Features of the Proline Synthesis of Pea Seedlings in Depend of Salt and Hyperthermia Treatment Coupled with Ionizing Radiation

Intriguing Role of Proline in Redox Potential Conferring High Temperature Stress Tolerance

Proline is a proteinogenic amino acid synthesized from glutamate and ornithine. Pyrroline-5-carboxylate synthetase and pyrroline-5-carboxylate reductase are the two key enzymes involved in proline synthesis from glutamate. On the other hand, ornithine-δ-aminotransferase converts ornithine to pyrroline 5-carboxylate (P5C), an intermediate in the synthesis of proline as well as glutamate. Both proline dehydrogenase and P5C dehydrogenase convert proline back to glutamate. Proline accumulation is widespread in response to environmental challenges such as high temperatures, and it is known to defend plants against unpropitious situations promoting plant growth and flowering. While proline accumulation is positively correlated with heat stress tolerance in some crops, it has detrimental consequences in others. Although it has been established that proline is a key osmolyte, its exact physiological function during heat stress and plant ontogeny remains unknown. Emerging evidence pointed out its role as an overriding molecule in alleviating high temperature stress (HTS) by quenching singlet oxygen and superoxide radicals. Proline cycle acts as a shuttle and the redox couple (NAD+/NADH, NADP+/NADPH) appears to be highly crucial for energy transfer among different cellular compartments during plant development, exposure to HTS conditions and also during the recovery of stress. In this review, the progress made in recent years regarding its involvement in heat stress tolerance is highlighted.

Proline content in the leaves of poplar and willow under water deficit

Water deficiency is one of the most important abiotic factors limiting the growth and productivity of plants. Under conditions of water deficiency, plants can synthesize osmoprotectors, in particular proline. The aim of our work was to estimate the accumulation of free proline in the leaves of two poplar clones ‘Slava Ukrainy’, ‘Guliver’ and willow clone ‘Pechalna’ in water-deficient conditions. Plants were grown outdoors, providing protection from the rain with a plastic wrap, with a differentiated watering: normal watering –100% (control) and water deficit – 75%, 50 % and 25% moisture by volume from the control. The content of free proline was determined by a modified Bates method by measuring the optical density of the ninhydrin-proline solution on a spectrophotometer at a wavelength of 520 nm. Experimental observations have shown that the total content of proline differs among poplar and willow clones. The poplar ‘Guliver’ had a lower content of proline compared to the poplar ‘Slava Ukrainy’ and the willow ‘Pechalna’. The level of free proline also differed between the samples of poplar ‘Guliver’ in the first and second years of growth under water deficiency. However, on the 30th day of treatment we did not find any differences in the content of proline between the stressed and control plants. Thus, the clone factor has the only obvious effects on proline content while the factor of water regime showed no effects on the level of proline. We hypothesize that water deficiency is more likely to alter proline levels as a shorter time response to stress than the terms we applied.

Identification of Phenotypic and Physiological Markers of Salt Stress Tolerance in Durum Wheat (Triticum Durum Desf.) through Integrated Analyses

Salinity is one of the most important stresses that reduces plant growth and productivity in several parts of the world. Nine Tunisian durum wheat genotypes grown under hydroponic conditions were subjected to two levels of salt stress (100 and 170 mM NaCl) for 21 days. An integrative analysis revealing the impact of salinity on key phenotypic and physiological marker traits was then conducted. Principal component analysis grouped these traits into three different clusters corresponding to the absence of salt stress and the two levels of salt stress. This analysis also allowed the identification of genotypes exhibiting various levels of tolerance to NaCl. Among the nine genotypes of Triticum durum Desf., cultivar Om Rabiaa was the most tolerant whereas cultivar Mahmoudi genotype was the most sensitive. Following the multivariate analysis of the examined phenotypic and physiological traits, we found that shoot length, shoot fresh weight, leaf area, the whole-plant stable isotope ratios of nitrogen (δ15N), shoot ammonium and proline contents, and shoot glutamine synthetase activity could be used as markers for the selection of salt-tolerant wheat genotypes.