Roles of Exogenous 5-Aminolevulinic Acid and Dihydroporphyrin Iron in Chlorophyll Precursor Synthesis and Chlorophyll-Related Enzyme Activities in Wheat Under Different Light Intensities

Aminolevulinic acid (5-ALA) and dihydroporphyrin iron chelates (DHFe) play roles in plant growth regulation under normal and stressful conditions. However, definitive data on their roles in regulating chlorophyll synthesis in wheat are lacking. In this study, the optimal concentrations for foliar-spray application of 5-ALA and DHFe to promote wheat seedling growth and leaf chlorophyll content were assessed. The optimal concentrations of 5-ALA or DHFe (50 mg/L and 0.01 mg/L, respectively) were applied as foliar sprays to seedlings of wheat ‘Bainong 4199’ (high light efficient) and ‘Zhoumai No. 18’ (average light efficient) under different light intensities. Chlorophyll precursor contents and activities of three chlorophyll synthesis-related enzymes were altered, and the combined application of 5-ALA and DHFe more strongly increased the leaf chlorophyll content. 5-ALA significantly increased the contents of the chlorophyll precursors porphobilinogen, uroporphyrinogen III, protoporphyrin IX, and magnesium-protoporphyrin IX, and the activities of 5-amino-ketovalerate dehydratase and uroporphyrinogen III synthase. DHFe resulted in an increase in chlorophyll content but a significant decrease in chlorophyllase activity and protochlorophyllide content. 5-ALA promoted the synthesis of chlorophyll precursors by regulating the activities of 5-amino-ketovalerate dehydratase and uroporphyrinogen III synthase. DHFe decreased chlorophyllase activity, thereby slowing chlorophyll degradation and increasing the chlorophyll content.