Elsevier

Plant Science

Volume 175, Issue 5, November 2008, Pages 706-716
Plant Science

Effect of waterlogging on carbohydrate metabolism in pigeon pea (Cajanus cajan L.): Upregulation of sucrose synthase and alcohol dehydrogenase

https://doi.org/10.1016/j.plantsci.2008.07.013Get rights and content

Abstract

The objective of this study was to examine the role of root carbohydrate levels and metabolism in the waterlogging tolerance of contrasting pigeon pea genotypes. An experiment was conducted with 4 pigeon pea (Cajanus cajan) genotypes, 2 tolerant (ICPL 84023 and ICP 301) and 2 susceptible (ICP 7035 and Pusa 207) to waterlogging stress. Waterlogging treatment was given by placing pots with 25 days old plants in plastic troughs filled with water. Waterlogging resulted in decrease in leaf area, dry matter, relative water content and chlorophyll content in leaves, and membrane stability index in root and leaf tissues. The decline was greater in ICP 7035 and Pusa 207, which also suffered almost 100% mortality during recovery of 6 days waterlogged plants, than ICPL 84023 and ICP 301. Tolerant genotypes ICPL 84023 and ICP 301 showed higher total, reducing and non-reducing sugars content than ICP 7035 and Pusa 207. Waterlogging resulted in decline in total and non-reducing sugars in all the genotypes and reducing sugars in ICP 7035 and Pusa 207, while the content of reducing sugars increased in ICPL 84023 and ICP 301. The pattern of variation in reducing sugar content in the 4 genotypes was parallel to sucrose synthase activity. ICPL 84023 and ICP 301 also showed fewer declines in total and non-reducing sugars and greater increase in reducing sugar and sucrose synthase (SuSy) activity than ICP 7035 and Pusa 207. Waterlogging resulted in increase in alcohol dehydrogenase (ADH) activity, and increase was higher in ICPL 84023 and ICP 301 than ICP 7035 and Pusa 207. Gene expression studies done by RT-PCR under 24 h waterlogging showed enhanced expression of ADH and SuSy in the roots of ICPL 84023, while in ICP 7035 there was no change in expression level in control or treated plants. The susceptible genotype ICP 7035 showed mutation in the CAAT box region of the ADH promoter, which could be the possible reason of lower ADH gene expression, activity and sensitivity to waterlogging. The results suggest that waterlogging tolerance of pigeon pea genotypes ICPL 84023 and ICP 301 depends on the availability of sufficient sugar reserve in the roots, activity of sucrose synthase to provide reducing sugars for glycolytic activity and ADH for the recycling of NADH for the continuation of glycolysis, the major source of energy under hypoxia. This was reflected in better RWC and Chl content in leaves, and membrane stability of leaf and root tissue in ICPL 84023 and ICP 301.

Introduction

Waterlogging is a serious problem affecting crop growth and productivity. Waterlogging blocks the oxygen supply to the roots thus inhibiting root respiration, resulting in a severe decline in energy status of root cells affecting important metabolic processes of plants. Plants react to an absence of oxygen by switching from an oxidative to a solely substrate-level phosphorylation of ADP to ATP; the latter reactions predominantly involve glycolysis and fermentation. The overall yield of ATP produced during fermentation is only 2 molecules of ATP per glucose molecule as against 38 molecules of ATP produced during oxidative phosphorylation.

The anaerobic response of maize root cells studied using two-dimensional electrophoresis revealed a set of about 20 anaerobic proteins, which were synthesized during low oxygen treatment, while synthesis of the normal aerobic proteins was drastically repressed [1]. Many of these induced proteins were subsequently identified as enzymes of the glycolytic and fermentation pathways [2], [3]. The identified ANP include sucrose synthase, phosphohexose isomerase, fructose-1,6-diphosphate aldolase, pyruvate decarboxylase (PDC), lactate dehydrogenase (LDH), and alcohol dehydrogenase (ADH) [4], [5], [6]. Alcohol dehydrogenase is a major ANP expressed under hypoxic/anoxic conditions. Its activity is critical for the recycling of NADH and thus for the continuation of glycolytic pathway [4]. Peng et al. [7] demonstrated that ADH induction is linked to ethylene production. Ethanol has been shown by a number of research workers to be the major product of fermentation in rice seedlings [8], [9]. The dominance of alcoholic fermentation is further supported by rapid increases in the activity of ADH in germinating seeds of rice [10] and 3- to 4-day-old rice roots [11] when oxygen supply was severely restricted.

Sucrose synthase (SuSy), which catalyzes the reversible conversion of sucrose and UDP to UDP-glucose and fructose, plays a crucial role in providing an adequate sugar supply during anoxic stress [12]. Presence of glucose in the anoxic incubation medium significantly alleviated meristem death, indicating that an increase in glycolytic flux alone was sufficient to restore root tip viability of the rice root tips [13]. Guglielminetti et al. [14] reported that during the anoxic germination of rice invertase activity was depressed and that of SuSy was enhanced, and suggested that SuSy was the enzyme mainly responsible for sucrose breakdown under anoxia. The essentiality of SuSy for anoxic tolerance has recently been demonstrated in maize, using double mutants of the enzyme [13].

Together to chickpea, pigeon pea is an important pulse crop of South Asia. Being a summer-rainy season crop, pigeon pea is exposed to waterlogging condition during germination and early vegetative growth phases. This is the crucial period, which determines the crop stand and ultimately crop growth and productivity [15]. Our preliminary trials with 15 pigeon pea genotypes, done to screen tolerant and susceptible types, indicated greater loss in yield and dry matter when waterlogging treatment was given to 20–30 days old crop than at flowering stage (unpublished data). However, in spite of the seriousness of the problem, very little physiological studies have been done on the effect of waterlogging in legumes, except for soybean and pea.

Since glycolytic-fermentation pathway is the only source of energy, which in turn yields only 2 ATP per mole of glucose as against 38 via glycolysis-Krebs Cycle-Electron transfer chain, it would thus seem that a species or its genotype with greater carbohydrate concentration in roots, and an efficient metabolic mechanism associated with carbohydrate mobilization and fermentation pathway will be more suited to face oxygen deprivation. The present investigation, therefore, has been planned to validate the role of sucrose synthase and alcohol dehydrogenase, and carbohydrate levels in imparting hypoxia tolerance by using 2 tolerant and 2 susceptible pigeon pea genotypes at early vegetative stage.

Section snippets

Plant material and growth conditions

An experiment was conducted with 4 pigeon pea (Cajanus cajan) genotypes, 2 tolerant (ICPL 84023 and ICP 301) and 2 susceptible (ICP 7035 and Pusa 207) to waterlogging stress, procured from ICRISAT, Hyderabad, India and Division of Genetics, Indian Agricultural Research Institute, New Delhi, India. Sowing was done in 30 cm × 30 cm (h × dia) earthen pots filled with clay-loam soil and farm yard manure in 3:1 ratio during the summer-rainy season. Pots were supplied with basal dose of 60 kg ha−1 each of

Physiological parameters

Tolerant genotypes ICPL 84023 and ICP 301 did not show any mortality (%) during recovery even after 6 days of waterlogging, while susceptible genotypes ICP 7035 and Pusa 207 showed 25.0 and 29.2% and 91.7 and 95.8% mortality during recovery in 4 and 6 days waterlogged plants, respectively (data not reported).

Relative water content decreased under waterlogging condition in all the genotypes and the decline was greater in ICP 7035 and Pusa 207 than ICPL 84023 and ICP 301. By 6th day ICP 7035 and

Discussion

In tropical and subtropical regions, severe crop losses are caused by prolonged seasonal rainfall. Excess water produces hypoxic soil condition within a few hours, and prolonged waterlogging results in anoxia. Plant roots, consequently, suffer hypoxia or anoxia. As a result of 6 days of waterlogging pigeon pea genotypes suffered a sever loss in RWC and Chl in leaves, and MSI both in roots and leaves. The decline in all the parameters was less in ICPL 84023 and ICP 301 than ICP 7035 and Pusa

Acknowledgements

Authors are thankful to the Head, Division of Plant Physiology for providing the necessary facilities. D. Kumutha and K. Ezhilmathi are also thankful to University Grant commission, New Delhi, and Council of Scientific and Industrial Research, New Delhi, respectively, for providing Senior Research Fellowships during the course of the study.

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