Physiological analysis reveals the mechanism of accelerated growth recovery for rice seedlings by nitrogen application after low temperature stress

Abstract

Low temperature and overcast rain are harmful to directly seeding early rice, it can hinder rice growth and lower rice biomass during the seedling stage, which in turn lowers rice yield. Farmers usually use N to help rice recuperate after stress and minimize losses. However, the effect of N application on the growth recovery for rice seedlings after such low temperature stress and its associated physiological changes remain unclearly. Two temperature settings and four post-stress N application levels were used in a bucket experiment to compare B116 (strong growth recovery after stress) with B144 (weak growth recovery). The results showed that the stress (average daily temperature at 12°C for 4 days) inhibited the growth of rice seedlings. Compared to the zero N group, the N application group’s seedling height, fresh weight and dry weight significantly increased after 12 days. In particular, the increases in all three growth indicators were relatively higher than that of N application at normal temperature, indicating the importance of N application to rice seedlings after low temperature stress. The antioxidant enzyme activity of rice seedlings increased significantly after N application, which reduced the damaging effect of ROS (reactive oxygen species) to rice seedlings. At the same time, the soluble protein content of seedlings showed a slow decrease, while the H2O2 and MDA (malondialdehyde) content decreased significantly. Nitrogen could also promote nitrogen uptake and utilization by increasing the expression of genes related to NH4+ and NO3− uptake and transport, as well as improving the activity of NR (nitrate reductase) and GS (glutamine synthetase) in rice. N could affect GA3 (gibberellin A3) and ABA (abscisic acid) levels by regulating the anabolism of GA3 and ABA. The N application group maintained high ABA levels as well as low GA3 levels from day 0 to day 6, and high GA3 levels as well as low ABA levels from day 6 to day 12. The two rice varieties showed obvious characteristics of accelerated growth recovery and positive physiological changes by nitrogen application after stress, while B116 generally showed more obvious growth recovery and stronger growth-related physiological reaction than that of B144. The N application of 40 kg hm-2 was more conducive to the rapid recovery of rice growth after stress. The above results indicated that appropriate N application promoted rice seedling growth recovery after low temperature stress mainly by increasing the activities of antioxidant enzymes and nitrogen metabolizing enzymes as well as regulating the levels of GA3 and ABA. The results of this study will provide a reference for the regulation of N on the recovery of rice seedling growth after low temperature and weak light stress.

Combined Analysis of Root Transcriptome, Metabolome and physiology on the mechanism of rapid growth recovery for rice seedlings after low temperature stress

“…Firstly, the active oxygen compounds represented by H 2 O 2 and MDA are cleared, and then the absorption area of the root system is expanded to absorb more nutrients for the overall recovery and growth of the plant. After low temperature, the nitrogen application treatment of the root system makes the above ground part grow rapidly [31], The effect of nitrogen application under different root systems on plant salt tolerance supports our study [44].…”

“…Multi-omics method is used to explain the promoting effect of heterooctone, a Carotenoid growth regulator, on rice growth [30]. The Transcriptome association analysis found that the genes of photosynthesis, active oxygen metabolism, starch and carbohydrate metabolism, phenylpropane biosynthesis and other related metabolic pathways changed signi cantly after low temperature stress in rice [31], and the extensive metabolome study found that sugars were signi cantly enriched after low temperature stress in rice, and the content increased signi cantly [32].…”

Elucidation of the Mechanism of Rapid Growth Recovery in Rice Seedlings after Exposure to Low-Temperature Low-Light Stress: Analysis of Rice Root Transcriptome, Metabolome, and Physiology

“…Following exposure to combined stress from low temperatures and low light intensities, the roots first entered a period of rapid growth recovery. Initially, the reactive oxygen compounds, represented by H 2 O 2 and MDA, were removed, and then, the absorption area of roots expanded to absorb more nutrients for the overall growth recovery of plants [35].…”

“…The growth recovery and related mechanism of the root system after low-temperature low-light stress was relieved, the main hazard factor in meteorological disasters was tracked, and no single stress factor was studied. Therefore, it is not clear which of the two stress factors, low temperature or low light, was dominant, although it is generally believed that low temperature is the main hazard factor [35]. Late spring cold is generally accompanied by rainfall and significant changes in humidity [25].…”