Response of maize stalk to plant density on cellulose accumulation by modulating enzymes activities

Hybrids and plant density are the main factors affecting maize lodging resistance, and cellulose plays an important role in lodging resistance. High plant density often decreases the stalk cellulose, but the cause is unclear. Therefore, we hypothesized that enzymatic activity might be the main factor affecting maize cellulose accumulation. For testing this hypothesis, three plant densities (4.5, 9.0 and 13.5 plants m(-2)) were set up and three maize hybrids (high lodging resistant cultivars: Xianyu 335, Zhengdan 958; low lodging resistant cultivar: Xinyu 41)with different lodging resistance were selected as materials. The results showed that high plant densities reduced the stalk cellulose contents and strength, and hence lodging risk increased. Through logistic curve fitting, we found that the period of rapid accumulation of cellulose in stalks was 10-26 DPV6 (days post 6-leaf stage). Analyse changes of stalk sucrose and related enzyme activity during 10-26 DPV6 showed that with the increase of plant density, the sucrose content of the stalks significantly decreased (P<0.05), sucrose content began to differ at 16-DPV6. Both sucrose phosphate synthase(SPS) and sucrose synthase(SS) activity of stalks in this stage decreased with the increase of plant densities. At 20 DPV6, there has a great difference in SPS among different plant densities during this period. Compared with 4.5 plants m(-2), the decreases for SPS in Xianyu 335 and Zhengdan 958 was lower than Xinyu 41 at 9.0 plants m(-2) and 13.5 plants m(-2). The SPS for Xianyu 335 decreased by 10.0% 16.0% and 28.7% 37.7% at 9.0 plants m(-2) and 13.5 plants m(-2), respectively. However, the SPS for Xinyu 41 decreased by 24.4% 27.3% and 40.2% 50.2%, respectively. At 16 DPV6, there was a large difference in SS among different plant densities, the decreases for SS in Xianyu 335 and Zhengdan 958 was lower than Xinyu 41. Xianyu 335 decreased by 3.6% 15.9%, 18.8% 32.7% at at 9.0 plants m(-2) and 13.5 plants m(-2), respectively. Similarly Xinyu 41 decreased by 18.2% 26.4% and 31.8% 50.6%, respectively. Thus, under high plant density, the activities of SS and SPS in maize stalks were decreased, the accumulation and conversion of sucrose into cellulose were inhibited, and the activity of cellulose synthesis-related enzymes in varieties with poor lodging resistance were more sensitive to the increase of density. Therefore, we concluded that higher activity of SS and SPS increased cellulose accumulation and stalk strength in maize varieties with better lodging resistance reduced the lodging percentage under close density conditions.