Abstract:
Evaluation of tissue tolerance of potentially toxic ions (Na+
and/or Cl–
) can be complicated by
differences in ion exclusion by the roots resulting in differences in tissue ion concentrations in
the leaves. This research tested two approaches to ‘deliver’ NaCl to leaves to assay tissue
tolerance: (i) injection of NaCl into the stem or petiole of intact plants and (ii) an excised leaf
method (transpiring leaf with petiole in a saline solution) and determined whether measurements
of leaf ion concentrations and leaf function can be used to assess ‘tissue tolerance’. The infusion
and excision methods were conducted on 18–day–old of soybean and common bean grown in
aerated non–saline nutrient solution culture for over 5 days. The NaCl infusion system was not
successful since Na+
and/or Cl–
in lamina of soybean and common bean did not significantly
increase. In contrast, the excised leaf system resulted in approximately equal increases in Na+
and Cl–
in lamina in the two soybean genotypes, which was 20% lesser than that in common
bean. The Na+
concentrations in the lamina of excised leaves reached or exceeded the critical
levels for toxicity; however, there was no relationship between leaf Na+
and/or Cl–
)
concentrations and leaf photosynthesis (Pn). It was likely that the cavitation of the xylem which
would impede water flow along the petioles and impacted on Pn even in the non–saline controls. |
