| Longan(Dimocarpus longan Lour.),also known as guiyuan and yizhi,has higher nutrition andhealth-keeping values,particularly with both tender and sweet taste characteristics ofthe pulp,which has a ―southern small ginseng reputation‖,which is well received by consumers.However,the longan is mature in the summer with high temperature and high humidity,and its physiology metabolism is exuberantafter postharvest,the fruit is difficult to keep fresh due to its colorchange and easiness to deterioration.Under ambient temperature,it will show a phenomenon: rapid softening,dissolving,juice-flowing and rotting of pulp in 3 d-4 d after harvest,which is called ―pulp breakdown‖,seriously restricts the postharvest storage life.Previous studies have shown that the pulp breakdown of postharvest Longan fruitmay is a kind of programmed cell death(PC D),and Caspase-3 is a key enzymefor PC D.This experiment analyzed the storage effect of longan fruit with six packaging methodsunder normal temperature(25℃).Analysing the longan pulp breakdowncharacterof four different varieties and the enzyme activity changeof Caspase-3andCaspase-4in the process ofpulp breakdown,and studying the correlation between the two enzyme activity andpulp breakdownindex.C loning of Metacaspase(DlMCⅡ-1 and Dl MC-1)gene sequence,and carring out theanalysis of subcellular localization,the expression pattern of pulp breakdown、different tissuesand salt stress-induced in the process of leaf senescence,expecting to explore theMetacaspase role in pulpbreakdown under room temperature storage condition.The main results were as follows:1.This six packaging methods all could prolong the storage time of postharvestlongan fruit to some extent under normal temperature(25℃).However,from the composite ofpericarpcolor value,pericarp browning index,pulp breakdown index and the fruit quality loss rate,the effect of ZSMA(modified-atmosphere package of ZhongShan)treatmentwas thebest,followingwas BOPP(bi-oriented polypropylene film),PE(polyethylene film)and ―tray + double-layer0.01 mmPE film‖,―tray + single-layer 0.01mmPE‖ was the worst.Considering the factor that EVA(ethylene-vinyl acetate copolymer)treatmentwas more special,the pericarp browning was the most serious,but the pulp quality was the best.2.Thepericarp a* values(chromaticity values)、pulp water contentand browning index offour longan varietieswere all increasedwith the extension of storage time by using BOPP package bag,andpulp water contenthad no obvious correlation with pulp breakdown index,while there had a significant positive correlation betweenbrowning index and pulp breakdown of the other three varietiesbesides?C huliang‘;the L*、b*、C* values and TSS contentwere all decreased,L* valueshad a significant negetive correlation with pulp breakdown of four longan varieties,while a*、b*、C* values and TSS contenthadno obvious correlation with pulp breakdown index of?Shixia‘ and ?Dongbi‘;the b* values and TSS contenthad a significant negetive correlation with pulp breakdown of?Chuliang‘and?Shuiyan‘,while a*and C*values,the only a*values respectively had no obvious correlation with pulp breakdown index of the former and the latter.3.The pulp Caspase-3 activity were all increasedof hanging tree period with the extention of harvest time;the Caspase-3 andCaspase-4activity were all risedin the process of pulp breakdownwith the extension of storage time,hada very significant positive correlation with pulp breakdown index of four varieties in 2015;the Caspase-3 and Caspase-4 activity were all increasedin the process of pulp breakdown with the extension of storage time and Caspase-4 activity had a significantpositive correlation with pulp breakdownindex of four varieties;Caspase-3 activity had a significant positive correlation with pulpbreakdownindex of ?Shixia‘ and ?Dongbi‘,while there had no obvious correlationof?C huliang‘and?Shuiyan‘in 2016.4.The results through factor analysis of browning index and pulp breakdown index in the period of storage showedthatthe level of pulp breakdown and browning respectively was the lowest and mediate of ?Chuliang‘;the level of browning was all lower and the level of pulp breakdown was mediate of?Shixai‘ and ?Shuiyan‘;while the level of pulp breakdown and browning were both the highest of ?Dongbi‘,which was the most unresistant to storage at roomtemperature condition.5.The two PCD-related genes of Metacaspase CDS sequence of longan fruit had been successfully cloned,respectively named DlMCⅡ-1 and Dl MC-1.Amino acid sequence analysis showed that the translation of the proteins were unstable acidic protein,of which the homology of Dl MCⅡ-1gene and LcMCⅡ-1(AMB51354.1)was 94%,the homology ofDl MC-1 gene andCsMC-1(KDO57066.1)was 83% by the speculating of the amino acid sequence;Phylogenetic tree analysis indicated that Dl MCⅡ-1 gene and LcMC Ⅱ-1(AMB51354.1)were at the same branch team,which had a recent evolutionary distance;theevolutionary ofDlMC-1was near toCsMC-1.It can be speculated that DlMCⅡ-1may be related to LcMCⅡ-1,which has similar functions,while Dl MC-1 has a similar function with Cs MC-1.6.The results of subcellular localization of tobacco leaves and tobacco protoplast by the induced transformation with agrobacterium both showed that the DlMCⅡ-1 protein was positioned in the cytoplasm,which was consistentto the positioning resultof the LcMCⅡ-1,and also similar to the Caspases positioningin animals.7.Quantitative RT-PCR analysis of the expression patternsofDl MCⅡ-1and DlMC-1 in four different varieties and different organization revealed that theexpression of DlMCⅡ-1 and DlMC-1gene were higher in pulp of ?Dongbi‘(higher pulp breakdown index)was parallelly higher than that in pulp of ?Shixia‘(lower pulp breakdown index);Two genes bothhad a highexpression in leaf,followed in pulp,while had a low expression in root,young fruit and the pericarp;Two genes were both up-regulate expressing in the process of leaf senescence bysalt stress-induced. |
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