EFFECTS OF CHILLING ON CHLOROPLAST DEVELOPMENT IN BARLEY PRIMARY FOLIAGE LEAVES

Effects of chilling on chloroplast development were investigated in ap ical sections of barley primary foliage leaves. During chloroplast dev elopment at 23 degrees C photosynthetic capacity per unit chlorophyll decreases while PSII efficiency and chlorophyll content increase until day 8 after sowing. Thereafter, constant values are reached. Cold tre atment at 5 degrees C retards the decrease in photosynthetic capacity per unit chlorophyll and the increase in total chlorophyll content occ urring in the first phase of chloroplast development. PSII efficiency is affected even more drastically: it slightly decreases during the fi rst day after transfer to 5 degrees C and then stays constant for at l east 7 further days. Due to these impacts on chloroplast development, cold-treated chloroplasts exhibit a higher photosynthetic capacity per unit chlorophyll, a smaller chlorophyll content per fresh weight and a decreased efficiency of PSII centers. Besides the retardation of dev elopmental processes, two specific impacts of cold treatment on the ph otosynthetic apparatus have been observed. On the one hand, immunologi cal analysis of PSI and PSII content revealed a decrease in the level of PSI centers after exposure to 5 degrees C. Spectrophotometric analy sis confirmed this result, showing that the PSII/PSI ratio is clearly increased after cold treatment. On the other hand, immunological analy sis also revealed a distinct reduction in the amount of CP 29, which p lays an important role in energy transfer to PSII centers. This reduct ion correlates with the low efficiency of PSII centers in cold-treated plants. The results demonstrate that besides retarding chloroplast de velopment chilling has a specific impact on the organization of the ph otosynthetic apparatus.