APPEARANCE OF LONG-WAVELENGTH EXCITATION FORM OF CHLOROPHYLL-A IN PS-I FLUORESCENCE DURING GREENING OF BARLEY LEAVES UNDER CONTINUOUS LIGHT

The development of light harvesting complexes (LHCs) of both photosyst ems in the course of greening of barley leaves was investigated using the following three typical changes in 77 K chlorophyll a (Chl a) fluo rescence spectra: (i) shift of PS I emission maximum to 741-743 nm tog ether with its substantial increase; (ii) relative increase of Chl b e xcitation maximum in the Soret region; (iii) shift of the red Chl a ex citation maximum from 677 to 680 nm. Moreover, a pronounced long-wavel ength excitation maximum of Chl a, E698, appeared in the red region of 77 K excitation spectrum for photosystem (PS) I emission after 32 h o f greening. The rise of E698, which was observed for the first time as a main excitation maximum in the red region of the excitation spectru m for fully green barley leaves, is related to an increasing efficienc y of energy transfer from LHCs to Chl a forms fluorescing both at 685 nm and 743 nm. For broken chloroplasts isolated from mature barley lea ves the E698 band disappeared almost completely from the excitation sp ectrum and a pronounced decrease of the efficiency of energy transfer from Chl b to fluorescing Chl a occurred both within PS II and PS I. T hese findings support the relation between the appearance of E698 in t he excitation spectrum of Chl a fluorescence originating from LHC I an d a high functional integrity of LHCs. (C) 1997 Elsevier Science S.A.