Effects Of ABA On Physiological Mechanism Of Tomato Under Waterlogging

ABA,as a stress hormone,plays an important role in regulating several physiological processes in abiotic plant stress.The effects of ABA on physiological characteristics of Tomato under Waterlogging.In five different lines,i.e.ABA-deficient mutant(LA0673)and its control(LA0535),high ABA content strain rd29A:NCED1(#2,#7)and Mill.L.cv.New Yorker(WT)were investigated.The waterlogging was mimicked by treating pot plants with flooding.The main results of the study are as follows.1.The effects of ABA on the phenotype,chlorophyll content,root vigor,and photosynthetic parameters of tomato under waterlogging stress were investigated.The results showed that the leaves of LA0673 were wilting and showed a gray-green color,and there is no aerial roots in LA0673 under waterlogging.but there are a lot of aerial roots in the other 4tomato lines;the root activity of five lines significantly decreased and LA0673 was dead at 7d of waterlogging treatment,The root activity of LA0535 decreased to 6.34% of 0d,9.62% of#7,3.14% of WT and 6.43% of #2;LA0673 showed a significant increase in chlorophyll content due to wilting on the 7d of flooding treatment,and the other 4 lines showed a downward trend,The chlorophyll content of LA0535 was 57.13% of 0d,60.98% of #7,60.67%of WT and 80.30% of #2;the net photosynthetic rate(Pn)?stomatal conductance(Gs)and transpiration rates(Tr)of five lines showed a downward trend;the Gs of LA0535,WT,#2 and#7 decreased immediately in the early waterlogging treatment,they were earlier than LA0673;the intracellular carbon dioxide concentration(Ci)of five lines increased significantly or stabilized at a high level.In this study,only ABA-deficient LA0673 had no aerial root production,and the chlorophyll content of the high-ABA content strains(#2 and #7)was maintained at relatively high levels,suggesting that ABA may improve its waterlogging tolerance by delaying chlorophyll degradation and maintaining a high photosynthetic assimilation capacity.The net photosynthetic rate of the high ABA content lines(#2 and #7)was significantly higher than that of the ABA-deficient LA0673 at 7 d of flooding stress.Combined with the observation of external morphological changes under waterlogging stress,ABA improves waterlogging tolerance by participating in the photosynthesis of the plants and promoting the aerial root or adventitious root formation of tomato.2.Effect of ABA on antioxidant system and anaerobic respiratory system in tomato under waterlogging stress.The MDA content,soluble protein content,antioxidant enzyme activity,and root anaerobic respiratory enzyme activity of five strains were measured.The results reflected that the MDA content of the five strains showed a general trend of increasing and then decreasing with the increase of waterlogging time,and the malondialdehyde content of ABA-deficient LA0673 was significantly higher than that of the other four strains after 4 d of waterlogging stress,1.1,1.5,1.5 and 1.2 times that of LA0535,#2,#7 and WT,respectively;the trend of soluble protein content in the high ABA content strains #2,#7 and the trend of soluble protein content in WT and ABA-deficient strains and wild type was significantly lower than that of the high-ABA strains at 7 d of waterlogging;meanwhile,the leaf antioxidant enzyme activities of ABA-deficient and its control LA0535 were significantly lower than that of the high-ABA strains(#2 and #7),indicating that the high-ABA strains had higher tolerance to flooding.The trend of anaerobic respiratory enzyme activity of tomato plants under flooding stress was increasing and then decreasing,and was generally higher than 0 d,indicating that plants adapt to the low oxygen environment by enhancing their own anaerobic respiration;the PDC activity of the ABA-deficient strain LA0673 increased rapidly and reached a peak at 1 d of waterlogging treatment,whereas the PDC activity of the high-ABA content strain had no significant effect.Presumably the ABA deficient strains are more sensitive to flooding.The ADH and LDH activities of the wild-type and ABA-deficient strains were generally significantly higher than those of the high-ABA strains throughout the flooding treatment period,suggesting that ABA may play a key role on improving the resistance of plants to waterlogging by regulating anaerobic respiration and reducing the toxic effects of metabolites such as lactic acid and ethanol on cells.3.The results showed that WT > #7 > #2 > LA0535 > LA0673,in which the ABA-deficient LA0673 showed the worst performance and died after 7 d.The overall score of the strain with high ABA content was higher than that of LA0673,indicating that ABA plays an important role in improving the waterlogging tolerance of the plants under flooding stress conditions.The highest D value for the overall flooding tolerance of the wild-type WT strain compared to the other four strains,combined with the observation of external morphology,indicated that the WT strain was more tolerant to waterlogging under waterlogging stress,and that plant waterlogging tolerance was determined by a combination of factors,probably as a result of natural evolution.