Research Of Physiological Mechanism On Barren Stalk In Maize (Zea Mays.L) Caused By Low Light Intensity

Two novel rare and precious materials of maize(Zea mays L.)were first described in this paper.The stable strain A and B in the study which were isolated from a high-generation hybrid maize combination were rare germplasm resources,they have the similar genetic bacground.A and B had significant differences in response to low irradiance,A was sensitive to low irradiance,the growth and development of the ear were unnormal under low irradiance and produced many barren stalks;B was tolerant to low irradiance and its ear development were normal.They are of great valuable to the research of the physiological mechanism and molecular genetic field producing barren stalk under low irradiance in maize.In this study,we compared the differences between A and B in plant morphological characteristics,main agricultural characteristics,photosynthetic and chlorophyll fluorescence characteristics,chlcrophyll biosynthesis,carbon-nitrogen metabolism and relative photosythetic enzyme activity and esterase isozyme.The main results were as follows:1.The percentage reduction in silking of A was significantly greater than that of B,indicating that the percentage of silking in A was more sensitive to low irradiance than in B.The reduction of LAI was also greater than that of B under low irradiance.The tassel length and tassel flower numbers of B were reduced under low irradiance,the tassel branch numbers were increased;however,A showed the opposite trend.In low irradiance and ambient sunlight,the tassel fresh weight and dry weight of A were more greater than that of B;the tassel dry weight was significantly reduced by low irradiance.Low irradiance also restrained the ear development of A,and the ear remained smaller.The development of ear in B was less influenced by low irradiance.The pollen viability,germination percentage and germination rate of B were all higher than that of A,and compared to ambient light,the pollen viability of A was greater influenced by low irradiance.2.After shading 10 d,15 d and 25d,the Pn of B were significantly higher than that of A;in both light environments,the Ci of A were higher than that of B;taking Gs with Pn and Ci together consideration,indicating that non-stomatal limitations played the important role for the maize A under different levels of radiation;and photosynthetic parameters more likely exhibited greater changes in A than in B under low light intensity stress;A was more sensitive to low irradiance than B.The study of chlorophyll fluorescence parameters of leaves shown that,the value of Fv/Fm、Y(Ⅱ)、ETR and qP in B were higher than that in A,the Fv/Fm of A was decreased by low irradiance after shading 10 d,compared to ambient light;The Fv/Fm of B was always higher under low light intensity than that under ambient sunlight;The reduction of qP in A was greater than that in B;The change of qN in B was relative smoothly.3.The value of a in B was 1.03～1.21 times the value of A under ambient sunlight,under low irradiance 1.05～1.24 times the value of A,shown that B can maintain the more stronger ability of low irradiance than A,B had high utilization rate of light energy;The value of rETRmax in B was 1.04～1.46 times the value of A under ambient sunlight,under low irradiance 1.07～1.26 times the value of A;The value of Ik in B was 1.00～1.43 times the value of A under ambient sunlight,under low irradiance 1.14～1.56 times the value of A;The value of Ik in A was reduced 0.01%～30.7%under low irradiance during the treatment,but increased 0.06%～6.50%in B except for DAS 25 d.4.At shading 10 d and 15 d,some enzyme converting Glu to ALA was inhibited in A,resulting the reduction of chlorophyll.The reduction of chlorophyll content in B was blocked at the step of converting Pchlide to chlorophyll and PBG to Urogen III.At shading 20 d,the reduction of chlorophyll content in A was blocked at the step of converting ALA to PBG and PBG to Urogen III;the reduction of chlorophyll content in B was blocked at the step of converting Glu to ALA and Urogen III to Proto IX.At shading 25 d,the inhibited step in A and B were the same,converting ALA to PBG,but the extent of A was more greater.5.The contents of soluble sugar,sucrose and soluble protein in B were higher than that in A under ambient sunlight and low irradiance,the extent of reduction in A were greater;The content of starch in B was higher than that in A under low irradiance,while lower than that in A under ambient sunlight,the content of starch in A reduced 48.0%～70.7%,and the content of starch in B reduced 13.2%～41.4%.Compared to ambient sunlight,the activity of RuBPCase in A and B were lower under low irradiance,and the extent of reduction in A was greater.There was a shortly increased tend in the activity of PEPCase in A and B after shading,the activity of PEPCase in B displayed a higher level during the treatment,and was higher than that in A,the activity of PEPCase in A displayed a decreased tend after a short abduction.6.In order to ascertain the differences of the activity of esterase between A and B,the stduy compared the changes of esterase isozyme spectrum in both light environments.The results suggested that the activity of esterase in A was higher than that in B under ambient sunlight,indicating that A didn’t produce barren stalk under ambient sunlight becacuse of the high activity of esterase,The high activity of esterase could transform the carbohydrate into energy for life activities.Under shading treatment,the activity of esterase in A during the vigorous growth period was increased by low irradiance,probably beacause of the metabolic pathway of esterase produced some substances inhibitting the development of ear.