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

Abstract

Preincubation of dwarf, Rht3-containing deembryonated seed for 4 hours in 342 nanomolar indoleacetic acid (IAA) induced maximum sensitivity to GA3. In addition, the 4-hour IAA pretreatment caused a 2-fold increase in total phospholipids which coincided identically on a temporal basis with the induced GA3 sensitivity. Changes in absolute levels of individual phospholipids and their acyl groups were recorded and compared with the changes observed in several Rht-containing aleurone tissues which were induced to develop GA3 sensitivity by exposure to low temperature (5°C). Several distinct similarities between all tissues were recorded as they develop GA3 sensitivity. One parameter, the percentage phospholipid composition, was quite similar in all tissues after they had become maximally sensitive to GA3, suggesting that there is at least one membrane phospholipid composition which is particularly responsive to GA3. The results indicate that (a) the basis of the GA3 insensitivity of the Rht mutation resides in an aberrant phospholipid/fatty acid composition and/or metabolism; (b) exposure to low temperature (5°C) for 20 hours or longer, or 342 nanomolar IAA for 4 hours or longer reverses or corrects the genetic lesion, enabling the tissue to adopt a GA3 responsive membrane composition. Finally, an hypothesis is discussed which indicates that IAA may play a controlling role in the mobilization of endospermal reserves, at least in Rht3-containing wheat aleurone.In the preceding paper, auxin pretreatment of Rht3 (dwarf) aleurone was shown to alter the GA3 sensitivity of the tissue. More specifically, a 24 h pretreatment with 342 nm IAA produced a 2.5-fold increase in the response to GA3 of the F5 Rht3 dwarf aleurone tissue, and the magnitude of this IAA-induced increase was comparable to the low temperature-induced increase in the GA3 response. In this paper we report the effects of IAA pretreatment on the phospholipids/fatty acids of the dwarf aleurone tissue and compare them to the low temperature-induced changes in phospholipids and fatty acids.

Further characterization of auxin-regulated mRNAs in hypocotyl sections of mung bean [Vigna radiata (L.) Wilczek]: Sequence homology to genes for fatty-acid desaturases and atypical late-embryogenesis-abundant protein, and the mode of expression of the mRNAs

“…However, available results are consistent with the present identification of ARG1 as the gene for a fatty-acid desaturase. The amount of linolenate (18:3) in phosphatidylcholine increases in light-grown pea stems (Moore et al 1983) and in the aleurone tissue of deembryonated seeds of dwarf wheat (Singh and Paleg 1986) after treatment with IAA for 1 h. The results support my suggestion that ARG1 is more likely to encode the A 15 fatty-acid desaturase than other fatty-acid desaturases.…”