Aluminum effects on embryo suspensor polytene chromosomes of Phaseolus coccineus L

Abstract

Aluminum (Al) represents a widespread environmental pollutant, with severe toxic impacts on plants. In this study, we documented for the first time the structural and functional responses induced by two concentrations of AlCl₃ (10⁻² M and 10⁻¹ M) in the polytene chromosomes that characterize the chromatin organization in the embryo suspensor cells of Phaseolus coccineus. Polytene chromosomes showed signs of dose-dependent genotoxicity following AlCl₃ treatments with a significant increase in both chromatin stickiness and chromatin fragmentation. Polytene chromosomes specifically reacted to AlCl₃ also in terms of DNA and RNA puffing activity: with respect to the control, the treatments promoted ex-novo and/or inhibited puff formation along chromosome arms, suggesting a fine modulation of the differential genome activity in response to the treatments. The nuclei of suspensors from control and treated seeds showed nucleoli mainly arranged by more than one NOR-bearing chromosome. In addition, AlCl₃ treatments affected the frequency of nucleoli organized by singular organizer chromosomes, with an increase in the frequencies of nucleoli organized by chromosome II and a reduction in the frequencies of those organized by chromosomes I or V. These results confirm that, also in our system, nucleolus may react as stress response organelle.

Keywords:

• Aluminum
• DNA/RNA puffs
• nucleolus
• Phaseolus coccineus
• polytene chromosomes
• toxicity

Acknowledgements

The authors are grateful to Professors Laura Forino and Anna Maria Tagliasacchi for their helpful discussion and critical reading of the manuscript. The authors thank Prof. Patrick Johnson for the final linguistic revision of the manuscript.