Effects Of Exogenous Calcium On Photosynthetic Characteristics Of Sweet Pepper Seedlings Under High Temperature And Light Stress

Sweet pepper growth process often suffer stress,in the north of China,high temperature and light from August to September often results in the decrease of the yield.When plants suffer high temperature and light stress,calcium can reduce cell membrane damage.Therefore,to explore the factors affecting the yield of sweet pepper is important to guide agricultural production.Pepper has important significance status in the vegetable cultivation of China.With the expansion of planting area and the increasing human destruction on the environment improving the yield,improving the quality of sweet pepper has become imminent.By using sweet pepper,we studied the effects of different exogenous calcium concentration of photosynthetic and physiological characteristics of seedling leaves under high temperature and light.The main results are as follows:1.Under high temperature and light stress,photosynthetic rate,stomatal conductance and transpiration rate of T10(10 mM CaCl2)were higher than CK.Pn-light responsing curves showed that calcium-application can significantly reduce the stress caused by the increasing of dark respiration.The apparent quantum efficiency(AQY)and light compensation point(LCP)of T10 were lower than control groupunder high temperature and light stress.calcium-application can significantly improve the ability of sweet pepper seedlings to adapt to stress.2.Under normal culture conditions,Rubisco activity of among the three experimental groups showed no significant difference,but when exposed to stress,Ribulose-1,5-bisphospate carboxylase/oxygenase(Rubisco)activity of CaCl2 treatment group and control group were both decreased,and it decreased significantly lower in CaCl2 treatment group with 10 mM CaCl2,but Rubisco activity of CaCl2 group with 5 mM CaCl2 under stress increased firstly,and then decreased.3.Rubisco is composed of subunits coded by a nuclear gene(rbcS)and chloroplast gene(rbcL),respectively.Under high temperature and light stress,the relative expression of the control group of the small subunit and the subunit deceased obviously.While the small subunit of CaCl2 group 5 mM relative expression quantity has no obvious change under the stress process,large subunit expression decreased firstly and then increased.The small subunit of CaCl2 group 10 mM relative expression quantity is always increasing trend,but the large subunit of the relative expression amount was significantly higher than that under normal condition in the control group,but increased with the stress time prolonging.The relative expression amount decreased,and it decreased lower than the control group.4.Under the high temperature and light stress,relative to CK,the maximal photochemical rate(?P0)of T10 and T5 decreased slowly,and VK(300 ?s QA reduction degre)value,which is related to the oxygen evolving complex(OEC)integrity,rises slowly,and T10 treatment was the most obvious.During the stress that Vj value,which is related to 2 ms reaction center close,had different degrees of rise among three treatments.Under high temperature and light stress,various quantum efficiency per unit area per unit area such as light absorption(ABS/CSm),capture light energy per unit area(TR/CSm)and unit area for electron transfer energy(ET/CSm)of three treatments were decreased in different degree,and CK decreased most obviously,T10 decreased most slowly.Three experimental groups of units of active reaction center area(RC/CSm)during stress of three treatments also had different decline,and the trend was the same as that of quantum efficiency.5.High temperature and light stress leads to the imbalance between ROS production and scavenging.The activityof superoxide dismutase system(SOD),peroxidase(POD)and catalase(CAT)of CK group increased,and the spraying 5 mM,10 mM CaCl2 further enhanced the activity of the enzyme scavenging activity,with the most obvious treatment effect of spraying 10 mM.6.The contents of proline and soluble sugar of experimental groups were significantly higher than CK.The activity of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)increased during the stress,and malondialdehyde(MDA)as the main indicator of plant membrane peroxidation were significantly lower,under normal conditions of the experimental groups.The trend of relative electrical conductivity was in accordance with the above results.7.Most soluble proteins of plant cells are enzymes involved in cellular physiological and biochemical reaction,levels of them can be used as an important index of plant metabolism level.Under normal conditions,there was no significant difference among different treatments,at the same time,the content of soluble protein also increases slowly.Pretreatment of 5 mM,10 mM CaCl2 has increased the content of soluble protein but the effect is not significant.