Abstract
The number of chloroplasts per cell is maintained virtually constant by chloroplast division and chloroplast partition at the time of cell division. Protonema of Physcomitrella patens grows by tip growth or branching. It is also noted that ampicillin decreases number of chloroplasts. But how single large chloroplasts are formed remains unclear. When protonemata of Physcomitrella patens were treated with ampicillin, the number of chloroplasts decreased earlier than expected, assuming equal partitioning. We analyzed chloroplast partitioning at the time of cell division, and found that unequal partitioning occurs preferentially when the number of chloroplasts is small.
