Department of Plant Sciences

Phosphate (Pi) the fully oxidized and assimilated form of P influences virtually all developmental and biochemical processes in plants. Paradoxically, although P is abundant in the lithosphere, the elusive soil chemistry of Pi, renders the element the most dilute and the least mobile in natural and agricultural ecosystems due to its low mobility and high fixation capacity in soil. Non-mycorrhizal Brassica does not produce specialized cluster/dauciform roots but is an effective P-user compared to other crops. In addition to P-uptake, utilization and remobilization, acquisition of orthophosphate from extra cellular sparingly P-sources can be enhanced by biochemical rescue mechanisms such as copious H+-efflux and/or carboxylates exudation into rhizosphere by roots via plasmalemma H+-ATPase and anion channels triggered by P-starvation. P-stress induced dissolution of sparingly soluble Ca-phosphate, rhizospheric pH changes due to H+-efflux, redesigning in root architectural system, and carboxylates exudations were estimated by low P-tolerant (class-I) and low P-sensitive (class-II) cultivars in different culture experiments. P-contents of cultivars were inversely related to decrease in culture media pH. Elongation rates of primary roots decreased but length of lateral roots increased under P-starvation. Class-I cultivars presented enhanced H+-efflux, carboxylates exudation and rhizosphere acidification than class-II cultivars, evidencing their adaptability to P-starved environment. These classical P-stress induced rescue strategies provided the basis of enhanced P-solublization and acquisition from sparingly soluble P-sources by Brassica cultivars to thrive in a typically stressful environment.