The effects of salinity on corn plants (Zea mays L.) are influenced by
the concentration of nutrient orthophosphate. Salinity (-2 bars each of
NaCI and CaCI2) was more injurious in combination with a high concen-
tration of orthophosphate (2 mM) (that gave optimum yields in the
absence of salinity) than it was with a lower concentration (0.1 mM). With
2 mm orthophosphate, salinity seemed to damage the plant mechanisms
that normally regulate the internal concentration of orthophosphate re-
sulting in excessive accumulation and P toxicity. On the other hand, with
0.1 mM orthophosphate, salinity decreased orthophosphate concentration
in mature leaves. This effect was paralleled by decreases in the concentra-
tion of adenosine 5'-triphosphate and in the energy charge of the adenyl-
ate system, indicating an orthophosphate deficit. Even so, plants sur-
vived salinity better under these conditions than in the presence of 2 mM
orthophosphate. The data indicated that salinity affected the phosphoryl-
ated state of the adenine nucleotides only indirectly through its effect on
the concentration of orthophosphate in the cells.
Salinity, especially in the presence of 2 mM orthophosphate, resulted in
an increase in the concentrations of sugar phosphates in mature photosyn-
thesizing leaves, suggesting that translocation rather than photosynthesis
was a limiting process. Decreased translocation could be a secondary
effect of decreased growth. However, a decreased translocation rate could
cause decreased growth by limiting the supply of essential metabolites
reaching growing tissues.