Downton W J, Grant W J, Robinson S P
Commonwealth Scientific and Industrial Research Organization, Division of Horticultural Research, G.P.O. Box 350, Adelaide 5001, South Australia, Australia.
Plant Physiol. 1985 May;78(1):85-8. doi: 10.1104/pp.78.1.85.
The gas exchange of spinach plants, salt-stressed by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar, was studied 3 weeks after starting NaCl treatment. Photosynthesis became light saturated at 1100 to 1400 micromoles per square meter per second in salt-treated plants and at approximately 2000 micromoles per square meter per second in control plants. Photosynthetic capacity of the mesophyll measured as a function of intercellular partial pressure of CO(2) at the light intensity prevailing during growth and at light saturation were both decreased in the salttreated plants. The CO(2) compensation points and relative enhancements of photosynthesis at low O(2) were not affected by salinity. The lower photosynthetic rates in salt-treated leaves at 450 micromoles per square meter per second were associated with a 70% reduction in stomatal conductance and low intercellular CO(2) (219 microbars; cf. 285 microbars for controls). Increasing photon flux density to light saturation extended the linear portions of the CO(2) response curves, increased stomatal conductances, increased intercellular CO(2) in the salt-treated plants, but lowered it in controls, and accentuated differences in photosynthetic rate (area basis) between the treatments.Leaves from salt-treated plants were thicker but contained about 73% of the chlorophyll per unit area of control plants. When photosynthetic rates were expressed on a chlorophyll basis there was no difference in initial slope of assimilation versus intercellular CO(2) between treatments. Photosynthetic rates (chlorophyll basis) at light saturation differed only by 20% which was also observed earlier with isolated, intact chloroplasts (Robinson et al. 1983 Plant Physiol 73: 238-242).Measurement of carbon isotope ratio revealed less discrimination against (13)C with salt treatment and confirmed the persistence of low intercellular partial pressures of CO(2) during plant growth. The development of a thicker leaf with less chlorophyll per unit area during salt treatment permitted stomatal conductance and intercellular partial pressure of CO(2) to decline without restricting photosynthesis and had the benefit of greatly increasing water use efficiency.
通过在营养液中每天以25毫摩尔的增量添加氯化钠直至最终浓度达到200毫摩尔对菠菜植株进行盐胁迫处理，并在开始氯化钠处理3周后研究其气体交换情况。在盐处理的植株中，光合作用在1100至1400微摩尔每平方米每秒达到光饱和，而在对照植株中约为2000微摩尔每平方米每秒。以生长期间的光照强度和光饱和时细胞间二氧化碳分压的函数来衡量的叶肉光合能力，在盐处理的植株中均有所下降。二氧化碳补偿点以及在低氧条件下光合作用的相对增强不受盐度影响。在450微摩尔每平方米每秒时，盐处理叶片较低的光合速率与气孔导度降低70%以及细胞间二氧化碳浓度较低（219微巴；对照为285微巴）有关。将光通量密度增加至光饱和会延长二氧化碳响应曲线的线性部分，增加盐处理植株的气孔导度，提高其细胞间二氧化碳浓度，但对照植株的细胞间二氧化碳浓度会降低，且会加剧处理间光合速率（以面积计）的差异。盐处理植株的叶片更厚，但单位面积叶绿素含量约为对照植株的73%。当以叶绿素为基础表示光合速率时，各处理间同化作用与细胞间二氧化碳的初始斜率没有差异。光饱和时的光合速率（以叶绿素为基础）仅相差20%，这与之前对分离的完整叶绿体的观察结果一致（罗宾逊等人，1983年，《植物生理学》73: 第238 - 242页）。碳同位素比率测量显示，盐处理对¹³C的歧视较小，并证实了植物生长期间细胞间二氧化碳分压持续较低。在盐处理期间叶片变厚且单位面积叶绿素减少，这使得气孔导度和细胞间二氧化碳分压能够下降而不限制光合作用，并且极大地提高了水分利用效率。
