Summer 2011 Dhalia Field Projects
Meta-report 6: Investigating the Impact of Light on Stem Anthocyanin

Foil covered dhalia (left) with control dhalia

Introduction

        This experiment has been performed on many varieties over the years. The purposes this summer were to test new varieties and to establish the phenocritical period. Seven days always gave a strong phenotype for light-dependent varieties.

1. Petal edge pigmentation is light-independent in CG Real.

Figure 1. CG Regal, natural experiment of a full sun (right) and shade flower (left). The shade bloom has strong pigmentation along the petal margin, but little pigmentation in the main field of the petal.

Figure 2. CG Regal, foil covered for 7 days. Foil is placed over just ready to open buds. Note the outer petal margin has purple anthocyanin; this is likely to be light-independent pigmentation. The main petal field is light-dependent for anthocyanin pigmentation. This confirms the "natural" experiment of a mainly in the shade flower.

2. Valley Porcupine pigmentation on petal tips and margins is light-dependent.

Figure 3. Full sun Valley Porcupine has bright pink petal tips and edges, shading to a warm yellow-pink petal base. The backs and tips of petals synthesize pigment in a light-dependent manner during floral opening.

Figure 4. Foil covered Valley Porcupine (left) and close-up view (left). Not the absence of pigmentation in most petals and petal edges. There is faint pigmentation on some petals, possibly caused by a few photons that penetrated the sepals prior to foil covering.

Figure 5.Foil set up on Valley Porcupine with match opening buds nearby for comparison.

3. Bracken Lorelei. Foil covered flower on the right, sun-exposed on the left. Note that the orange anthocyanin pigmentation depends on light. Yellow pigment is the first step in the anthocyanin biosynthetic pathway; white represents achieving step 2 (or any step through ~step 7). The results suggest that in the foil covered flower the anthocyanin pathway is activated, but only the first few steps occur. In many dicot plants, there is separate control of the initial steps and the later steps in the pathway. This could be true in dahlias. It is also very interesting that the patterns of yellow and white "stripes" on the foil-covered flower (right) are mainly along the long axis of the petal, following the veins.

Figure 6. Foil covering of an entire branch of Smooth Operator, on the right. Green chlorophyll pigmentation is reduced, and purple anthocyanin pigmentation is dramatically reduced. The small picture on the left illustrates that giant foil covering required to shield a stem and its leaves in Bracken Lorelei.

5. Ferncliff Illusion stem after 7 days being foil-wrapped. The control tissue is above and below the wrapping. Stem compression occurred because of the tightly wrapped foil

6. CG Regal foil wrapping; after 7 days most pigment is lost but there there is slight purple pigmentation.

7. Penhill Dark Monarch is highly light dependent in the stem.

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