Short communicationLodging resistance of winter wheat (Triticum aestivum L.): Lignin accumulation and its related enzymes activities due to the application of paclobutrazol or gibberellin acid
Introduction
Lodging, the permanent displacement of stems from an upright position due to internal and external factors (Pinthus, 1973), is an important constraint limiting wheat yields and quality in both developed and developing countries (Fischer and Stapper, 1987, Berry et al., 2003). It occurs either due to stem lodging, resulting from the bending or breaking of the lower culm internodes, or root lodging results from a failure in root soil integrity (Pinthus, 1973, Baker et al., 1998, Sterling et al., 2003). Plant height has been the main target for improvement of lodging resistance. Plant breeders have reduced lodging risk by introducing dwarfing genes to produce shorter varieties. Application of growth inhibitors, like ethephon or chlormequatchloride (CCC), was reported to be useful in decreasing plant height and subsequently reducing lodging (Pinthus, 1973, Crook and Ennos, 1995, Rajala et al., 2002, Tripathi et al., 2003). However, several studies have shown that yield is reduced when plants are shortened too much with dwarfing genes or plant growth regulators (Guoping et al., 2001, Acreche and Slafer, 2011). Because a reduction in plant height to improve lodging resistance may reduce the photosynthetic capacity of a canopy, another target is needed for further improvement in lodging resistance. The basal part of the culm internode plays an important role in lodging resistance as it provides a lever to hold the plant upright. Improving the physical strength of the basal part of the culm internode is the new major target for improving the lodging resistance.
Lignin, which is frequently a major structural component of secondary cell walls in vascular plants, is not only associated with plant growth and development, but also with conferring mechanical strength to the plant body (Ma, 2009). Significant correlation was found between the lignin accumulation and the mechanical strength of arabidopsis (Arabidopsis thaliana L.) shoots (Jones et al., 2001). The accumulation of lignin and hemicellulose of culms in lodging wheat varieties were lower than that in lodging-resistant varieties (Berry et al., 2003, Chen et al., 2011). Environmental factors, including temperature, light, water conditions, fertilizer, such like phosphorus (P) application, and soil texture that regulate the biosynthesis and accumulation of lignin in plants, have been heavily investigated. For example, UV-B radiation could induce the accumulation of lignin in the cotyledons of Cucumis sativus L. (Yamasaki et al., 2007). It was also reported that at least three factors could affect lignin synthesis in plants: light intensity, circadian rhythms and sugar perception (Chen et al., 2002, Akgül et al., 2007). Growth reduction and tolerance to desiccation were associated with less lignin in plants leaves (Vincent et al., 2005) and more lignin in plants roots (Yoshimura et al., 2008). Pitre et al. (2007) found that the accumulation of lignin in grasses was increased by N due to elevated phenylalanine ammonia-lyase (PAL) activity. Gibberellin spraying during flower-bud induction significantly inhibited the activities of PAL, polyphenol oxidase (PPO), peroxidase (POD) and IAA-oxidase, delaying the biosynthesis of lignin in leaves (Li et al., 2003).
Previous studies have shown that application of growth regulators such as paclobutrazol (PP333) or gibberellin acid (GA3) regulate internode elongation in wheat production (Guoping et al., 2001, Magome et al., 2004, Iqbal and Ashraf, 2013). However, little is known about the exogenous spraying of PP333 or GA3 on the physical strength of the wheat basal internode, especially regarding how lignin biosynthesis and accumulation in culms impacted by treatments. The objective of present study was to investigate the effects of spraying PP333 or GA3 at the beginning of wheat stem jointing (Digit code [DC] 3.0; Zadoks et al., 1974) on the wheat lodging behavior, lignin accumulation in culms and its relation to lodging resistance. A greater understanding of that information can provide a theoretical basis to enhance the physical strength of the basal part of culm internode to prevent wheat lodging and improve grain yield and quality.
Section snippets
Plant material and experimental design
The field experiments were carried out at Tai’an Experimental Station of Shandong Agricultural University, Tai’an, Shandong, China (36°09′ N, 117°09′ E) in two growing seasons from October 2010 to June 2011 and from October 2011 to June 2012. The soil was a sandy loam, and the 0–200 mm soil layer contained 10.6 g total organic matter kg−1, 72.5 mg kg−1 available N, 24.3 mg kg−1 available phosphate, and 80.1 mg kg−1 available potassium. Maize (Zea mays L.) was the previous crop. In both seasons, 120 kg N ha
The plant height, basal second internode characteristics, lodging behavior and grain yield of wheat
Compared with the control, application of PP333 significantly reduced the plant height and the length of basal second internode, and significantly increased the diameter, wall thickness and filling degree of basal second internode. However, the exogenous GA3 led to converse effects on those characteristics (Table 1).
There was no lodging happened under the control and exogenous PP333 treatments for JM22 in both seasons (Table 2). Time of lodging happened for SN16 was the early dough stage (DC
Discussion
Lodging causes poor grain filling and yield loss, reduces grain quality, and reduces mechanical harvesting efficiency (Acreche and Slafer, 2011, Berry and Spink, 2012). Enhancing the physical strength of the basal part of the culm internode is one of important targets to resist lodging. Lignin is important for structural integrity of stems and it contribute to the mechanical properties of these stems (Dixon, 2001, Ma, 2010). In the present study, the data clearly demonstrated that the total
Acknowledgements
This research was supported by the Shandong Modern Agricultural Technology and Industry System, the National Natural Science Foundation of China (No. 31271661), the National Basic Research (973) Program of China (2009CB118602), the Special Fund for Agro-scientific Research in the Public Interest of China (Nos. 201203100 and 201203029), and the National Science and Technology Support Program of China (No. 2012BAD04B05).
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