Table II.

Latencies of enzyme activities in plastid-enriched pellets from Hordeum endosperms

Species	Enzyme	Activity		Latency
		Intact	Ruptured
		nmol min−1 mL−1		%
H. spontaneum	Alkaline pyrophosphatase	451 ± 9	896 ± 380	51 ± 6
	Alcohol dehydrogenase	410 ± 19	431 ± 13	5 ± 3
	AGPase	190 ± 4	220 ± 14	14 ± 3
H. murinum	Alkaline pyrophosphatase	120 ± 1	690 ± 1	82 ± 5
	Alcohol dehydrogenase	129 ± 1	131 ± 1	12 ± 2
	AGPase	190 ± 1	303 ± 1	38 ± 14

Duplicate samples of homogenate were prepared as described for Table I. Plastids in one of the two samples were broken by repeated extrusion through a fine-bore needle. The activities of AGPase and the cytosolic marker enzyme in the two samples were assayed in the presence of 0.6 m sorbitol. The activity of the plastidial marker enzyme alkaline pyrophosphatase was assayed in the presence of 0.6 m Suc because sorbitol has been shown to inhibit this activity (Tetlow et al., 1993). The activity in the ruptured sample minus that in the intact sample is expressed as a percentage of that in the ruptured sample, and this is presented as the latency value. In each experiment, each enzyme in the two samples was assayed three times. Values are means ± se of measurements from three separate experiments.