Spectroscopic properties of protochlorophyllide analyzed in situ in the course of etiolation and in illuminated leaves

The spectroscopic properties of photoactive (ie. flash-transformable) and n onphotoactive protochlorophyll(ide)s (Pchl(ide)) were reinvestigated during the development of bean leaves in darkness. Two phases in the process of P chl(ide) accumulation were apparent from quantitative measurements of pigme nt content: a lag phase (first week) during which photoactive Pchl(ide) acc umulated faster than nonphotoactive Pchl(ide); and a fast phase (second wee k), showing parallel accumulation of both types of Pchl(ide). 'Flashed-minu s-dark' absorbance difference spectra recorded in situ at 77 K showed that P650-655 was the predominant form of photoactive protochlorophyllide regard less of developmental stage. Quantitative analysis of energy migration proc esses between the Pchl(ide) forms showed the existence of energy transfer u nits containing a 1:8 ratio of nonphotoactive and photoactive Pchl(ide)s du ring development. Gaussian deconvolution of in situ 77 K fluorescence spect ra indicated that the 633 nm band of nonphotoactive Pchl(ide) was made of f our bands, at 625, 631, 637 and 643 nm, whose relative amplitudes only slig htly changed during development. The emission band of photoactive Pchlide w as also analyzed using the same method. Three components were found at 644, 652 and 657 nm, The emission band of P650-655 included the last two compon ents, which become predominant only in fully etiolated plants. Photoactive Pchlide with an emission maximum at 653 nm was detected in the light during development of leaves of photoperiodically grown plants.