Abstract
Malus hupehensis is an excellent Malus rootstock species, known for its strong adverse-resistance and apomixes. In the present study, stem cuttings of M. hupehensis were treated with three types of exogenous hormones, including indole acetic acid (IAA), naphthalene acetic acid (NAA), or green growth regulator (GGR). The effects and mechanisms of exogenous hormone treatment and antioxidant enzyme activity on adventitious root formation were investigated. The results showed that the apparent morphology of the adventitious root had four stages, including root pre-emergence stage (S0), early stage of root formation (S1), massive root formation stage (S2), and later stage of root formation (S3). The suitable concentrations of the three exogenous hormones, IAA, NAA and GGR, were 100 mg·L-1, 300 mg·L-1, and 300 mg·L-1, respectively. They shortened the rooting time by 25–47.4% and increased the rooting percentages of cuttings by 0.9–1.3 times, compared with that in the control. The dispersion in S0 stage was 3.6 times of that in the S1 stage after exogenous hormone application. The earlier the third critical point (P3) appeared, the shorter the rooting time and the greater the rooting percentage of the cuttings. During rhizogenesis, the activities of three antioxidant enzymes (POD, SOD, and PPO) showed an A-shaped trend. However, peak values of enzyme activity appeared at different points, which were 9 d before the P3, P3, and the fourth critical point (P4), respectively. Exogenous hormone treatment reduced the time to reach the peak value by 18 days, although the peak values of the enzymatic activities did not significantly changed. Our results suggested that exogenous hormone treatment mainly acted during the root pre-emergence stage, accelerated the synthesis of antioxidant enzymes, reduced the rooting time, and consequently promoted root formation. The three kinds of antioxidant enzymes acted on different stages of rooting.
Highlights
Malus hupehensis (Pamp.) Rehd. is a major accession of Malus spp. and is widely distributed across China [1, 2]
By using exogenous hormone treatment, this paper studied the dynamics of rooting of M. hupehensis cutting and the changes in the activity levels of antioxidant enzymes (POD, SOD, and polyphenol oxidase (PPO))
The dynamic observation graph and explanation of rooting of cutting of Malus hupehensis treated with indole acetic acid (IAA) 100 mgÁL−1 are shown in Fig 1 and Table 1
Summary
Malus hupehensis (Pamp.) Rehd. is a major accession of Malus spp. and is widely distributed across China [1, 2]. M. hupehensis has been cultivated as an ornamental tree and utilized as medicine and food It has been considered as a prime rootstock species in the southern region of the China Yellow River Basin [3]. Vegetative propagation using the stem cutting method can be considered as a post-operation root regeneration process. Once a stem is cut from its parent plant, its nutrient and water supply is lost Under such conditions, the plant is exposed to oxidative stress, and its redox balance is destroyed [6]. How to increase cellular antioxidant resistance, restore redox balance, and promote adventitious root formation (ARF) are critical to stem survival [7, 8]. Exogenous hormone treatment increases peroxidase (POD) and polyphenol oxidase (PPO) activity, decreases the activity of IAAO and subsequently promotes root formation. Most current studies have focused on microscopic cellular features prior to the formation of root primordia as well as other physiological and biochemical changes, whereas the importance of specific critical points such as adventitious root cortical breakthrough and massive root formation have not been established completely
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