老芒麦种子离区酶活变化及组织学分析

通过对青藏高原东北缘6种野生老芒麦不同时期种子离区组织结构的观察和细胞壁水解酶活性的测定,在组织学和生理学层面阐释老芒麦种子落粒的成因。结果表明,老芒麦种子离区结构的形成时期早于种子脱落,离层由2~3层小体积、椭圆形的细胞紧凑排列组成且这些细胞木质化程度高于周围组织细胞,低落粒材料离层木质化细胞数量多于高落粒材料;低落粒材料在种子成熟期无明显的离层断裂,其断裂面粗糙,离层结构完整,而高落粒材料在种子成熟期出现明显的离层断裂,断裂面光滑且离层结构不完整;6种材料纤维素酶(CE)与多聚半乳糖醛酸酶(PG)活性的变化趋势在种子发育各时期均有差异,落粒关键期(抽穗后4~5周)这两种酶活性均与种子脱落密切相关;供试材料在落粒关键期CE与PG活性排序一致,且与同时期电镜观察结果相近;高落粒材料XH09在落粒关键期的两种酶活性均为最高(XH09_CE=479.52 IU·L^-1,XH09_PG=188.87 pg·mL^-1),而低落粒材料ZHN03两种酶活性均为最低。研究表明,老芒麦高落粒与低落粒材料在离层木质化程度、断裂面光滑度、离层结构完整性及落粒关键期细胞壁水解酶活性等方面具有差异。同时,离层木质化程度与落粒关键期细胞壁水解酶活性是造成野生老芒麦种子脱落的重要因素。

Enzyme activity and histological analysis of the abscission zone of Elymus sibiricus

Histological and enzyme activity analysis of the abscission zone of seed from six Elymus sibiricus accessions from the northeast margin of the Qinghai-Tibet Plateau at different stages of seed maturation was undertaken. The results showed that the abscission layer of seeds were present before seed shattering. The abscission layer was composed of 2 to 3 layers of small volume cells, oval in shape and with a compact arrangement. The degree of lignification of these cells was higher than surrounding cells. The lignified cell number of low seed shattering accessions was higher than high seed shattering accessions; low seed shattering accessions did not have an abscission layer at the seed maturity stage. These accessions had a rough fracture surface and an integrated abscission layer structure. High seed shattering accessions developed a clear fracture or abscission layer during seed maturation. These materials had a smooth fracture surface and incomplete abscission layer structure. Changes in cellulase (CE) and polygalacturonase (PG) activity among accessions differed at different seed developmental stages. The activities of these cell wall hydrolases were both closely related to seed shattering; the CE and PG activity of high seed shattering accessions at the time of shattering was high and consistent with electron microscopy observations. The high seed shattering accession (XH09) possessed the highest enzyme activity (XH09_CE=479.52 IU·L^-1, XH09_PG=188.87 pg·mL^-1) during the seed shattering period while the low seed shattering accession (ZHN03) had the lowest enzyme activity. This study showed that there were clear differences in the degree of lignification of the abscission layer, fracture surface smoothness, structural integrity of the abscission layer and the activities of cell wall hydrolases between low and high seed shattering accessions during the critical period of seed shattering. The degree of lignification of the abscission layer and activities of cell wall hydrolases at the seed shattering stage were the most important factors influencing seed shattering in wild E. sibiricus accessions.