Temperature-induced absorbance changes in developing barley chloroplasts

Absorbance changes on cooling and heating of barley ( Hordeum vulgare L. cv. IB65) chloroplasts greened for 12, 48 and 72 h were investigated to understand the structural changes during biogenesis of chloroplast membranes. Upon cooling the chloroplast suspension from 24 to 8°C, a positive absorbance change occurred at 678, 435 and 495 nm in 12, 48 and 72 h greened chloroplasts. During heating from 24 to 45°C negative absorbance changes were observed with some shifts in positions in different chloroplast preparations and a simultaneous increase in absorbance between 690 and 735 nm. For chloroplasts developed for 12, 48 and 72 h the changes in absorbance on cooling were 3.8, 3.3 and 1.9% at 678 nm, and on heating, 8.9, 8.3 and 4.1% at 680 nm.
The differences in absorbance changes are considered as an indication of variations in the structural organization and composition of developing chloroplasts. The reversibility of the absorbance changes was maximum in chloroplasts greened for 72 h and minimum in chloroplasts greened for 12 h. This would suggest that fully developed chloroplasts have more flexibility towards temperature-induced changes in the membranes.