弱光胁迫对西洋杜鹃生理特性和叶片超微结构的影响

Effect of Low Light Stress on Physiological Characteristics and Ultrastructure of Rhododendron hybridum Leaves

【目的】西洋杜鹃属弱光植物,研究其耐受弱光的能力,得到适合其生长的光照强度,可为栽培生产提供理论依据。【方法】以1年生西洋杜鹃为材料,采用盆栽试验研究不同低光照强度（16000,12000,8000,4000和500 lx）处理对其生长状态、生理生化及叶片超微结构的影响。【结果】随着处理天数的增加,不同光照强度处理的西洋杜鹃叶片数、开花数均有所增加,但光照强度越弱,增加数量越少;叶片颜色、形状随光照强度降低而出现失绿变红,叶缘皱缩枯萎等现象,在光强12000 lx下,杜鹃的生长状况最好。当光强高于8000 lx时,叶绿素含量总体呈现上升趋势,而光强低于8000 lx的处理叶绿素含量逐渐降低,处理90天后,光强低于8000 lx的处理其叶绿素含量要显著低于处理前（P〈0.05）。不同光强下叶片光合速率先明显下降后上升,之后又有所下降,至试验结束时,光合速率与光照强度成正比。在500 lx光照下其叶片丙二醛（MDA）的含量增长最快且过氧化氢酶（CAT）、过氧化物酶（POD）以及超氧化物歧化酶（SOD）活性下降幅度最大;在4000-8000 lx光照下,MDA的含量增长较快但可溶性蛋白,CAT,POD及SOD活性下降幅度不大;在12000-16000 lx光照下,MDA的含量增长最慢且可溶性蛋白,CAT,POD以及SOD活性下降幅度也最小。光照强度减弱对西洋杜鹃叶片超微结构的影响较大：叶绿体数量减少,结构破损缺失现象加重,并逐渐出现空洞现象,细胞器结构遭到破坏。当光强大于8000 lx时其细胞结构正常;光强低于8000 lx时叶绿体数量有所减少,类囊体结构开始模糊,质体小球和淀粉颗粒增大;光强为4000 lx时,叶绿体被膜部分破损缺失,基粒片层模糊不清,质体小球和淀粉颗粒明显增多、增大;而光强为500 lx时,细胞膜开始解体,叶绿体被膜破损缺失严重,基粒片层解体,仅存少量无序的片层结构,空洞化程度严重,部分细胞甚至成为空细胞。【结论】综合各指标变化情况,西洋杜鹃可以耐受4000 lx的低光强,而12000-16000 lx光强的光照条件比较适合西洋杜鹃的生长。

【Objective】Rhododendron hybridum is a famous ornamental species with flowers and tree crowns. The species has beautiful flowers with gorgeous flower colors,and long florescence,thus,it is a common urban afforestation tree species and indoor potted flowers. R. hybridum belongs to the weak light plant. In this study,we investigated the tolerance mechanism of Rhododendron to weak light to find the suitable light intensity for its growth,so as to provide theoretical basis for cultivation production. 【Method】A series of pot experiments were conducted to study the effects of weak light on physiological characteristics and leaves＇ submicroscopic structure of R. hybridum with different intensity treatments of low light（ 16 000,12 000,8000,4000 and 500 lx）. 【Results】The results indicated that in all of the treatments,the amount of leaves and blooms increased with the treatment time of days,but the amount was fewer with the decreased light intensity. The leaves gradually lost green and turned red,leaf margin became shrunk and withered with thedecreased light intensity. R. hybridum grew best at the light intensity of 12 000 lx. The content of chlorophyll overall showed a rising trend when the light intensity was above 8000 lx,but gradually reduced when the light intensity was less than 8000 lx. After 90 days,the chlorophyll contents under less than 8000 lx were significantly lower than that before the treatment（ P〈0. 05）. The photosynthetic rate of all treatments decreased significantly first,then rising,and declined subsequently,and was directly proportional to the light intensity by the end of the experiment. The malondialdehyde（ MDA） contents increased fastest,and the activity of catalase（ CAT）,peroxidase（ POD） and superoxide dismutase（ SOD） all decreased significantly over treatment time when the light intensity was 500 lx. From 4000 lx to 8000 lx light intensity,the MDA contents gradually increased but the soluble protein contents,CAT,POD and SOD activities didn＇t drop very much. The MDA contents increased slowest,and the decrease in soluble protein contents,CAT,POD and SOD activities was lowest from 12 000 to 16 000 lx light intensity. As the light intensity receded,the ultrastructure of R.hybridum leaves was steadily damaged： the number of chloroplasts decreased; the structure of chloroplast was seriously damaged gradually; the degree of cavity in chloroplasts increased; and the structure of cell organelles were also broken.When light was over 8000 lx the cell structure was relatively normal. With the light intensity at 8000 lx and lower,the chloroplast number decreased,thylakoid structure began to fuzzy,plastid balls and starch granules enlarged. Under 4000 lx light intensity,part of chloroplast membrane was damaged,grana lamellas were blurring,plastid balls and starch granules obviously increased and enlarged. Under the light intensity of 500 lx,the cell membrane began to collapse,chloroplast membrane was heavily damaged,grana lamella disintegrated and only had a small amount of unordered lamella structure,the degree of inanition was serious, some cells even became empty cells. 【Conclusion 】 Based on the comprehensive analyses of various indexes,we draw a conclusion that R. hybridum is able to tolerate the low light intensity of 4000 lx,however a suitable light intensity for R. hybridum growth is between 12 000- 16 000 lx.