The language of GABA in pollen tube growth and guidance

The achievement of double fertilization in higher plants requires the successful transport of sperm cells to the female gametes,the ovules.Pollen tubes,the tubular structure protruding from pollens,carrying the sperms play an important role in this process.How a pollen tube precisely guides its direction to gain its goal is of mystery.Previous investigation indicated that multiple signal clues from the pistils function as the route signs to regulate the pathway of pollen tube growth.Among the signal clues,c-aminobutyric acid(GABA)seems to be universal.Its gradient concentration has been found both in tobacco and Arabidopsis pollen tube guidance.In the communication of pollens and pistils,what on earth GABA tells pollen tubes is of great interest.The GABA receptors on the pollen membrane are thought to be the hinge in the language conversation.In this review,the mechanism of GABA gradient formation is investigated.The possible GABA receptor on the pollen membrane is examined and its function is discussed.To decipher the possible language of GABA in pollen tube growth and guidance,multiple methods are needed.The combination of transcriptome and proteomics assay is expected to unveil the secret.

The Dominant Glutamic Acid Metabolic Flux to Produce γ-Amino Butyric Acid over Proline in Nicotiana tabacum Leaves under Water Stress Relates to its Significant Role in Antioxidant Activity

γ-Amino butyric acid （GABA） and proline play a crucial role in protecting plants during various environmental stresses. Their synthesis is from the common precursor glutamic acid, which is catalyzed by glutamate decarboxylase and △1-pyrroline-5-carboxylate synthetase respectively. However, the dominant pathway under water stress has not yet been established. To explore this, excised tobacco leaves were used to simulate a water-stress condition. The results showed GABA content was much higher than that of proline in leaves under water-deficit and non-water-deficit conditions. Specifically, the amount of GABA significantly increased compared to proline under continuous water loss for 16 h, indicating that GABA biosynthesis is the dominant pathway from glutamic acid metabolism under these conditions. Quantitative reverse transcription polymerase chain reaction and protein Western gel-blot analysis further confirmed this. To explore the function of GABA accumulation, a system producing superoxide anion （O 2 - ）, peroxide hydrogen （H 2 O 2 ）, and singlet oxygen （ 1 O 2 ） was employed to investigate the scavenging role on free-radical production. The results demonstrated that the scavenging ability of GABA for O 2 - , H 2 O 2 , and 1 O 2 was significantly higher than that of proline. This indicated that GABA acts as an effective osmolyte to reduce the production of reactive oxygen species under water stress.

Identification of superoxide dismutase isoenzymes in tobacco pollen

We investigated the possible existence of superoxide dismutase(SOD;EC 1.15.1.1)isoenzymes in the pollen of Nicotiana tabacum(Petit Havana SR-1 cultivar).To detect SOD activity,crude extracts from tobacco pollen were subjected to native polyacrylamide gel electrophoresis followed by staining with nitroblue tetra-zolium(NBT).The presence of six SOD isoenzymes was detected in tobacco pollen.Treatment with SOD inhibitors indicated the presence of one manganese SOD(Mn SOD),five copper-zinc SOD(Cu/Zn SOD)isoenzymes,and the absence of iron SOD(Fe SOD).