Lincomycin‐induced alteration in the contents of chlorophyll‐protein complexes of dimorphic maize chloroplasts and its effect on the temperature‐induced spectral changes

Abstract

The difference spectroscopy technique has been utilized to investigate the temperature‐induced spectral changes in mesophyll and bundle sheath chloroplasts of maize (Zea mays L. cv. Ganga‐5) in order to assess the role of different pigment‐protein complexes in the manifestation of temperature effect on the chloroplast membranes. Cooling and heating of both mesophyll and bundle sheath chloroplasts resulted in absorbance difference (AA) bands at similar wavelengths but the degree of absorb‐ance changes were significantly higher in bundle sheath chloroplasts. For example, upon cooling to 7‐8°C, positive AA bands were observed at 440, 490 and 680 nm in mesophyll chloroplasts and at 440, 495–500 and 680 nm in bundle sheath chloroplasts but the absorbance change at 680 nm was ca 2% in mesophyll chloroplasts, whereas it was ca 5% in bundle sheath chloroplasts, which have a lower content of light‐harvesting pigment‐protein complex. The role of chlorophyll‐protein complexes was further investigated by monitoring the temperature‐induced spectral changes of mesophyll and bundle sheath chloroplasts isolated from lincomycin‐treated maize plants where lincomycin selectively inhibits the biosynthesis of specific chlorophyll‐protein complexes. Results indicated that depletion of certain pigment‐protein complexes in mesophyll chloroplasts made them more susceptible (a ca 4% vs ca 2% absorbance change upon cooling and a ca 6% vs ca 4% absorbance change upon heating) and less tolerant to temperature variation (a 76% vs 39% reversibility during ambient→Cooling→ambient temperature cycle). The data indicate that pigment‐protein complexes play a significant role in protecting the chloroplast membranes against temperature variation.