Abstract
Arid and semiarid apple producing areas suffer from severe alkalinity of soil, which strongly affects the yield and quality of apples. Dopamine (DA) is involved in metabolic activities in response to abiotic stress in plants. To detect the effects of exogenous DA application on the adaption of apple (Malus hupehensis) seedlings to alkali stress and as a protection from oxidative stress, 0.1 mM DA was identified as the most suitable concentration by hydroponic culture. Further experimentation showed that the growth and photosynthesis of apple seedlings were significantly inhibited under alkali stress, and more reactive oxygen species accumulated, compared with control. However, exogenous DA application suppressed the loss of the plant height, root length, chlorophyll levels, and photosynthetic capacity of apple seedlings that were caused by alkali stress. In the leaves of alkali stressed seedlings, the catalase, superoxide dismutase, and peroxidase activities were lower and hydrogen peroxide and malondialdehyde levels were higher than in the untreated plants. The presence of DA significantly alleviated such effects of alkali stress. In addition, exogenous DA application increased the antioxidant capacity of apple seedlings under alkali stress by increasing the level of chlorogenic acid. These results are significant for improving the alkali tolerance of apple in apple-producing areas with alkalized soil.
Highlights
The loess plateau of Northwest China has a large diurnal temperature range and sufficient sunshine, both of which contribute to the production of high-quality apples; the climate is arid or semiarid
This study was conducted to enhance our understanding of the physiological processes of apple seedlings in alkaline environments
Exogenous DA application can reduce the effects of drought stress, salt stress, and nutritional deficiency [12,13,21], the effect of DA on alkali stress has not been studied to date
Summary
The loess plateau of Northwest China has a large diurnal temperature range and sufficient sunshine, both of which contribute to the production of high-quality apples; the climate is arid or semiarid. To promote the production of high-quality apples, agritechnological measures to improve the alkali tolerance of apple trees are of great importance. How plants respond to salt stress has been widely studied, but little attention has been focused on the response mechanisms of plants to alkali stress. The effects of alkali stress on plant growth mainly manifested in the damage of partial root function, decreases of water content and root activity, destruction of the photosynthetic system, and a decrease of photosynthetic pigment levels [3]. Previous studies have shown that alkali stress can significantly inhibit the growth of apple seedlings, damage plasma membrane, and cause a series of reductions of physiological functions [4,5,6]
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