Maternal Effect on Embryogenesis in Tobacco Overexpressing Rice Phytochrome A *

When analyzing tobacco lines overexpressing various types of rice phytochrome A, we observed seedlings with fused cotyledons. Phytochrome A is a member of the phytochrome family of plant red/far‐red absorbing photoreceptors. Reciprocal crossings with wild‐type tobacco indicated that this abnormal phenotype was maternally inherited. Mother plants that were expected to produce abnormal seedlings, were raised under different conditions and seeds collected separately from individual capsules. The frequency of abnormal seedlings increased in seeds from later flowers but decreased when mother plants were raised under continuous white light. The interaction of the overexpressed phytochrome A proteins with endogenous plant hormones might be responsible for cotyledon fusion. The abnormal phenotype could partially be recovered by application of gibberellic acid to intact flowers at the time of pollination. In contrast, the synthetic auxin NAA slightly enhanced the degree of cotyledon fusion. Even wild‐type tobacco seedlings exhibited partial fusion of cotyledons if flowers were treated with 2,4‐D and occasionally the shoot apex was replaced by a second root. Application of GA 3 to the flowers, in contrast, impaired the development of the radicule. These observations are discussed with respect to maternal effects in plant embryogenesis.