To understand the pathway of anthocyanin accumulation during grain filling of wheat (
Triticum aestivum L.) and its response to light, we used three red-gain, two black-grain, and one white-grain (control) varieties/lines to investigate the dynamic changes of anthocyanin accumulation and activities of related enzymes during grain filling. Shading treatments were conducted during the whole filling stage (14–34 d post anthesis, treatment T1) and at early (14–24 d post anthesis, treatment T2) or late filling stage (24–34 d post anthesis, treatment T3), and natural light condition without shading was used as the control. The effects of treatments T1 and T3 on anthocyanin content were larger than that of treatment T2, indicating that late grain filling period is critical for anthocyanin biosynthesis. The changing degree of anthocyanin content induced by shading varied across varieties with larger changes in D4 Hong (red grain), Hong 5 (red grain), and Heixiaomai 76 (purple red grain). In the treatment T1, the grains of three red-grain varieties with anthocyanin content less than 1U g
-1 were colorless, similar to the white-grain control “Jimai 19”. In the treatment T2, the anthocyanin began to be synthesised after the shading was removed in late grain filling period. The anthocyanin contents of black-grain wheat varieties Changyi Heimai and D4 Hei were significantly reduced in shading treatments, but the absolute content was higher than 2 U g
-1 in the treatment T1. This result suggested different pathways of anthocyanin biosynthesis probablylight-dependent in red-grain wheat. While both light-dependent and non-light-dependent pathways in black-grain wheat, of which the latter was the main pathway. In colored-grain wheat, the activities of plenylalanine ammonialyase (PAL) and chalcone ismoerase(CHI) were low in early grain-filling period, and increased to a higher level in middle to late filling period. However, the activity of polyphenol oxidase (PPO) varied from a high level in early filling period to a low level in middle to late filling period.In the control treatment without shading, the activities of PAL and CHI were positively associated with anthocyanin content at a significant level, indicating that CHI and PAL are the key enzymes in anthocyanin biosynthesis. The PPO activity was negatively correlated with anthocyanin content in black-grain wheat rather than red-grain wheat.
Under the shading conditions, the activities of PAL, CHI, and PPO were not closely associated with the anthocyanin content. Therefore, it is inferred that the effect of light on anthocyanin biosynthesis is not based on the direct regulations of PAL, CHI, and PPO activities.
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