Morphology, photosynthesis, and internal structure alterations in field apple leaves under hidden and acute zinc deficiency
Introduction
Zinc deficiency is the most widespread micronutrient deficiency in soil and crops (Alloway, 2008). It is estimated that approximately 30% of the agricultural soil in the world are Zn deficient (Cakmak et al., 1996). In China, Zn deficiency affects more than 48.6 Mha of soil, primarily calcareous soil distributed in Northern China (Zou et al., 2008). Apple plants, as the main economic fruit trees planted in China, are considered to be very sensitive to Zn deficiency (Rashid and Ryan, 2004). It was recorded that China is the largest producer of apple in the world and Shandong Province accounts for over half of China’s apple exports (Miyata et al., 2009). Zinc deficiency is now very common in apple orchards in China, especially in Shandong Province, resulting in severe losses in yield and deterioration in fruit quality.
In the field, Zn deficiency occurs naturally, and the symptoms of deficiency develop depending on the degree of stress (Brennan et al., 1993). Visual symptoms of Zn deficiency only occur in cases of relatively severe deficiency (Alloway, 2008) and are described as stunted growth, small leaves, chlorosis, rosette and even shoot die back (Swietlik, 2002, Sharma et al., 2013). Rosette and little leaf at the shoot tip are the most characteristic symptoms of Zn deficiency in fruit trees (Swietlik, 2002). In marginally Zn deficient soils, yield and quality can be affected without the obvious appearance of symptoms; this is called ‘hidden’ (or ‘latent’) deficiency (Alloway, 2008, Alloway, 2009). Some studies have reported that dry matter production is reduced by 40% or more by hidden Zn deficiency (Carroll and Loneragan, 1968). Given these circumstances, the understanding to the intrinsic changes in the physiological processes of leaves affected by hidden Zn deficiency may be helpful to determine the initial damages caused by Zn deficiency along with the final development of deficiency symptoms.
Zinc deficiency depresses plant growth especially shoot growth and chlorophyll concentrations (Balakrishnan et al., 2001), leading to chlorosis in leaves along with abnormalities in leaf structure and ultimately affecting chloroplast structure (Kim and Wetzstein, 2003). A decline in the net photosynthetic rate (Pn) induced by Zn deficiency is often observed. The reasons for this decline may be associated with a decrease in stoma conductance (Hu and Sparks, 1991), a decrease in carbonic anhydrase activity (Sasaki et al., 1998), a reduction in carbon fixation (Sharma et al., 1995) or damage to the photosynthetic apparatus (Balakrishnan et al., 2001, Chen et al., 2008). However, the mechanism by which Zn deficiency damages photosynthetic activity, especially in field-grown apple leaves, is not yet known.
Although Zn deficiency can alter a variety of physiological processes, the primary site of its effect is probably the cell membrane systems (Candan and Tarhan, 2003). Severe Zn deficiency can induce a general disorganization of chloroplast thylakoids (Henriques, 2001) and extensive degeneration of chloroplast membranes (Chen et al., 2008). The loss of chloroplast membrane integrity and thylakoid disorganization can affect the photochemical processes on thylakoids, thus inhibiting the biophysical processes of photosynthesis (Cakmak, 2000, Daub et al., 2013). Zinc deficiency also reduces the actual photochemical efficiency of PS II (ϕPS II) and affects the activity of some related enzymes (Tavallali et al., 2009, Billard et al., 2015). However, most of the above mentioned reports were conducted under severe Zn deficiency or after the formation of typical deficiency symptoms, when noticeable damage to chloroplasts and photosynthetic centers in affected leaves has already occurred. Little information is available about the structural and functional alterations of leaves at the transitional stage of hidden Zn deficiency.
The aim of this study is to elucidate the mechanism by which Zn deficiency affects the physiological function and internal structure of apple leaves at various Zn levels under field conditions. With this aim, we use pigment and photosynthesis analyses as well as microstructure and ultrastructure observation to characterize the physiological and structural changes induced in apple leaves by Zn deficiency at latent and deficient levels. Chlorophyll fluorescence was also investigated to better understand alterations of the photosynthetic center on chloroplast membranes under different Zn deficiency conditions. This work presents detailed microscopic evaluation of Zn deficiency in apple leaves and elucidates how progressive Zn deficiency affects leaf structure and function.
Section snippets
Field site and plant materials
Experiments were conducted in 2012 and 2013 using 13-year-old ‘Fuji’ apple trees in an orchard in Chaoquan (latitude 36°14′N; longitude 116°50′E), Feicheng County, Tai’an, Shandong Province, China. In field-grown apple trees, leaves at the tops of shoots on Zn-deficient trees are more likely to appear tufted or in a rosette formation. Other leaves on the same branch or on other shoots of the same tree exhibit no visible deficiency symptoms; this is referred to as ‘hidden’ deficiency. Both
General leaf characteristics under zinc deficiency
The first characteristic reaction of plants to zinc deficiency was the reduction in shoot elongation and leaf size (Fig. 1, Table 1). The visible symptoms induced by Zn deficiency were observed in field apple trees as short internodes and small and narrow leaves with chlorosis in a rosette formation on the top of the shoot (Fig. 1). Under Zn-deficiency, HRL and RL had lower Zn concentrations and leaf areas than the NL. The reductions in Zn concentration were 31.2% and 51.6% for HRL and RL, and
Discussion
In most fruit and other crops, the critical Zn deficiency level is considered to be below 15–20 mg kg−1 dry weight of leaves (Swietlik, 2002). The HRL in this study showed no visible rosette symptoms at a Zn concentration of 14.92 mg kg−1. This indicated that the content of Zn in HRL was at the latent level; thus, the physiological differences between HRL and RL is more helpful for us to understand the progression of damage induced by Zn deficiency in apple leaves under field conditions.
In the
Conclusions
The damage of Zn deficiency on apple leaves were mainly reflected in the reduction of leaf area, chlorophyll content and net photosynthesis rate (Pn), and the alterations in internal leaf structure. Among these deficient characters, Pn showed to be very sensitively regulated by Zn. Under hidden Zn deficiency, the decrease of photosynthesis was related to the inhibition of PS II intrinsic efficiency (Fv′/Fm′), the actual PS II photochemical efficiency (ϕPS II) and electron transport rate (ETR).
Acknowledgements
This work was financially supported by the Natural Science Foundation of China (Grant No. 31372015 and 31401683), the Special Fund for Agro-scientific Research in the Public Interest (Grant No. 201103003) and the Natural Science Foundation of Shandong Province, China (Grant No. ZR2013CM022). The authors are grateful to Prof. Huiyuan Gao for help in review our English composition and to Mr. Chengjun Yin for the management of apple trees in field, and to Mr. Yuankui Guo for operation of the TEM
References (36)
- et al.
Zn deficiency in Brassica napus induces Mo and Mn accumulation associated with chloroplast proteins variation without Zn remobilization
Plant Physiol. Biochem.
(2015) - et al.
The correlation between antioxidant enzyme activities and lipid peroxidation levels in Mentha pulegium organs grown in Ca2+, Mg2+, Cu2+, Zn2+ and Mn2+ stress conditions
Plant Sci.
(2003) Loss of blade photosynthetic area and of chloroplasts’ photochemical capacity account for reduced CO2 assimilation rates in zinc-deficient sugar beet leaves
J. Plant Physiol.
(2001)- et al.
Identification of nutrient deficiency in maize and tomato plants by in vivo chlorophyll a fluorescence measurements
Plant Physiol. Biochem.
(2014) - et al.
Impact of contract farming on income: linking small farmers, packers, and supermarkets in China
World Dev.
(2009) - et al.
Zinc influence and salt stress on photosynthesis, water relations, and carbonic anhydrase activity in pistachio
Sci. Hortic.
(2009) Zinc in soils and crop nutrition
International Zinc Association, Brussels
(2008)Soil factors associated with zinc deficiency in crops and humans
Environ. Geochem. Hlth.
(2009)Copper enzymes in isolated chloroplasts: polyphenoloxidase in Beta vulgaris
Plant Physiol.
(1949)- et al.
Differential responses of iron, magnesium, and zinc deficiency on pigment composition, nutrient content, and photosynthetic activity in tropical fruit crops
Photosynthetica
(2001)
Nonstomatal inhibition of photosynthesis in sunflower at low leaf water potentials and high light intensities
Plant Physiol.
Diagnosis of zinc deficiency
Tansley review No. 111. Possible roles of zinc in protecting plant cells from damage by reactive oxygen species
New Phytol.
Role of magnesium in carbon partitioning and alleviating photooxidative damage
Physiol. Plant.
Zinc deficiency as a critical problem in wheat production in Central Anatolia
Plant Soil
Response of plant species to concentrations of zinc in solution. I. Growth and zinc content of plants
Aust. J. Agr. Res.
Differential changes in photosynthetic capacity, 77 K chlorophyll fluorescence and chloroplast ultrastructure between Zn-efficient and Zn-inefficient rice genotypes (Oryza sativa) under low zinc stress
Physiol. Plant.
Carbon partitioning and assimilation as affected by nitrogen deficiency in cassava
Photosynthetica
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Both authors contributed equally to the work.