Mo Beixin, Bewley J Derek
Department of Botany, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
J Exp Bot. 2003 Nov;54(392):2503-10. doi: 10.1093/jxb/erg274. Epub 2003 Sep 25.
beta-Mannosidase and endo-beta-mannanase are involved in the mobilization of the mannan-containing cell walls of the tomato seed endosperm. The activities of both enzymes increase in a similar temporal manner in the micropylar and lateral endosperm during and following germination. This increase in enzyme activities in the micropylar endosperm is not markedly reduced in seeds imbibed in abscisic acid although, in the lateral endosperm, endo-beta-mannanase activity is more suppressed by this inhibitor than is the activity of beta-mannosidase. Gibberellin-deficient (gib-1) mutants of tomato do not germinate unless imbibed in gibberellin; low beta-mannosidase activity, and no endo-beta-mannanase activity is present in seeds imbibed in water, but both enzymes increase strongly in activity in the seeds imbibed in the growth regulator. For production of full activity of both beta-mannosidase and endo-beta-mannanase in the endosperm, this tissue must be in contact with the embryo for at least the first 6 h of imbibition, which is indicative of a stimulus diffusing from the embryo to the endosperm during this time. These results suggest some correlation between the activities of beta-mannosidase and endo-beta-mannanase, particularly in the micropylar endosperm, in populations of tomato seeds imbibed in water, abscisic acid and gibberellin. However, when individual micropylar endosperm parts are used to examine the effect of the growth regulators and of imbibition in water on the production of the two enzymes, it is apparent that within these individual seed parts there may be large differences in the amount of enzyme activity present. Micropylar endosperms with high endo-beta-mannanase activity do not necessarily have high beta-mannosidase activity, and vice versa, which is indicative of a lack of co-ordination of the activities of these two enzymes within individuals of a population.
β-甘露糖苷酶和内切-β-甘露聚糖酶参与番茄种子胚乳中含甘露聚糖细胞壁的分解。在萌发期间及之后，这两种酶的活性在珠孔端和侧端胚乳中以相似的时间模式增加。在脱落酸处理的种子中，珠孔端胚乳中这两种酶活性的增加并没有明显降低，尽管在侧端胚乳中，脱落酸对内切-β-甘露聚糖酶活性的抑制作用比对β-甘露糖苷酶活性的抑制作用更强。番茄赤霉素缺陷型（gib-1）突变体种子，除非用赤霉素处理，否则不会萌发；在水中浸泡的种子中，β-甘露糖苷酶活性较低且没有内切-β-甘露聚糖酶活性，但在生长调节剂处理的种子中，这两种酶的活性都显著增加。为了使胚乳中β-甘露糖苷酶和内切-β-甘露聚糖酶都产生完全活性，该组织在吸水的至少前6小时必须与胚接触，这表明在此期间有刺激信号从胚扩散到胚乳。这些结果表明，在用水、脱落酸和赤霉素处理的番茄种子群体中，β-甘露糖苷酶和内切-β-甘露聚糖酶的活性之间存在一定相关性，特别是在珠孔端胚乳中。然而，当用单个珠孔端胚乳部分来研究生长调节剂和水浸对这两种酶产生的影响时，很明显在这些单个种子部分中，酶活性的量可能存在很大差异。内切-β-甘露聚糖酶活性高的珠孔端胚乳不一定具有高β-甘露糖苷酶活性，反之亦然，这表明在一个群体的个体中这两种酶的活性缺乏协调性。
