| Tomato(Lylopersicon esculentum Mill)is one of the most cultivated vegetables in China.The low light intensity,suboptimal temperature during autumn and winter and soil salinization in the solar greenhouse of northern China had inhibited protected vegetable sustainability production.Although most soils contains higher iron contents,the bioavailability of iron contents in plants is often insufficient due to different soil factors and plant genotypes,leading to plants growth inhibition and leaf chlorosis.Exogenous nitric oxide(NO)could improve the resistance of plants to abiotic stress.At present,there are few reports on the effects of NO3-and iron deficiency stress on tomato seedlings growth and iron absorption under suboptimal temperature and studies on NO mitigates the injury of plants induced by related stress.Therefore,it has important theoretical and practical significance for mitigate the chlorosis by investigating the response of tomato seedling growth and iron absorption to NO3-and iron deficiency under suboptimal temperature as well as exogenous NO on alleviating the stress of NO3-and iron deficiency in tomato seedlings.On the basis of the existing research,the effects of low light and suboptimal temperature adaptability of seedlings of different tomato varieties were firstly investigated.Secondly,the effects of tomato seedlings growth and iron absorption on NO3-and iron deficiency under suboptimal temperature were studied.Then,effects of sodium nitroprusside(exogenous NO donor)on the respiration of tomato seedlings under NO3-and iron deficiency were explored in order to provide theoretical guidance and measures for mitigating the symptom of green loss of tomato seedling.The main results are as follows:1.Compared with the normal temperature treatment,ten tomato varieties showed that the growth,leaf chlorophyll content and root activity of tomato seedlings decreased;electrolyte leakage,MDA and proline content increased after treated for 14 days under low light and suboptimal temperature.There were significant differences among these varieties for the tolerance.All these indicated that the adaptability of ‘Hongfen champion'(6#)to suboptimal temperature under low light condition was superior to the others,so it was suitable for cultivation in solar greenhouse in winter of northern China.‘Zhongshu4'(10#)and ‘Jinyu x1'(4#)had low adaptability to suboptimal temperature under low light condition and other varieties were moderate.2.The growth was significantly inhibited under suboptimal temperature compared with appropriate temperature treatment;the plant heights,leaf areas and dry matter accumulations were markedly decreased.The effects of iron deficiency under suboptimal temperature on the growth of tomato seedlings were larger than that of under appropriate temperature treatments.Under suboptimal temperature,the plant heights of tomato seedlings in iron deficiency and/or NO3-stress treatments were not significantly different from no stress treatment,but leaf areas of tomato seedlings were decreased obviously.The leaf electrolytic leakage,root activity and Fe3+ reductase activity of tomato seedlings were markedly increased under suboptimal temperature,but chlorophyll content,total root length,root surface area,root tip number and root volume were obviously reduced.The iron contents in roots,stems and leaves of tomato seedlings were also remarkably decreased.The NO3-stress and the combined stress of iron deficiency and NO3-stress under suboptimal temperature aggravated the reduction of dry matter,leaf electrolytic leakage and the inhibition of iron ion absorption in tomato seedlings.The iron ion absorption showed the antagonistic impact on the absorption of potassium and calcium ion,but showed different effects among different organs.3.Study the effects of sodium nitroprusside(SNP)on alleviating iron deficiency and NO3-stress of tomato seedlings.The results indicated: iron deficiency inhibited the tomato seedlings growth,decreased chlorophyll(a and b)and carotenoid contents,and led to obvious chlorosis;iron deficiency also reduced the activity of SOD,POD and CAT,resulting in significant accumulation of MDA contents and higher electrolytic leakage;proline and soluble sugar contents were not significantly changed;contents of N,P,K,Ca,Mg and Fe in both leaves and roots of tomato seedlings were decreased under iron deficiency to different extent.The combined stress of NO3-stress and iron deficiency,promoted the inhibiting of plant growth,the decreased degrees of chlorophyll(a and b),carotenoid contents and the activity of SOD,POD and CAT in tomato seedlings were more obvious and electrolytic leakage,MDA,proline and soluble sugar contents were more significantly increased under combined stress;contents of N,P,Mg,Fe in both leaves and roots of tomato seedlings were much lower,but the contents of K and Ca were significantly increased.Compared the treatment without SNP,adding 0.1 mmol·L-1 SNP could mitigate the inhibition of growth indicators and physiological indexes of tomato seedlings by iron deficiency or the combined stress of NO3-stress and iron deficiency,indicating that sodium nitroprusside had significant alleviating effects on iron deficiency and NO3-stress in tomato seedlings,and increased tomato seedlings tolerance to salt stress and iron absorption capacity.while adding 0.1 mmol·L-1 sodium ferrocyanide(SF)also showed alleviating or promoting effect on some above indexes including the activity of SOD,POD and CAT to some degree,but the other physiological indexes were not significantly changed,the reason was that SF also contains iron.4.With adding 0.1 mmol·L-1 SNP,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),ps? maximum photochemical efficiency(Fv/Fm),ps? actual photochemical efficiency(?ps?),photochemical quenching coefficient(qP),nitrate reductase(NR),glutamine synthase(GS),glutamate synthase(GOGAT)and glutamate dehydrogenase(GDH)were significantly higher or had rising tendency than those of tomato seedlings treated with no SNP under iron deficiency and combined stress of iron deficiency and NO3-stress.The values of Fo under iron deficiency and the values of Ci under the combined stress of iron deficiency and NO3-stress with adding 0.1 mmol·L-1 SNP were significantly decreased.There was no significant change in the treatment of adding SF than that the treatment adding SNP.5.Exogenous nitric oxide influenced on ascorbate-glutathione cycle in tomato seedlings roots under iron deficiency and combined stress of iron deficiency and NO3-stress.Ascorbate peroxidase(APX),dehydroascorbate reductase(DHAR),glutathione reductase(GR)activities were increased markedly,monodehydroascorbate reductase(MDHAR)activity was decreased dramatically,AsA/DHA,GSH/GSSG ratios,ascorbic acid(As A)and glutathione(GSH)contents were increased markedly in tomato seedlings roots by adding exogenous nitric oxide,at the same time,contents of dehydroascorbic acid(DHA)and oxidized glutathione(GSSG)were decreased.The effects of sodium ferrocyanide(SF)are less than that of SNP.These results indicated that exogenous NO can clean reactive oxygen species(ROS)caused by iron and combined stress of iron deficiency and NO3-stress through increasing the activities of antioxidant enzyme and non-enzymatic antioxidant contents,such as ASA and GSH,and can thus improve the ascorbate-glutathione cycle to protect tomato seedlings roots from damage caused by iron and combined stress of iron deficiency and NO3-stress. |
PDF Full Text Request