Development of photosynthetic activities in dark-grown spruce seedlings

The chloroplasts in dark-grown, 5-day-old seedlings of Piceaabies contained doubly stacked primary thylakoid membranes connectedwith prolamellar bodies. The photo-system II reaction centerand photosystem II-associated electron transfer were assembledin the primary thylakoid membranes, but the oxygen-evolvingsystem remained latent unless the seedlings were exposed tolight. The photoactivation of this system was strongly dependenton temperature during pre-illumination. This implies that somethermal process, in addition to the photoprocess, is involvedin the photoactivation of the oxygen-evolving system. ¹Laboratory of Plant Physiology, The Institute of Physical andChemical Research, Wako-shi, Saitama 351, Japan. ²Department of Biology, Fukuoka Dental College, Fukuoka 814,Japan. (Received June 22, 1977; )