Phyto-hormones play critical roles in the coordination of plant growth and development. Generally, plant hormones promote, inhibit, or qualitatively modify plant growth and development. This complex process requires signal transduction, specific information pathways, translating intra- or extra-cellular signals into specific cellular responses within a cell. Auxins represent an important class of plant hormones. Plant growth is regulated by auxin via the regulation of various genes responsible for different metabolic processes in the plant. The impact of toxic heavy metals like cadmium and transition metals like copper and manganese in the soil, on plant defence reactions and their implications for plant growth have been extensively investigated. However, how auxin is involved in mediating environmental stresses and heavy metal stress is still not understood.
This study was designed to address the following questions in poplar: Are there changes in the expression pattern of GH3:GUS promoter-reporter constructs in relation to seasonal changes under natural field conditions? What is the effect of cadmium stress on the auxin physiology? What is the effect of excessive manganese on auxin physiology? What are the copper requirements for poplar growth? Poplar was chosen for this study as it is a model forest tree for molecular studies. Grey poplar, Populus x canescens (a hydrid of P. tremula and P. alba) and three transgenic lines transformed with a GH3:GUS construct responsive to auxin, were used. The plants were grown in compost soil outdoors as well as in hydroponic media under greenhouse conditions to investigate auxin pattern in the tissues.