Effects Of 5-Aminolevulinic Acid (ALA) On Photosynthesis, Chlorophyll Fluorescence And Activity Of Antioxidant Enzymes Of Watermelon

Studies on the effects of 5-aminolevulinic acid (ALA) with concentrations 50-200 mg/L on the photosynthesis and antioxidant enzyme activities of watermelon (Citrullus lanatus Thunb. Mansfeld) seedlings grown under low light and low temperature in autumn-winter plastic tunnel indicated that ALA could increase photosynthetic rate (Pn), transpiration rate (Tr), Stomatal conductance (Gs) and intercellular CO₂ concentration (Ci). It also significantly increased the activities of the antioxidant enzymes, especially the activities of superoxidate dismutase (SOD) and peroxidase (POD). Additionally, ALA treatments enhanced the plant mass accumulation with 42%-54% higher than the control, the starch content with 62.2% -207.0% higher and the soluble sugar concent with 32.0%-87.1% higher, suggesting that ALA treatment promoted aetabolism of carbohydrates stress resistance and plant growth.ALA enhanced the minimal fluorescence (F_o) (P < 0.05), and ALA did also have obvious effect on the maximum fluorescence (F_m), PS â…¡ maximal photochemical efficiency (F_v/F_m), latent PS II photochemical efficiency (F_v/F_o) and the ability of PS II reaction center to obtain energy from antenna (1/F_o-1)/F_m).In 5 days after ALA treatment, under the same actinic light intensity, along with the time increased, increased PS II actual photochemical efficiency (Φ_psâ…¡), photochemical quench (qP), non-photochemical qnench(NPQ), electron transfer rate(ETR), photochemistry rate (PCR), photochemistry(P) and antenna heat dissipation (D) of the watermelon (Citrullus lanatus Thunb. Mansfeld) seedlings, decreased stable fluorescence (F_t) and non-photochemistry in PSâ…¡ reaction center (E). Under the 600 and 1600μmol m^-2 s^-1 actinic light intensity, the curves of Φ_psâ…¡, qP, PCR, ETR, P and E undulated large. The concentration 50-200 mg/L of ALA could enhanceΦ_psâ…¡, qP, photochemistry rate, ETR, P and E, decreased F_t and E under the 400, 600 and 1600μmol m^-2 s^-1 actinic light intensity, and the effect of 200 mg/L ALA was better. Under 600μmol m^-2 s^-1 actinic light intensity,...