Changes in the Pigment Composition of the Thylakoids of Phaseolus vulgaris Leaves During Chloroplast Development

Abstract

The formation of thylakoids is a multistep process. First, the cores of PSI and PSII units are formed, followed by the formation of LHCP and CPIa (Akoyunoglou 1982). Chlorophyll synthesis starts upon illumination, whereas the carotenoids are already present in the etiolated tissue in considerable amount (Tsimilli-Michael, Akoyunoglou 1978) and part of them — mainly xanthophylls — are located in the osmiophilic plastoglobuli (Lichtenthaler 1969b), whose number decreases during greening (Lichten-thaler 1969a). Earlier studies in our laboratory (Tsimilli-Michael, Akoyunoglou 1978) have shown that when etiolated leaves are exposed to continuous light (CL), the chlα/car and xanth/β-car ratios change during greening. The question is, whether these changes reflect changes in the thylakoid pigment composition. Our results showed that the relative pigment composition of the plastoglobuli-free thylakoids of etiolated plants directly exposed to CL remains constant throughout the greening process (from 3 hrs in CL and on). The relative pigment composition of the primary thylakoids formed under intermittent illumination (LDC) is different from that of the green control and moreover, it changes as exposure in LDC increases, the only exception being the chip/car ratio, which remains constant throughout LDC and the same as in the green control. The relative pigment composition of etiolated plants preexposed to LDC and then transferred to CL, either reaches the corresponding composition of the green control (28 LDC+CL), or not (86 LDC+CL).