ENVIRONMENTALLY-INDUCED NUCLEAR 2C DNA CONTENT INSTABILITY IN HELIANTHUS-ANNUUS (ASTERACEAE)

Experiments were conducted to detect developmental and environmental f actors that influence nuclear DNA content in H. annuus inbred lines RH A 271 and RHA 299. DNA content (2C) was determined by laser flow cytom etry of nuclei isolated from the first leaf pair of seedlings grown in a greenhouse and in growth chambers. DNA content of greenhouse grown seedlings was highly variable, ranging from approximate to 3.2 to 8.0 pg for RHA 299 and approximate to 5.2 to 8.2 pg for RHA 271. DNA conte nt only weakly correlated to the position of the achene in the head fr om which the seedlings derived, and not at all to the position of the head on the plant. Experimentally varied environmental parameters of h eat stress and water deficit, phosphate fertilizer levels in the subst rate, and pH had little or no effect on the DNA content of seedlings. Seedlings grown with increased levels of substrate nitrogen in the for m of NH,NO, showed a significant increase in the mean DNA content. Pla nts grown in one of two types of growth chambers possessed less variab ility in DNA content, approximate to 6.2 - 8.4 pg for RHA 299 and appr oximate to 6.8 - 7.4 pg for RHA 271. Plants grown in a second growth c hamber were highly variable with DNA content ranging from approximate to 3.0 to 8.6 pg for RHA 299 and approximate to 3.0 to 7.8 pg for RHA 271. Measurable physical differences between the growth chambers were irradiance level and the ratio of red to far red light. The hypothesis is presented that DNA stability of sunflowers is influenced by light quantity and/or quality.