Submitted to: Plant Cell and Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/15/1998
Publication Date: N/A
Citation: Interpretive Summary: Phosphorous (P) is a major nutrient required for plant growth and development. The world P reserves are projected to be depleted within 60 years. Research on P acquisition by plants must focus on how plants adapt to growth in a P deficient environment. White lupin forms extensive root growths in response to P stress. These root growths are called proteoid roots. The chemistry of proteoid roots is altered in order to acquire mor P under P limited conditions. In experiments reported here we show that P stressed white lupin proteoid roots release an enzyme (protein catalyst) called acid phosphatase into the soil surrounding the roots. This acid phosphatase is not found in roots of normal P sufficient plants. The acid phosphatase that is released from the roots of white lupin can solubilize unavailable P from the soil and thus improve P acquisition under nutrient stress conditions. This research is important because it identifies a unique adaptive strategy that plants have to acquire P under nutrient stress conditions. It also identifies a target that may be modified by plant breeding to improve P nutrition.
Technical Abstract: White lupin (Lupinus albus L.) develops proteoid roots when grown in phosphorus (P) deficient conditions. These short, lateral, densely clustered roots are adapted to increase P availability. Previous studies from our laboratory have shown proteoid roots have higher rates of nonphotosynthetic carbon fixation and altered metabolism to support organic cacid exudation, which serves to solubilize P in the rhizosphere. The present work indicates that proteoid roots possess additional adaptations for increasing P availability and possibly for conserving P in the plant. Roots from P-deficient (-P) plants had significantly higher acid phosphatase (APase) activity in both endogenous samples and root exudates than comparable samples from P-sufficient (+P) plants beginning 10 days after emergence. The increase in activity in -P plants was most pronounced in the proteoid regions. In contrast, no induction of phytase activity was sfound in -P plants compared to +P plants. Native-PAGE demonstrated that under P-deficient conditions, a unique isoform of APase was induced between 10 and 12 days after emergence. This isoform was found not only within the root, but it also comprised the major form exuded from proteoid roots of -P plants. The fact that exudation of proteoid-root-specific APase occurs coincident with proteoid root development and increased exudation of organic acids indicates that white lupin has more than one adaptive strategy to enhance P acquisition.