Exogenously applied gibberellic acid improves the growth and yield performance of inferior rice tillers grown under different nitrogen levels

Abstract

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 (GA3) 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, GA3 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 GA1+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 GA3 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 GA3 under an insufficient N supply. In contrast, when sufficient N was made available, GA3-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.