Grain development and endogenous hormones in summer maize (Zea mays L.) submitted to different light conditions.

Low light is a type of abiotic stress that seriously affects plant growth and production efficiency. We investigated the response mechanisms of summer maize to low light by measuring the changes in endogenous hormones in the grains and during grain filling in summer maize at different light intensities to provide a theoretical basis for the production and management of summer maize under light stress. We applied different light treatments in a field experiment as follows: S, shading from tassel stage (VT) to maturity stage (R6); CK, natural lighting in the field; and L, increasing light from VT to R6. The shading level was 60%, and the maximum illumination intensity of the increasing light treatment on cloudy days was 1600-1800 µmol m-2 s-1. Compared with the control, shading significantly increased the grain abscisic acid (ABA) content at 5-20 days after pollination and decreased the indole acetic acid (IAA), zeatin riboside (ZR), and gibberellin (GA) contents (P < 0.05). The grain-filling rate decreased under shading conditions. Meanwhile, the grain volume, grain weight, and yield all decreased; the yields in 2013 and 2014 decreased by 61 and 60%, respectively. The grain IAA, ZR, and GA contents were increased by increasing light. The grain ABA content at 5-20 days after pollination did not significantly differ from that of CK (P < 0.05). After 20 days after pollination, the ABA content decreased, the grain-filling rate and the filling duration increased, and the yield increased. However, shading after anthesis increased the grain ABA content and reduced the IAA, ZR, and GA contents. Grain growth and development were inhibited, and the yield decreased. The grain ABA content decreased; the IAA, ZR, and GA contents increased; and the yield increased after increasing light. The results indicate that different light intensities regulated the levels of grains endogenous hormones, which influenced the grain-filling rate and duration, and consequently, regulated grain weight and yield.

[Effects of light intensities after anthesis on the photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize (Zea mays L. )]. / èŠ±ç²’æœŸå ‰ç §å¯¹å¤çŽ‰ç±³å ‰åˆç‰¹æ€§å’Œå¶ç»¿ä½“è¶ å¾®ç»“æž„çš„å½±å“.

We examined the changes of photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize in response to different light intensities in the field, with the summer maize hybrid Denghai 605 as experimental material. Two treatments of both shading (S) and increasing light (L) from flowering to physiological maturity stage were designed, with the ambient sunlight treatment as control (CK). Under shading treatment, poorly developed thylakoid structure, blurry lamellar structure, loose granum, large gap between slices and warping granum were the major characteristics in chloroplast. Meanwhile, photosynthetic rate (Pn), transpiration rate, stomatal conductance, chlorophyll content, and actual photo-chemical efficiency (ΦPSII) decreased, whereas the maximal photochemical efficiency and non-photochemical quenching increased, which resulted in decreases in grain yield under shading treatment. However, a better development was observed in chloroplasts for L treatment, with the number of grana and lamellae increased and lamellae arranged compactly. In addition, Pn and ΦPSII increased under L treatment, which increased grain yield. The chloroplast arrangement dispersed in mesophyll cells and chloroplast ultrastructure was destroyed after shading, and then chlorophyll synthesis per unit leaf area and photosynthetic capacity decreased. In contrast, the number of grana and lamellae increased and lamellae arranged compactly after increasing light, which are beneficial for corn yield.