Abstract
The intensity and quality (red to far-red (R/Fr) ratio) of light directly affect growth of plant under shading. Gibberellins (GAs) and auxin [indole-3-acetic acid (IAA)] play important roles in mediating the shading adaptive responses of plants. Thus, the intensity and quality of the uncoupling light from shading were assessed to identify the influence of each component on the morphology and matter distribution of the leaf, stem, and petiole. This assessment was based on the changes in endogenous Gibberellin 1 (GA1) and IAA levels. Soybean plants were grown in a growth chamber with four treatments [normal (N), N+Fr, low (L), and L+Fr light]. Results revealed that the reductions in photosynthetically active radiation (PAR) and R/Fr ratio equally increased height and stem mass fractions (SMFs) of the soybean seedling. The light intensity significantly influenced the dry mass per unit area and mass fraction of soybean leaves, whereas the light quality regulated the petiole elongation and mass fraction. Low R/Fr ratio (high Fr light) increased the soybean biomass by improving the photosynthetic assimilation rate and quantum yield of photosystem II. In addition, the IAA and GA1 levels in the leaf, stem, and petiole did not reflect the growth response trends of each tissue toward light intensity and quality; however, trends of the IAA-to-GA1 content ratios were similar to those of the growth and matter allocation of each soybean tissue under different light environments. Therefore, the response of growth and matter allocation of soybean to light intensity and quality may be regulated by the IAA-to-GA1 content ratio in the tissues of the soybean plant.
Highlights
Light is one of the most important environmental factors because it regulates photosynthetic assimilation and partitioning in plants (Slewinski and Braun, 2010; Jiang et al, 2011)
The data on leaf traits (Figure 2C) revealed that the change trends of the indole-3-acetic acid (IAA) level and IAA-to-GA1 ratio of the leaf were strongly similar to the trends of mass per unit area (MA) of the leaf and leaf mass fraction (LMF) (Figures 5A, 6A)
The growth (MA and LMF) of soybean leaves was greatly influenced by light intensity
Summary
Light is one of the most important environmental factors because it regulates photosynthetic assimilation and partitioning in plants (Slewinski and Braun, 2010; Jiang et al, 2011). Reductions in the red-to-farred (R/Fr) light ratio and the photosynthetically active radiation (PAR) strongly impair the growth and development of plants under shading (Kurepin et al, 2007a; Yang and Li, 2017). Plants can adjust their morphology and physiology to acclimatize toward a modified light quality (e.g., reduced R/Fr ratio) and a decreased PAR (Kurepin et al, 2007a; Valladares and Niinemets, 2008). Many studies investigated the effects of the interaction between the quality (R/Fr ratio) and intensity of light on the growth of hypocotyls (Kurepin et al, 2007a) or anatomical structure of leaves (Wherley et al, 2005), these studies focused only on the responses of single organs and not of the whole plant
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