Is protein carbonylation a biomarker of seed priming and ageing?

For a long time, it has been known that seed priming allows the improvement of plant production and tolerance to abiotic stresses. However, a negative effect on the longevity of the seeds thus primed was observed; these mechanisms are still poorly understood. In addition, it has been shown by several authors that seed ageing is associated with the oxidation and particularly with carbonylation of protein. Our work consisted in studying the AOPP and carbonyl protein at the different parts of the embryo from freshly primed seeds and from those that have been primed for 4 years (after storage). We subjected Vigna unguiculata (L.) Walp. seeds to a single or double hydropriming. Our study showed that hydropriming, and more particularly a double cycle of hydration-dehydration, makes it possible to attenuate the oxidation of the protein while it favours a certain threshold of carbonylation in the freshly dehydrated seeds in order to better trigger the germination process. On the other hand, after a storage period of 4 years, these dehydrated seeds are characterised by a strong accumulation of the products of oxidation and especially carbonylated protein, compared with the untreated seeds, which could explain the decrease of the longevity of these seeds.

Biochar and compost effects on the remediative capacities of Oxalis pes-caprae L. growing on mining technosol polluted by Pb and As.

Selection of plant species with a great remediating capacity and a high biomass production is an important step for depolluting soils especially mine soils. Hyperaccumulators are used in phytoextraction for extracting metals from soil to roots and to translocate them to aerial parts. While in phytostabilization that usually requires amendment, metals are accumulated in the plant roots. The purpose of this study is to investigate Oxalis pes-caprae L. tolerance to Pb and As from Pontgibaud mine soil in France amended with compost and/or biochar. Oxalis bulbils were harvested in three sites located around Algiers: (1) an agricultural land in Reghaïa, (2) an area planted with Pines at the USTHB university campus, and (3) the polluted bank of the El Harrach river. The small and medium bulbil sizes were selected from each locality. Concerning the experimental soil, five mixtures of Pontgibaud technosol (P) with amendments compost (C) and biochar (Bc) were prepared: PC, PBc5, PBc10, PBc5 C, PBcC (w/w). The results indicate that amendments alter the soil physico-chemical characteristics and the mobility of metal(loid)s. They also reveal that As and Pb are differently distributed in plant organs. Medium bulbils especially from El Harrach river and the university campus have shown a better growth. Seedlings growth rate has been the highest in Pontgibaud amended with PC and the lowest in PBc10.

Vigna unguiculata seed priming is related to redox status of plumule, radicle and cotyledons.

Pre-germination treatments represent the physiological methods that improve plant production by modulating the metabolic activities of germination before the emergence of the radicle. It was suggested that reactive oxygen species (ROS) play a crucial role in signalling seed germination. Our work consisted in studying changes in the redox status in the embryonic axis (radicle and plumule) and in cotyledons of Vigna unguiculata (L.) Walp. non-primed, osmoprimed (30% PEG6000), hydroprimed or twice hydroprimed seeds, by estimating antioxidant activities and production of ROS. Some antioxidant enzymatic activities as well as total non-enzymatic antioxidant capacity were measured. The production of hydrogen peroxide (H2O2) and superoxide anion (O2-) was also assessed by 3,3'-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) respectively. The results obtained showed, on the one hand, that priming allows activation of antioxidant enzymes, especially in the plumule. On the other hand, these results showed that priming caused an accumulation of ROS in embryonic tissues. This may explain the improvement of seed germination performance according to the oxidative window model. Priming induced changes in the redox environment at the seed level. These changes were closely related to the pre-germination treatments. Indeed, a double cycle of hydration-rehydration induced the broadest spectrum of modifications of the redox status, which would explain the improvement of the seed vigour.

Variation in relative water content, proline accumulation and stress gene expression in two cowpea landraces under drought.

Many landraces of cowpea [Vigna unguiculata (L.) Walp.] are adapted to particular geographical and climatic conditions. Here we describe two landraces grown respectively in arid and temperate areas of Algeria and assess their physiological and molecular responses to drought stress. As expected, when deprived of water cowpea plants lose water over time with a gradual reduction in transpiration rate. The landraces differed in their relative water content (RWC) and whole plant transpiration rate. The landrace from Menia, an arid area, retained more water in adult leaves. Both landraces responded to drought stress at the molecular level by increasing expression of stress-related genes in aerial parts, including proline metabolism genes. Expression of gene(s) encoding proline synthesis enzyme P5CS was up regulated and gene expression of ProDH, a proline catabolism enzyme, was down regulated. Relatively low amounts of proline accumulated in adult leaves with slight differences between the two landraces. During drought stress the most apical part of plants stayed relatively turgid with a high RWC compared to distal parts that wilted. Expression of key stress genes was higher and more proline accumulated at the apex than in distal leaves indicating that cowpea has a non-uniform stress response at the whole plant level. Our study reveals a developmental control of water stress through preferential proline accumulation in the upper tier of the cowpea plant. We also conclude that cowpea landraces display physiological adaptations to water stress suited to the arid and temperate climates in which they are cultivated.

Respiratory complex I deficiency induces drought tolerance by impacting leaf stomatal and hydraulic conductances.

To investigate the role of plant mitochondria in drought tolerance, the response to water deprivation was compared between Nicotiana sylvestris wild type (WT) plants and the CMSII respiratory complex I mutant, which has low-efficient respiration and photosynthesis, high levels of amino acids and pyridine nucleotides, and increased antioxidant capacity. We show that the delayed decrease in relative water content after water withholding in CMSII, as compared to WT leaves, is due to a lower stomatal conductance. The stomatal index and the abscisic acid (ABA) content were unaffected in well-watered mutant leaves, but the ABA/stomatal conductance relation was altered during drought, indicating that specific factors interact with ABA signalling. Leaf hydraulic conductance was lower in mutant leaves when compared to WT leaves and the role of oxidative aquaporin gating in attaining a maximum stomatal conductance is discussed. In addition, differences in leaf metabolic status between the mutant and the WT might contribute to the low stomatal conductance, as reported for TCA cycle-deficient plants. After withholding watering, TCA cycle derived organic acids declined more in CMSII leaves than in the WT, and ATP content decreased only in the CMSII. Moreover, in contrast to the WT, total free amino acid levels declined whilst soluble protein content increased in CMSII leaves, suggesting an accelerated amino acid remobilisation. We propose that oxidative and metabolic disturbances resulting from remodelled respiration in the absence of Complex I activity could be involved in bringing about the lower stomatal and hydraulic conductances.

Light and oxygen are not required for harpin-induced cell death.

Nicotiana sylvestris leaves challenged by the bacterial elicitor harpin N(Ea) were used as a model system in which to determine the respective roles of light, oxygen, photosynthesis, and respiration in the programmed cell death response in plants. The appearance of cell death markers, such as membrane damage, nuclear fragmentation, and induction of the stress-responsive element Tnt1, was observed in all conditions. However, the cell death process was delayed in the dark compared with the light, despite a similar accumulation of superoxide and hydrogen peroxide in the chloroplasts. In contrast, harpin-induced cell death was accelerated under very low oxygen (<0.1% O(2)) compared with air. Oxygen deprivation impaired accumulation of chloroplastic reactive oxygen species (ROS) and the induction of cytosolic antioxidant genes in both the light and the dark. It also attenuates the collapse of photosynthetic capacity and the respiratory burst driven by mitochondrial alternative oxidase activity observed in air. Since alternative oxidase is known to limit overreduction of the respiratory chain, these results strongly suggest that mitochondrial ROS accumulate in leaves elicited under low oxygen. We conclude that the harpin-induced cell death does not require ROS accumulation in the apoplast or in the chloroplasts but that mitochondrial ROS could be important in the orchestration of the cell suicide program.