古林箐秋海棠叶斑结构对叶色的影响

该研究以古林箐秋海棠(Begonia gulinqingensis)为材料,通过分析叶片形态特征、上表皮光学特性、组织结构、叶绿素含量及叶绿素荧光参数(F_v/F_m),探讨了叶片色斑的形成原因。结果表明:(1)古林箐秋海棠叶斑发生频率和数量无明显规律,但发生部位相对稳定,叶斑主要发生在正对叶柄的两条主脉之间。(2)斑区有两种光反射模式,点状反射和多角形反射,栅栏组织细胞呈近等轴的圆形,排列疏松,与上表皮细胞间存在空隙;非斑区只有点状反射模式,栅栏组织细胞为漏斗型,排列紧密,与上表皮细胞间不存在空隙。(3)斑区和非斑区叶绿体均有密集的堆积基粒和丰富的类囊体膜,斑区叶绿素a、b及总叶绿素含量仅比非斑区分别低24.9%、25.2%、25.1%。(4)叶绿素荧光参数(F_v/F_m)值斑区为0.793,非斑区为0.790。虽然斑区叶绿素含量比非斑区略低,但叶绿体结构完整,且叶绿素荧光参数与非斑区无显著差异。斑区上表皮与栅栏组织细胞间的空隙可使光线到达绿色组织时发生二次反射,在叶片表皮细胞边缘形成白色多边形光反射使该区域相对周围正常叶片区域偏白,基于上述结果可推测古林箐秋海棠的淡绿色块斑形成与特殊的叶片结构有关。

Effects of foliar variegation structure on leaf color in Begonia gulinqingensis

Using Begonia gulinqingensis as experimental material, the causes of variegated leaves were discussed through analyzing leaf morphological feature, optical properties of adaxial surface, tissue structure, chlorophyll content and chlorophyll fluorescence parameter(F_v/F_m). The results were as follows:(1)The frequency and number of the patch on a leaf had no obvious regularity. In the same plant, some leaves had patches, some had none, the variegated leaf usually had only one patch, while sometimes also had two or several ones, and the occurrence site of the patch was relatively stable, which often occured between the two main veins opposite the petiole.(2)There were two kinds of light reflection patterns in variegated areas, spotted pattern(SP)and polygonal pattern(PP). The cells of palisade tissue were nearly equiaxed and arranged loosely, with intercellular space between the abaxial epidermis cells and palisade tissue cells. The non-variegated areas only had the spotted pattern reflection and the palisade tissue cells were funnel-shaped, arranged closely, there was no intercellular space between theabaxial epidermis cells and palisade tissue cells.(3)Chloroplasts from both variegated areas and non-variegated areas showed dense stacking of grana and stroma thylakoid membranes, chlorophyll a, b and total chlorophyll contents in the variegated areas were only 24.9%, 25.2% and 25.1% lower than those in the non-variegated areas respectively.(4)Chlorophyll fluorescence parameter(F_v/F_m)value was 0.793 in variegated areas, and non-variegated areas was 0.790. Although the contents of chlorophyll in the variegated areas were slightly lower than those in the non-variegated areas, the chloroplast structure was intact, and chlorophyll fluorescence parameter(F_v/F_m)did not differ significantly between the variegated areas and the non-variegated areas. The intercellular space between the abaxial epidermis cells and palisade tissue cells could cause secondary reflection when the light reached the green tissue, and white polygon light reflection was formed at the edge of the epidermal cell, which made this area was whiter than the surrounding normal areas. Based on the above results it can be inferred that the pale green patch on a leaf in B. gulinqingensis is related to a special leaf structure.