The accumulation of the stress metabolite praline in plantago lanceolata as a response to lead pollution

The amino acid proline is known to accumulate in the tissues of several plant species as a result of environmental stress. High concentrations of certain toxic metals are one form of stress that can induce proline accumulation, and in some cases praline accumulation is considered to be an adaptive response to toxic metals by tolerant ecotypes. The proline accumulation responses of Plantago lanceolata (Ribwort plantain) were assessed in individuals taken from lead tolerant and non-tolerant populations when these plants were stressed with applications of lead nitrate solutions. Results suggested that there was no significant difference between the proline levels that had accumulated in the leaves and roots of plants taken from both populations, although proline levels in control plants were significantly lower than in lead stressed plants. Fieldwork, investigating the possibility of a proline gradient along roadside verges as a response to the graduated deposition of lead from motor vehicle exhaust fumes, failed to reveal any significant correlations. The effects of water stress during a dry summer period were thought to be more important at the time the investigation was made.