Abstract
Adventitious root (AR) is a kind of later root, which derives from stems and leaf petioles of plants. Many different kinds of small signaling molecules can transmit information between cells of multicellular organisms. It has been found that small molecules can be involved in many growth and development processes of plants, including stomatal movement, flowering, fruit ripening and developing, and AR formation. Therefore, this review focuses on discussing the functions and mechanisms of small signaling molecules in the adventitious rooting process. These compounds, such as nitric oxide (NO), hydrogen gas (H2), hydrogen sulfide (H2S), carbon monoxide (CO), methane (CH4), ethylene (ETH), and hydrogen peroxide (H2O2), can be involved in the induction of AR formation or development. This review also sums the crosstalk between these compounds. Besides, those signaling molecules can regulate the expressions of some genes during AR development, including cell division genes, auxin-related genes, and adventitious rooting-related genes. We conclude that these small-molecule compounds enhance adventitious rooting by regulating antioxidant, water balance, and photosynthetic systems as well as affecting transportation and distribution of auxin, and these compounds further conduct positive effects on horticultural plants under environmental stresses. Hence, the effect of these molecules in plant AR formation and development is definitely a hot issue to explore in the horticultural study now and in the future.
Highlights
The root system of a plant is made up of the primary, lateral, and adventitious roots
The development of Adventitious root (AR) is a vital step in the vegetative propagation of plants, which is regulated by various endogenous factors such as plant hormones, metabolic constituents, enzyme activities, and external environmental stimulations, and it plays a key function for plant adaptation to abiotic stresses, including salt, drought, heavy metal, and osmotic stresses [5]
In ground-cover chrysanthemum, 200 μM H2 O2 was the most suitable dosage to promote AR. Development, at which this dosage increased the activities of polyphenol oxidase (PPO), indoleacetic acid oxidase (IAAO), and water-soluble carbohydrate (WSC), as well as total nitrogen content, and decreased the total polyphenol content [28]. These results indicate that H2 O2 could enhance AR development via increasing some enzyme activities, and carbohydrate and nitrogen contents, and inhibiting polyphenol production
Summary
The root system of a plant is made up of the primary, lateral, and adventitious roots. NO was discovered to influence the interactions between plants and microbes during pathogenesis [11,12] They are involved in numerous plant growth and development processes, including cell division, stomatal movement, adventitious rooting, flowering, fruit ripening and development, and seed dormancy or germination [5,13,14,15]. Multiple researchers suggest that small-molecule compounds can promote AR formation and development via mediating a variety of growth and developmental processes, which help to improve the resistance against environmental stress conditions in plants. The innovational application of small-molecule compounds is necessary to promote AR formation, and its great importance in horticultural study cannot be ignored. The interactions between NO and other signaling molecules are discussed
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