Proline Concentration and Its Metabolism Are Regulated in a Leaf Age Dependent Manner But Not by Abscisic Acid in Pea Plants Exposed to Cadmium Stress.

Edyta Zdunek-Zastocka,Sławomir Orzechowski,Beata Michniewska,Agnieszka Grabowska

doi:10.3390/cells10040946

Abstract

The accumulation of proline is one of the defense mechanisms of plants against the harmful effects of adverse environmental conditions; however, when pea plants were treated for 12 h with CdCl2, the proline concentration decreased in the youngest A (not expanded) and B1 (expanded) leaves, and did not change significantly in the B2 (mature, expanded) or C (the oldest) leaves. After 24 h of cadmium (Cd) stress, the proline concentration remained low in A and B1 leaves, while in B2 and C leaves, it increased, and after 48 h, an increase in the proline concentration in the leaves at each stage of development was observed. The role of proline in the different phases of plant response to the Cd treatment is discussed. Changes in proline accumulation corresponded closely with changes in the transcript levels of PsP5CS2, a gene encoding D1-pyrroline-5-carboxylate synthetase involved in proline synthesis, and PsPDH1, a gene encoding proline dehydrogenase engaged in proline degradation. CdCl2 application induced the expression of PsProT1 and PsProT2, genes encoding proline transporters, especially during the first 12 h of treatment in A and B1 leaves. When the time courses of abscisic acid (ABA) and proline accumulation were compared, it was concluded that an increase in the proline concentration in the leaves of Cd-treated pea plants was more related to a decrease in chlorophyll concentration (leaves B2 and C) and an increase in the malondialdehyde level (A and B1 leaves) than with an increase in ABA concentration alone. Exogenous application of ABA (0.5, 5, 50 µM) significantly increased the proline concentration in the A leaves of pea plants only, and was accompanied by an elevated and repressed expression of PsP5CS2 and PsPDH1 in these leaves, respectively. The presented results suggest that under Cd stress, the accumulation of proline in leaves of pea plants may take place independently of the ABA signaling.

Highlights

Over the past few decades, increased anthropogenic activity, rapid industrialization, and the use of metal-based pesticides have led to an increased contamination of soil and water with heavy metals, which in turn causes toxicity to living organisms [1,2]
A 945-bp nucleotide sequence fragment, sharing a high percentage identity with the sequences of P5CS2 genes from Medicago truncatula (MtP5CS2, JN809240, 83%) [23,56], Arabidopsis thaliana (AtP5CS2; NM_115419, 72%) [16,22], and Brassica napus (BsP5CS2, AF314812, 67%), was identified in pea plants and designated Pisum sativum P5CS2 (PsP5CS2, MW423825) (Supplementary Figure S2)
A 460-bp nucleotide sequence fragment that shared 88% identity with the sequence of MtProT2 and 81% identity with the sequence of GmProT2 was identified in pea plants and designated Pisum sativum ProT2 (PsProT2, MW030635) (Supplementary Figure S5)

Summary

Introduction

Over the past few decades, increased anthropogenic activity, rapid industrialization, and the use of metal-based pesticides have led to an increased contamination of soil and water with heavy metals, which in turn causes toxicity to living organisms [1,2]. Cadmium (Cd) is one of the most common heavy metals in a contaminated environment, which negatively affects plant growth and development, even when available in low concentrations. Cd inhibits photosynthesis and transpiration in leaves [4], limits water uptake, and disrupts the uptake and movement of mineral nutrients [5]. Cd is not a redox-active metal, it can induce oxidative stress, possibly by interfering with an antioxidant defense, by increasing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, or by disrupting the electron transport chain [7,8]

Methods

Results

Conclusion