Fig. 2

Autophagosome-like compartments enclosing amyloplasts and lipid bodies during lily pollen germination and tube elongation. Lily pollen grains, subjected to in vitro germination for 60 min (A-B; D-E; and G-H) or in vivo-grown pollen tubes collected from 2-day pollinated styles (C–I), were carefully embedded in Spurr’s resin (A, C, D, F, G-H) or prepared using rapid-freeze and freeze substitution techniques (B, E) for subsequent ultrastructural examination. A-B. Throughout lily pollen germination and pollen tube elongation process, tubular structures originating from the tubular endoplasmic reticulum (ER) double membrane structure, indicated by arrows, encased distinct organelles, specifically amyloplasts (A-C) and lipid bodies (D-F), culminating in the formation of autophagosome-like compartments. Sections of samples prepared using rapid freeze and freeze substitution techniques unveiled autophagosome-like structures encompassing amyloplast (B) and lipid bodies (E). Occasionally, partially digested starch granules (s) and membrane debris (arrow) were found in the vacuolar lumen (v, in G). (H-I) are typical vacuolar lumens containing various stages of engulfed lipid bodies, especially in H starting from on-the-way delivery into the vacuole (I3 and I4), engulfed into the vacuolar lumen (I1 and I2), and digested in the vacuole (I1), I0 signifies the eldest uptaken lipid body with only a small portion of the lipid body is visible within the vacuolar lumen. Significant cellular components are denoted as follows: a: (amyloplast), g (Golgi apparatus), l (lipid body), m (mitochondria), s (starch granule), v (vacuole). Scale bars = 1 μm (A), 0.2 μm (B), 0.1 μm (C), 0.5 μm (D–I)