Characterization of a 31 kDa polypeptide that accumulates in the light-harvesting apparatus of maize leaves during chilling

Abstract

A 31 kDa polypeptide that accumulates in the thylakoids when maize leaves are chilled to 5°C in the light is characterized using monoclonal antibodies and analyses of chlorophyll-protein complexes. This polypeptide reacted with a monoclonal antibody, MLH2, that was specific for the 28 kDa polypeptide of the light-harvesting complex (LHCII) of pea leaves. On chilling leaves the appearance of a chlorophyll-protein complex having an apparent molecular weight of 31 kDa coincided with the appearance of a 31 kDa polypeptide and a decrease in the 29 kDa chlorophyll-protein, CP29. Returning the leaves to 25°C for 1 h produced a loss of both the 31 kDa chlorophyll-protein and 31 kDa polypeptide from the thylakoids, and an increase in the amount of CP29. Breakdown of the 31 kDa polypeptide in vitro was Mg²⁺-dependent and inhibited by EDTA and transition metal ions. It is suggested that the 31 kDa polypeptide may be a precursor of the apoprotein of CP29 and can bind chlorophyll. The appearance of the 31 kDa polypeptide correlated with a marked change in the 77 K fluorescence emission spectra of isolated LHCII particles, which did not revert with the disappearance of the 31 kDa on returning the leaves to 25°C for 1 h. The physiological significance of this spectral perturbation is discussed.