A novel insight into the regulation of light-independent chlorophyll biosynthesis in Larix decidua and Picea abies seedlings

Abstract

Light-independent chlorophyll (Chl) biosynthesis is a prerequisite for the assembly of photosynthetic pigment-protein complexes in the dark. Dark-grown Larix decidua Mill. seedlings synthesize Chl only in the early developmental stages and their Chl level rapidly declines during the subsequent development. Our analysis of the key regulatory steps in Chl biosynthesis revealed that etiolation of initially green dark-grown larch cotyledons is connected with decreasing content of glutamyl-tRNA reductase and reduced 5-aminolevulinic acid synthesizing capacity. The level of the Chl precursor protochlorophyllide also declined in the developing larch cotyledons. Although the genes chlL, chlN and chlB encoding subunits of the light-independent protochlorophyllide oxidoreductase were constitutively expressed in the larch seedlings, the accumulation of the ChlB subunit was developmentally regulated and ChlB content decreased in the fully developed cotyledons. The efficiency of chlB RNA-editing was also reduced in the mature dark-grown larch seedlings. In contrast to larch, dark-grown seedlings of Picea abies (L.) Karst. accumulate Chl throughout their whole development and show a different control of ChlB expression. Analysis of the plastid ultrastructure, photosynthetic proteins by Western blotting and photosynthetic parameters by gas exchange and Chl fluorescence measurements provide additional experimental proofs for differences between dark and light Chl biosynthesis in spruce and larch seedlings.

Tetrapyrrole Metabolism inArabidopsis thaliana

“…This is probably because these organisms do not accumulate a high level of Pchlide in darkness, and accordingly, they do not need a large amount of POR in darkness. The expression patterns of the genes encoding the DPOR subunits (ChlL, ChlN, and ChlB) in response to light conditions are varied among plant species (Demko et al 2009;Skinner and Timko 1999;Suzuki et al 2001). Meanwhile, in adult Arabidopsis plants, PORA and PORB show circadian rhythmic expression patterns that are similar to the lightinducible Chl synthesis genes, although the oscillation peak is somewhat delayed (Matsumoto et al 2004).…”

Influence of irradiance on chlorophyll synthesis in Picea abies calli cultures

“…They demonstrated the presence of two C to U editing sites in the central region of chlB transcript in P. sylvestris and P. abies and one editing site in L. eurolepis. The presence of two editing sites was also detected in L. decidua (Demko et al 2009). Our preliminary results indicate, that these previously described codons of chlB transcripts can be edited also in P. abies calli cells (data not shown).…”

“…Enzymatic reduction of Pchlide to Chlide, catalyzed by DPOR enzyme in the dark, represents another regulatory step in the Chl biosynthesis (Fujita 1996). Constitutive expression of plastid genes chlL, chlN and chlB has been reported in photoautotrophically, mixotrophically and heterotrophically cultivated Chlorella protothecoides cells and in various conifer species grown in the dark (Spano et al 1992, Skinner and Timko 1999, Kusumi et al 2006, Shi and Shi 2006, Demko et al 2009). In contrast to previous studies, we observed very low expression of chlLNB genes in darkgrown calli suggesting that chlLNB expression can be modulated by light in P. abies calli.…”

“…In green light-grown calli, GluTR and FLP levels were higher compared to white calli cultures. Demko et al (2009) described presence of GluTR in 7-and 14-d-old P. abies dark-grown seedlings. They observed increase of the Chl content, ALA synthesis and GluTR content after 24 h of irradiance of 14-d-old seedlings.…”

A Novel Structural and Functional Insight Into Chloroplast-Encoded Central Subunit of Dark-Operated Protochlorophyllide Oxidoreductase (Dpor) of Plants

“…However, darkness promotes etiolation in the seedlings of angiosperms because they lack DPOR genes. Consequently, the distribution of DPOR and LPOR entails that the two systems coexisted throughout evolution from the cyanobacteria to the gymnosperms but that the genes encoding DPOR subunits were lost during the evolution from gymnosperms to angiosperms and, as a result, lost their ability to green in the dark (Shi and Shi, 2006;Demko et al, 2009). Hence, the reduction of protochlorophyllide to chlorophyllide in the absence of light in most dark-grown organisms, other than etiolated angiosperms, correlates with the presence of the ChlL, ChlN, and ChlB genes (Shi and Shi, 2006).…”