Regulation of programmed cell death in endosperm by different phosphorus managements under post-anthesis drought stress in wheat

Objectives The effects of different phosphorus (P) managements on programmed cell death (PCD) of wheat endosperm cells under post-anthesis drought stress were investigated, and it was verified that different phosphorus managements could delay the process of endosperm PCD and reduce the harm of post-anthesis drought stress.

Methods The winter wheat Xindong 20 was selected as the material to carry out the regional test. The main factor was water, and the secondary factor was the application method of phosphate fertilizer. The two water treatments were drought stress (DT, stop irrigation after flowering) and suitable water irrigation (WT, flowering to maturity, irrigation every 12 days). Under the P₂O₅ application rate of 105 kg/hm², 3 kinds of phosphate fertilizer managements were setup, as: P1 (applying all P fertilizer at wheat regreening stage), P2 (applying 50% P fertilizer at regreening stage and 50% at jointing stage), and P3 (applying 40% at regreening stage, 30% at jointing stage and 30% at grain filling stage). Wheat spike samples were taken every 7 days after flowering, a total of 5 times. The ultrastructure of endosperm cells, the chemical localization of acid phosphatase (ACPase), the number of endosperm nuclei, and the DNA fragments in the endosperm cell genome were observed. The ACPase activity of endosperm cells and the relative expression of endosperm PCD-related genes were analyzed.

Results 1) Under noremal water and drought stress, the nuclear deformation and nuclear membrane depression of wheat treated with P3 were lighter than those of P1 and P2, the nuclear deformation of P3 was less, and the number of P3 cell nuclei labeled by TUNEL was less, P3 prolonged the process of endosperm nucleus deformation to disintegration. 2) Under drought stress, DNA fragmentation occurred late at P3; under suitable water condition, DNA fragmentation appeared later at P3, and the time of DNA fragmentation under drought stress was earlier than that under suitable water condition. 3) Under suitable water treatment and drought stress, the number of nuclei in P3 was significantly higher than that in P1 and P2, and the nuclease activity was also significantly higher than that in P1 and P2, ACPase activity in endosperm cells of P3 was higher than that of P1 and P2. 4) dad1 negatively regulate PCD process, under drought stress, the relative expression of dad1 genes increased at 7 days post anthesis, and then decreased at 14 days post anthesis. The relative expression of dad1 reached the peak at 28 days post anthesis under P3 treatment. Bcl2 negatively regulate PCD process, At 7 days post anthesis, the relative expression of P3 was higher than that of suitable water, The relative expression of dad1 reached the peak at 28 days post anthesis under P3 treatment. Under suitable water conditions, the expression of dad1 gene was concentrated at 14 and 28 days post anthesis, and the expression of Bcl2 gene was concentrated at 21 and 28 days post anthesis of P1 was higher than that of P2 and P3. 5) Under drought conditions, the maximum filling rate and average filling rate P1 were the highest, the maximum filling rate P3 was the latest, the duration of grain filling weight gain P3 was longer, and the theoretical maximum 1000-grain weight of P3 was higher than that of P1 and P2. Under the suitable water condition, the maximum filling rate and average filling rate P2 were the highest, the maximum filling rate P3 appeared the latest, the grain filling weight gain duration P3 was longer, and the theoretical maximum 1000-grain weight of P3 was higher than that of P1 and P2.

Conclusions Under post-anthesis drought stress, three times of phosphorus application reduced the DNA breakage of endosperm cells in post-anthesis wheat grains, delayed the speed of nuclear deformation and disintegration, maintained a high number of cells, and effectively delayed the process of endosperm PCD. Drought aggravated the programmed cell death process of endosperm cells, and the effect of three times of phosphate fertilizer on delaying the programmed cell death of endosperm cells was more prominent than that under suitable water conditions, therefore. When water is deficient in production, phosphorus management can regulate the nutritional status of plants by multiple phosphorus application according to the growth needs of wheat, delay the PCD process, and reduce the damage degree of drought stress post anthesis.