Changes in growth pattern and phenol levels were studied in sal seedlings in response to low temperature (9–14.1°C, night temp.) in the field and under greenhouse conditions (Temp. 30–32°C, RH 70–76%, Light intensity 33523 Lux). Constant exposure of field grown seedlings to low-temperature (during November to March) resulted in injury. Nearly 80–86% seedlings exhibited desiccated, necrotic leaves and shoots along with severe reduction in dry mass. Abrupt increase in the phenol levels (1.8–2.2 folds) was discernible both in the leaves and shoots with the drop in air temperature below 14.1°C. Overproduction of phenols in aerial parts during this period commensurate with both enhanced activity (1.5 and 1.7 folds in the leaves and shoots respectively) of its synthesizing enzyme L-phenylalanineammonia lyase (PAL) and simultaneous reduction (8 and 13 folds in the leaves and shoots, respectively) in its degrading enzyme polyphenol oxidase (PPO). As a result, accumulation of excess levels of phenolics culminates into irreversible injury in aerial parts of sensitive sal seedling in response to low-temperature that is one of the causes of mass scale mortality in these seedlings.
Low temperature injury, L-phenylalanine ammonia lyase, phenols, polyphenol oxidase, Shorea robusta
