Changes in the chlorophyll fluorescence characteristics of chloroplasts from intact pumpkin cotyledons, caused by organ excision and kinetin treatment

The chlorophyll (Chi) fluorescence emission as well as excitation and polarization characteristics of chloroplasts from intact cotyledons were determined in pumpkin seedlings after removal of one cotyledon (co-cotyledon) or apical bud or primary root, or after kinetin treatment of derooted seedlings. Qualitatively, the fluorescence emission and excitation spectra of chloroplasts were similar. The fluorescence emission spectra showed a maximum at 685 (F-685) and a hump at 735 nm (F-735), whereas the excitation spectra showed peaks at 439, 471, 485, and 676 nm. The fluorescence intensities at F-685 and F-735 differed in various groups of seedlings, as indicated by changes in their ratios. Similarly, the ratios of 471/439, 485/439, and 676/439 nm were also different. Variability in the Chi fluorescence intensity values and the fluorescence polarization of chloroplasts prepared from various seedling types may suggest a different degree of binding between the pigment complexes and light-harvesting Chi-protein (LHCP), resulting in different rates of photoexcitation energy loss in the form of fluorescence emission. Kinetin treatment improved the coupling of pigment complexes with reaction centre, as indicated by low polarization values in derooted and kinetin-treated seedlings, which suggests the development of a suntype chloroplast.