Effect of light spectral composition on the hormonal balance, growth, and photosynthesis in plant seedlings.
Growth, photosynthesis and the contents and activities in bioassays of IAA, ABA, gibberellins (GA), zeatin and zeatin riboside were studied in Bergenia crassifolia, Rhaponticum carthamoides, Lychnis chalcedonica, Avena sativa and Avena fatua plants adapted to monochromatic light of different spectral compositions. In red light (RL), leaves attained the highest area and weight. The highest number of cells per leaf area unit was observed in leaves grown in blue light (BL). Light quality affected the activities and contents of the major phytohormones. RL decreased the level of IAA and increased GA activity. Green light (GL) enhanced the ABA content and BL increased the cytokinin content. In all plant species studied, the number of chloroplasts per cell was constant under all light regimes. Differences in the light curves of photosynthesis correlated with the number of assimilating cells per leaf area unit. The latter was the evident cause for a higher rate of CO2 assimilation in BL-grown leaves. An interrelation between photoregulatory systems controlling growth and photosynthesis was postulated.