Chlorophyll-Proteins and Electron Transport during Iron Nutrition-Mediated Chloroplast Development

Abstract

Chlorophyll-protein complexes and electron transport activities were measured during iron nutrition-mediated chloroplast development in sugar beet (Beta vwlgaris L. cv F58-554H1). Results showed that the chlorophyll-protein complexes associated with the reaction centers of photosystem I (CP1) and photosystem II (CPa) and the electron transport activities of these two photosystems per leaf area increased rapidly during the first 24 to 48 hours of iron resupply to iron-deficient sugar beet plants. Bulk chlorophyll and the amounts of light-harvesting chlorophyllproteins increased after a lag period of 24 hours. The changes in chlorophyll-proteins with time were apparently the cause ofan initial increase, then decrease, in the chlorophyll a/b ratio during iron resupply. There was evidence that iron deficiency diminished photosystem I more than photosystem II. We propose that there are two distinct phases in iron nutrition-mediated chloroplast development: (a) the commencement of the synthesis of the lipid matrix of the thylakoid membrane, including a fully functioning electron transport (and photosynthetic) system, during the first 24 hours of iron resupply, and (b) after 24 to 48 hours, the formation of the bulk of the thylakoid proteins, including the lightharvesting chlorophyll-proteins with which the large increase in total chlorophyll is associated.Earlier work showed that when Fe was resupplied to Fedeficient sugar beet plants, the synthesis of thylakoid membrane lipids (galactolipids) was linear over a 96-h period (12). The PSI electron transport components, P70o and Cyt f, also increased linearly with time (13). However, total Chl and total thylakoid protein exhibited a lag of24 h before maximum rates ofsynthesis were attained (12). Chl a/b ratios have been shown to increase over the first 24 h of resupply, then decrease (12,13,17).These experimental observations suggest that during Fe nutrition-mediated chloroplast development, the membrane matrix is laid down first with reaction centers and electron carriers, and that after 24 h there is increased synthesis of the LHCPs3 (majority of Chl) and other thylakoid proteins. Thus, during the first 24 h, the reaction center Chl-proteins (mainly Chl a-containing) would be accumulated more rapidly than the Chl b (and Chl a) containing LHCPs. Thereafter, the LHCPs would (according to

A Program for Iron Economy during Deficiency Targets Specific Fe Proteins

“…It is of interest to place our findings in the context of studies that have reported on the general effects of Fe deficiency on chlorophyll synthesis and photosynthesis that have been well documented in the literature (Spiller and Terry, 1980;Andaluz et al, 2006;Nishio and Terry, 1983;Nishio et al, 1985;Sharma, 2007;Timperio et al, 2007;Laganowski et al, 2009;Msilini et al, 2011;Ciaffi et al, 2013;Paolacci et al, 2014;Rodríguez-Celma et al, 2013). Some studies on Fe depletion in plants reported that PSI was the major target of Fe deficiency (Nishio et al, 1985;Timperio et al, 2007), whereas we saw a major effect on the cytochromeb 6 f complex and less on PSI.…”

Enhanced Secondary- and Hormone Metabolism in Leaves of Arbuscular Mycorrhizal Medicago truncatula

“…Iron (Fe) is an essential mineral nutrient for plants and serves as a cofactor for enzymes involved in respiration, chlorophyll biosynthesis, and chloroplast development (Nishio et al, 1985;Kobayashi and Nishizawa, 2012). However, excess free Fe(II) is toxic for cells due to the formation of hydroxyl radicals, causing deleterious effects to cellular constituents (Orino et al, 2001).…”

Photochemical Apparatus Organization in the Chloroplasts of Two Beta vulgaris Genotypes

“…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).…”