Changes in Chloroplast DNA Levels during Development of Pea (Pisum sativum)

Abstract

Determinations were made of the percentage of chloroplast DNA (ct DNA) in total cell DNA isolated from shoots of pea at different stages of development. Labeled pea ct DNA was reassociated with a high concentration of total DNA; the percentage of ct DNA was estimated by comparing the rate of reassociation of this reaction with that of a model reaction containing a known concentration of unlabeled ct DNA. The maximum change in ct DNA content was from 1.3% of total DNA in young shoots to 7.3% in fully greened shoots. Analyses were also performed on DNA from embryos, etiolated tissue, roots, and leaves. The first leaf set to develop in pea was excised over a growth period of 8 days during which leaf length increased from 4 to 12 millimeters. Young leaves contained about 8% ct DNA; in fuly greened leaves the level of ct DNA approached 12%, equivalent to as many as 9,575 copies of ct DNA per cell. Root tissue contained only 0.4% ct DNA.Chloroplast development is essentially a light-induced phenomenon. The process includes reorganization of the prolamellar bodies to form the thylakoids and grana, reduction of Pchl to Chl, and plastid enlargement (11). In higher plants the number of chloroplasts per cell can increase by as much as a factor of 20 during greening and leaf expansion (19).There is some evidence that chloroplast development is accompanied by ct DNA2 synthesis (6, 19, 20). However, the contribution of ct DNA to the total cellular DNA complement at any stage of higher plant development has not been accurately determined. A major difficulty is the similar base composition of chloroplast and nuclear DNAs (10), which has prevented resolution of these components by CsCl density gradient analysis of total cell DNA.In the algae the buoyant densities of the two DNAs may differ considerably. It has been found that ct DNA comprises about 5% of total DNA in the primitive alga Olisthodiscus throughout the growth cycle (2), and as much as 11 to 15% in Chlamydomonas (22,26). Although 9% ct DNA has been estimated for tobacco leaves by the density method (23), reassociation kinetics analysis has indicated that tobacco leaves contain 4% ct DNA and roots less than 1% (21).The purpose of this study was to determine the amount of ct DNA in total DNA extracted from shoots throughout development of peas using reassociation kinetics analysis. In an earlier report we noted that ct DNA could increase by a factor of 2.5

Phytochrome‐mediated accumulation of chloroplast DNA in pea leaves

“…Total DNA from pea leaves contains both nuclear and extra-nuclear DNA. The amount of extra-nuclear DNA is at most 13% of the total DNA in mature pea leaves, because mitochondrial DNA is about 1% [14] and chloroplast DNA about 12% [15]. So, the bulk of total DNA is nuclear and we can assume that the gene dosage in total DNA is nearly equal to that per nuclear DNA level.…”

Microspectrofluorometric Measurement of Chloroplast DNA in Dividing and Expanding Leaf Cells of Spinacia oleracea

“…There are a number of papers in the literature reporting changes in chloroplast DNA amounts determined by methods involving DNA extraction and cell and chloroplast counting (3,6,16,17). Problems with these methods include incomplete DNA extraction, difficulties in determining the ratio of nuclear to chloroplast DNA and inherent errors in averaging cell and chloroplast numbers from tissues with cellular heterogeneity.…”

“…By contrast, the distribution of nuclear DNA amounts in the same leaf tissues in which cell division was known to be occurring showed a clear bimodal distribution. We consider that the distribution of chloroplast DNA in the plastid population shows that there is no S-phase of chloroplast DNA synthesis, all chloroplasts in the population in young leaf cells synthesize DNA, and all chloroplasts divide.There are a number of papers in the literature reporting changes in chloroplast DNA amounts determined by methods involving DNA extraction and cell and chloroplast counting (3,6,16,17 …”

“…There are a number of papers in the literature reporting changes in chloroplast DNA amounts determined by methods involving DNA extraction and cell and chloroplast counting (3,6,16,17 …”

Benzyladenine-Induced Increase in DNA Content per Chloroplast in Intact Bean Leaves

“…The proportion of ctDNA in total cellular DNA was determined by several workers using reassociation kinetics (5,(14)(15)(16). To correctly estimate the DNA content per chloroplast, Boffey and Leech (3) measured the DNA content ofisolated chloroplasts after DNase treatment.…”