Photosynthetic oxygen evolution of Zea mays leaf slices measured by polarography

A comparative analysis of the photosynthetic activity of Zea mays (flint type) leaf slices was performed using Ullrich's polarographic method (Ullrich et al., Z. Pflanzenphysiol. 79:336-346, 1976) with slight modifications. Maize plants were grown in the field.

After 6 weeks from emergence, a part 35 cm long was excised from the 6th leaf (from the base), delimited by the central vein and a cut made 35 cm from the tip. The bottom of the excised area was put in a glass vial with 2 ml of cold distilled water and transported to the laboratory in an isolated box kept at low temperature. Rectangles of approximately 1 cm2, cut 20 cm from the tip, 14-19 mg fresh weight, were briefly washed with distilled water and sliced by hand with razor blades to produce slices of about 1 mm x 10 mm. Slices were submerged for at least 30 min. in 15 ml of cold distilled water (5-10 C) to reach a steady-state respiratory activity. Washing with calcium salts (sulfate, nitrate, chlorhydrate) did not increase O2 production in light in comparison to control washed with distilled water only. A 400 W (658 u moles m-2s-1) Hg-HPL R lamp was used as the light source.

The experimental solution contained 20 m mol Na phosphate (pH 5.6) and 10 m mol NaHCO3 (final pH 6.5). The solution was pre-flushed in the dark with pure N2 (3 1 h-1) before the addition of NaHCO3 until 70% of O2 saturation was reached. The calibration of YSI polarographic instrument, the final volume of solution and the experimental temperature agreed with the original method. O2 evolution rates were not corrected for the concurrent rates of respiratory O2 uptake.

This method was used to analyze apparent photosynthesis in inbred lines and hybrid-derived populations (MNL 58, 1984). In 1982 three inbred lines, selected for further experimentation, showed high (2) and low (1) activity, with values between 250.0 and 168.8 u moles O2 g FW-1h-1 (mean 205.0). In 1983 the extreme values of the same lines were 253.9 and 157.3 (mean 205.3).

Jaime R. Jatimliansky


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