light; additionally, they bound more carotenoids per protein than the latter. Thus the altered organization of the photosynthetic apparatus of plants from intermittent light is caused by two different factors: (i) the altered stoichiometry of chlorophyll-binding proteins and (ii) a different ratio of pigment to protein within individual chlorophyll-proteins.

Pigment Binding of Photosystem I Light-harvesting Proteins

“…This finding may be of interest with regard to the in vivo situation because it indicates that the pigment composition of LHCIs may depend not only on the protein structure but also on the pigments available during LHCI formation. This was proposed for Chl binding by LHCI in barley (60), and results obtained with maize seedlings exposed to intermittent light also revealed flexibility in pigment binding in vivo (61). Additionally, reconstitution studies demonstrated the interchangeability of LHC proteins and carotenoids from alga and higher plants (21,62,63).…”

Chlorophyll a/b-Binding Proteins, Pigment Conversions, and Early Light-Induced Proteins in a Chlorophyll b-less Barley Mutant

“…Neoxanthin is associated with the Lhcb polypeptides (Bassi et al, 1993;Thornber et al, 1993), which are severely depleted in chlorina f2. As a consequence, neoxanthin (and of course Chl b) was largely reduced in chlorina f2 if compared to wild type, as reported by Simpson et al (1985).…”

“…The approximately 100 Chl a and 10 to 15 p-carotene molecules of the PSI core antenna (Britton, 1993) are bound to the two RC polypeptides, the products of the PsaA and PsaB genes. The core antenna of PSII consists of two proteins, named CP 43 and CP 47, binding in total 50 Chl a, 5 P-carotene, and perhaps a few lutein molecules (Bassi et al, 1993). Most photosynthetic antenna pigments are, however, bound to the different LHC proteins associated with either PSI or PSII (Jansson, 1994).…”

“…Because the xanthophyll cycle is known to regulate PSII activity, the investigation of its action has almost entirely focused on PSII. Although violaxanthin is found in a11 PSII LHC proteins (Thornber et al, 1993), severa1 authors have suggested that Lhcb4, Lhcb5, and Lhcb6 (CP 29, CP 26, and CP 24) regulate the energy flow from the outer antenna to the RC through the action of the xanthophyll cycle (Bassi et al, 1993;Jansson, 1994;Ruban et al, 1994). The xanthophyll cycle functions also in PSI (Thayer and Bjorkman, 1992), but it is not known whether it has any regulatory effect there.…”

“…Typically, these plants lack the major LHC proteins, Lhcbl and Lhcb2 (Simpson et al, 1985;White and Green, 1987;Allen et al, 1988) but still contain various amounts of minor LHC proteins (White and Green, 1988;Peter and Thornber, 1991;Marquardt and Bassi, 1993;Jahns and Krause, 1994). The barley (Hordeum vulgare L.) chlorina f2 mutant (Simpson et al, 1985) is the most wellcharacterized Chl b-deficient mutant.…”