Azetidine-2-carboxylic acid and lily pollen tube elongation | Azetidine-2-carboxylic acid and lily [Lilium longiflorum] pollen tube elongation
1980
Dashek, W.V. | Mills, R.R.
Azetidine-2-carboxylic acid (AZC), which occurs naturally in Liliaceous plants, is reported to be a proline (pro) analogue Plant cell walls contain ‘extensin’, which is rich in hydroxyproline (hyp). Peptidyl hyp arises through hydroxylation of peptidyl pro followed by glycosylation (arabinose attachment) of hyp Because AZC replaces peptidyl prolyl residues, it may be a useful tool for evaluating the significance of hyp-o-arabinose linkages in cell elongation. Therefore, we determined the effect of AZC on [14C]pro uptake, incorporation and conversion to wall-bound [14C]hyp in relation to elongation of lily pollen tubes whose walls consist, in part, of hyp-containing glycopeptides The AZC suppressed pollen germination 9–42 per cent (1–10 mM) and subsequent tube elongation 40–54 per cent (0·1–1 mM without affecting respiration In contrast, similar hyp concentrations were without effect on tube elongation Whereas uptake of [14C]pro was 16·5–6·2 per cent of the control at 0·1–1 mM AZC, [14C]leucine uptake was 85–25 per cent of the control. Light microscope radioautography revealed fewer silver grains over tubes elongated in 0·1–1 mM AZC than in its absence. Incorporation of [14C]pro into tnchloroacetic acid (TCA)-precipitable cytoplasm was reduced by only 10 per cent at 0·01–1 mM but 43 per cent at 10 mM AZC Gel filtration of cytoplasm from pollen germinated without AZC but with [14C]pro resulted in labelled void volume (V) and three retarded peaks (RI–III) Incorporation into V and RI was inhibited at both 0·01 and 1 mM AZC These AZC concentrations reduced conversion of [14C]pro to wall-bound hyp by ∼ 20 per cent However, total incorporation of [14C]pro into salt-water-purified wall fractions was suppressed 47–53 per cent (0·1–1 mM AZC).
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