Effect Of Potassium Deficiency On Photosynthetic Characteristics And Antioxidant Enzymes In Leaves Of Rice Plants And The Research Of Premature Senility Mechanism

Physiological, photosynthetic characteristics and antioxidant enzymes activities were studied in leaves of rice plant during natural senescence and under Potassium Deficiency. Meanwhile, the cause of natural senescence and premature senility under potassium deficiency were also discussed.After rice heading, Pn, Fv/Fm, Φps(?), and qP were decreased in flag leaves, and so was photosynthetic pigments, soluble protein. As the time extending, NPQ and SOD activity were also declined. During natural senescence, photosynthetic ability was reduced in leaves, and its photosynthetic system was damaged irreversibely. In the end, thermal dissipation mechanism was suppressed, the excessive excitation energy couldn't be dissipated efficiently which accelerated the damage to the photosynthetic system. Furthermore, the activity of antioxidant enzyme (SOD) was decreased and accelerated the membrance liquid peroxidation, and led the plant to senescence.The net photosynthetic rate (P_n) and stomatal conductance (G_s) decreased significantly, in the potassium deficient leaves. At the same time, the photosynthetic pigments and soluble protein declined. The further study on chlorophyll fluorescence measurement showed that F_v/F_m, Φps(?), qP and ETR were declined as time extended under potassium deficiency, indicating that the PS II reaction center was damaged. Potassium deficiency also decreased the light- saturation points in both cultivars. In that conditions, the light energy absorbed by PS II was in excess of the need for assimilation. We also detected a significant increase of NPQ in the stressed leaves of both cultivars, which indicated that the mechanism of thermal dissipation had been started to dissipate excess light energy, and protect the plants from photo-inhibition and photo-oxidation. During the whole potassium deficiency period, the activities of antioxidant enzymes were first increased and then decreased. Antioxidant enzymes were involved in scavenging active oxygen species. In our results, YFZ's antioxidant...