FORMATION OF SHORT-WAVELENGTH CHLOROPHYLL(IDE) AFTER BRIEF IRRADIATION IS CORRELATED WITH THE OCCURRENCE OF PROTOCHLOROPHYLL(IDE)(636-642) IN DARK-GROWN EPICOTYLS AND HYPOCOTYLS OF BEAN (PHASEOLUS-VULGARIS)

Chlorophyll formation capacity along the seedling of bean (Phaseolus v ulgaris L. cv. Brede tender draad) was investigated. After 7 days of i rradiation a gradient was formed, where the primary leaf contained ca 300 times more chlorophyll per gram fresh weight than the lower hypoco tyl section and ca 20 times more than the epicotyl. Similar chlorophyl l gradients but at lower levels were seen when the seedlings were firs t placed in darkness for 7 days and then irradiated for 1, 2 or 7 days . Ultrastructural investigation of seedlings grown for 7 days in darkn ess and then irradiated for 24 h revealed a more developed inner membr ane system with grana stacks in plastids of cells in the uppermost hyp ocotyl section compared to plastids of cells in lower hypocotyl sectio ns. The higher up on the seedling the more the ratio increased of prot ochlorophyll(ide) emitting at 657 nn to short-wavelength protochloroph yll(ide). After flash irradiation of the different sections, fluoresce nce emission spectra with maxima at 680 and 690 nm, respectively, were observed, indicating the formation of short- and long-wavelength chlo rophyll(ide) forms. The lower the ratio of protochlorophyll(ide) emitt ing at 657 nm to the short-wavelength protochlorophyll(ide), the less long-wave length chlorophyll(ide) was formed after irradiation. Howeve r, after continuous irradiation long-wavelength chlorophyll(ide) was f ormed. In dark-grown roots, where only short-wavelength protochlorophy ll forms were present, it was not possible to transform protochlorophy ll to chlorophyll by flash irradiation. Possible explanations for this phenomenon are discussed.