Abstract:Low light intensity environment remarkably affected growth, development and metabolism in tobacco plants and quality of tobacco leaves. In the present study, by spraying different concentrations of calcium chloride [3.0 (C1) and 6.0 (C2) mmol/L CaCl2], gibberellins [100 (G1) and 200 (G2) mg/L GA3] , salicylic acid [1.0 (S1) and 2.0 (S2) mmol/L SA] and paclobutrazol [100 (P1) and 200 (P2) mg/L PP333] on tobacco (Nicotiana tabacum L.) seedlings, we investigated the effects of these pretreatments with the abovementioned four chemical regulators on growth, development, low light tolerance and photosynthetic characteristics of tobacco seedlings under low light intensity stress(80 μmol·m-2·s-1), and carried out comprehensive evaluation by subordinate function. The results showed that: (1) as compared with the control spraying with distilled water (CK), the pretreatments with the four chemical regulators all enhanced dry weight, root vigor, contents of total chlorophyll and proline, and photosynthetic capacity of tobacco seedlings, and improved the seedling quality. (2) After exposed to low light stress for 6 days, as compared with the CK, the pretreated seedlings with the four chemical regulators relatively enhanced dry weight, root vigor, total chlorophyll content and photosynthetic capacity, reduced the electrolyte leakage and MDA level, and delayed the decline level of relative growth rate and dry matter accumulation rate of tobacco seedlings, which in turn enhanced the tolerance of these tobacco seedlings to the low light stress. (3) Comprehensive effects of these treatments with four chemical regulators on improving the quality of tobacco seedlings were S1 > S2 > C1 > C2 > P2 > G2 > P1 > G1, respectively, and SA and CaCl2 pretreatments received better effects than those with spraying GA and PP333. In addition, the relieving effects of these treatments with different concentrations of the four chemical regulators on the low light stress were demonstrated from strong to weak was S1 > C1 > S2 > P1 > P2 > G2 > G1 > C2, respectively, after exposing to low light condition for 6 days. The results indicated that these pretreatments with the four chemical regulators all improved growth and quality of tobacco seedlings, and enhanced their low light tolerance and photosynthetic capacity to some extent, and 1.0 mmol/L SA displayed the optimal effects in this study.