Daylength affects both free and conjugated indole-3-acetic acid levels in leaves and flowering in Doritis pulcherrima (orchid)

Total indole-3-acetic acid (IAA) levels (free IAA plus IAA conjugates) in Doritis pulcherrima (Doritis pulcherrima Lindley, cv. S84-335-2) leaves were threefold lower in plants exposed to 30 d of short-day (SD) conditions than in plants exposed to 30 d of long-day (LD) conditions. Free IAA levels were also significantly lower in SD-treated leaves than those in 0 day of photoperiodic treatment and 30 d of LD. Results indicate that plants exposed to 30 d of SD contained significantly higher levels of ester-IAA and reduced amide-IAA concentrations compared to those grown under LD conditions. A high level of ester-IAA and a reduction of amide-IAA in leaves may be related to increased SD floral initiation ability in D. pulcherrima.