MOLECULAR APPROACHES TO ENHANCE PLANT NUTRIENT CONTENT, SHELF-LIFE AND STRESS TOLERANCE
Title: Polyamines and cellular metabolism in plants: Transgenic approaches reveal different responses to diamine putrescine versus higher polyamines spermidine and spermine
Submitted to: Amino Acids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 2009
Publication Date: December 3, 2009
Citation: Mattoo, A.K., Minoch, S., Minocha, R., Handa, A.K. 2009. Polyamines and cellular metabolism in plants: Transgenic approaches reveal different responses to diamine putrescine versus higher polyamines spermidine and spermine. Amino Acids. Available: http://www.springerlink.com/content/05h3202610227w87/fulltext.html
Interpretive Summary: Polyamines are ubiquitous organic nitrogenous molecules found essential for growth and development of living cells. Generally, researchers have grouped them together under the assumption that they play similar functions. Most common polyamines are the diamine putrescine (Put) and higher polyamines, spermidine (Spd) and spermine (Spm). Their synthesis is intimately linked with dietary amino acids, which are essential for protein synthesis and human nutrition. To understand their function in plants, a reverse genetics approach was used by a team of scientists from USDA-ARS, Purdue University, and the University of New Hampshire. Two genes, ornithine decarboxylase and S-adenosylmethionine decarboxylase, were engineered and stably introduced, respectively, into cell cultures and tomato plants. Molecular and physiological analyses of these novel lines demonstrated that alterations in the levels of either Put or Spd and Spm caused changes in the contents of other amino acids. Notably, contrasting physiological functions for Put versus Spd and Spm were apparent. The results demonstrated here show that Put, and Spd and Spm, play a role not just as nitrogenous compounds but also as signaling molecules with specific biological functions. These findings are of particular significance to plant biologists, agriculturists, biochemists and molecular biologists.
Distribution of biogenic amines – the diamine putrescine (Put), triamine spermidine (Spd), and tetraamine spermine (Spm) - differs between species with Put and Spd being particularly abundant and Spm the least abundant in plant cells. These amines are important for cell viability and their intracellular levels are tightly regulated, which have made it difficult to characterize individual effects of Put, Spd and Spm on plant growth and developmental processes. The recent transgenic intervention and mutational genetics have made it possible to stably alter levels of naturally occurring polyamines and study their biological effects. We bring together an analysis of certain metabolic changes, particularly in amino acids, to infer the responsive regulation brought about by increased diamine or polyamine levels in actively growing poplar cell cultures (transformed with mODC gene to accumulate high Put levels) and ripening tomato pericarp (transformed with ySAM decarboxylase gene to accumulate high Spd and Spm levels at the cost of Put). Our analyses indicate that increased Put has little effect on increasing the levels of Spd and Spm, while Spd and Spm levels are inter-dependent. Further, Put levels were positively associated with Ala (' and '), Ile and GABA and negatively correlated with Gln and Glu in both actively growing poplar cell cultures and non-dividing tomato pericarp tissue. Most amino acids showed positive correlations with Spd and Spm levels in actively growing cells. Collectively these results suggest that Put is a negative regulator while Spd-Spm are positive regulators of cellular metabolism.