Paclobutrazol Application Favors Yield Improvement of Maize Under Semiarid Regions by Delaying Leaf Senescence and Regulating Photosynthetic Capacity and Antioxidant System During Grain-Filling Stage

Muhammad Kamran,Irshad Ahmad,Peizhi Xu,Tehseen Javed,Misbah Ullah,Shakeel Ahmad,Qingfang Han,Xiangping Meng,Izhar Hussain,Wenjie Gu,Ruixia Ding,Xudong Zhang

doi:10.3390/agronomy10020187

Abstract

In the present study, we examined the potential role of paclobutrazol in delaying leaf senescence, in causing changes in the activities of antioxidants, and in the maintenance of photosynthetic activity during the senescence process, and, therefore, on the grain yield of maize under semiarid field conditions. Maize seeds were pretreated with 0 (CK), 200 (PS1), 300 (PS2), and 400 (PS3) mg paclobutrazol L−1. Our results indicated that elevated levels of reactive oxygen species (ROS) and higher accumulation of malondialdehyde (MDA) contents were positively associated with accelerated leaf senescence during the grain-filling periods. The leaf senescence resulted in the disintegration of the photosynthetic pigments and reduced the net photosynthetic rate after silking. However, the resultant ROS burst (O2− and H2O2) was lessened and the leaf senescence and chlorophyll degradation were evidently inhibited in leaves of paclobutrazol-treated maize plants, which was strongly linked with upregulated activities of antioxidant enzymes in treated plants. The enhanced chlorophyll contents and availability of a greater photosynthetic active green leaf area during the grain filling period facilitated the maintenance of higher photosynthetic rate, and light-harvesting efficiency of photosynthesis associated with photosystem II (PSII) resulted in higher kernel number ear−1 and thousand kernel weights, and thus increased the final grain yield. The average maize grain yield was increased by 18.8% to 55.6% in paclobutrazol treatments, compared to untreated control. Among the various paclobutrazol treatments, PS2 (300 mg L−1) treatment showed the most promising effects on enhancing the activities of antioxidative enzymes, delaying leaf senescence and improving the yield of maize. Thus, understanding this effect of paclobutrazol on delaying leaf senescence introduces new possibilities for facilitating yield improvement of maize under semiarid conditions.

Highlights

Maize is one of the world’s most important summer crops, which is used as a staple food crop and as animal feed, bioenergy, and industrial crop [1]
The results indicated that the rate of leaf senescence was relatively low at 15 and 30 Days after silking (DAS), but sharply increased after grain filling period to physiological maturity, indicating a rapid degradation of green leaf area
Results from our present study showed that CAT activity primarily increased from 0 to 15 DAS and later substantially declined; while, POD and ascorbate peroxidase (APX) activity continuously decreased with the progression in leaf senescence during both years

Summary

Introduction

Maize is one of the world’s most important summer crops, which is used as a staple food crop and as animal feed, bioenergy, and industrial crop [1]. Plateau, characterized by low rainfall and water scarcity, and drought span often prevails during the maize growing periods [3]. The precipitation in these regions (250–600 mm each year) during the crop growing season is always insufficient to meet the crop water requirements (500–800 mm) for higher maize productivity [4]. After reaching the reproductive stage, leaf chlorophyll contents gradually degrade with the onset of leaf senescence, which seriously declines the photosynthetic capacity [8,9]. Leaf senescence is a natural phenomenon associated with aging, the rate and timing of leaf senescence can be significantly influenced by several environmental perturbations [7,10]

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Results

Discussion

Conclusion