COMPARATIVE STUDIES ON THE PHOTOSYNTHETIC CHARACTERISTICS OF TWO MAIZE (ZEA MAYS L.) NEAR-ISOGENIC LINES DIFFERING IN THEIR SUSCEPTIBILITY TO LOW LIGHT INTENSITY
The objective of our study was to quantify the effect of low light intensity on chlorophyll (Chl) content, photosynthetic parameters, chlorophyll fluorescence parameters and growth of two maize (Zea mays L.) near-isogenic lines (NILs) differing in their susceptibility to low light to reveal the cause of the resistance to weak light in maize. A field-experiment was conducted in the central plain of Liaohe river in northeast China (41°49′N, 123°34′E), on a meadow brown soil. Two levels of photosynthetically-active radiation (removal of 0% and 40% of sunlight) were tested on SN98A (shading sensitive) and SN98B (shading tolerant) lines. The results showed that shading lengthened the anthesis-silking interval (ASI), increased the percentage of barren stalk and reduced the percentage of silking, and shading decreased leaf Chl content, net photosynthetic rate (Pn), quantum yield of PS II (Y(II)), electron transport rate (ETR), and photochemical quenching (qP) in the two maize NILs. The shading tolerances differed between different near-isogenic lines. Maximum efficiency of PSII photochemistry under dark-adaption (Fv/Fm) of SN98B was increased under low light intensity, meanwhile relatively more stable contents of Chl, Pn, Y(II), ETR, and qP were able to enhance light-use efficiency and reduce the dissipation of light energy, which relieved the reduction in photosynthetic efficiency which caused reduced production of ear assimilative products, thus resulting in a smaller reduction in percentage of barren stalk in SN98B under shading. These fidings demonstrate that low light intensity depressed photosynthetic activity and growth of SN98A more than that of SN98B. SN98A could be more restricted by limited carbon assimilation, leading to the production of barren stalks in low light intensity than that of SN98B. Therefore, improvements in light-harvesting and -use capability and increasing ear filling under low light intensity stress might be important characteristics for plant breeders. Selection of SN98B as a shade-tolerant germplasm for breeding in maize would alleviate the problem of barren stalk development under low light intensity.