Phytochrome control of its own accumulation and leaf expansion in tentoxin‐ and norflurazon‐treated mung bean seedlings

Primary leaves of 4‐day‐old, dark‐grown mung bean [Vigna radiata (L.) Wilczek cv. Berken] seedlings were exposed to 24 h of white light (200 μmol m−2 s−1) which was terminated by a 15 min, phytochrome‐saturating red or far‐red light exposure. Phytochrome content (in vivo and in vitro) and leaf area were monitored during the subsequent dark period. Red light treatments resulted in lower phytochrome content and greater leaf expansion than did far‐red treatments. Phytochrome accumulation and leaf expansion were less in norflurazon‐ (no carotenoids and very low Chl) than in tentoxin‐ (very low Chl) treated leaves. After 3 days of darkness, leaf expansion was about 25% greater and phytochrome content was about 50% less in red‐ than in far‐red‐treated leaves of all treatments. These effects generally took longer to develop in norflurazon‐ than in tentoxin‐treated tissues. Norflurazon‐treated tissues exposed to long white light periods apparently do not as accurately reflect phytochrome‐controlled photomorphogenic events of green tissues as do tentoxin‐treated tissues of mung bean seedlings.