Short communicationZinc deficiency affects physiological and anatomical characteristics in maize leaves
Introduction
Zinc (Zn) deficiency is the most widespread micronutrient deficiency problem globally. It is commonly associated with reductions in crop yield (Cakmak et al., 1996, Wissuwa et al., 2006, Hossain et al., 2008, Hafeez, 2013, Mousavi et al., 2013) and food quality (Cakmak, 2008, Cakmak et al., 2010a, Velu et al., 2014). Therefore, when Zn fertilization is used, crop productivity usually increases. This has been demonstrated for a variety of crops, in particular for maize (Zea mays L.) (Bukvic et al., 2003, Potarzycki and Grzebisz, 2009, Galavi et al., 2011, Wang et al., 2012).
The function of Zn in plants has been extensively studied (Cakmak, 2000, Wang and Jin, 2005, Sharma et al., 2013, Höller et al., 2014). Zinc plays a key role as a structural constituent and regulatory co-factor in a wide range of enzymes and proteins (Broadley et al., 2007, Hänsch and Mendel, 2009, Figueiredo et al., 2012). The vast majority of plant enzymes that are activated by Zn are involved in carbohydrate metabolism, maintenance of cell membrane integrity, protein synthesis and in the regulation of auxin synthesis(Skoog, 1940, Coleman, 1992). It should be noted that when plants are deficient in Zn, protein synthesis is reduced as amino acids and amides accumulate in plant tissues (Marschner, 1995). Zinc is also essential for tryptophan biosynthesis, which is fundamental for auxin formation(Mašev and Kutáček, 1966, Marschner, 1995). It has been observed that under some specific conditions, leaf concentrations of tryptophan may increase due to the impairment of protein and auxin synthesis (Marschner, 1995). The importance of Zn to enzyme function is particularly evident in chloroplasts and the cytoplasm. In these organelles, several enzymes are dependent on Zn for photosynthesis, biomass production and for the prevention of cell membrane damage (Cakmak, 2000).
The diagnosis of Zn plant status is important to ensure optimal crop productivity and food quality. Currently, there are several methods that can be used to diagnose plant nutritional status. However, the two most commonly used methods are (1) examination of visual symptoms and (2) analysis of plant Zn concentrations. Zinc deficiency symptoms initially appear on young leaves and meristems of plants due to the low mobility of Zn. Such symptoms include leaf chlorosis and a decrease in leaf size, which in turn causes stunting and a decrease in the number of tillers (Cakmak et al., 1998, Mousavi, 2011). It is important to note that visual symptoms of Zn deficiency normally occur when plants are suffering severe stress. Therefore, using visual inspection as a method for diagnosing Zn deficiency is considered a late diagnostic tool. In this case, it is reasonable to assume that late diagnosis reduce the possibility to correct the problem by fertilization—particularly for annual crops. However, the information obtained can still be of crucial importance for the next crop and for perennial crops. Before the appearance of visible symptoms, other changes such as those to physiological, anatomical and chemical parameters may occur. Monitoring such modifications are important in order to understand and manage plant nutrition.
Although several studies have investigated nutritional status and the anti-oxidative responses of Zn deficiency in maize (Singh et al., 2005, Wang et al., 2009, Afsharnia et al., 2013, Hafeez, 2013) and other plants (Cakmak et al., 1997, Cakmak et al., 1998, Daneshbakhsh et al., 2012, Daneshbakhsh et al., 2013, Impa and Johnson-Beebout, 2012, Höller et al., 2014), the physiological and anatomical responses of maize under Zn deficiency is largely unknown. In addition, it is still debated whether the chemical analysis of young leaves is suitable for diagnosing Zn deficiencies in maize. The two aims of this study were to (1) investigate the effects of Zn deficiency on physiological and anatomical parameters as well as the chemical composition of the leaf and (2) to determine if the analysis of young leaves could be used as a diagnostic tool for Zn status in maize.
Section snippets
Plant and experimental design
The experiments were carried out in Viçosa (20°45′S, 42°54′W, 650 m altitude) in south-eastern Brazil, during January and February 2003. Maize (Zea mays L.) plants from hybrid BRS1010 were hydroponically grown in plastic pots (1.5 L volume) in a greenhouse under semi-controlled conditions. The greenhouse temperature was maintained at 30 ± 5 °C and had a light intensity of 1500 μmol photons m−2 s−1 (maximum photosynthetic photon flux density, PPFD).
After germination in Germitest® paper, seedlings were
Plant growth and physiological parameters
After 16 days of Zn omission, visual Zn deficiency symptoms were apparent; including chlorotic stripes and purple shades on leaf edges and the leaf sheath. Following Zn omission, the Fv/Fm ratio and A decreased (X and Y%, respectively), which was followed by significant reductions in the amount of dry matter and leaf Zn concentrations (Table 1 and Fig. 1). Accordingly, when plants first exhibited visible symptoms, a number of other parameters were also reduced; Zn leaf concentrations, dry
Discussion
In recent years, the level of understanding in regards to plant responses to Zn deficiencies has increased, yet the effects on physiological and anatomical parameters is still unknown. Zinc deficiency has been a serious challenge in several parts of world as it decreases crop yields and food quality (Alloway, 2009, Cakmak et al., 2010b, Sadeghzadeh, 2013, Velu et al., 2014). Diagnosing Zn deficiency, by either visual field observations or plant analysis, has been efficiently and widely used;
Acknowledgements
This work was supported by funding from Coordination for Scientific Support for Post-Graduate Level Training-CAPES, Brazil. We also acknowledge Dr Casey Doolette (The University of Adelaide) for critical review of and suggestions regarding this work.
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