The Physiological Role Of Salt Stress-induced GABA Accumulation In Zea Mays

Gamma-aminobutyric acid is a four-carbon non-protein amino acid that is widely distributed in virtually all prokaryotic and eukaryotic organisms as a significant component of the free amino acid pool. In animal, GABA functions as the predominant inhibitory neurotransmitter in the central nervous system, adjusts much behavior and participates in nosogenesis by acting through the GABA receptors and alternant operating with other neurotransmitters. GABA exists in the higher plants far and wide too, Its physiological role has been payed more attention under multifarious stresses in recent years.. The physiological role of GABA accumulation and the relationship between ABA and GABA under stresses were investigated.GABA was detected in root, stem and leaves of maize seedling under natural circumstance and salt stress. GABA accumulated in root under salt stress prior to the stem and leaves. The mutative extent of GABA content was bigger than the overground part. It was perhaps that the root was the original part which recepted the salt stress. GABA distribution in root tip cell was localized by immuno-electron microscopy techniques. It showed that GABA mainly existed in the cytoplasm and nucleus, it was also detected in the cell wall and mitochondria. It deduced that a mass of GABA localized in cytoplasm probably had something to do with glutamate decarboxylase localized in cytoplasm, The function of GABA localized in nucleus is not clear, GABA was localized in cell wall probably because of transportation and distribution of GABA.Pharmacological experiments indicated that low concentration of GABA could promote the growth of radicle and coleoptile and high concentration of GABA could restrained their growth, Presumedly the inhibitory effect had something to do with increase of endogenous ethylene level. GABA analog ( 2-aminobutyric acid, 3-aminobutyric acid )and GABA receptor's antagonists bicuculine and picrotoxin could inhibit GABA mediated elongation of radicle and coleoptile appreciably, GABA receptor's agonist balclofen could increase GABA mediated elongation of radicle and coleoptile appreciably. These results could perhaps gave some indirect evidence for the existence of GABA receptors in plants like in animal. But the existence, structure and localization of plant GABA receptors are needed to be further studied all the same.GABA could decrease relative exosmic ratio of radicle and coleoptile, enhanced the content of endogenous soluble sugar, proline and betaine, promoted the absorb of K+ , excluded Na+ coming in the root, stem and leaves of maize seedling, increased K7 Na+ ratio under salt stress. The effects of ABA and NaCl on GABA content in maize seedling was investigated. The results showed that GABA content increased responding to different ABA and NaCl concentration. The promoting effect on GABA content under the treatment of the solution containing 100 umol/L ABA and 150 mmol/L NaCl was bigger thanthe effect of the treatment by 100 umol/L ABA or 150mmol/L NaCl respectively. We speculated that there was relationship between ABA and NaCI in the promoting GABA accumulation. Both the content of ABA and GABA was enhanced in maize seeding, but ABA accumulated prior to GABA under the treatment of 150 mmol/L NaCl. The content of GABA was increased by 2.3S times in radicle and 2.23 times in coleoptile compared with control. Pretreated with 10uumol/L fluridone following 150 mmol/L NaCl, the change of GABA content was decreased greatly. It proves that ABA may regulate the accumulation of GABA under salt stress. Treatment of salt stress and ABA resulted in the accumulation of GABA by activating glutamate decarboxylase.In summy, the characteristic of GABA accumulation and distribution in tissue.organ and cell level was observed, ABA regulated the accumulation of GABA and the physiological role of GABA were made art elementary study under salt stress.