THE EFFECT OF ZINC ON THE GROWTH AND PHOTOSYNTHETIC APPARATUS OF WHEAT UNDER OPTIMAL AND HYPOTHERMIC CONDITIONS

Abstract

The effect of zinc in a high concentration (1000 µM) on the growth and the photosynthetic apparatus of winter wheat plants (Triticum aestivum L.) was investigated in the laboratory under optimal (22 °C) and low (4 °C) temperatures. It was shown that irrespective of the temperature, zinc in the stated concentration had a pronounced negative effect on the plants, causing a decrease in the content of the main photosynthetic pigments (chlorophylls and carotenoids) in the leaves, and a decline of the potential quantum efficiency ofphotosystem II. In addition, the exposure of the experimental plants to this metal caused a partial closure of stomata and a decrease of the stomatal pore size. These changes, along with other possible modifications and/or disruptions of physiological processes, inhibited the photosynthetic activity and growth of the plants. Where the temperature was optimal, however, the detrimental effect of zinc on the plants was attenuated toward the end of the experiment (3 days). Namely, the rate of photosynthesis, as well as the accumulation of shoot biomass reached a level typical of the control plants. Under hypothermic conditions, on the contrary, the inhibitory effect caused by the simultaneousaction of these two stress factors, which was manifest in a number of the studied growth indices (shoot height and aboveground biomass) and the state of the photosynthetic apparatus (photosynthetic pigments content, rate of photosynthesis, leaf tissue water content) tended to build up. The approximately equal decrease in the values of the maximum quantum yield of the PS II photochemical activity (Fv/Fm) detected experimentally under temperature optimum and hypothermia is obviously connected with the weak dependence of light-dependent reactions on temperature.

Keywords

• triticum aestivum l.
• heavy metals
• low positive temperature
• photosynthesis.