Low Temperature-Induced GA₃ Sensitivity of Wheat

Abstract

Exposure of isolated aleurone tissue from the wheat (Triticam aetirum) variety Kite which contains the Rht2 allele, to low temperature (5°C) for 20 h prior to addition of exogenous GA3, resulted in significant changes in the content of lipids, especially phospholipids. Sigificat low temperature-induced changes in both the head group and acyl contents of two phospholipids, phosphatidylcholine and phosphatidylethanolamine, were detected. More importantly, these changes displayed a very close temporal relationship with the low temperature-induced increase in GA3 sensitivity. Further, this relationship was paralleled by a highly significant correlation between the changes in the phospholipids and the changes in a-amylase production. These results underline the possibility that the GA3 receptor sites are membranbased lipids.Aleurone tissue of cereal seeds, when exposed to GA3, synthesizes and secretes hydrolytic enzymes, including a-amylase, into the starchy endosperm (5). Deembryonated seed or isolated aleurone layers thus provide convenient experimental systems for the study of GA3-induced a-amylase production. In the preceding paper, low temperature was shown to increase the GA3 sensitivity of otherwise GA3-insensitive aleurone tissue of several wheat varieties. More cubation of the isolated aleurone layers were as described in the preceding paper. Where dry seeds were involved, the aleurone layers were dissected from deembryonated seeds after boiling them for 5 min.Extraction and Analysis of Phospholipids. At the end of the preincubation period, the aleurone layers were immediately frozen in liquid N2 and freeze-dried and lipids were extracted using hot, water-saturated butan-l-ol (28). The total lipid extract was subjected to partition chromatography on Sephadex G-25 to yield a purified total lipid fraction, which was further fractionated by adsorption chromatography on silicic acid column. This fractionated the total lipids into neutral lipids, glycolipids, and phospholipids. These methods have been described in detail previously (1, 28).Phospholipids were separated into individual classes by TLC as described earlier (13) and quantified by GLC according to Douglas and Paleg (3). All experiments were replicated three times, and data were subjected to analysis of variance as well as multivariate analysis of variance.

A Possible Role for Indoleacetic Acid, Low Temperature, and Phospholipid Metabolism in the Induction of GA3 Responsiveness in GA3 Insensitive (Rht3-Containing) Dwarf Wheat Aleurone

“…The acyl part of the phospholipids was comprised of five different fatty acids, viz., 16:0, 18:0, 18:1, 18:2, and 18:3 (Table III) and this agreed with reports published earlier (8,10). Imbi- bition of water for 12 h at 30°C produced increases only in the 16:0 and 18:2 components of PG (Table III) and Table IV reports the effect of IAA preincubation on the fatty acids of PI and PC as they were the only two phospholipids whose levels were significantly affected by IAA pretreatment (Table II).…”

“…The major difference was that IAA pretreatment had no effect on PE whereas low temperature induced a significant change in PE levels. Also, the effect of 5C preincubation on the phospholipids agreed quite well with our earlier findings (8,10). Table VI (Tables V and VI).…”

“…Only one concentration of IAA was used in these experiments; thus, deembryonated seed was preincubated in 342 nm IAA at 30C for 1, 4, 8, 16, or 24 h and then either extracted for the analysis of phospholipids or challenged with 0.1 g ml-' GA3 for 24 h, at the end ofwhich the a-amylase produced was assayed. All methods for the analysis of a-amylase and phospholipids were the same as described earlier (7)(8)(9)(10). RESULTS It was of interest, initially, to determine the time course of the IAA effect on GA3 sensitivity of the dwarf (Rht3) aleurone, and Figure 1 shows that a 4 h preincubation period was sufficient to produce the maximal increase in GA3 sensitivity.…”

Transcriptome and metabolomic analysis to reveal the browning spot formation of ‘Huangguan’ pear

“…Cold temperatures have been shown to inhibit plant growth by reducing auxin accumulation [ 59 ]. Alternatively, a previous study showed that low temperature induces an increase in GA 3 sensitivity [ 60 ]. We predict that low temperature causes the differential expression of plant hormone signalling pathway genes, which indicates that low temperature might be the most important cause of BS.…”