Temperature and Leaf Shape in Seedlings of Acacia aneura

Abstract

The fourth seedling leaf of Acacia aneura is developed as a phyllode at normal temperatures (20–22 °C). When seedlings are raised at higher (30–35 °C) temperatures the fourth leaf is bipinnate. The pathways of development of the bipinnate leaf and the phyllode are described. The pathways diverge when further development of an adaxial meristem on the leaf primordium is suppressed and two sub-terminal pinna meristems are formed. It is shown that although the primordium of the fourth leaf is present in the embryo at germination its further development is insensitive to temperature at that stage. Exposure of the seedling to as little as 2 days cf the higher temperatures is sufficient to bring about the change in leaf development. Sensitivity to this treatment begins at about 2 days and extends to about 7 days from germination. The phenomenon is discussed in relation to earlier experimental work on leaf shape in Acacia and to other reports of temperature effect on leaf shape.