Abstract:
Developmental rates of pigment–protein complexes and of thylakoid electron transfer chain components were investigated during the greening process of etiolated leaflets of young maize (Zea mays L.) and barley (Hordeum vulgare L.) plants, while treating them with herbicides and heavy metals in toxic amounts. Investigation of the functional state and energetic efficiency of the thylakoidal components, involved in the photochemical reactions, was based on the induced chlorophyll–fluorescence parameters. We found that with no herbicides present in the watering solutions and under a constant light of 600 μmol m–2 s–1 photon flux density, both plant species needed only 24 or less hours to develop enough pigment–protein complexes and thylakoidal electron transfer chains to achieve efficient photochemical energy conversion. Despite the abrupt rise of the efficiency of the photochemical reactions, the chlorophyll content of the leaves and the a/b chlorophyll ratio increased only gradually in the four–day experimental period. When supplying the developing plantlets with different photosynthesis–inhibiting herbicides, the photochemical efficiency and the chlorophyll content of developing leaves of barley plantlets were negatively affected by 10 μM DCMU, but they were unaffected by the presence of 100 μM CdCl2. In the presence of 100
μM CuCl2 and of 10 μM paraquat (also called methylviologen, MV) the greening leaves of the barley plants exhibited efficient photochemical reactions, high chlorophyll content but a slowly increasing a/b chlorophyll ratio. The maize plants showed disturbed photochemical reactions in the presence of both herbicides (DCMU and MV), but only beginning with the fourth day of the experiment.
