Abstract

We characterized the growth and physiological responses of five wild Malus species indigenous to China to acid and alkaline abiotic stresses. At the six-leaf stage, seedlings of Malus sieversii, Malus prunifolia, Malus robusta, Malus mandshurica and Malus hupehensis were transferred to hydroponic systems in which the solution pH was 5.5, 7.0 or 8.5. Fresh and dry weights, plant heights and root lengths were measured over time. After 20 days of treatment, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), ascorbic acid (AsA), andglutathione (GSH) contents were determined, as well as the rate of superoxide radical (O₂^.-) generation and antioxidant enzyme activities in the roots. When the pH was raised from 7.0 to 8.5, seedlings of M. sieversiidisplayed significant increases in their growth parameters whereas values for all other traits were significantly decreased. The opposite trend was observed with M. prunifolia and M. hupehensis. When the pH was decreased from 7.0 to 5.5, seedlings of M. sieversii showed a significant decline in their dry weights but a significant improvement in root MDA, H₂O₂, AsA, and GSH contents, O₂^.- generation and enzyme activities. In conclusions, these results suggest that growth is not severely inhibited for M. prunifolia, M. mandshurica, andM. hupehensis under acidic conditions (pH 5.5) or alkaline conditions for M. sieversii, M. robusta and M.mandshurica (pH 8.5). In fact, M. sieversii grew better at pH 8.5, whereas growth was significantly inhibited forM. sieversii and M. robusta at pH 5.5 and for M. prunifolia and M. hupehensis at pH 8.5.

Key words: Antioxidant enzymes, antioxidants, growth traits, hydroponics pH, Malus species, oxidative stress.