Adaptation of photosynthesis under iron deficiency in maize

doi:10.1016/j.jplph.2007.02.004

Journal of Plant Physiology

Volume 164, Issue 10, 19 October 2007, Pages 1261-1267

https://doi.org/10.1016/j.jplph.2007.02.004 Get rights and content

Summary

This paper explores the effects of high light stress on Fe-deficient plants. Maize (Zea mays) plants were grown under conditions of Fe deficiency and complete nutrition. Attached, intact leaves of Fe-deficient and control plants were used for gas exchange experiments under suboptimal, optimal and photoinhibitory illumination. Isolated chloroplasts were used to study photosynthetic electron transport system, compromised by the induction of Fe deficiency. The reaction centers of PS II (measured as reduction of Q, the primary electron acceptor of P 680) and PS I (measured as oxidation of P 700) were estimated from the amplitude of light induced absorbance change at 320 and 700 nm, respectively. Plants were subjected to photoinhibitory treatment for different time periods and isolated chloroplasts from these plants were used for electron transport studies. Carbon dioxide fixation in control as well as in Fe-deficient plants decreased in response to high light intensities. Total chlorophyll, P 700 and Q content in Fe-deficient chloroplasts decreased, while Chl a/b ratio and Q/P 700 ratio increased. However, electron transport through PS II suffered more after photoinhibitory treatment as compared to electron transport through PS I or whole chain. Electron transfer through PS I+PS II, excluding the water oxidation complex showed a decrease in Fe-deficient plants. However, electron transport through this part of the chain did not suffer much as a result of photoinhibition, suggesting a defect in the oxidising side of PS II.

Introduction

Fe deficiency causes chlorosis in plants due to decreased chlorophyll biosynthesis (Chen and Barak, 1982). Light-dependent synthesis of δ-amino levulinic acid (δ-ALA) is impaired under conditions of Fe deficiency (Miller et al., 1982). Light-saturated rates of electron transport have been found to decrease during conditions of Fe deficiency as a consequence of reduction in reaction centers and electron carriers (Terry, 1980; Nishio et al., 1985). A loss in photosynthetic capacity would render the photosynthetic electron transport system susceptible to damage by light intensities normally encountered during growth, with PS II being especially susceptible due to the rapid degradation of D1. The photosynthetic system exhibits short term as well as long-term adaptation mechanisms in response to elevated temperatures and/or irradiance to avoid photoinhibitory damage (Anderson and Osmond, 1987; Anderson and Andersson, 1988). The more important characteristics of the acclimation response are a change in the PS II/PS I ratio (Anderson, 1986), change in antenna size and distribution (Anderson and Andersson, 1988) and a change in the relative amounts of photosystem II (PS II) in the appressed and nonappressed regions of the thylakoid (Hundal et al., 1990). Photosystem PSI appears to be a prime target of Fe deficiency and cyanobacteria are known to surround their PS I centers by the isiA protein that binds chlorophyll and could function either as a light-harvesting system (Bibby et al., 2001) or as a nonradiative dissipater of light energy (Sandstrom et al., 2001). In maize plants, the component of the photosynthetic electron transport system showing greatest decrease in activity is the Cyt bf complex (Sharma and Sanwal, 1992). Adaptive alteration in electron transport efficiency has been attributed to deficiency-induced remodeling of the light-harvesting apparatus (Moseley et al., 2002; Naumann et al., 2005). Reduced rates of carbon dioxide fixation in Fe-deficient plants could be attributed to decreased electron transport capacity leading to reduced availability of ATP and the reductant for carbon fixation. This could also be related to photoinhibitory damage in plants with reduced amount of chlorophyll.

The present paper is an attempt to explore the Fe deficiency response on photosynthetic electron transport, P 700 (reaction center of PS II), Q (primary electron acceptor of P 680 and therefore a measure of PS II) and CO₂ fixation rates under normal and photoinhibitory conditions.

Section snippets

Plant growth

Maize (Zea mays L. var.Ganga 5) was grown on refined sand in glass house during April–August, when PAR levels at noon approached 1500–1700 μM quanta m⁻² s⁻¹. The control plants were supplied with nutrient solution containing in mM: 4 Ca(NO₃)₂, 2 MgSO₄, 1.33 (NH₄)₂HPO₄, 0.1 NaCl, 0.1 Fe-EDTA; and in μM: 10 MnSO₄, 1 CuSO₄, 1 ZnSO₄, 33 H₃BO₃, 0.2 Na₂MoO₄, 0.1 CoSO₄ and 0.1 NiSO₄. The sand and the nutrients were purified against Fe (Hewitt, 1966). Fe deficiency was induced in a set of plants by

Results

The chlorotic appearance of the Fe-deficient plants was reflected in the reduced concentration of chlorophyll in these plants (Table 1). Chl a was reduced to 59% of control and Chl b to 51%. Greater decrease of Chl b caused a rise in Chl a/b ratio.

Fe deficiency resulted in reduced electron transport capacity through all the segments of the photosynthetic electron transport chain (Table 2). Electron transport through the segment PS II (excluding the WOC) to PS I, was reduced to 35% of the

Discussion

Iron plays important roles in the formation and maintenance of structure and functioning of the photosynthetic apparatus (Terry and Abadia, 1986). Fe deficiency in higher plants is characterised by chlorosis or yellowing of leaves due to reduced amounts of chlorophyll per unit leaf area (Morales et al., 1994), as has also been observed in the present study. Spiller et al. (1982) have demonstrated the accumulation of Mg-protoporphyrin IX and/or Mg-protoporphyrin IX monomethyl ester under

Acknowledgments

The work presented in this paper was funded by The Department of Science and Technology, GOI, in the form of a SERCYS project under Samir Sharma.

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Adaptation of photosynthesis under iron deficiency in maize

Summary

Introduction

Section snippets

Plant growth

Results

Discussion

Acknowledgments

Trends Biochem Sci

Cell

Adv Agron

Biochim Biophys Acta

Biochim Biophys Acta

J Biol Chem

Biochim Biophys Acta

J Plant Physiol

Photoregulation of the composition, function, and structure of the thylakoid membranes

Annu Rev Plant Physiol

Shade-sun responses: compromises between acclimation and photoinhibition

The effect of light on the biosynthesis of the light-harvesting chlorophyll a/b protein. Evidence for the requirement of chlorophyll a for the stabilization of the apoprotein

Planta

Mechanisms for redox control of gene expression

Annu Rev Microbiol

Fe deficiency induces the formation of an antenna ring around trimeric photosystem I in cyanobacteria

Nature

Recent advances in chlorophyll biosynthesis

Photosynth Res