Euploidy in Ricinus

Abstract

The effects of nuclear genome duplication on the chlorophyll-protein content and photochemical activity of chloroplasts and photosynthetic rates in leaf tissue, were evaluated in haploid, diploid and tetraploid individuals of the castor bean, R. communis L. Analysis of this euploid series revealed that both photosystem II (2,6-dichlorophenolindophenol reduction) and photosystem I O2 uptake (N,N,N'',N''-tetramethyl-p-phenylenediamine to methyl viologen) decreases in plastids isolated from cells with increasingly larger nuclear complement sizes. Photosynthetic O2-evolution and 14CO2-fixation rates in leaf tissue from haploid, diploid and tetraploid individuals also decreased with the increase in size of the nuclear genome. Six chlorophyll-protein complexes, in addition to a zone of detergent complexed free pigment, were resolved from sodium dodecyl sulfate-solubilized thylakoid membranes from cells of all 3 ploidy levels. In addition to the P700-chlorophyll a-protein complex and the light-harvesting chlorophyll a/b-protein complex, 4 minor complexes were revealed, 2 containing only chlorophyll a and 2 containing both chlorophyll a and b. The relative distribution of chlorophyll among the resolved chlorophyll-protein complexes and free pigment was similar for all 3 ploidy levels.