The Response Mechanism Of Photosynthesis In Tomato Leaves To Low Night Temperature And Recovery

Facilities vegetables have become an important part in China’s modern agricultural production, and china will continue to increase agricultural facilities, ensure people "basket " safe and adequate. " winter basket" project has become the important drives that guarantees the supply of national winter vegetables and meets people the demand in" 12 5"period. However, early spring cultivation in China, tomato cultivation under glasshourse easily suffers low night temperature, which resulting in drop of photosynthesis and the serious influence on its yield and quality.Therefore, It is important to study how the low night temperature affect on photosynthetic function of tomato leaves, which help us artificial regulation to eliminate the limiting factor of photosynthesis, reduce the harm on plants caused by low night temperature, and achieve high yield and high quality cultivation purposes.The effects of low night temperature at 9℃and 6℃then recover for 9 d at optional temperature 15℃simulated by climate chambers on the mechanism of photosynthesis and regulation of calcium in tomato leaves were studied. It is important both in scientific and practical fields. The main research results are as follows:1.It was clear that different low night temperature (LNT, i.e.,9℃and 6℃) stress led to the decrease of photosynthesis. LNT led to irreversible inhibition of photosynthesis mainly accompanying by the decrease in Gs, Ci and the increase in Ls, and the lower Rubisco activity occurred in transcription level.So stomatal limitation and the lower Rubisco activity were factors causing the net photosynthetic rate reduce under LNT at 9℃and 6℃for 9 d.In recovery process at 15℃for 9 d after LNT, stomatal limitation was mainly the reason that affected recovery speed and degree of photosynthesis.2.It was clear that different LNT at 9℃and 6℃caused carbohydrates feedback inhibition phenomenon in tomato leaves.There were abundant accumulations of sucroses; LNT inhibited the activities of sucrose phosphate synthase (SPS),which occurred in mRNA transcription level by analyzing RT-PCR.There were significantly negative linear correlations between sucrose and starch content and Pn, as well as sucrose content and SPS activity. Reduced photosynthesis under LNT could be explained by the hypothesis of carbohydrates feedback inhibition; the following influence of photosynthesis was not the result of feedback inhibition in recovery process after LNT.3. Effects of different LNT on photoinhibition and photochemical activity of PSⅡin tomato leaves were studied.It was shown that the maximum photochemical efficiency(Fv/Fm), potential activities of PSII(Fv/Fo), the actual photochemical efficiency of PSⅡreaction center (ΦPSⅡ), rate of electronic transmission of photosynthesis (ETR), photochemical quenching coefficient (qP) of leaves deceased at 9℃and 6℃for 9 d, while the non-photochemical quenching coefficient (NpQ) increased. During recovery, Fv/Fm could completely come back to control, other chlorophyll fluorescence parameters could reached more than 85% of control. LNT caused the reversible of PSII photoinhibition, the reduce in PSII photochemical activity played the major role to protect photosynthetic institutions.Excessive light energy consumed by the increase in protons power potential of both sides on thylakoid membranes, the allocation of absorbed light to thermal dissipation (D), excessive energy (Ex) and the state conversion to protect photosynthetic institutions. D was predominant among.4.Effects of different LNT on PSI photoinhibition in tomato leaves were studied.LNT increased the photochemical yield of PSI Y(I), quantum yield of non-photochemical energy dissipation in PS I due to acceptor side limitationY(NA) and the reduced of P700. LNT led to the limitation of the acceptor side of PSI,which caused PSI photoinhibition.5.The effects of different LNT on the active oxygen metabolism and Ascorbate-Glutathione cycle of tomato leaves were studied.The results showed that LNT caused the reduce in the rate of [Je(PCR)] mainly accompanying by the increase in [Ja(O2-dependent)].We found that LNT increased the active oxygen (O2- and H2O2) and MDA contents; improved the activities of antioxidant enzymes (SOD, APX, DHAR, GR) and the contents of antioxidant (AsA,GSH). In addition, the decrease in O2- production rate and H2O2 and MDA under recover condition at 15℃for 9 d after LNT for 9 d; at the same time, SOD, APX, DHAR and GR activities as well as AsA contents,AsA/DHA and GSH/GSSG were all decline. It indicated that the increase in SOD activitie and scavenging activity of Ascorbate-Glutathione cycle did not keep pace with the rate of oxygen reduction since the increase in O2-, H2O2 and MDA levels were observed,especially in 6℃treated plants.Reactive oxygen removal needed the coordination function between antioxidant enzymes and the whole antioxidant defense system.6.It was clear that short-term LNT at 6℃led to the decrease of photosynthesis in tomato leaves. Pn declined by 9.8% when plants were treated 1 h at 6℃, with the synchronical decline in Gs,Ci and Tr (up to 19%,8.9% and 12%). We found that there was a drastical reduce in the area and the stomatal open percentage through the scanning electron microscope (SEM) at 1 h of 6℃.The stomatal open percentage reached 44.31%,while the ratio of that control plants was 65.16%. The reduce in CE after 3 h at 6℃. Stomatal was very sensitive to LNT. LNT at 6℃for 11 h caused chloroplasts shape became relatively slightly rounded,the increase in the number of starch grains and the ratio between chloroplast and starch grains, and the reduce in eosinophilic granular osmium tetroxide.So the primary factors of the decline in Pn caused by short-term LNT was stomatal close.7. The effect of short-term LNT at 6℃on the sucrose metabolis internal regularity of tomato leaves. There were abundant accumulations of sucrose(31.2%) at 6℃for 1h, and sucrose accumulation caused by sucrose internal regularity beening broke after 3 h. And LNT at 6℃for 11h caused rhythmic lag phenomenon in AI, NI and SPS, which were 2 h behind compared with controls and did not occur in mRNA transcription level by analyzing RT-PCR.8.The effects of short-term LNT at 6℃on photosystemsⅠandⅡof tomato leaves were studied. We investigated direct information on PSI and PSII in vivo tomato plants using the Dual-PAM-100 fluorometer. The results showed that LNT led to the slight decrease in Fv/Fm,and the ratio of Fv/Fm maintained the normal the scope(0.79-0.83) under 6℃for 11h. The Y(NPQ)and Y(NO) was always lower than that of control plants, and the photochemical yield Y(II) of PSII was higher, Which indicated that 11 h of LNT did not cause photoinhibition and photo-damage of PSII. At the same time, LNT increased the photochemical yield of PSI Y(I) and decreased the donor side limitation of PSI Y(ND) and acceptor side limitation of PSI Y(NA).9. The effects of short-term LNT at 6℃for 11h simulated by climate chambers on the Water-water cycle in chloroplasts of tomato leaves were studied.The results showed that LNT increased ROS(O2- and H2O2), but did not increased MDA contents; improved the activities of antioxidant enzymes (SOD,DHAR) and the contents of antioxidant (AsA, GSH) after 3 h.So, it was very important to start up water-water cycle in chloroplast as for matching oxygen reduction rate.ROS accumulation in the chloroplasts occured behind the decrease in carbon assimilation.10. Regulation of calcium on the photosynthesis parameters in tomato leaves under LNT at 6℃for 7d. Pretreatment with 0.3% CaCl2 increased widen and area of the stomata by SEM, alleviated the reduce of Gs, improved Ci and the Pn of tomato seedlings under LNT; Ca2+ increased widen and area of chloroplasts under LNT and the area of starch grains,but decreased the amount more, so led to the great decrease in the ratio between starch grains and chloroplast, which promoted the absorb of the light energy and photosynthesis.11. Regulation of calcium on the water-water cycle in chloroplasts of tomato leaves under LNT. Pretreatment with CaCl2 further improved the activities of antioxidant enzymes (SOD, APX, DHAR, GR) and the contents of antioxidant (AsA, GSH) in the chloroplasts, So Ca2+ improved scavenging ability to reactive oxygen species by regulating Ascorbate-Glutathione cycle and decreased the accumulation of reactive oxygen species (O2- and H2O2) in the chloroplasts.It indicated that Ca2+ mainly activated protective enzyme activity and antioxidants contents to eliminate the reactive oxygen species under LNT, so as to protect the plant from harm.