PHYTATE METABOLISM IN BEAN SEEDLINGS DURING POSTGERMINATIVE GROWTH

The phytate metabolism of snap and pinto beans seedlings was studied during post-germinative growth. Rapid phytate degradation in embryonic axis started at the time of root emergence and continued for two days of post-germinative growth. Surprisingly, phytate synthesis was observed in the embryonic axes of both races after 2-3 days and the original amount of phytate for the embryonic axis had doubled the amount in the axis of dry seed. The phytate synthesis was inferred because the phytate level in embryonic axis reached a plateau per unit of fresh weight after 3 days of post-germinative growth. Inorganic phosphate (P-i) at the 10 and 20 mM level significantly increased the endogenous P-i content in the embryonic axes, but showed no effect on the phytate levels in the embryonic axes or cotyledons. The phytate content of bean embryonic axes underwent a significant increase upon cultivation with extremely high levels of P-i (40 mM): A similar effect was observed using lower P-i levels (20 mM) if the axes had been excised prior to cultivation. Both treatments resulted in the phytate accumulation, but adverse effects on the growth and development of embryonic axes were associated with both these treatments. We conclude that phytate synthesis in the embryonic axis is a regular event during post-germinative growth of bean seedlings. Furthermore, the phytate degradation in cotyledons reflected the growth rate of the embryonic axis irrespectively of the P-i content in the embryonic axis.