Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2011
Publication Date: July 1, 2011
Citation: Cheng, L., Bucciarelli, B., Shen, J., Allan, D., Vance, C.P. 2011. Update on white lupin cluster roots acclimation to phosphorus deficiency. Plant Physiology. 156(3):1025-1032. Interpretive Summary: Phosphorus (P) is a critical element for crop growth and quality. Because P is a nonrenewable resource, it is imperative that agriculture research develop plants that are more efficient in uptake and utilization of P. The legume plant white lupin is highly efficient at obtaining scarce P. It has evolved several root developmental and morphological features that enhance P uptake and use. One of the most unusual root traits that is displayed by white lupin grown under P-deficiency stress is that it forms dense clusters of tertiary lateral roots. These roots are called cluster roots. We report here that the interaction of the plant growth hormones auxins and cytokinin appears to regulate cluster root formation. We also note that formation of cluster roots requires sugar derived from leaves to complete their development and to fully express genes involved in acclimation to P-stress. This work is useful because it shows that acclimation to P-deficiency stress involves the integration of molecular signals between the shoot and root. The genes identified provide targets to manipulate through biotechnology that may increase crop tolerance to low P or may enhance the efficiency of P utilization.
Technical Abstract: Phosphorus (P) is one of 17 essential elements required for plant growth. Although bound P is quite abundant in many soils, it is largely unavailable for uptake. As such, P is frequently the most limiting element for plant growth and development. Crop yield on 40% to 60% of the world's arable land is limited by P availability. Mined rock phosphate is the primary source of P fertilizer. Approximately 90% of all mined rock phosphate is used for agriculture. However, rock phosphate is a non-renewable resource, and easily mined, high-quality rock phosphate sources are projected to be depleted within 30 to 50 years. Peak P production is projected to occur in 2035-2040. In addition, the world's major reserves of rock phosphate are located in geographical areas where uncertain political issues could limit access to the world's P resources. Sustainable management of P in agriculture requires that plant biologists discover mechanisms that enhance P acquisition and exploit these adaptations to make plants more efficient at acquiring P, develop P-efficient germplasm, and advance crop management schemes that increase soil P availability. Cluster roots, extremely specialized tertiary lateral root structures, are an important adaptive strategy of plants to cope with nutrient-poor, P-depleted soils. They are produced on plants from a diverse range of families. White lupin forms cluster roots in response to P starvation. Cluster roots are characterized as concentrated zones of tertiary lateral roots emerging in waves from secondary roots. Root hair density appears to be greater in mature cluster root zones than typical lateral roots. Such an adaptation leads to a striking increase in root surface area available for P uptake from the rhizosphere. Cluster root development and function involves a highly synchronous series of molecular and biochemical processes including: highly enhanced lateral root initiation; increased root hair formation; root exudation of organic acid chelators (citrate and malate); modified carbon assimilation; release of enzymes (acid phosphatase, ferric chelate reductases) into the rhizosphere; and more efficient uptake of P from the rhizosphere. Advances have recently been made in understanding molecular and biochemical events surrounding cluster root formation and function. As a crop, white lupin (Lupinus albus) is a practical alternative to evaluate acclimation to P-deficiency particularly as related to cluster-rooted species.