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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #126384
Title: THE EFFECT OF PHOSPHORUS AND ZINC FERTILIZER LEVELS ON PERCENT PHYTIC ACID IN NAVY BEAN

Author
item CICHY, K - MICHIGAN STATE UNIVERSITY
item MORAGHAN, J - N DAKOTA STATE UNIVERSITY
item GRAFTON, K - N DAKOTA STATE UNIVERSITY
item Hosfield, George

Submitted to: Bean Improvement Cooperative Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: In navy bean (Phaseolus vulgaris L.) variability exists for the ability of a plant to take up and use zinc from the soil. Plants that grow normally under conditions of low soil zinc are called zinc efficient, whereas plants that show deficiency symptoms under low soil zinc are zinc inefficient. In this experiment, two navy bean cultivars, 'Voyager' and 'Albion', zinc efficient and nonefficient, respectively, were grown in pots in a greenhouse and with 15 different treatment combinations of phosphorus and zinc fertilizer. The seed harvested from plants of each cultivar were analyzed for levels of phosphorus, zinc, and the amount of phosphorus in phytic acid, a molecule that is a carrier of inorganic cations in plants. 'Voyager' had a higher concentration of seed zinc at each fertilizer treatment and a higher percentage of total seed phosphorus in the form of phytic acid than 'Albion'. The relationship between phytic acid and zinc in ndry bean is of particular importance to humans who choose restricted diets (vegetarians) and rely on dry bean as their major source of dietary protein. Phytic acid in food legumes is an antinutrient because it severely limits zinc and iron bioavailability. The data from this research encourages plant breeders to search for new genetic stocks that combine low phytic acid and high zinc levels in seed. Bean cultivars with high zinc and low phytic acid levels in seeds would be good news for vegetarians because it would alleviate their concern of having to take zinc supplements to ensure their health is not impaired because of zinc deficiency. Freedom from having to rely on zinc supplements has the potential to save vegetarians who are heavy bean consumers considerable money annually.

Technical Abstract: Phytate, a mixed cation salt of phytic acid (myo-inositol hexakis phosphoric acid) is the major storage form of phosphorus in seed of dry bean (Phaseolus vulgaris L.). In human nutrition, phytate is considered an antinutrient because it forms tight complexes with cations in the seed and decreases their bioavailability upon consumption. The relationship between phytate and zinc is of particular importance to humans who rely on legumes as the major protein source of their diet. Zinc also plans an important role in growth and development of dry bean plants. An experiment was conducted to study the relationship between seed zinc and phosphorus concentration-[Zn] and [P]- respectively, and percent of phytic acid phosphorus in a zinc efficient and inefficient navy bean cultivar. Fifteen phosphorus (0, 60, 120 g/kg P) and zinc (0.5, 1.0, 2.0, and 4.0 mg/kg Zn) fertilizer combinations were applied as treatments to plants grown in pots in the greenhouse. At each phosphorus fertilizer level, the total seed [P] was slightly higher in Albion, the zinc inefficient bean. Conversely, at each phosphorus fertilizer level, the percent of seed phosphorus stored as phytic acid was significantly higher in Voyager, the zinc efficient variety. Voyager also had higher seed zinc concentration than Albion. This increase was most visible at low phosphorus fertilizer levels and high zinc fertilizer levels. Based on data from this study, apparently [Zn] and phytic acid percent P are not strongly associated. Efforts to increase seed zinc and lower phytic acid through plant breeding will be difficult because each trait must be selected independently, although it is important to consider both traits simultaneously when breeding for improved human nutrition.