Table I.

PSK production by transgenic Arabidopsis cells

Construct	PSK-β	[Ser4]PSK-β
PMAT037	413 ± 30	0
[Ser4]PSK AtPSK2 cDNA	387 ± 41	3,750 ± 40
[Ser4]PSK AtPSK3 cDNA	350 ± 36	4,785 ± 50

Transgenic cells (0.8 g) harboring pMAT037 alone or mutated cDNAs were incubated in 100 mL of fresh B5 liquid medium supplemented with 0.5 mg L⁻¹ of 2,4-D and 0.05 mg L⁻¹ of KIN at 25°C in the light with rotary shaking at 120 rpm. After 2 weeks of culture, PSK-β and its analog concentrations in the CM were quantified by LC/MS. PSK concentrations are presented in pm. Averages of three independent experiments are given with the sd. PSK-α was not detectable by this assay because its amount was beyond the detection limit.