Synthesis of chlorophyll and photosynthetic competence in etiolated and greening seedlings of Larix decidua as compared with Picea abies

Abstract

Summary The development of the photosynthetic apparatus was studied in seedlings of Picea abies and Larix decidua grown both in darkness and in light. In light the pattern of differentiation was similar in the two species, and mature chloroplasts showed a well developed thylakoid system arranged into granal and intergranal regions. In the dark, etio-chloroplasts were formed that had different lamellar and tubuliform membrane amounts in the two species. Spruce chloroplasts contained small prolamellar bodies and many thylakoids; in L. decidua chloroplasts, voluminous prolamellar bodies and only a few thylakoids were formed. Fluorescence emission spectra of cotyledons at 77 K as well as pigment analyses showed different behaviour of L. decidua compared with P. abies when grown in the dark. When etiolated seedlings were exposed to the light, the rate of phototransformation of the etio-chloroplast and the achievement of photosynthetic functionality was fast in spruce and slow in larch. Spruce cotyledons attained normal values of in vivo chlorophyll fluorescence characteristics, i.e. Fv/Fm and quenching coefficients qP and qNP within 1.5 hours of light exposure; with larch, the control value of qP was reached much more quickly (ca 3 h) than that of Fv/Fm (ca 20 h), indicating that PS I becomes fully active before PS II. After exposure to light, etiolated larch seedlings behave like those gymnosperms lacking the ability to synthesize chlorophyll in the dark.