LMA or vivipary? Wheat grain can germinate precociously during grain maturation under the cool conditions used to induce late maturity alpha-amylase (LMA)

Authors: Peery, Sarah; CARLE, S - Washington State University; WYSOCK, MATTHEW - Washington State University; PUMPHREY, MICHAEL - Washington State University; Steber, Camille

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2023
Publication Date: 6/29/2023
Citation: Peery, S.R., Carle, S., Wysock, M., Pumphrey, M., Steber, C.M. 2023. LMA or vivipary? Wheat grain can germinate precociously during grain maturation under the cool conditions used to induce late maturity alpha-amylase (LMA). Frontiers in Plant Science. 14. Article 1156784. https://doi.org/10.3389/fpls.2023.1156784.
DOI: https://doi.org/10.3389/fpls.2023.1156784

Interpretive Summary: Wheat grain yield and quality can be compromised by the presence of the enzyme alpha-amylase as a result of preharvest sprouting or of late-maturity alpha-amylase (LMA). Preharvest sprouting is the germination of mature grain on the mother plant when rain occurs before harvest, whereas LMA is the expression of alpha-amyalse in reponse to cold temperature shock during the grain filling stage of seed development. We discovered that the conditions used to trigger LMA can also result in vivipary, the germination of immature grain on the mother plant. Vivipary was previously observed in maize mutants. This work showed that it can also occur in wheat if the plants experience wet and cool conditions before the grain is fully mature. This either means that LMA is actually a incomplete version of vivipary or the vivipary is a new potential cause of quality problems from alpha-amylase and low falling number in wheat.

Technical Abstract: This study examined the germination of wheat (Triticum aestivum) prior to physiological maturity, a phenomenon called vivipary. Farmers receive severe discounts for grain with low falling number (FN), an indicator that grain may contain sufficiently elevated levels of the starch-digesting enzyme alpha-amylase to pose a risk to end-product quality. Alpha-amylase can be induced by preharvest sprouting when mature wheat is rained on before harvest or by late maturity alphaamylase (LMA) when grain experiences cool temperatures during the soft dough stage of grain maturation (Zadok 85). In an LMA-induction experiment performed on 452 winter wheat lines, low FN was associated with premature germination or vivipary, presumably due to cool, humid chamber conditions. This suggested that alpha-amylase expression might result from premature germination during LMA experiments or on a cool, rainy day in a farmer’s field. When a spring wheat panel with known LMA phenotypes was subjected to cool misting (18°C day/7.5°C night) during grain maturation, 5 of the 6 LMA susceptible lines and one of the two LMA resistant lines showed visible sprouting on the mother plant. Thus, susceptibility to vivipary did not always correspond to LMA susceptibility. However, vivipary resulted in lower levels of alpha-amylase expression similar to LMA rather than mature-grain germination. Vivipary was more strongly induced during the soft to hard dough stages of grain maturation (Zadok 83-87) at the cooler incubation temperatures used for LMA-induction (18°C day/7.5°C night versus 25°C day/18°C night), suggesting that thermodormancy prevents germination during grain maturation. When LMA-inductions were performed with a dehumidifier, cool temperatures alone could induce LMA without visible sprouting, suggesting that LMA and vivipary could be different phenomena. Since higher temperatures prevent both LMA and vivipary during grain maturation, future work will need to examine if similar molecular mechanisms are involved.