Effects of nitric oxide on the GABA, polyamines, and proline in tea (Camellia sinensis) roots under cold stress

Abstract

Tea plant often suffers from low temperature induced damage during its growth. How to improve the cold resistance of tea plant is an urgent problem to be solved. Nitric oxide (NO), γ-aminobutyric acid (GABA) and proline have been proved that can improve the cold resistance of tea plants, and signal transfer and biosynthesis link between them may enhance their function. NO is an important gas signal material in plant growth, but our understanding of the effects of NO on the GABA shunt, proline and NO biosynthesis are limited. In this study, the tea roots were treated with a NO donor (SNAP), NO scavenger (PTIO), and NO synthase inhibitor (L-NNA). SNAP could improve activities of arginine decarboxylase, ornithine decarboxylase, glutamate decarboxylase, GABA transaminase and Δ1-pyrroline-5-carboxylate synthetase and the expression level of related genes during the treatments. The contents of putrescine and spermidine under SNAP treatment were 45.3% and 37.3% higher compared to control at 24 h, and the spermine content under PTIO treatment were 57.6% lower compare to control at 12 h. Accumulation of proline of SNAP and L-NNA treatments was 52.2% and 43.2% higher than control at 48 h, indicating other pathway of NO biosynthesis in tea roots. In addition, the NO accelerated the consumption of GABA during cold storage. These facts indicate that NO enhanced the cold tolerance of tea, which might regulate the metabolism of the GABA shunt and of proline, associated with NO biosynthesis. Tea plant is an important economic crop which is widely planted in many regions of China. Adverse environmental conditions, mainly cold stress, impose major limitations on the suitable geographical locations for tea growth and impact both in tea production and quality 1. The GABA is a non-protein amino acid, C 4 H 9 NO 2 3 , and is widely distributed in nature among prokaryotes and eukaryotes as an important free amino acid. Some special treatments of fresh tea leaves, such as charging the nitrogen and removing oxygen can result in accumulation of GABA 2. It is widely known as a neurotransmitter in the sympathetic nervous system 4,5. Moreover, previous study also revealed its function on improving cold tolerance of tea plant 6. There are several GABA metabolism pathways, including glutamate catalyzed by glutamate decarboxylase (GAD) and the reversible conversion of GABA to succinic semialdehyde by GABA transaminase (GABA-T) followed by irreversible oxidization of succinic semialdehyde. Polyamines (PAs) include spermidine (Spd), spermine (Spm) and their diamine obligate precursor putrescine (Put) 3,7 , PAs catabolism can provide raw materials for GABA synthesis which means PAs degradation pathway is an important component of the GABA biosynthesis pathway 8. The Put and Spd are catalyzed by diamine oxidase and polyamine oxidase, respectively 3. PAs are widely present in plants, and the enzymes related to their biosynthesis have strong connections with environmental stresses such as cold, heat, salt and drought stress 9,10. The expression and a...

Exogenous Nitric Oxide Confers Tolerance to Cr(VI) in Maize (Zea mays L.) Seedlings by Modulating Endogenous Oxido-Nitrosative Events

“…In our case, PAs may play a dual role; as antioxidant compounds and controller of NO biosynthesis. A similar finding was reported by Wang et al (2020); PAs concentration in tea roots showed different trend by applying exogenous NO scavenger and inhibitor. Based on these results we can assume an existing relationship between the biosynthesis of NO and its intracellular amount.…”

“…Such wider impacts have been noted in NO effects on proline and polyamines (PAs) metabolism (e.g. Wang et al 2020).…”

The versatile GABA in plants

“…56 Though many studies report high levels of GABA in response to low temperature exposure, GABA content in tea roots, on the other hand, decreases under cold treatment. 57 High content of GABA is associated with plant tolerance to low temperatures. Exogenous GABA application induces an increase of endogenous GABA and improves cold tolerance in tomato seedlings, 58 banana, 59 anthurium cut-flowers, 60 and tea plants.61 Potential mechanisms by which high levels of GABA alleviate low temperature injury may be due to enhancement of plant antioxidant systems, 58,59 which reduces malondialdehyde (MDA) and ROS contents, 58 and proline accumulationmediated osmoregulation.…”

“… 56 Though many studies report high levels of GABA in response to low temperature exposure, GABA content in tea roots, on the other hand, decreases under cold treatment. 57 …”

MicroRNA Omics Analysis of Camellia sinesis Pollen Tubes in Response to Low-Temperature and Nitric Oxide

“…Low temperature (LT) is one of the momentous factors restricting plant growth and development, geographical distribution and yield expansion, and is reflected in germination, growth, development, flowering and colonization [1]. Particularly, LT often negatively regulates the reproduction process which is an indispensable process in the growth of plants, especially pollen tube germination and elongation [2].…”