Physiological Characteristics Of Potassium Accumulation And Delaying Senescence Of Different Maize (Zea Mays L.) Under Low Potassium Stress

Based on the previous studies, maize inbred lines tolerant to K deficiency （90-21-3,099）and sensitive to K deficiency （D937,835） were grown in potassium deficiency fieldconditions. The current experiment was conducted from2009to2011in Manduhu village,Liaozhong County, Shenyang City. The objective of this experiment was to measure theimpact of low potassium stress on root morphology and activity, leaves stay green,photosynthetic and chlorphyll fluorscent parameters and leaf senescense from seedling stageto grain filling stage. This paper will propose to verify the features of maize inbred linestolerant to low potassium stress including root function in K absorption and utilization,physiological mechanism of delaying leaf senescence. The main findings were as follows.1Compare with maize inbred lines sensitive to potassium deficiency, the tolerant maizedemonstrated some obvious advantages in root morphology and activity under low potassiumstress, which was beneficial to potassium uptake. The effect of low potassium stress on totalroot length, root volume, root surface area and average diameter in maize tolerant topotassium deficiency were more slightly. Specific root length increased more soundly, thisindicated the fine root increased more, which was benefit to absorb much more potassium.Moreover, root exude rate, active absorption area and root activity were relatively higher,which could ensure the supply of nutrient for shoot development.2The decline of potassium accumulation in various organs in maize inbred lines tolerant tolow potassium stress were smaller than sensitive ones, especially embodied in panicle leaves.K content of root, leaf, ear increased slightly in tolerant maize, but the K content of eachorgans in sensitive maize were decreased much more; K content of each leaf and leaf sheathsin tolerant maize declined much smaller than that in sensitive ones, particularly where itfound in three ear-leaves and sheaths, which could ensure the growth of grain. And that thedry matter accumulation was much more. K use efficiency was higher.3Compared with D937,90-21-3showed a lower stomatal restriction and a higher electronictransition capacity after accelerated ageing due to K deficiency; FPSⅡ、Fv、Fm in90-21-3were higher than that in D937, while F0was lower than that in D937; In addition, under lowpotassium stress, activities of PEPC and NADK in90-21-3were less decreased and PSⅡ was less damaged. Therefore, compared with D937, the leaf senescence of90-21-3wasrelatively slower, which could prolong the functional period of leaves; The activity of NADKcould provide NADP to electronic receptors for photoreaction, at the same time the increasedactivities of PEPC and led to more effective fixation of CO₂, and the synergistic effect oflight reactions and dark reactions contributed to the higher photosynthetic rate and yield of90-21-3. Moreover, correlation analysis indicated that extremly significant positivecorrelation was between the leaf stay green and net photosynthetic rate, the biggestphotochemical efficiency, NADK and PEPC activities. That indicated higher NADK andPEPC activities could delay leaf senescence; On the contrary, the correlation of Ls and leafstay green was extremely significant negative, the increase in Ls could accelerate the leafsenescense process.4Results of antioxidant enzymes showed that, during the period of grain filling, theactivities of superoxide dismutase （SOD）, peroxidase （POD）, and catalase （CAT） in ear leafof90-21-3were obviously higher than those of D937under low potassium stress. And thecontent of malondialdehyde （MDA） was lower in90-21-3than that in D937under lowpotassium stress, which indicated that the antioxidant enzymes could eliminate reactiveoxygen species, inhibit the membrane lipid peroxidation and decrease the content of MDAmore efficiently in90-21-3. Correlation analysis results showed that the MDA and leaf greenwere extremely significant negative correlation That means the more MDA content, the fasterthe leaf senescence; SOD, POD and CAT and leaf stay green were extremely significantpositive correlation, so the three enzymes could delay leaf senescense effectively.5Under low potassium stress, the root system of90-21-3and099was relatively strongenough to absorb K, moreover the K contents in three ear leaves and sheaths were maintained.The leaf stay-green could keep longer photosynthesis prolonged. Thus dry weight and yieldwere relatively higher than that of D937and835. The correlation analysis between yield androot system indicated that total root length, root volume and potassium content were benefitfor yield per plant.