Chlorophyll(ide) forms after partial phototransformation of protochlorophyll(ide) in etiolated wheat leaves

Abstract

Dark‐grown wheat leaves (Triticum L. cv. Starke II Weibull) were illuminated repeatedly with light flashes giving partial phototransformation of protochlorophyllide to chlorophyllide. After short flashes (e.g. 15 ms red light, 250 W m−2), transforming only a minor part of the protochlorophyllide present, the first more stable chlorophyll(ide) measured ca 15 s after the phototransformation had its absorption maximum in the red around 672 nm. It stayed there during the following 30 min in darkness. After longer flashes (e.g. 125 ms), transforming a larger portion of the protochlorophyllide, the chlorophyll(ide) formed had its maximum absorption more towards 684 nm and shifted to 672 nm during a subsequent period in darkness. Thus, in this case a Shibata shift took place.The conditions which produce the “stable” 672 nm form, without a Shibata shift, are discussed. The presence of large amounts of non‐transformed protochlorophyllide remaining after the phototransformation seems to be important. Under such conditions it is possible that the Shibata shift is completed within a very short time.Also the possible existence of two kinds of phototransformable protochlorophyllide is discussed. According to this idea one of the two protochlorophyllide forms produces a chlorophyllide absorbing at 672 nm shortly after phototransformation without having passed a Shibata shift. The other protochlorophyllide form photo‐transforms to a chlorophyllide which proceeds through the Shibata shift.