Maize (Zea mays L.) endogenous seed phosphorus remobilization is not influenced by exogenous phosphorus availability during germination and early growth stages.

摘要

Background and aims: Phosphorus (P) nutrition is very important during early maize seedling growth. Remobilization of endogenous seed P and uptake of exogenous P are therefore of prime importance during this period. Our objectives were to study the effect of the availability of endogenous and exogenous P on (i) remobilization of endogenous seed P, (ii) the beginning of exogenous P uptake and its intensity, (iii) their interaction and effect on seedling development. Methods: Seeds with high and low reserves of endogenous seed P were cultivated at three rates of availability of exogenous P (0, 100, 1,000 micro M) over a growth period of 530 cumulated degree days after sowing. Exogenous P was labeled with radioactive P (32P) to distinguish the two fluxes of P in seedlings, one due to remobilization of seed P and the other to uptake of exogenous P. Results: Initially, 86% of endogenous seed P was localized in the scutellum, mainly in the form of phytate, regardless of initial endogenous seed P. At 89 cumulated degree days after sowing (base temperature: 10 degrees C), 98% of seed phytate was hydrolyzed in all treatments. In treatments with available exogenous P, significant uptake of exogenous P started at 71 cumulated degree days after sowing. Efficient uptake of exogenous P depended on its availability, but was independent of phytate hydrolysis and seedling P status. Significant loss of P from germinating seeds due to efflux was observed and was also independent of the availability of exogenous P. Conclusions: Our results show that hydrolysis of seed P was not influenced by the availability of exogenous P, and conversely, that uptake of exogenous P was not influenced by endogenous P in the seed. This suggests that remobilization of endogenous seed P and uptake of exogenous P by seedling roots are controlled independently.