EFFECTS OF CHILLING ON EPISCIA AND DIEFFENBACHIA

Leaves of chilled 'Moss-Agate' Episcia (Mart.) plants exhibited direct chilling injury (i.e., watersoaked browning of leaf blade interveinal areas within 24 h of exposure to low temperature) immediately followi ng exposure in darkness to 10C for 0.5 or 1.0 h. Chlorophyll fluoresce nce peak : initial ratios and terminal : peak ratios of chilled Episci a were reduced 20% and 25%, respectively, 3 h after chilling, a result suggesting possible photosystem II damage. Total leaf chlorophyll con tent was reduced by 17% within 3 h of chilling and CO2 uptake also was reduced at this time. Leaves of chilled 'Rudolph Roehrs' Dieffenbachi a maculata (Lodd.) (D. Roehrsii Hort.) plants expressed no visible inj ury within 24 h of 1.2C chilling in darkness for 36,48, or 60 h, but C O2 uptake was reduced by 70% compared to the control 3 h after chillin g. Visible injury began to appear 27 h after chilling, and the older l eaf blades of all chilled plants exhibited a watersoaked appearance 75 h after chilling. Chlorophyll fluorescence peak : initial ratios of c hilled Dieffenbachia did not vary, and terminal : peak ratios were not reduced until 147 h after chilling, when the injured tissue was extre mely flaccid and translucent. Chilling reduced the chlorophyll content of Dieffenbachia by 10% in some plants 27 h after chilling and by 35% in all plants 75 h after chilling. Transpiration rate was reduced and stomatal diffusive resistance increased 27 h after chilling.