Accumulation of the antioxidant indole alkaloid brachycerine under high temperature and high irradiance in leaf disks of Psychotria brachyceras

Abstract

Psychotria brachyceras Müll.Arg. (Rubiaceae) is an understorey shrub of the Atlantic Forest whose leaves accumulate brachycerine, an antioxidant monoterpene indole alkaloid (MIA). This work aimed at evaluating the response of this MIA in leaf disks upon exposure to different temperatures and irradiance, similar to those experienced by the plant in its environment. Leaf disks obtained from growth room-acclimated cuttings were submitted to three distinct series of treatments: 1) Light - two days under control condition (50 μmol.m-2.s-1) in a growth chamber followed by three days treatment of exposure to high irradiance (500 μmol.m-2.s-1); 2) Temperature Cold/Heat – three days under control conditions (25ºC) and then exposure for two days to 10°C or 40°C; 3) Acclimation – gradual heat increase from 25°C up to 40°C. Brachycerine, chlorophyll, and lipid peroxidation levels were not significantly affected by high light or cold exposure, although a decrease in chlorophyll a/b ratio was observed under high irradiance. In contrast, there was increased accumulation of brachycerine at elevated temperatures (where higher cell damage was expected) and significantly lower lipid peroxidation, indicating that this MIA is possibly playing a central role in preventing or mitigating cell damage. A threshold temperature to trigger alkaloid accumulation was identified at approximately 40ºC.