Influence of light on DNA content of Helianthus annuus Linnaeus.
Price H.J. | Johnston J.S.
Mean nuclear 2C DNA content (C equaling haploid DNA per nucleus) of the first leaf of the sunflower, Helianthus annuus L., is influenced by the quality and the quantity of light. Seedlings of two inbred lines, RHA 299 and RHA 271 were germinated and grown in controlled environmental conditions. Lighting was adjusted to provide different combinations of photon flux densities and red to far red (R:FR) ratios. At R:FR = 5.8 and photon flux densities of 170 micromoles. m-2. s-1, 200 micromoles. m-2. s-1, and 230 micromole. m-2. s-1, DNA content remained high and relatively constant (mean = 6.97 pg for RHA 271 and mean = 7.32 pg for RHA 299). When the photon flux density range (R:FR = 5.8) was elevated to 350 micromole. m-2. s-1, 410 micromole. m-2. s-1, and 470 micromole. m-2. s-1, mean DNA content was reduced to 6.23 pg (RHA 271) and 6.46 pg (RHA 299). At R:FR = 1.5, mean DNA content was consistently high (7.2-7.9 pg) only at the lowest photon flux density of 170 micromole. m-2. s-1. Significant decreases in DNA content (less than or equal to 12%) were observed at photon flux densities of 200 micromole. m-2. s-1 and 230 micromole. m-2. s-1. At the higher photon flux densities (350 micromole. m-2. s-1, 410 micromole. m-2. s-1, and 470 micromole. m-2. s-1) and R:RF = 1.5, the plants had extremely low DNA contents (mean = 3.36 pg for RHA 271 and 3.41 pg for RHA 299) and high between-plant variance. The instability of DNA content, particularly for plants grown under light that is far red rich, suggests that phytochromes may be involved in regulating DNA content of the sunflower.
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