研究盐胁迫对秀丽四照花（Cornus hongkongensis subsp. elegans)幼苗的生物量分配、光合特性和叶绿体超微结构的影响，探讨植物体对盐胁迫的响应机制。

用海盐配制5 个盐含量（质量分数）梯度［（0(CK）、0.20%、0.30%、0.40%、0.45%）］的1/2 Hogland进行秀丽四照花水培处理，期间观察植株盐害症状、测定幼苗的气体交换参数、叶绿素荧光参数、叶绿素含量，并观察叶绿体超微结构;处理结束时分析了幼苗生物量的分配情况。

盐胁迫下，秀丽四照花幼苗叶片由下及上逐渐出现发黄、块状发紫和拟炭疽病斑等盐害症状;随着盐胁迫的加深，出现落叶、新梢枯萎，甚至死亡现象;>0.20%盐处理的幼苗半活期<20 d。尽管根茎生物量比随着盐浓度的增加而提高，但盐胁迫对生物量的分配影响并不显著。随着盐浓度的升高和培养时间的延长，幼苗的净光合速率（P_n）、气孔导度（G_s）、胞间CO₂浓度（C_i）和蒸腾速率（T_r）逐渐降低，而叶片水分利用效率（E_WUE）逐渐增加，其中0.20%（质量分数,下同） 盐处理的幼苗其光合参数受影响最小。另外，盐胁迫对秀丽四照花的最大光量子产量（F_v/F_m）影响较小，而对光系统Ⅱ(PSⅡ）潜在光化学活性（F_v/F₀）影响较大。当盐溶液质量分数>0.20%时，叶绿素a(Chl a）、叶绿素b(Chl b）、总叶绿素(Chla+b)和类胡萝卜素（Car）的含量显著下降。同时，盐胁迫显著改变了叶绿体的超微结构，表现为随着盐胁迫的加深，叶绿体内的淀粉粒、脂滴、噬锇颗粒数量增多，基质片层结构松散、肿胀。

盐胁迫显著影响了秀丽四照花幼苗的光合特性和叶绿体超微结构，从而引起植株不同程度的盐害特征和半活期差异。综合各指标的盐胁迫响应，秀丽四照花在0.20%盐处理下的生长、光合特性和叶绿体超微结构与对照差异不显著，与秀丽四照花的田间栽培试验表现一致。

To illustrate the response mechanism to salt stress, effects of different concentrations of salt stress on biomass partitioning, photosynthetic characteristics and chloroplast ultrastructure in seedlings of Cornus hongkongensis subsp. elegans were analyzed.

The seedlings were cultured in the 1/2 Hogland nutrients solution with five salt gradient concentrations［0(CK), 0. 20% , 0. 30% , 0. 40% , 0. 45%)］. During culture, salt injury symptoms in seedlings were recorded, photosynthetic parameters(including gas exchange parameters, chlorophyll fluorescence parameters, chlorophyll content)were measured, and changes of chloroplast ultrastructure were observed. Also, the responses of biomass partitioning to salt stress were assessed at the end of experiment.

Salt-damage symptoms such as yellowing, purplish and anthracnose-like gradually appeared in the leaves of seedlings from bottom to top under salt stress. With the increment of salt concentration and the elongation of stress, leaves and new shoots withered, until the whole plant wilted and died. Periods of 50% survival for treatments with >0. 20% salt concentrations were lower than 20 days. Although gradual increments were monitored in biomass of root /shoot with strength of salt stress, the effects of salt stress on biomass partitioning was still not significant. With the increase of salt concentrations and the lasting duration of culture, net photosynthetic rate(P_n), stomatal conductance(G_s), intercellular CO₂ concentration(C_i)and transpiration rate(T_r) were decreased, but leaf water use efficiency(E_WUE)was improved. Of all salt treatments, photosynthetic parameters in seedlings suffering from 0. 20% salt stress were affected slightly. Compared with a little effect of salt stress on maximum optical quantum yield(F_v/F_m), the potential photochemical activities of PSⅡ(F_v/F₀)were significantly affected by salt stress. Significantly, treatments with >0.20% salt concentrations decreased the contents of chlorophyll a(Chl a), chlorophyll b(Chl b), total chlorophyll(Chl a+b) and carotenoid(Car). Meanwhile, salt stress obviously changed chloroplast ultrastructure, showing that number of starch grains, lipid droplets and osmiophilic globules in chloroplast were increased, and stromal lamellae structure was loose and getting swell with strengthen of salt stress.

Salt stress exerted significantly inhibitions on photosynthetic characteristics and chloroplast ultrastructure, resulting in various salt-damage symptoms on leaves of seedlings and different survival rates corresponding to salt concentrations. Considering the responses of all measured indexes to salt stress, growth, photosynthetic characteristics and chloroplast ultrastructure in seedlings of Cornus hongkongensis subsp. elegans treated with 0.20 % salt concentration were similar to that of CK, which is in accord with the results of field trial.