Study On Mechanism Of Quick Endodormancy Release Of Peach Buds Induced By Three Treatments

For deciduous fruit trees, endodormancy is a biological characteristic developed to resistthe cold conditions in winter. The release of endodormancy requires accumulation of chillingtemperatures. Chilling deficiency leads to aberrant budburst and tree growth, which reduceproduction capability of fruit trees seriously. For this reason, endodormancy became one ofthe important limiting factors of protected fruit production and fruit production in warmregions. Studies on dormancy release mechanim now involved various fields such asphysiology, ecology, biochemistry and molecular biology. Experiments also showed thatmany treatments have the effect of breaking dormancy besides chilling temperature. In orderto explore mechanism of short time required endodormancy release, find out the key controlfactors and provide basis for the research of efficiency dormancy-breaking technology,dormancy release processes induced by50℃high temperature（physical treatment）, hydrogencyanamide （chemical treatment） and TDZ （plant growth regulator treatment） were studied inthe experiment.Our study was focused on positions and mutual relationships of respiration, H₂O₂metabolism and Ca²⁺for the reason that they all changed significantly during endodormancyrelease and Ca²⁺was an important regulatory factor of cell division. The experiments wereconducted in College of Horticulture Science and Engneering, Shandong AgriculturalUniversity during2010²013, using one-year-old shoots of ‘shuguang’ nectarine （Prunuspersica var. nectariana cv. Shuguang）. Cell cycle characters of endodormant buds wereanalyzed and effects of the three dormancy-breaking treatments on budburst, respiration,H₂O₂metabolism and hormone contents were studied. Effects of hydrogen cyanamide, TDZand H₂O₂on Ca²⁺transports of dormant bud tissues were also measured. And a preliminarysummary on relations among respiration, H₂O₂metabolism and Ca²⁺were also made. Themain results were as follows:1. Diploid cell group （G1phase） and tetraploid cell group （G2phase） exsited in budmeristem during budburst. But no tetraploid cell group （G2phase） exsited in bud meristemduring endodormancy, which indicated the inhibition of chromosome replication.2.50℃high temperatureand hydrogen cyanamide were more effective in breaking budendodormancy and TDZ showed poorly effects. For floral buds, hydrogen cyanamide resulted in the earliest budburst and highest budburst rate and was the most effective in breakingendodormancy.50℃high temperature was less efficiency and TDZ was the worst. But forvegetative buds,50℃high temperature was the most effective and TDZ had the lowestefficiency. Hydrogen cyanamide also showed toxic effects, which performed as bark colourchanging, shoot tip drying and bud necrosis.3. In endodormant bud meristem cells, high level of Ca²⁺existed in the region of nucleusand cytosol. The Ca²⁺channel was active and meristems were at the state of absorbing Ca²⁺.Hydrogen cyanamide and TDZ at low concentration showed little effects of Ca²⁺transport ofendodormant bud meristem. However, at the effective concentration for dormancy-breaking,hydrogen cyanamide reduced and TDZ raised the absorbing rate of Ca²⁺.4. On H₂O₂metabolism, both50℃high temperature and hydrogen cyanamide inhibitedCAT expression and CAT activity in buds and induced H₂O₂accumulation. POD activitychanged little. The CAT inhibition and H₂O₂accumulation induced by50℃high temperatureoccurred earlier and lasted shorter than that in hydrogen cyanamide treatment. TDZ showedno significant effects on H₂O₂content and activity of CAT and POD.5. Exogenous H₂O₂showed little dormancy breaking effects after application. However,exogenous H₂O₂affected the Ca²⁺tansport of dormant primordiums. H₂O₂reduced theabsorption rate of Ca²⁺at lower concentration and led to transfer direction altering fromabsorption to release at higher concentration. Exogenous H₂O₂also induced the increase of K+release and Mg²⁺absorption, and decrease Na+absoption.6. Respiration of dormant buds was influenced differently by the treatments. Both50℃high temperature and hydrogen cyanamide reduce respiration rates of dormant buds whileTDZ showed no significant effect. Bud respiration rate remained low several hours after50℃treatment. Inhibitory effects of hydrogen cyanamide were in direct proportion to itsconcentration. Interestingly, hydrogen cyanamide also showed promoting effect on respiration1d after treatment. For respiratory electron transfer pathways, both50℃treatment andhydrogen cyanamide inhibited the CYT pathway but show no regularly on the ALT pathway.For the substrate pathway, the PPP pathway was activated in the1st to the4th day after50℃and hydrogen cyanamide treatment, and the TCA pathway was activated before budburst. Nosignificant effects of TDZ on respiratory pathways were detected except the activation of PPPpathway12d after treatment.7.50℃high temperature and hydrogen cyanamide also affect content of hormones suchas GA, ZR, IAA and ABA. In50℃treatment, contents of the4hormones decreasedsignificantly at the4th day. At the time of budburst, contents of GA, ZR and IAA rised and ABA content were still less than control. In hydrogen cyanamide treatment, contents of GA,IAA and ABA also decreased but the range was smaller than that in with50℃treatment.