Specificity of Cd, Cu, and Fe effects on barley growth, metal contents in leaves and chloroplasts, and activities of photosystem I and photosystem II

Abstract

Cd, Cu, and Fe were used to reveal the specificity of their toxic actions. We studied the effects of heavy metals on the growth of barley seedlings, contents of cations in leaves and chloroplasts, induced chlorophyll fluorescence and P700 light absorption. Differences were found at each level of research. We measured the contents of Cd, Cu, Fe, Mn, Zn, Ca, Mg, and K. The proportion of cations in leaves targeted to chloroplasts varied from 0.1% (K) to >90% (Fe). Their levels changed in different ways. We found no correlation between changes in cation contents in leaves and chloroplasts. Treatment with Cd, Cu, and Fe increased the contents of some cations. The extra portions were targeted primarily out of chloroplasts, which was most noticeable in the case of Cu and Fe. Cd treatment decreased non-photochemical quenching with concomitant increases in closed photosystem II. We introduced new coefficients qC for closed photosystem II and X(II) to compare the yields of photosystem II and photosystem I. Cd likely decreased both PSI content in leaves and its quantum yield. In control plants, the quantum yield ratio of PSI/PSII increased gradually from 1.25 under low light to 4 under high light. Cd treatment prevented the increase under moderate light; under high light the ratio reached 2. Cu treatment increased the acceptor side limitation of photosystem I under low light; components of the Calvin cycle likely demand more light for activation in Cu-treated plants.