桑菌根初生结构对梯度水分胁迫的细胞学生态响应

为探索菌根桑在石漠化地区的生态修复和生态重建功能,采用0,10%,15%,20%,25%5种不同浓度的PEG6000溶液与培养基质混合,模拟自然条件下的土壤梯度水分胁迫生境,将接种丛枝菌根真菌玫瑰红巨孢囊霉的桑苗(F+)培养5个月后,挑选长势与未接种对照(F-)基本一致的植株分别移栽入备好的梯度水分胁迫基质中,胁迫8d后,石蜡切片观察初生根成熟区的细胞学特征.结果表明:桑树初生根成熟区由表皮、皮层和维管柱组成,表皮上有少量的根毛,内皮层明显,其上有凯氏带增厚,二原型维管束与初生韧皮部相间排列.水分胁迫时,0～10%PEG处理的F-根表皮存在,皮层薄壁组织发达,细胞饱满;15%～20%PEG时,表皮死亡脱落,皮层细胞开始失水、变形,随着PEG浓度的增大失水情况加剧,细胞扭曲、收缩变小;0～20%PEG时F+表皮存在,还可见少量根毛,25%PEG时,表皮死亡脱落,多数皮层细胞仍然近圆形、饱满;中柱中初生韧皮部最晚受到水分胁迫的影响,初生木质部受影响不显著.推测:F+桑苗对水分胁迫能力的提高主要是通过根外菌丝网络系统把根际以远更加广泛土壤中存在的水分吸收过来并由根内菌丝运送到皮层细胞,满足桑树根内和地上部分的水分需求,提高植株对高达-0.49Mpa水分胁迫的忍耐性,表皮延后脱落死亡,根皮层细胞正常形态更加持久.

EcologicalResponseattheCytologicalLevelofthe RootPrimaryStructureinMycorrhiza-Inoculated MulberrySaplingstoGradientWaterStress

In order to explore the ecological reconstruction potential of mycorrhiza-inoculated mulberry plants in rocky desertification areas,simulated water stress environments were created by PEG 6000 at 0,10%,15%,20% and 25% mixed with the substrate.The mulberry saplings inoculated with Gigaspora rosea(F+) were cultured for 5 months.Then the treated samplings(F+) and the un-treated samplings(F-) of similar size were potted and subjected to simulated drought treatments.Eight days later,the structure features of the maturation region of the primary roots were examined microscopically in paraffin sections.The investigation showed that the maturation region of the primary root of Morus alba L.consisted of epidermis,cortex and vascular cylinder.Some root hairs grew from the epidermis.The inner-cortex rounded by the Casparian strip was distinct,with xylem and phloem spaced in-between.Under the condition of water stress of 0-10% PEG,the epidermis still existed in F-,and the cells in the cortex were normal.But the epidermis cells died and dropped,and the cells of the cortex were dehydrated and deformed when the PEG concentration was from 10 to 15%.In F+,epidermis and root hair existed in the 0-20% of PEG.When the concentration of PEG was about 25%,most of the cortex cells were still morphologically normal.The structure of the primary phloem of the stele was affected by water stress in the last period,while the primary xylem was hardly affected by it.It was speculated that the improvement of drought tolerance of F+ plants was attributed to the fact that inoculation of AM fungi could improve the resistance to water stress by the hyphal net which can absorb more water from the rhizosphere soil and deliver it to the cortex cells by intra-radical mycelium and,as a result,the water needed of plant growth was satisfied,the death or drop of the epidermis was postponed and the cortex cells survived longer.