Heat stress and spermidine: effect on chlorophyll fluorescence in tomato plants

Two tomato (Lycopersicon esculentum L.) cultivars: Robin (tolerant) and Roma (sensitive to heat stress) were studied. Chlorophyll fluorescence induction parameters (Fv/Fp, A(max), and Rfd) at 25 degreesC showed that the PS2 activity was similar for both cultivars. The parameters, measured at 38 degreesC, decreased in both cultivars, but more in cv. Roma. Exogenous application of 4 mM spermidine improved the plant heat-resistance in both cultivars, and especially in cv. Roma. Analysis of chlorophyll fluorescence changes during linear increase in temperature showed that cv. Robin plants have higher ability to hardening and higher resistance to thermal damage of the pigment-protein complexes structure and the activity of PS2 than cv. Roma.