Modification of Petunia seedling Carbohydrate Partitioning by Irradiance

Abstract

Petunia × hybrida Villm. `Red Flash' plants were irradiated for either 10 or 20 mol day1 photosynthetic photon flux (PPF) in growth chambers using one of the following treatments: 175 μmol m-2 s-1 for 16 h, 350 μmol m-2 s-1 for 8 or 16 h or 350 μmol m-2 s-1 for 8 h plus 8 h incandescent day extension (5 μmol m-2 s-1 PPF). These four treatments were designed to examine the effects of increased peak and total daily integrated PPF as well as increased photosynthetic (Pn) period and photoperiod resulting from supplemental irradiance treatment of seedlings. Previous seedling petunia research indicated a greater response to supplemental lighting during expansion of the second true leaf. Therefore, seedlings were sampled for analysis at the two leaf stage and also later at the four leaf stage to examine effects at a later stage of growth.Increasing total integrated PPF increased total carbohydrate production, seedling dry weight, rate of seedling growth, and acid invertase activity once the seedlings reached the two leaf stage. Increasing total PPF resulted in greater partitioning into ethanol soluble sugars rather than starch at the two leaf stage. Increasing the photoperiod only, with an incandescent day extension treatment, reduced total carbohydrate production at the two leaf stage.Maximal oxygen evolution was observed when seedlings received 350 μmolm-2s-1 for 8 h when expressed on a leaf area or dry weight basis. The use of an 8 h day extension treatment to extend the photoperiod from 8 to 16 h resulted in the lowest rates of oxygen evolution on a leaf area basis.