Seedling Establishment: A Dimmer Switch-Regulated Process between Dark and Light Signaling

Abstract

A balance between dark and light signaling directs seedling establishment through integrating internal and environmental information.

Figure 1.

Arabidopsis seedling establishment after the switch from dark to light. Representative pictures of 2-d-old dark-grown seedlings (A) exposed to, left to right, 0 h, 2 h, 6 h, or 24 h of low light (approximately 5 μmol m⁻² s⁻¹ photosynthetically active radiation), and 3-d-old dark-grown (B) and light-grown (C) seedlings. Scale bar = 2 mm.

Figure 2.

Photomorphogenesis among crop species. Representative pictures of tomato, quinoa, and sorghum seedlings grown for 2 d in the dark exposed to, from left to right, 0 h, 6 h, or 24 h of low light (approximately 5 μmol m⁻² s⁻¹ photosynthetically active radiation), and 3 d in the dark. Scale bars = 1 cm.

Figure 3.

Dark and light signaling induce organ-specific developmental traits in Arabidopsis seedlings. Simplified representation of the traits that accompany development in the dark (left) and upon first light signaling (right). For each organ (apical hook, A; cotyledons, B; hypocotyl, C; and root, D), the most important regulatory factors are shown. Schematic seedling cartoons are modified from the pictures in Figure 1.

Figure 4.

Night length strongly affects photomorphogenesis in Arabidopsis seedlings. Hypocotyl length (mm) of 3-d-old Arabidopsis wild-type (Columbia-0) and pifq (pif1-1 pif3-3 pif4-2 pif5-3; Leivar et al., 2008) seedlings, grown in continuous white light (WLc), long days (LD; 16 h light/8 h dark), SDs (8 h light/16 h dark), or continuous dark (Dc). Above the graph are pictures of representative seedlings in the same order. All were grown in continuous temperature (22°C) and a light intensity of approximately 5 μmol m⁻² s⁻¹ photosynthetically active radiation. Scale bar = 2 mm.