–SH and S–S involvement in Chlamydomonas mating

Abstract

AbstractReagents that block or cross‐link sulfhydryl (–SH) groups and those that reduce disulfide (S–S) bonds have been tested for their effects on mating in Chlamydomonas reinhardii. Wild‐type (wt) gametes of mating type + (mt+) and mt−, and a fusion‐defective mt− mutant, gam‐11, were studied. Differential sensitivities of mt+ vs mt− and of wt mt− vs gam‐11 mt− were analyzed. Concentrations of reagents that did not disrupt flagellar agglutination, the first stage of the mating reaction, were generally used. Pretreatment of mt+ gametes with the membrane permeable –SH reducing agent dithiothreitol (DTT) inhibits flagellar sexual signaling at concentrations that do not inhibit any part of the mating reaction of mt− gametes. Wt mt− is more sensitive than wt mt+ to inhibition by low concentrations of p‐chloromercuribenzoate sulfonate (pCMBS), an organic mercurial. The membrane‐impermeable reducing agent, reduced glutathione (GSH), also preferentially inhibits wt mt−. Gam‐11 mt−, a fusion‐defective mutant, which has been used to study the sensitivity of the adhesion of the plasma membrane‐associated mating structures, is less sensitive to GSH and pCMBS inhibition that is wt mt−. DDT and pCMBS cause an increase in mating structure adhesion in pretreated gam‐11. The differential inhibition of pair and group formation during gam‐11 × wt mt+ matings has suggested a possible mechanism for mating structure adhesion.