Microcalorimetric evaluation of metabolic heat rates in coffee (Coffea arabica L.) roots of seedlings subjected to chilling stress

In numerous tropical and sub-tropical plant species, such as coffee, exposure to low temperatures can cause extensive tissue damage, the seedlings being particularly sensitive to chilling stress. This condition usually induces changes in the metabolic rates, and there are indications that this process can be evaluated by monitoring heat evolution by microcalorimetry. We studied the responses of coffee seedlings to chilling stress by measuring root growth and metabolic heat rates in apical root segments of coffee seedlings exposed for 6 days to temperatures ranging from 5 to 25°C. The metabolic heat rates were measured in a heat conduction calorimeter. Root growth was progressively hindered as the seedlings were exposed to temperatures below 15°C; low temperature-induced growth inhibition was closely correlated with the lowering of metabolic heat rates. An Arrhenius plot of metabolic heat rate revealed a break in the line at 15°C, suggesting the occurrence of a metabolic transition at this temperature. The microcalorimetric technique provides a sensitive, non-invasive method for evaluating plant growth responses to chilling stress.