The metabolism and subcellular organization of the jack pine embryo (Pinus banksiand) during germination

Abstract

Water imbibed by jack pine seeds induced rapid oxygen uptake and over 95% germination. As cells of cotyledons expanded and divided the redistribution of carbohydrates, proteins, and nucleic acids, followed cytochemically, corresponded to changes in subcellular organization.In dormant cotyledons, cells lacked chloroplasts and were packed with lipid reserves, protein bodies, and amyloplasts. After 96 h of imbibing water, storage materials were consumed as new cytoplasm appeared and numerous polysome-like particles extended from the nucleus into the cytoplasm. Levels of acid-soluble nucleotides, RNA, and DNA increased up to the fourth day of germination coinciding with the completion of the first mitotic cycle. RNA was concentrated in phragmosomes and at the newly formed cell plates. Acidic proteins, found mainly in the protein bodies of dry cells, were now localized in nucleoli. Histones were associated mainly with chromosomes, although in dormant cells, reserve protein, rich in arginine, occurred in protein bodies Proplastids, which eventually developed into chloroplasts, remained close to the nucleus until most reserves in the cytoplasm were depleted.As cotyledons became independent of the nutrition of the female gametophyte, the cytoplasm of proliferating cells contained more mitochondria, a rough endoplasmic reticulum, ribosomes, golgi bodies, and chloroplasts with up to four starch grains. After 10 to 12 days, the cytoplasm appeared at the periphery of cell walls as a result of the accumulation of water in a large vacuole.