Effects of Salt Stress on the Antioxidant Activity and Malondialdehyde, Solution Protein, Proline, and Chlorophyll Contents of Three Malus Species

Abstract

Understanding the different physiological responses of Malus species under salt stress in the seedling stages will be useful in breeding salt-tolerant dwarfing apple rootstocks. Seedlings of Malus Zumi (Mats.) Rehd. (M. zumi), Malus sieversii (Led.) Roem. (M. sieversii), and Malus baccata (L.) Borkh. (M. baccata) were treated with solution of 0, 0.20%, 0.40%, and 0.60% salinity. Physiological parameters of their leaves and roots were measured at 0 d, 4 d, 8 d and 12 d after salinity treatments. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), solution protein (SP), and proline (PRO) initially increased and then decreased. The activities and contents of these parameters were higher in the 0.40% and 0.60% NaCl treatments than in the 0.20% treatment and in the 0% control. M. zumi was the most resistant to salt stress, showing the lowest content of MDA in the leaves and roots, which increased slightly under salt stress. M. baccata had the highest increase in both the content and proportion of MDA. High enzyme activity was shown to play an important role in the salt resistance of M. zumi. Moreover, it can be speculated that there are other substances that also play a major role. We found that osmotic regulation played a key role in response to salt stress for M. baccata even though it was sensitive to salt stress. For M. sieversii, both the osmotic regulation and enzymatic antioxidants were observed to play a major role in mitigating salt stress.

Keywords: Malus seedlings; NaCl treatments; enzyme activity; membrane damage; osmotic regulation.

Figure 1

Change curve of leaf SOD and POD activities for the three Malus species under four levels of NaCl treatments.

Figure 2

Change curve of leaf CAT activity and MDA content for three Malus species under four levels of NaCl treatments.

Figure 3

Change curve of leaf SP and PRO contents for the three Malus species under four levels of NaCl treatments.

Figure 4

Change curve of leaf CHLa and CHLb contents in the three Malus species under four levels of NaCl treatments.

Figure 5

Change curve of root SOD and POD activities in the three Malus species under four levels of NaCl treatments.

Figure 6

Change curve of root CAT activity and MDA in the three Malus species under four levels of NaCl treatments.

Figure 7

Change curve of root SP and PRO contents in the three Malus species under four levels of NaCl treatments.

Figure 8

PCA of physiological parameters in leaves and roots for the three Malus species. Loading and scores plot of the first two principal components of the principal component analysis model. The left and bottom coordinates were the loading scores of the first two principle components, and the top and right coordinates were the scores of all the physiological parameters in the first two principle components. MZL—leaves of M. zumi; MSL—leaves of M. sieversii; MBL—leaves of M. baccata; MZR—roots of M. zumi; MSR—roots of M. sieversii; MBR—roots of M. baccata.