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Physiology and Regulation of Seasonal Nitrogen Cycling in Woody Plants

Summary Seasonal nitrogen cycling in trees is a mechanism for conserving and reusing nitrogen that may contribute to nitrogen use efficiency. In this review the physiological and molecular regulation of seasonal nitrogen storage is examined. Research using the 32 kDa bark storage protein gene, bspA of poplar (Populus) as a model system has revealed important facets regulating gene expression and subsequent nitrogen storage. Recent progress has demonstrated that bspA expression is a photoperiod response mediated by phytochrome and secondary messengers including Ca2+ and protein phosphorylation are involved in signaling pathways. Furthermore, evidence indicates that photoperiod modulated expression likely involves metabolic signaling mediated by glutamine and sucrose. A model is proposed that integrates the various facets of poplar bspa expression.