Abstract
The bioactivity of humic acids (HA) is mainly due to the presence of auxin analogs. In turn, nitric oxide (NO) production in plants affects root growth and may result from endogenous auxin production or the application of synthetic auxin analogs or HA. Nitric oxide signaling may be related to the bioactivity of the HA. Although the auxin, NO, and ROS-mediated activity of HA has been studied, no studies exist on their effects in Ocimum basilicum L., commonly known as basil. A study under controlled in vitro conditions was performed using hairy roots (hairy roots) of basil grown in medium with N-NO3- (0.5 or 5.0 mM) and subjected to treatments with HA (3 mMC·L-1) or sodium nitroprusside (SNP; 100 μM), an NO donor, either without or with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO; 200 μM), an NO scavenger. The addition of HA and SNP resulted in significant increases in the root growth, associated with increased NO and reactive oxygen species (ROS) contents. The application of the NO scavenger cPTIO with the SNP and HA decreased the effects of both substances on the root growth and endogenous levels of the NO and ROS. The increased root growth promoted by the NO donor (SNP) and HA was also associated with increased proton pump and catalase activity for both N-NO3- levels tested. The results showed that the effects of HA are dependent on NO and ROS, which act as messengers, inducing root growth.
Highlights
Plant adaptation and survival under adverse conditions may be directly related to the ability of roots to respond to several factors, such as water, light, and nutrient availability
Increases in root size were observed for both the treatments with humic acids (HA) and sodium nitroprusside (SNP), even when tested with the lower N- NO3− supply, indicating that the association of nitric oxide (NO) donor may activate a cascade of biochemical events related to cell growth, culminating in the induction of root morphogenesis
HA resulted in a significant increase in root growth in basil, in association with increased NO and reactive oxygen species (ROS) contents
Summary
Plant adaptation and survival under adverse conditions may be directly related to the ability of roots to respond to several factors, such as water, light, and nutrient availability. Regarding plant adaptation and survival, roots may adapt to adverse conditions due to their high plasticity, being able to induce the initiation of root primordia, resulting in the emission of lateral roots to better explore the available environmental resources [1]. In agricultural and aerobic soils, nitrate ( NO3− ) is the main N source and plays a crucial role in root growth [3]. Its uptake by roots depends on specific plasma membrane transporters, enzyme activity for N reduction and assimilation, and energy availability for both processes [4]. Studies have confirmed the association of HS with exogenous auxins, with both present in the environment, resulting in lateral root induction [8]
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