Gene expression profiling in the stem of young maritime pine trees: detection of ammonium stress-responsive genes in the apex

The shoots of young conifer trees represent an interesting model to study the development and growth of conifers from meristematic cells in the shoot apex to differentiated tissues at the shoot base. In this work, microarray analysis was used to monitor contrasting patterns of gene expression between the apex and the base of maritime pine shoots. A group of differentially expressed genes were selected and validated by examining their relative expression levels in different sections along the stem, from the top to the bottom. After validation of the microarray data, additional gene expression analyses were also performed in the shoots of young maritime pine trees exposed to different levels of ammonium nutrition. Our results show that the apex of maritime pine trees is extremely sensitive to conditions of ammonium excess or deficiency, as revealed by the observed changes in the expression of stress-responsive genes. This new knowledge may be used to precocious detection of early symptoms of nitrogen nutritional stresses, thereby increasing survival and growth rates of young trees in managed forests.