Physiological,Biochemical and Chlorophyll Fluorescence Characters of Light Green Stripe Mutant in Oncidium Effects of Nitrogen Supplement on Chlorophyll Synthesis and Chloroplast Ultrastructure of Poplar Plants Under Cadmium Stress Effect of Foliar-spraying Spermidine on Seedlings Growth and Contents of Chlorophyll Biosynthesis Precursors in Leaves of Tomato under Saline-alkaline Stress