遮荫对两个基因型玉米叶片解剖结构及光合特性的影响

Response of anatomical structure and photosynthetic characteristics to low light stress in leaves of different maize genotypes

以耐荫性不同的玉米品种郑单958(ZD958,耐荫性较强)和豫玉22(YY22,耐荫性较弱)为材料,研究了苗期50%遮荫对玉米叶片形态结构和光合特性的影响。结果表明:形态结构上,苗期遮荫处理后,玉米叶片变薄,单位面积叶绿体数目减少,基粒数、基粒厚度和片层数增加,但是YY22的叶绿体大部分发育不良,肿胀呈球形,基粒片层和基质片层出现不同程度的松散;而ZD958大部分叶绿体结构良好,各部分发育基本正常。光合特性上,弱光胁迫使玉米叶片叶绿素含量升高,净光合速率(Pn)、PSⅡ最大光化学量子产量(Fv/Fm)和实际光化学效率(ΦPSⅡ)降低,胞间CO2浓度(Ci)和非光化学猝灭(NPQ)增加,但是YY22的Pn、Fv/Fm和ΦPSⅡ显著下降,Ci和NPQ显著升高;而ZD958的Fv/Fm和ΦPSⅡ下降幅度较小,且NPQ增加亦不显著。研究结果提示,弱光胁迫对玉米叶片形态结构和光合特性影响较大,且存在基因型差异,耐荫性较强的品种对弱光环境的适应性较强。

Prolonged rainy weather during the maize growing season can lead to insufficient light,and thus dramatically lower yields.Maize,Zea mays L.,is one of the most important food crops in China,and around the world,and a high and stable yield is necessary to guarantee food safety.Previous studies into the effects of low light stress on maize have predominantly focused on aboveground biomass,leaf area,chlorophyll content,net photosynthetic rate,root activity,soluble protein content,grain yield,nutrient levels,and the activity of some enzymes,including superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,sucrose-phosphate synthase（SPS）,sucrose synthase（SS）,soluble starch synthase（SSS）,granule-bound-starch synthase（GBSS）,adenosine diphosphate glucose pyrophorylase（ADPGPPase）,and uridine diphosphate glucose pyrophorylase（UDPGPPase）.However,the potentially damaging effects of low light stress on the anatomical structure of maize photosynthetic systems have seldom been mentioned in the literature,and the relationships between anatomical structure and photosynthetic characteristics remain unclear.Our objective was to determine the effects of low light stress on the anatomical structure of maize photosynthetic systems,and the relationship between photosynthetic characteristics and anatomical structure,in different maize cultivars at the seedling stage. We experimented on the seedling leaves of two maize cultivars： the shade-tolerant cultivar Zhengdan 958（ZD958） and the shade-sensitive cultivar Yuyu 22（YY22）.These were grown in experimental pots in the field.50% shade treatment was used,with non-shaded seedlings as controls.Under low light stress,plant growth was inhibited;leaves became thinner,numbers of chloroplasts per unit of leaf area decreased,number of grana increased,grana thickness increased,and the thickness of the grana lamellae increased.In the shade-sensitive cultivar YY22,most of the chloroplasts became dysplastic,the stroma lamellae swelled and the grana lamellae became loose.In contrast,in the shade-tolerant cultivar ZD958 the chloroplasts were almost normal with some healthy parts.The net photosynthetic rate（Pn）,photochemical efficiency（Fv/Fm）,and actual photochemical efficiency（ΦPSⅡ） all decreased under shade.Chlorophyll content,intercellular CO2 concentration（Ci） and non-photochemical quenching（NPQ） increased;however these were all reversible.The values of all variables investigated were significantly higher or lower in the shade-sensitive cultivar YY22 than in the corresponding control.Shading had no significant influence on the shade-tolerant cultivar ZD958 except for Pn and Ci.We speculate,therefore,that low light stress has different significant effects on the anatomy and photosynthesis of maize with different genotypes.The shade-tolerant cultivar ZD958 maintains more normal anatomical structure and higher photosynthetic function than the shade-sensitive YY22 under low light stress;these are the major anatomical and physiological traits necessary for shade tolerance.