The effect of methyl jasmonate on selected physiological parameters of copper-treated Phaseolus coccineus plants

Abstract

Phaseolus coccineus plants in the early growth stage were preincubated with 10−5 M methyl jasmonate (MJ) for 1 or 24 h and subsequently transferred to a Hoagland solution or treated with 50 or 100 μM copper (Cu). After 6-day exposure to the metal, plant growth, relative water content, electrolyte leakage, the content of Cu and photosynthetic pigments, and chlorophyll fluorescence parameters were assayed. Generally, under Cu excess, MJ did not modulate growth parameters such as leaf area, root growth, shoot and root fresh weight, and the shoot/root fresh weight ratio. The content of chlorophyll a, b, and carotenoids increased with the increasing Cu content in the leaves. However, a correlation between the reduction of the leaf area and the lower content of the three photosynthetic pigments for 24-h MJ + 100-µM Cu treatment compared with metal alone was noted. The decrease in the Cu concentration was MJ-dependent only after 1-h MJ + 50-µM Cu treatment in leaves and after 24-h MJ + 100-µM Cu treatment in roots. Chlorophyll fluorescence was a weak indicator of the effect induced by MJ in Cu excess, and the most spectacular increase was observed for 1-h and 24-h MJ + 50 µM Cu in the LNU and for 1-h MJ + 50 µM Cu in the NPQ parameter. These results suggested a lack of a clear pattern for MJ altering the Cu stress in the runner bean plants. The most important finding was that photosynthesis seemed to be quite resistant to Cu stress and slight modifications in chlorophyll fluorescence were accompanied by significant changes in growth parameters, photosynthetic pigment content, and metal content in the plant. The results obtained may have been strongly related to the plant growth stage, as the measured parameters transform greatly during plant growth and development.