Plant Physiology Preview
Published on March 16, 2007; 10.1104/pp.106.092130
OPEN ACCESS ARTICLE
Received October 27, 2006
Accepted March 10, 2007
Differential Effects of Sucrose and Auxin on Localized Pi-deficiency Induced Modulation of Different Traits of Root System Architecture in Arabidopsis
Ajay Jain , Michael D. Poling , Athikkattuvalasu S. Karthikeyan , Joshua J. Blakeslee , Wendy A. Peer , Boosaree Titapiwatanakun , Angus S. Murphy , and Kashchandra G. Raghothama *
Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907-1165
* Corresponding author; email: kragu{at}purdue.edu.
Phosphorus, one of the essential elements for plants, is often a limiting nutrient in soils. Low phosphate (Pi) availability induces sugar-dependent systemic expression of genes and modulates the root system architecture (RSA). Here, we present the differential effects of sucrose (Suc) and auxin on the Pi-deficiency responses of the primary and lateral roots of Arabidopsis thaliana. Inhibition of primary root growth and loss of the meristematic activity were evident in the seedlings grown under Pi-deficiency with or without Suc. Although auxin supplementation also inhibited primary root growth, loss of meristematic activity was observed specifically under Pi-deficiency with or without Suc. The results suggested that Suc and auxin do not influence the mechanism involved in localized Pi-sensing that regulate growth of the primary root and therefore delineated it from sugar-dependent systemic Pi-starvation responses. However, the interaction between Pi and Suc was evident on the development of the lateral roots and root hairs in the seedlings grown under varying levels of Pi and Suc. Although Pi+ Suc- condition suppressed lateral root development, induction of few laterals under Pi-Suc- condition point to increased sensitivity of the roots to auxin during Pi deprivation. This was supported by expression analyses of DR5::uidA, root basipetal transport assay of auxin and RSA of the pgp19 mutant exhibiting reduced auxin transport. A significant increase in the number of lateral roots under P-Suc- condition in chalcone synthase mutant (tt4-2) indicated a potential role for flavonoids in auxin-mediated Pi-deficiency induced modulation of RSA. The study thus demonstrated differential roles of Suc and auxin in the developmental responses of ontogenetically distinct root traits during Pi-deprivation. In addition, lack of crosstalk between local and systemic Pi-sensing as revealed by the seedlings grown under either Pi-Suc- condition or in heterogeneous Pi-environment highlighted the coexistence of Suc-independent and Suc-dependent regulatory mechanisms that constitute Pi-starvation responses.
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