Effects Of Low Light Stress On The Root Growth Of Two Different Genotypic Maize

The effect of low light stress on root growth of two maize(Zea mays L.) cultivars, Zhengdan 958(ZD958, shade-tolerance) and Yuyu 22(YY22, shade-sensitive), were investigated by pot method under PFD42% and PFD27% during V3 to V6 at seeding stage. 1.The growth and development of root was inhibited by low light stress.Low light stress is not conducive to the growth of maize seedlings.It reduced the amount of dry matter accumulation and decreased root-shoot ratio significantly. While the dropping of root-shoot ratio of ZD958 is higher than YY22.With the stress level increased, the total root length, root surface area, root volume and root mean diameter of the two cultivars showed a decreasing trend.While the impact on the ZD958 is relatively minor. Low light stress can also cause changes in transverse structure of maize roots at seeding stage.It makes a larger proportion of catheter accounts pillar.while the change width of YY22 is greater, indicating that the stability of root structure of ZD958 is better. 2.Low light stress weakened the root activity.With the level of low light stress increased, the bleeding intensity of two cultivars of maize decreased, suggesting that the root activity of the whole plant is gradually weakened.While the root activity of apical of per unit mass first increased and then decreased,indicating that moderate low light stress can enhance root activity of per unit mass apical in a certain extent in order to maintain the normal growth of plants.But when the degree of stress beyond the self-regulation of root, root activity of per unit mass apical will decrease. There is a phenomenon that when heavily shaded, the root activity of per unit mass apical of ZD958 is higher then its control,but which of YY22 is lower than its control. 3.Low light stress breaked the balance of root cellular antioxidant systems.With the increasing of level of weak light stress,it induced the accumulation of reactive oxygen species,subsequently resulted in the increase of MDA content and permeability of cell membrane as well as osmoticum(proline,soluble protein and soluble carbohydrate) content.The increasing rate of proline and soluble sugar of ZD958 is smaller and soluble protein’s increasing rate is greater.what’s more,the antioxidative enzymes(SOD、POD、CAT、APX and GR)activities and antioxidants(As A and GSH) contents increased gradually with the aggravation of low light stress.But As A/DHA ratio and GSH/GSSG ratio was gradually decreased.And the change width of ZD958 is larger. 4. Low light stress promoted nutrient transportation to the shoot.With the aggravation of low light stress,Nitrogen, phosphorus and potassium content of each organ(root, stem, leaf) of two cultivars gradually increased.But the increase rate of ZD958 is less.Due to the significant reduction in dry matter accumulation caused by low light, nitrogen, phosphorus and potassium nutrient accumulation in various organs still showed a decreasing trend. Judging from the distribution of nutrients, the proportion of nitrogen, phosphorus and potassium in root gradually decreased with the aggravation of low light stress.while their share in the stems and leaves gradually increased.Nitrogen metabolism enzyme glutamine synthetase(GS), glutamate synthase(GOGAT), glutamate dehydrogenase(GDH) and nitrate reductase(NR) activity of two cultivars showed an increasing trend under low light tress, and ZD958 increased greater.It shows that in low light stress, the nutrient absorbed by roots was preferentially transported to the aerial parts for the maintenance of above-ground growth, so that the plant can obtain more optical energy.