DIFFERENCES IN THE ETIOPLAST ULTRASTRUCTURE AND CHLOROPHYLL BIOSYNTHESIS TIME-COURSE OF COLD TOLERANT AND COLD-SENSITIVE MAIZE LINES UNDER COLD TREATMENT

For a better understanding of the origin of different cold stress resp onses of certain maize lines, low-temperature fluorescence spectroscop y and electron microscopy was done on dark-grown and illuminated leave s. The plants of both lines were grown in darkness at 25 degrees C for 7 days, then kept at 12 degrees C for 6 hours. After cutting out non- illuminated samples from the leaves, other groups of leaf segments wer e illuminated by two consecutive light flashes and samples were taken after different time periods of darkness at 12 degrees C. For comparis on, the same procedure was done keeping the plants at 25 degrees C dur ing the whole run of the experiment. An analysis of the low-temperatur e fluorescence spectra of the leaves showed a difference between the c old sensitive and cold tolerant lines at 12 degrees C, but not at 25 d egrees C, in respect of the relative amounts of the protochlorophyllid e forms. After illumination, a delay in the Shibata-shift was found in the cold sensitive line at 12 degrees C. Electron microscopy showed d ifferences in prolamellar body disintegration, depending on the cold s ensitivity and the applied temperature.