Effect Of Sub-High Temperature In Daytime On Sucrose Metabolism And Gene Expression About Sucrose-metabolizing Enzymes In Tomato

Sucrose is the main sugar along the assimilate transport in many plant species. Most of plant organa get sucrose from leaves firstly as photosynthates. So the mechanic of sucrose metabolism in plant organ, especially in stress condition is very important for plant growth, fruit development and fruit quality. The fact that the daytime temperature is high, otherwise night temperature is suitable occurs frequently in long-season cultivation. The plant growth, development and fruit quality often affect by such condition. So in this study we analyse the effect of sub-high temperature in daytime on sucrose metabolism and gene expression about sucrose-metabolizing enzymes in tomato leaves of different age and tomato fruits in simulative sub-high temperature condition in artificial climate chamber to discuss the variety mechanic of sucrose metabolism in sub-high temperature. The main results are as follows:1. Compare the differences of the diurnal changes in sugar contents in tomato leaves of seedlings and adult stage, it verifies that the regularity of sugar accumulation is similar between seedlings and adult stage. The content of fructose, glucose and sucrose increase sharply when the daytime coming. Both of them accumulate maximum in first half night, next dawn the sugar content decreases to the yesterday's levels. But the sucrose content in adult stage leaves could be detected after growing 6 hours in daytimes.2. During high temperature treated period, the fructose, glucose content in tomato seedlings reduce, reversely sucrose content increases, the content of hexose resumes normal after one night, but sucrose content is still significant more than control. During the treatment, the contents of three kinds of sugar in tomato leaves of adult increase, and after one night in normal temperature resume normally.3. The main activities involved in sucrose metabolism shows a significant diurnal changes in tomato seedlings. The activities of invertase (Ivr) and sucrose synthase (SS) in day time are lower than it in night, but the activity of sucrose phosphate synthase (SPS) increases sharply when turned into night condition. After treated with 35℃sud-high temperature, the regulation of diurnal changes is not changed. The activity of Inv in tomato adult leaves does not showed a significant diurnal changes, the activities between maximum and minimum have a little difference. The activities of SS and SPS increase gradually in day time then reach maximum at night.4. After treated the seedlings leaves, the Ivr activities decrease. The SS is not sensitive to high temperature, but the activities of SPS increases firstly, and then decreases. During the treatment the Max activity of SS and SPS appeared early than control and the activities of them increase but the Inv activity decreases in leaves of adult stage.5. The diurnal changes of hexose in mature tomato and green ripening tomato are similar: the hexose content increases in day time and reach max in dusk, then decreases to the level of yesterday; the rate of hexose degradation and accumulation in mature tomato is much higher than that of green ripening tomato. The diurnal change of sucrose is similar to hexose, but the sucrose content and the rate of sucrose synthase in mature tomato is less than green ripening tomato. During the treatment the hexose and sucrose content increases in both mature and green ripening tomato.6. It is clear that the diurnal changes of enzymes involved in sucrose metabolism between tomato green ripening tomato and mature tomato are different. The enzymes of sucrose metabolism in green ripening tomato shows a significant diurnal changes. The three kinds of sucrose-metabolisming enzymes activity increases in daytime, than reduces to minimum in dusk. The enzymes activities in mature tomato does not have an obviously maximum and minimum.7. The reaction of acid invertase activity (AI) to high temperature between green ripening tomato and mature tomato is different. After high temperature treatment the AI activity in green ripening tomato decreases otherwise increases in mature tomato; SS and SPS activities are not sensitivity to high temperature, but max activity increase after high temperature treatment. The activity of SS and SPS increases after treatment, then resumes normal in night.8. After treated the green ripening tomato by high temperature in different days, the fructose and glucose content in pericarp decreases by three day's high temperature, otherwise the hexose content in dissepiments and pectinic changes after six day's treatment; the sucrose content increase in all departments of tomato.9. After the high temperature treatment the Ivr activity in all tomato departments reduces, but the SS and SPS are different in different parts. SS and SPS activities in pericarp increase. The SS activity increase but the SPS activity decreases in dissepiments. The SS activity in pectinic increase firstly then decreases, SPS activity increases.10. The reaction of AI gene expression in green ripening fruit and mature fruit to high temperature is different. The AI gene expression decrease in green ripening fruit by high temperature and the diurnal change of AI activity belongs to the diurnal change of gene expression. The decrease of AI activity may caused by the decrease of gene expression. The gene expression of invertase in mature fruit is not affected by high temperature. Both in treatment and control the SS gene is not expressed. So the change of SS activity is not caused by the change of gene expression.11. During fruit ripening the gene expression of Ivr reduces in all parts by high temperature, the mRNA resumes in 3d treatment, but the mRNA could not detected in 6d and 9d treatment during resuming. So that the reduction of Ivr activity may belongs to the decrease of gene expression.