Wang Yang,Ren Tao,Lu Jianwei,Cong Rihuan,Hou Wenfeng,Liu Tao,Hussain Saddam,Li Xiaokun
Inferior tillers typically provide a minimal contribution to the grain yields of rice; however, with the proper regulation of light and nutrients, their yields may be significantly enhanced. The exogenous introduction of gibberellic acid (GA 3 ) may assist with extending the culm lengths of inferior tillers, the sequestration of additional sunlight, and the accumulation of further nutrients. In an attempt to verify our assumption while enhancing the grain yield of inferior tillers, GA 3 was applied to inferior tillers under different nitrogen (N) levels. Morphological alterations, photosynthetic parameters, endogenous GA content, N accumulation, and soluble sugars within the leaves of inferior tillers were assessed, as was the activity of sucrose synthase (SuSase) in the cleavage direction. Our results revealed that the belated emergence and low concentration of endogenous GA 1+3 translated to the stunted growth of inferior tillers, which ultimately had a reduced capacity to harvest sunlight. Furthermore, insufficient sunlight due to asymmetric competition might be the source of the reduction of inferior tiller source and sink activities. Foliar GA 3 spray enhanced the intercepted photosynthetically active radiation (IPAR) and SuSase activity in inferior tillers considerably; however, dry matter and N accumulation provided adequate resources to grains only when the tillers obtained sufficient N. The alterations in soluble sugars indicated that inferior tillers did not respond well to the application of GA 3 under an insufficient N supply. In contrast, when sufficient N was made available, GA 3 -treated inferior tillers received high-intensity light, and additional energy was allocated to the photochemical reactions of photosystem II (PSII). The high quantum efficiency of PSII contributed to the transportation of C- and N-assimilates from the source organ to the sink under adequate N conditions, and eventually increased the grain yields of the inferior tillers.
Microcystin (MC)-producing (MC+) and MC-free (MC−) Microcystis always co-exist and interact during Microcystis-dominated cyanobacterial blooms (MCBs), where MC+Microcystis abundance and extracellular MC-content (EMC) determine the hazard extent of MCBs. The current study elucidated intraspecific interaction between MC+ and MC−Microcystis at various nitrogen (N) levels (0.5–50 mg/L) and how such N-mediated interaction impacted algicidal and EMC-inhibiting effect of luteolin, a natural bioalgicide. Conclusively, MC+ and MC−Microcystis were inhibited mutually at N-limitation (0.5 mg/L), which enhanced the algicidal and EMC-inhibiting effects of luteolin. However, at N-sufficiency (5–50 mg/L), MC−Microcystis promoted MC+ ecotype growth and dominance, and such intraspecific interaction induced the cooperative defense of two ecotypes, weakening luteolin's algicidal and EMC-inhibiting effects. Mechanism analyses further revealed that MC+Microcystis in luteolin-stress co-culture secreted exopolymeric substances (EPSs) for self-protection against luteolin-stress and also released more EMC to induce EPS-production by MC−Microcystis as protectants, thus enhancing their luteolin-resistance and promoting their growth. This study provided novel ecological implications of MC−Microcystis toward MC+ ecotype in terms of assisting the dominant establishment of MC+Microcystis and cooperative defense with MC+ ecotype against luteolin, which guided the application of bioalgicide (i.e. luteolin) for MCBs and MCs pollution mitigation in different eutrophication-degree waters.
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