Figure 2.

Progressive Import of Actin in Cotyledon Mitochondria during Seed Germination.

(A) Actin associated with mitochondria isolated from mung bean cotyledons (from which the embryo was completely removed) of early germinated seeds was slightly sensitive to proteinase K (left section) and highly sensitive to high-salt (right section) treatment. It became resistant to both treatments when the mitochondria were harvested from cotyledons after 1 d of seed cultivation. Cotyledon mitochondria purified from seeds immersed at 4°C for 12 h, at 4°C for 12 h plus 27°C for 2 h, and at 27°C for 12 h and 1-d-old seedlings were then treated with proteinase K (10 μg mL⁻¹) and KCl (1.2 M) and analyzed by immunoblotting as described in Figure 1.

(B) Progressive import of actin into cotyledon mitochondria during seed germination and stability of actin levels in mitochondria of 1- to 4-d-old cotyledons. Cotyledon mitochondria were purified from seeds immersed at 4°C for 12 h and at 27°C for 12 h and from 1- to 5-d-old seedlings. Mitochondria were treated with proteinase K (10 μg mL⁻¹) and KCl (1.2 M) and analyzed by immunoblotting as described in Figure 1. The presence of cytosolic actin during cotyledon aging and seed germination was also analyzed (bottom row of left section). Two and three independent experiments were performed for the above study in (A) and (B), respectively. Equivalent results were obtained, and only one is presented here.

(C) Ultrastructures of cotyledon mitochondria during early seed germination reveal reorganization of mtDNA from invisible to chromatin-like or fibril-like structures in seeds immersed at 4°C for 12 h and at 27°C for 12 h or 1-d-old seedlings (indicated by arrows), respectively.