Study on Leaf Photosynthesis and Chlorophyll Fluorescence of Transgenic Tobacco Over-producing 5-Aminolevulinic Acid (ALA) Expression of Saccharomyces cerevisiae Hem1 Recombined with Arabidopsis thaliana hemA1 Promoter in Transgenie Tobacco Effects on Strawberry Photosynthesis and Relations to Anti-oxidant Enzymes of ALA Effects of exogenous 5-aminolevulinic acid on seed germination and physiological characteristics of Cassia obtusifolia seedlings under NaCl stress