Leaf senescence in a non-yellowing mutant of Festuca pratensis : I. Chloroplast membrane polypeptides

Soluble and thylakoid membrane polypeptides from senescing leaf tissue of Rossa, a normal yellowing Festuca pratensis genotype, were fractionated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and compared with those of the non-yellowing mutant Bf 993. Subunits of ribulose-1,5-bisphosphate carboxylase were the major soluble polypeptides and declined to low levels in senescing leaves of both genotypes. The major thylakoid polypeptides were those associated with the chlorophyllprotein complexes CPI and CPII. The levels of all thylakoid polypeptide species fell during senescence of Rossa leaf tissue but Bf993 lamellae retained CPI, CPII and a number of other hydrophobic low molecular weight polypeptides. The increasing hydrophobicity and decreasing protein complement of Bf 993 thylakoids were reflected in a fall in membrane density from 1.16 to 1.13 g cm(-3) over 8 d of senescence and a decline in the extractability of chlorophyll-containing membranes in the same period. In Bf993 the molar ratio of chlorophyll to hydrophobic membrane protein increased from 92 at day 0 to 296 at day 8. In the same time the ratio for Rossa increased from 88 to 722 and 8 d-senesced Rossa tissue yielded less than 2% of the solvent-soluble protein it contained at day 0 as compared with 24% for the protein of Bf993. These results are discussed in relation to the nature of the non-yellowing lesion.