Effects of exogenous ascorbic acid on seed germination and seedling salt-tolerance of alfalfa

Abstract

Alfalfa (Medicago sativa L.) is an important legume crop for forage, agriculture, and environment in the world. Ascorbic acid (AsA) plays positive roles in plants. However, its effects on germination and salt-tolerance of alfalfa are unknown. The effects of AsA applications on seed germination and seedling salt-tolerance of alfalfa were investigated. The results revealed that 0.1 and 1 mmol L-1 of exogenous AsA increased germination, amylase, and protease, as well as seedling length, fresh weight (FW), dry weight (DW), and endogenous AsA both in the shoots and roots, except that 1 mmol L-1 AsA reduced the activities of α-amylase, β-amylase and protease on day 3. However, 10 and 100 mmol L-1 AsA inhibited these parameters and even caused serious rot. It indicates that 0.1 mmol L-1 AsA has the optimal effects, whereas 100 mmol L-1 AsA has the worst impacts. Another part of the results showed that 0.1 mmol L-1 AsA not only enhanced stem elongation, FW and DW, but also increased chlorophyll and carotenoids both under non-stress and 150 mmol L-1 NaCl stress. Furthermore, 0.1 mmol L-1 AsA mitigated the damages of membrane permeability, malondialdehyde, and excessive reactive oxygen species (ROS) and ions both in the shoots and roots under 150 mmol L-1 NaCl stress. Hence, 0.1 mmol L-1 AsA improves growth and induces salt-tolerance by inhibiting excessive ROS, down-regulating the ion toxicity and up-regulating the antioxidant system. The principal component analysis included two main components both in the shoots and roots, and it explained the results well. In summary, the optimum concentration of 0.1 mmol L-1 AsA can be implemented to improve the seed germination and seedling growth of alfalfa under salt stress.

Fig 1

Effects of AsA on germination (a), germination indices (b), and rot rate (c). Lower case letters indicate the difference in each group. The significance level is 0.05, the same below.

Fig 2

Effects of AsA on α-amylase (a), β-amylase (b), and protease (c).

Fig 3

Effects of AsA on shoot length (a), shoot weight (b), root weight (c), and endogenous AsA (d).

Fig 4

Effects of AsA on shoot length (a), shoot weight (b), root weight (c), and Chl a, Chl b, Chl a+b and Cx+c (d).

Fig 5

Effects of AsA on RC (a), MDA (b), H₂O₂ (c), and O₂·^¯ (d).

Fig 6

Effects of AsA on SOD (a), CAT (b), POD (c), and endogenous AsA (d).

Fig 7

Effects of AsA on Na+ (a), K+ (b), and Cl^¯ (c).

Fig 8

The loading plots (a and c) and score plots (b and d) of shoot and root, respectively. In Fig 8A, x1-x18 were shoot length, FW, DW, Chl a, Chl b, Chl a+b, Cx+c, RC, MDA, H₂O₂, O₂·^¯, SOD, CAT, POD, AsA, Na⁺, K⁺, and Cl^¯ of shoots, respectively. In Fig 8C, x1-x13 were FW, DW, RC, MDA, H₂O₂, O₂·^¯, SOD, CAT, POD, AsA, Na⁺, K⁺, and Cl^¯ of roots, respectively.