As the immobility of inorganic phosphorus (P) in soil, the acquisition of P by sessile plants is limited. γ-Aminobutyric acid (GABA) as a signal molecule and a metabolite can regulate plants to cope with various stresses. However, whether GABA could contribute to the adaption to low P stress in apple plants remains unclear. This study combined different methods to detect the induction of auxin (IAA) synthesis by GABA to improve the tolerance of apple seedlings to low P stress (including growth and development analysis, reactive oxygen species (ROS) clearance effect, root structure analysis, multiple factorial analysis (MFA), gene expression analysis). Exogenous GABA improved the growth of apple seedlings under low P conditions, reduced the ROS accumulation, and promoted the photosynthetic capacity. GABA contributed to the root system architecture and the development of mature area of root tips. In addition, the intervention of exogenous GABA interfered with the homeostasis of endogenous IAA and activated the expression of P starvation induction (PSI) gene, leading to the significantly increase of the P uptake in apple plants. Meanwhile, transgenic roots with overexpressing MdGAD1 enhanced the tolerance of apple seedlings to low P stress, improved the root development through regulating IAA signaling pathway, and significantly improved the P uptake of apple seedlings under low P conditions. All results suggested that GABA could contribute to the adaption of apple seedlings to low P conditions, by decreasing ROS accumulation, maintaining photosynthetic capacity, and increasing IAA level to improve the root development and the P absorption.

Drought stress is an important factor limiting apple production. gamma-Aminobutyric acid (GABA) exists widely in plants and participates in the response to abiotic stress as a metabolite or signaling molecule. The role of exogenous GABA in apple plants, response to long-term drought stress remains unclear. Our study confirmed that exogenous GABA affects the drought resistance of apple plants under long-term drought stress. We found that 1 mM exogenous GABA improved the resistance of apple seedlings to long-term drought stress. The plants showed better growth, less reactive oxygen radical accumulation, less damage to cell membranes and greater active photosynthetic capacity. Under long-term drought stress, exogenous GABA facilitated GABA shunt, resulting in more accumulation of organic acids, namely citric acid, succinic acid and malic acid, in roots and stems of apple seedlings. In addition, exogenous GABA upregulated the expression of cellulose-related genes and lignin-related genes, and activated secondary cell wall-related transcription factors to synthesize more cellulose and lignin. A multiple factorial analysis confirmed that the GABA shunt and the biosynthesis of cellulose and lignin substantially contributed to the growth of apple seedlings with the application of exogenous GABA under long-term drought stress. Our results suggested that exogenous GABA improved the resistance of apple seedlings to long-term drought stress by enhancing GABA shunt and secondary cell wall biosynthesis.

Aims The main aim of this study was to investigate the response of various physiology indexes,e.g.,chlorophyll index value(stand for the relative content of chlorophyll,SPAD value),net photosynthetic rate(Pn),stomatal conductance(Gs),and root shoot ratio(R/S) in two genotypes of maize(Zea mays) to NH3 concentration enrichment.Methods We grew maize on Hoagland solution in PVC pots in open top chambers(OTCs).The experiment was a split-split plot design,which main treatments were two NH3 concentrations(10 and 1 000 nl·L-1).The sub-plot treatments of the experiment were two levels of nitrogen(high and low),and sub-sub-plot treatments were two N efficiency genotypes(high N efficiency,'NE5',and low N efficiency,'SD19').Air flow in OTCs was controlled by small fans and atmospheric NH3 concentration was measured accurately by two methods(NH3 determination tubes and GTL-C atmosphere detecting apparatus).Important findings Under elevated atmospheric NH3,there were significant differences(p0.05) for physiology indexes between the two varieties,'NE5' and 'SD19'.Under high N medium,compared with 10 nl·L-1 atmospheric NH3 concentration,the SPAD value,Pn and Gs of 'NE5' treated with 1 000 nl·L-1 decreased 7.0%,14.0% and 6.5%,respectively,and the corresponding targets of 'SD19' decreased 9.0%,11.0% and 6.9%,respectively.Under low N medium,various physiology indexes of the two varieties significantly increased,i.e.,the SPAD value,Pn and Gs of 'NE5' increased 5.7%,7.1% and 17%,respectively,and the relative value of 'SD19' increased 7.0%,11.0% and 22.0%,respectively.The results also demonstrated that under high N medium,the inhibition effect of increased atmospheric NH3 on 'SD19' shoot biomass was obviously lower than that of 'NE5',while under low N medium,NH3 concentration enrichment had more positive influence on 'NE5'(p0.05) than 'SD19'.Moreover,the ratio of roots to shoots of 'NE5' and 'SD19' in the two atmospheric NH3 concentrations was related to maize growth periods,i.e.,there were different changes for their root and shoot biomass in three sampling time,but still obeying certain laws.All these results indicated that the absorbed atmospheric NH3 by plants can improve crop nitrogen nutrition growing in low N medium,and there may be more significantly positive effect on low nitrogen efficiency genotypes.