Study On Regulating Mechanism Of Calcium On The Abscission Of Tomato Pedicel

Abscission is a very widespread process in nature. Flower abscission is one of the important obstacles in tomato production. Study of the mechanism of calcium on abscission may have great value in agronomy and industry of natural degradation of plant remnant bodies. Thus the like research will be helpful for understanding the theory of abscission and provide proper guidance for preventing flower abscission. This paper reports the calcium mediates abscission course in natural and ethylene conditions by influences physiological and biochemical processions, PG expression and accumulation and morphology of tissue and cells during the abscission of tomato pedicel explants. The more details are the following.1 .The role of calcium is delaying the abscission of tomato pedicel explants in natural. The abscission rate of the flower pedicel explants falls with the increasing calcium concentration. But VP, TFP and EGTA, the abscission rate goes up with the elevating those calcium inhibitors concentration. The 80mM calcium more effective to inhibit flower pedicel explants than to other concentrations. Exogenous applied calcium in ethylene condition can accelerate abscission of flower pedicel explants, and the acceleration become more obviously with the increasing concentration of applied calcium. However, in ethylene condition application of EGTA, VP and TFP delay abscission of tomato pedicel explants. Calcium can delay abscission of stage I effectively but little effect on stage II. Furthermore, the exo-calcium mainly convert into peptic calcium form which show significant converse relative to the abscission. It is document the calcium delay abscission by its slat bridge function.2.The effect of calcium on activities of cellulase (Cel), polygalacturonase (PG) and pectinesterase (PE) in pedicel explants is different in natural and ethylene condition. In natural, calcium could depress the rise of hydrolase activities especially in distal side and AZ. However, in ethylene induced abscission calcium could promote the of activities hydrolase. The activities of cellulase (Cel), polygalacturonase (PG) and pectinesterase (PE) have a high relative to the abscission procession.3.During the early hours of treatment with air or ethylene, the endogenous IAA concentration in the abscission zone (AZ) falls rapidly, and then rises gradually. However, ethylene has better effect on inducing the rise of AZ-IAA in the latter hours of the abscission, and promotes IAA in the distal side (DS) of tomato pedicels in the early treatment. There is an obvious peak of GA₁₊₃ concentration in AZ when abscising in air, but ethylene delays the GA₁₊₃-peak. In natural, calcium mainly in maintain IAA polar transport and depress ethylene production. Furthermore, calcium also inhibit the rise of ABA concentration in distal side and AZ. However, during ethylene induced-abscission calcium promote ethylene production, depress GA content of AZ and enhance the ABA concentration in distal side and AZ.4.Northern blot analysis show that the expression of TAPG in the three segments of pedicel explants is different. In natural, TAPGs only expression in AZ and not detect in proximal and distal segments. In ethylene induced abscission, TAPGs can detect in both AZ and distal side, but the AZ TAPGs were expression earlier than distal side. During natural abscission, calcium treatment depress the TAPGs expression before 32 h but enhance it after 40 h. VP and TFP treatments enhance the TAPGs expression after 32h. In contrast, during ethylene induced abscission calcium treatment enhance TAPGs expression in both AZ and distal side right after 8h. EGTA, VP and TFP treatments depress TAPGs expression. Furthermore, the patters of AI and PR expression no matter in natural or ethylene condition, calcium could only mediate abscission relate gene and no function on other gene expression. These data indicate calcium mediate function is highly special relative to the abscission.5. Western blot analysis show that the PG transcription and translation is highly accordingly no matter in natural or ethylene condition. However, the explants with calcium and TFP the PG transcription and translation is not consistent. These data document calcium also mediate PG activities on translation level. Although the mediate mechanism is still uncertain, the relation of calcium and ethylene may be an important role on mediate PG activities.6.The breakdown of AZ tissues accord to the following order: a small part of the cortex (outer) and vascular region→epidermis, main part of the cortex (inner) and vascular region→—^central parenchymatous region. Just before separation, the cells in AZ and the neighbour tissues exhibit senescence. Cell membranes degrade partly. The cell walls become rude fibrosis and break down lastly. There is some black crystal between two cells. The cell wall and membrane in some districts begin to separate. The number of mitochondium decrease and the ridges in mitochondium swell. The membranes disappear gradually. A lot of vesicles of double-layers membrane are discharged from the cells in AZ. All the results indicate senescence of all the cells in AZ and the neighbour tissues. The cell structure destroys and the content in cells exudes. The organelles disorder or disaggregate and finally the tissues of AZ breakdown. We also analysis the calcium distribution during ethylene induced abscission and summary different abscission phase characteristic. Compare the difference effect among calcium, TFP and EGTA treatments by SEM.7.The results make the changes of abscission-induction clear, and a relatively better experimental system has been put forward. It is proved that explants' direction in gravity field is relative to abscission and suggested that the Distal Side may plays an important role in abscission. Furthermore, we have raised a query about IAA gradient theory and characterized the features of Isozymes Zymograms in abscission. Expression of several EST isozymes has been found to be much more related with abscission. The change of tissues in AZ has been described and cell behaviors in the course also revealed.