Response of Chloroplasts and Photosynthetic Mechanism of Bean Plants to Excess Arsenic in Soil

E. MITEVA1 and M. MERAKCHIYSKA2
1 Plant Protection Institute, Department of Radiobiology and Technogenic Pollution, BG-2230 Kostinbrod, Bulgaria
2 Institute of Plant Physiology, Bulgarian Academy of Sciences, BG-1113 Sofia, Bulgaria

Abstract

MITEVA, E. and M. MERAKCHIYSKA, 2002. Response of chloroplasts and photosynthetic mechanism of bean plants to excess arsenic in soil. Bulg. J. Agric. Sci., 8: 151–156

The study traced out the response of the structure and functional activity of the photosynthetic mechanism of bean plants (Phaseolus vulgaris L.) to excess arsenic in soil. Arsenic was applied to soil as As2O3 in concentrations of 25, 50 and 100 mg.kg–1. It was established that increased arsenic concentrations caused an alteration of the chloroplast shape, manifested in its rounding and shortening of the longitudinal axis. Other manifestations were concave membrane, formation of grana with an increased number of thylakoids and their expansion, bending and partial destruction as well as changes in the accumulation and flow of assimilates. Arsenic concentration in soil of 25 mg.kg–1 did not have a negative effect on the photosynthetic process. The higher doses of 50 and 100 mg.kg–1, however, inhibited it to a considerable degree (42% and 32%, respectively). In all variants, transpiration was enhanced, the higher values being reported for the concentration of 100 mg.kg–1 but stomatal resistance was slightly reduced. All these process in the structural and functional activity of the photosynthetic mechanism are similar to changes in plants, observed under the effect of other stress factors such as heavy metals, temperature and water stress.

Key words: arsenic, arsenic toxicity, heavy metals, stress, chloroplasts, photosynthesis, transpiration