$re = '/\d+(?:[.,]\d+)*\s*mu|kinetin|zeatin/m';
$str = 'high-frequency somatic embryogenesis was achieved from an embryogenic cell suspension culture of acanthopanax koreanum nakai. stem segments were cultured on murashige and skoog (ms) medium containing auxins and cytokinins. opaque and friable embryogenic callus formed on ms medium with 4.5 mu m 2,4-dichlorophenoxyacetic acid (2,4-d) and 2.0 mu m kinetin or zeatin, but was highest on medium containing 4.5 mu m 2,4-d alone.';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php