Mazzucotelli Elisabetta, Tartari Alfredo, Cattivelli Luigi, Forlani Giuseppe
Dipartimento di Biologia, Università di Ferrara, via L. Borsari 46, 44100 Ferrara (FE), Italy.
J Exp Bot. 2006;57(14):3755-66. doi: 10.1093/jxb/erl141. Epub 2006 Sep 22.
Amino acid homeostasis was investigated in frost-resistant barley seedlings under either cold- or freezing-stress conditions. Total free amino acid content varied only slightly, but a substantial conversion of glutamate to gamma-aminobutyric acid (GABA) was found that was proportional to the severity of the stress. Cold acclimation caused a significant increase in amino acid pools, and induced the expression of the GABA-shunt genes. As a consequence, GABA accumulated to a higher extent during the subsequent exposure to lower temperature. A different picture was obtained with a frost-sensitive genotype, in which glutamate decarboxylation occurred during the stress as well, but the activation of the GABA shunt seemed not to take place, and free glutamate was almost depleted. Analogous results were found in frost-resistant and frost-sensitive wheat cultivars. Feeding non-hardened plants with exogenous glutamate resulted in increased GABA accumulation under low temperature. The possibility that glutamate decarboxylation and GABA metabolism would play a role in frost tolerance is discussed.
在抗冻大麦幼苗的冷胁迫或冻胁迫条件下研究了氨基酸稳态。总游离氨基酸含量变化甚微，但发现谷氨酸大量转化为γ-氨基丁酸（GABA），且这种转化与胁迫的严重程度成正比。冷驯化导致氨基酸库显著增加，并诱导了GABA分流基因的表达。因此，在随后暴露于较低温度期间，GABA积累到更高水平。对于一个霜冻敏感基因型则呈现出不同的情况，在该基因型中，胁迫期间也发生了谷氨酸脱羧，但GABA分流似乎未被激活，游离谷氨酸几乎耗尽。在抗冻和霜冻敏感的小麦品种中也发现了类似结果。用外源谷氨酸喂养未驯化的植物会导致低温下GABA积累增加。本文讨论了谷氨酸脱羧和GABA代谢在抗冻性中发挥作用的可能性。
