Characteristics Of Photosynthesis And Changes Of Physiology And Biochemistry During Seed Development Of Cucumber

Characteristics of photosynthesis, changes of photochemical efficiencyand RuBPCase activity, changes of physiology and biochemistry of thedifferent leaves in cucumber plant during seed development were studied.Meanwhile the change of electron transpiration, the positive function ofchlorophyll decomposition and inactive of PSII reaction center during seeddevelopment were discussed. The results were as follows:1. The diurnal changes of net photosynthetic rate were different indifferent stages. The curve of diurnal change of net photosynthetic rate has twopeaks, one peak is at 10:00, and the other at 14:00, having an obvious middydepression in prophase of seed development, whereas only has a peak at 12:00in anaphase seed development.2. With the development of seed, the amount of photons that were usedfor carbon assimilation was decreasing, while the amount of photons used forheat dissipation and other dissipative ways was increasing. So the apparentquantum yield (AQY) was decreasing, the photochemical fluorescencequenching was also decreasing, but the nonphotochemical fluorescencequenching was increasing with the development of seed.Maximal PSIIefficiency (Fv/Fm) and actual photochemical efficiency ofPSII(ΦPSII) were decreasing with the illumination intensity enhanced, havingits lowest value at noon, but the Fv/Fm and ΦPSⅡcan recover with theillumination intensity weakened, so we can conclude that the photosyntheticreaction center was not destroyed at noon. 3. The change of chlorophyll content and net photosynthetic rate wasdifferent. When Pn came to its peak, it decreased immediately, but chlorophyllcan keep about a week after its peak. So the decrease of chlorophyll content isnot the cause of the decrease of Pn, it was concomitance of the other elementsof photosynthetic organ decomposed. The decomposition of chlorophyll andinactive of PSII were a protective and adaptive mechanism during seeddevelopment. 4. The change of Ribulose bisphosphate carboxylic enzyme (RuBPCase)activiey is similar to the change of Pn, it increased first, and then declined. TheRuBPCase activity of 10th leaf come to its peak 7 days after blossoms, andthen decreased obviously. The decrease of Pn started 14 days after blossom.The decrease of RuBPCase activity was earlier than the decrease of Pn andchlorophyll content. Meanwhile the decrease of RuBPCase caused thecarboxylation efficiency (CE) declined. So the main reason of decrease of Pnwas the decrease of RuBPCase activity. 5. In different leaves of the cucumber plant, the chlorophyll content, Hillreaction activities, soluble protein contents and SOD,POD,CAT activitiesincreased first and then declined, while insoluble protein contents kept steady,and the MDA contents increased continually with lowering of leaf position. The decomposition of soluble protein was earlier than the decrease of Hillactivities, Pn, and chlorophyll content during seed development. With thedevelopment of seed development, the SOD, POD, CAT, activities increasedfirst and then declined. The decline of SOD activities was earlier than PODand CAT, the decrease of SOD cause the MDA content increasingcontinuously.