Leaf Epinasty Induced by Reflection of Light from Beneath Marigold Plants

The cotyledons of marigold, Tagetes erecta L., developed epinasty when reflective surfaces were maintained under the seedlings. Plain aluminum foil or white-painted foil induced up to 360° curvature as the cotyledons extended, whereas no epinasty occurred over the exposed surface of potting mix or black-painted foil. A gray-painted foil induced intermediate epinasty. Dry-weight accumulation of the seedlings was not significantly affected by the epinasty. We have observed epinasty of cotyledon- ary leaves on seedlings developing in con- trolled environments. This response is asso- ciated with the use of reflective coverings over the medium to reduce evaporative water loss. Epinasty occurred when white foam plugs were utilized to support lettuce ( Lactuca sativa L.) seedlings in nutrient-culture studies. The cotyledons developed epinasty during each light period and then regained a horizontal orientation during each dark period (authors' observation). We observed an apparent related epinastic response in tomato (Lysopersicon esculentum Mill.) plants growing in contain- ers widely-spaced on a flooded greenhouse bed in Naaldjvik, Netherlands. Several true leaves developed severe epinasty. The water apparently reflected sunlight unto the lower surfaces of the leaves. This study was under- taken with marigolds, Tagetes erecta L., to quantify the epinastic response of leaves to varying levels of reflectivity and to determine if epinasty inhibited dry-weight accumula- tion.