Peery Sarah R, Carle Scott W, Wysock Matthew, Pumphrey Michael O, Steber Camille M
Department of Crop and Soil Sciences, Washington State University, Pullman, WA, United States.
U.S. Department of Agriculture - Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA, United States.
Front Plant Sci. 2023 Jun 29;14:1156784. doi: 10.3389/fpls.2023.1156784. eCollection 2023.
This study found that wheat () grain can germinate precociously during the maturation phase of grain development, a phenomenon called vivipary that was associated with alpha-amylase induction. Farmers receive severe discounts for grain with low falling number (FN), an indicator that grain contains sufficiently elevated levels of the starch-digesting enzyme alpha-amylase to pose a risk to end-product quality. High grain alpha-amylase can result from: preharvest sprouting (PHS)/germination when mature wheat is rained on before harvest, or from late maturity alpha-amylase (LMA) when grain experiences cool temperatures during the soft dough stage of grain maturation (Zadoks growth stage 85). An initial LMA-induction experiment found that low FN was associated with premature visible germination, suggesting that cool and humid conditions caused vivipary.
To examine whether LMA and vivipary are related, controlled environment experiments examined the conditions that induce vivipary, whether LMA could be induced without vivipary, and whether the pattern of alpha-amylase expression during vivipary better resembled PHS or LMA.
Vivipary was induced in the soft to hard dough stages of grain development (Zadok's stages 83-87) both on agar and after misting of the mother plant. This premature germination was associated with elevated alpha-amylase activity. Vivipary was more strongly induced under the cooler conditions used for LMA-induction (18°C day/7.5°C night) than warmer conditions (25°C day/18°C night). Cool temperatures could induce LMA with little or no visible germination when low humidity was maintained, and susceptibility to vivipary was not always associated with LMA susceptibility in a panel of 8 varieties. Mature grain preharvest sprouting results in much higher alpha-amylase levels at the embryo-end of the kernel. In contrast, vivipary resulted in a more even distribution of alpha-amylase that was reminiscent of LMA.
Vivipary can occur in susceptible varieties under moist, cool conditions, and the resulting alpha-amylase activity may result in low FN problems when a farm experiences cool, rainy conditions before the crop is mature. While there are genotypic differences in LMA and vivipary susceptibility, overlapping mechanisms are likely involved since they are similarly controlled by temperature and growth stage, and result in similar patterns of alpha-amylase expression.
本研究发现，小麦（）籽粒在籽粒发育的成熟阶段会过早萌发，这种现象称为胎萌，它与α-淀粉酶的诱导有关。农民会因降落数值（FN）低的谷物而获得大幅折扣，降落数值是一个指标，表明谷物中淀粉消化酶α-淀粉酶的含量足够高，会对最终产品质量构成风险。谷物中高含量的α-淀粉酶可能由以下原因导致：收获前发芽（PHS）/在收获前成熟小麦遇雨时发芽，或由后期成熟α-淀粉酶（LMA）导致，即当籽粒在谷物成熟的软面团阶段（Zadoks生长阶段85）经历低温时。一项初步的LMA诱导实验发现，低FN与过早可见发芽有关，这表明凉爽潮湿的条件会导致胎萌。
为了研究LMA与胎萌是否相关，通过控制环境实验来研究诱导胎萌的条件、是否可以在不发生胎萌的情况下诱导LMA，以及胎萌期间α-淀粉酶的表达模式更类似于PHS还是LMA。
在籽粒发育的软面团到硬面团阶段（Zadok阶段83 - 87），无论是在琼脂上还是对母株进行喷雾后，都会诱导胎萌。这种过早发芽与α-淀粉酶活性升高有关。与温暖条件（25°C白天/18°C夜间）相比，在用于LMA诱导的较凉爽条件（18°C白天/7.5°C夜间）下，胎萌的诱导更强。当保持低湿度时，低温可以诱导LMA，几乎没有或没有可见发芽，并且在一组8个品种中，对胎萌的易感性并不总是与对LMA的易感性相关。收获前成熟籽粒发芽会导致籽粒胚端的α-淀粉酶水平高得多。相比之下，胎萌导致α-淀粉酶分布更均匀，这让人联想到LMA。
在潮湿、凉爽的条件下，易感品种可能会发生胎萌，当农场在作物成熟前经历凉爽、多雨的条件时，由此产生的α-淀粉酶活性可能会导致低FN问题。虽然在LMA和胎萌易感性方面存在基因型差异，但可能涉及重叠机制，因为它们同样受温度和生长阶段控制，并导致α-淀粉酶表达模式相似。
