Operates as a K(+)/H(+) antiporter or Na(+)/H(+) antiporter of the chloroplast envelope that functions in pH homeostasis and chloroplast development. Monovalent cation transporter with a preference for Cs(+), K(+) and Rb(+) relative to Na(+) or Li(+). Required for pollen tube guidance, but not for normal pollen development. May also be involved in the development or function of the female gametophyte. PubMed:15220473 shows a localization in chloroplasts while PubMed:21239645 shows a localization in ER. Specifically expressed in flower buds and pollen. Expressed in leaves, roots and stems (PubMed:15220473). Mutants with impaired chloroplast development that display aberrant chloroplast structure (PubMed:15220473). No defect in male fertility, due to redundancy with CHX21. Chx21 and chx23 double mutants are male sterile (PubMed:21239645). Belongs to the monovalent cation:proton antiporter 2 (CPA2) transporter (TC 2.A.37) family. CHX (TC 2.A.37.4) subfamily. The article by Evans et al was retracted by the editors due to concerns over image manipulation, which raised sufficient doubts regarding the credibility of the study.