Deoxyribonucleic Acid and Ribonucleic Acid Synthesis during the Cell Expansion Phase of Cotyledon Development in Vicia faba L

Abstract

In Vicia faba L., the tissue specific proteins, legumin and vicilin, are synthesized during the cell expansion phase of cotyledon development. During this growth period, RNA and nuclear DNA increase 8-to 10-fold. 'H-Uridine and 'H-adenosine are incorporated into ribosomal RNA, both 25S and 18S, and into transfer RNA. DNA isolated from cotyledons in the cell division phase of growth has been compared with DNA isolated from cotyledons undergoing expansion growth. Re In this paper, we examine the changes which take place in the levels of DNA and RNA in V. faba cotyledons during the period of maximum production of legumin, i.e. during the cell expansion phase of cotyledon growth. Some of the characteristics of the newly formed DNA and RNA are described. MATERIALS AND METHODSPlant Material. The data of Figure 1 After 1 week in a glasshouse at 24 C day, 19 C night temperature, plants were transferred to 18 C day, 13 C night temperature. Natural illumination was used, and the photoperiod was extended with supplementary low incandescent light. In summer, plants flowered 5 weeks from sowing. Cotyledons up to 13 mm length (about 25 days from flowering) correspond to phase I of Briarty et al. (3); cotyledons up to 28 mm, the initiation of dehydration, are equivalent to phases II and III (3). Cotyledons were 19 to 21 mm about 32 days from opening of the flower. Developing seeds were harvested, the testa and plant axis were removed, and the cotyledons were used for analysis. As described previously (19), the length of the long axis or the fresh weight of the cotyledons was used as a measure of development.Cell Number. The number of cells per cotyledon was determined as described by Rijven and Wardlaw (24).Estimation of DNA and RNA. Cotyledons were collected from developing seeds of all ages up to maximum fresh weight. Duplicate, pooled samples of each size were obtained. Fats and cold acid-soluble substances were extracted as described by Williams and Rijven (31) except that at step 5 four extractions (70% ethanol, 15 min) were employed. Nucleic acids were subsequently extracted with 0.5 N perchloric acid at 70 C for 15 min, and the UV absorption of the extracts was monitored. With older cotyledons (e.g., 25 mm in length) up to eight extractions were necessary for complete removal of nucleic acids. Total nucleic acid was estimated from absorbance at 260 nm of the combined perchloric acid extracts assuming that 1 mg nucleic acid/ml had E260 of 30 units. An aliquot of the perchloric acid extract was used to determine DNA (6), and RNA was obtained by difference.Uptake and Incorporation of Labeled Nucleosides. Detached cotyledons were incubated at 25 C, with gentle shaking in 5 ml of sterile nutrient (15), containing tritium-labeled nucleosides. Incorporation was measured following isolation of nucleic acids according to Solymosy et al. (27)

A procedure for the purification of DNA from tobacco cell cultures and isolation of tobacco single-copy DNA

“…Based on the rate of renatration of E. coli DNA (see Fig. These values are typical for DNAs from plant sources (19,20,21). Therefore, tobacco callus DNA consists of about 70% reiterated sequence DNA and about 30% singlecopy DNA (see Fig.…”

Dna Content and Heterochromatin Variations in Various Tissues of Peanut (Arachis Hypogaea)

“…Higher amounts of DNA in cotyledons of Leguminosae than found in other tissues have been observed in several studies (e.g., Aldana, Fites and Pattee, 1972;Millerd and Whitfeld, 1973;Scharpe and van Parijs, 1973;Davies, 1976). Observations in Vida faba showed up to 8-to lO-fold increase in DNA content which approximated a 16C level (Millerd and Whit-[Vol.…”

DNA contents and cell number in relation to seed size in the genus Vicia

“…The nuclei of the cotyledon cells of legume seeds can develop high DNA values--up to 640 being reported in Pisum arvense (Smith, 1973) and Pisum sativum (Sharpe and van Parijs, 1973; Millerd and Spencer, 1974;Davies and Brewster, 1975) and up to a mean value of 100C in Pisum sativum by Cullis (1976). Tn Viciafaba Millerd and Whitfield (1973) reported a mean value of 160, although as stated earlier this might well be more appropriately calculated to be 250. The relationship between DNA content and dry weight per cell exists over the whole range of Vicia species which were examined, although these have different basic genome sizes, different information content within their DNA and different extents of replication of their DNA.…”