Function of potassium in plants 5. Photosynthesis and translocation of photosynthates K stimulates the photosynthetic O2 production which means it has a promoting impact on the e- flux through the photosynthetic e- transport chain and therefore also on the reduction of NADPt and the generation of ATP K promoted the de novo synthesis of the enzyme ribulose bisphosphate caboxylase(Rubisco); decreased the diffusive resistance for co2 in the mesophyll(叶肉) High K concentration (100mol/m ) in the outer medium induced a broader ph optimum for the enzyme RuBP carboxylase as compared with low K(10mol/m)
Function of potassium in plants 5. Photosynthesis and translocation of photosynthates K stimulates the photosynthetic O2 production which means it has a promoting impact on the e- flux through the photosynthetic e- transport chain and therefore also on the reduction of NADP+ and the generation of ATP. K+ promoted the de novo synthesis of the enzyme ribulose bisphosphate caboxylase (Rubisco); decreased the diffusive resistance for CO2 in the mesophyll(叶肉）. High K+ concentration (100mol/m3 ) in the outer medium induced a broader pH optimum for the enzyme RuBP carboxylase as compared with low K(10mol/m3 )
Effects of K+ on the co assimilation photorespiration and dark respiration(People and koch 1979) K in leaves mg CO2-assimilation Photorespiration Dark respiration m am 128 4.00 19.8 21.7 587 38.4 340 8.96 3.06 Increasing CO2 assimilation was paralleled by an increase in photorespiration and a decrease in the dark respiration
Effects of K+ on the CO2 assimilation, photorespiration and dark respiration (People and koch 1979) K + in leaves mg K + /g DM CO2-assimilation Mg dm-2 h -1 Photorespiration Dpm dm-2 h -1 Dark respiration Mg dm-2 h -1 12.8 11.9 4.00 7.56 19.8 21.7 5.87 3.34 38.4 34.0 8.96 3.06 Increasing CO2 assimilation was paralleled by an increase in photorespiration and a decrease in the dark respiration
Function of potassium in plants Photosynthates translocation Numerous authors have shown that K+ enhances the translocation of photosynthates K promotes phloem transport, and is probably related to the beneficial effect on phloem loading According to Lang(1983) higher K uptake by the sieve tube- companion cell complex(筛管伴胞复合体 induces osmotic water flow into the complex topush the phloem mass flow a Release of k from the phloem tissue on the other hand leads to water release and thus contributes to the pull mechanism
◼ Photosynthates translocation ◼ Numerous authors have shown that K+ enhances the translocation of photosynthates. ◼ K+ promotes phloem transport, and is probably related to the beneficial effect on phloem loading. ◼ According to Lang(1983) higher K+ uptake by the sieve tube-companion cell complex(筛管伴胞复合体) induces osmotic water flow into the complex to “push” the phloem mass flow. ◼ Release of K+ from the phloem tissue on the other hand leads to water release and thus contributes to the “pull mechanism” Function of potassium in plants
Function of potassium in plants In storage sinks such as the sugar beet taproot and in sugarcane, sugar is stored at high concentrations in the vacuole. Where a K concentration around 100mol/m3 is required for efficient sucrose uptake into the vacuole Potassium nutrition favors the storage of starch sugars and proteins as observed in numerous crops Apart from favoring photosynthesis efficiency and phloem loading Kt may have also direct impact on the storage So, K has also been related to fruit quality and to the oil content of some seeds
In storage sinks such as the sugar beet taproot and in sugarcane, sugar is stored at high concentrations in the vacuole. Where a K concentration around 100mol/m3 is required for efficient sucrose uptake into the vacuole. Potassium nutrition favors the storage of starch, sugars and proteins as observed in numerous crops. Apart from favoring photosynthesis efficiency and phloem loading K+ may have also direct impact on the storage. So, K has also been related to fruit quality and to the oil content of some seeds. Function of potassium in plants
Replacement of potassium by sodium The question of whether Nat can replace K+ in physiological processes in the plant is not only of academic interest but also of practical importance in relation to fertilizer usage. The beneficial effects of Na+ on plant growth are particularly observable when the k+ supply is inadequate
Replacement of potassium by sodium ◼ The question of whether Na+ can replace K+ in physiological processes in the plant is not only of academic interest but also of practical importance in relation to fertilizer usage. ◼ The beneficial effects of Na+ on plant growth are particularly observable when the K+ supply is inadequate