Exogenous proline effects on water relations and ions contents in leaves and roots of young olive

The ability of exogenous compatible solutes, such as proline, to counteract salt inhibitory effects was investigated in 2-year-old olive trees (Olea europaea L. cv. Chemlali) subjected to different saline water irrigation levels supplied or not with exogenous proline. Leaf water relations [relative water content (RWC), water potential], photosynthetic activity, leaf chlorophyll content, and starch contents were measured in young and old leaves. Salt ions (Na⁺, K⁺, and Ca²⁺), proline and soluble sugars contents were determined in leaf and root tissues. Supplementary proline significantly mitigated the adverse effects of salinity via the improvement of photosynthetic activity (Pn), RWC, chlorophyll and carotenoid, and starch contents. Pn of young leaves in the presence of 25 mM proline was at 1.18 and 1.38 times higher than the values recorded under moderate (SS1) and high salinity (SS2) treatments, respectively. Further, the proline supply seems to have a more important relaxing effect on the photosynthetic chain in young than in old leaves of salt-stressed olive plants. The differential pattern of proline content between young and old leaves suggests that there would be a difference between these tissues in distinguishing between the proline taken from the growing media and that produced as a result of salinity stress. Besides, the large reduction in Na⁺ accumulation in leaves and roots in the presence of proline could be due to its interference in osmotic adjustment process and/or its dilution by proline supply. Moreover, the lower accumulation of Na⁺ in proline-treated plants, compared to their corresponding salinity treatment, displayed the improved effect of proline on the ability of roots to exclude the salt ions from the xylem sap flowing to the shoot, and thus better growth rates.     

Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO₂ concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F_v/F_m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.     

Leaf developmental stage modulates metabolite accumulation and photosynthesis contributing to acclimation of Arabidopsis thaliana to water deficit

We examined whether young and mature leaves of Arabidopsis thaliana in their response to mild water deficit (MiWD) and moderate water deficit (MoWD), behave differentially, and whether photosynthetic acclimation to water deficit correlates with increased proline and sugar accumulation. We observed that with increasing water deficit, leaf relative water content decreased, while proline and sugar accumulation increased in both leaf-developmental stages. Under both MiWD and MoWD, young leaves showed less water loss and accumulated higher level of metabolites compared to mature leaves. This, leaf age-related increase in metabolite accumulation that was significantly higher under MoWD, allowed young leaves to cope with oxidative damage by maintaining their base levels of lipid peroxidation. Thus, acclimation of young leaves to MoWD, involves a better homeostasis of reactive oxygen species (ROS), that was achieved among others by (1) increased sugar accumulation and (2) either increased proline synthesis and/or decreased proline catabolism, that decrease the NADPH/NADP⁺ ratio, resulting in a higher level of oxidized state of quinone A and thus in a reduced excitation pressure, and by (3) stimulation of the photoprotective mechanism of non-photochemical quenching, that reflects the dissipation of excess excitation energy in the form of harmless heat, thus protecting the plant from the damaging effects of ROS.     

Transformation of tomato with a bacterial codA gene enhances tolerance to salt and water stresses

Genetically engineered tomato (Lycopersicon esculentum) with the ability to synthesize glycinebetaine was generated by introducing the codA gene encoding choline oxidase from Arthrobacter globiformis. Integration of the codA gene in transgenic tomato plants was verified by PCR analysis and DNA blot hybridization. Transgenic expression of gene was verified by RT-PCR analysis and RNA blot hybridization. The codA-transgenic plants showed higher tolerance to salt stress during seed germination, and subsequent growth of young seedlings than wild-type plants. The codA transgene enhanced the salt tolerance of whole plants and leaves. Mature leaves of codA-transgenic plants revealed higher levels of relative water content, chlorophyll content, and proline content than those of wild-type plants under salt and water stresses. Results from the current study suggest that the expression of the codA gene in transgenic tomato plants induces the synthesis of glycinebetaine and improves the tolerance of plants to salt and water stresses.     

Accumulation of Free Proline in Citrus Leaves during Cold Hardening of Young Trees in Controlled Temperature Regimes

Free proline increased in leaves of orange (Citrus sinensis [L.] Osb. cv. Valencia) and grapefruit (Citrus paradisi Macfad. cv. Star Ruby) trees on a wide range of citrus rootstocks during cold hardening. Increases in sugars accompanied proline accumulation. During cold hardening, the rate of proline accumulation was greater in old than in young leaves. In leaves of grapefruit trees kept in the dark during cold hardening, neither proline nor sugars increased and the degree of cold hardiness was less than in trees exposed to light. Like sugar accumulations, proline accumulation does not reflect specific degrees of cold hardiness in citrus cultivars.     

Growth,physiological, biochemical and ionic responses of pistachio seedlings to mild and high salinity

Key message

Depending on salt concentrations, different mechanisms are involved in the tolerance of pistachio and an acclimation to salinity conditions occurs in the leaves that develop in the presence of salt.

Abstract

Pistachio (Pistacia vera L.) is a salt tolerant species that is considered an alternative crop for cultivation in salinzied orchard soils. In this work, 12-week-old pistachio seedlings cultivated in soil under greenhouse conditions were treated with five levels of salinity including control (0.63 dSm^?1), low (2 and 4 dSm^?1) and high (8 and 10 dSm^?1) salt concentrations for further 12 weeks. Plant growth parameters were not affected by mild salinity; a significant reduction was only observed from 8 dSm^?1. Considerable differences were observed between the young and mature leaves regarding osmotic and ionic stress effects of salt. Main compatible solutes were proline in mature leaves, proline and soluble sugars in young leaves, and soluble sugars and amino acids, other than proline, in roots. Concentration and content of Na in the leaves were not significantly increased at low levels of salinity and the K:Na and Ca:Na ratio of leaves were affected only by higher salt concentrations. Using the sequential extraction procedure for cell wall isolation, we observed that both absolute and relative amounts of Na in the cell wall fraction increased under low salinity, while decreased under higher levels of salt supply. Stable water relations, photochemistry and CO₂ assimilation rates particularly of young leaves, as well as ion homeostasis were mechanisms for maintenance of plants growth under mild salinity. Under severe saline conditions, the impaired ability of mature leaves for synthesis of assimilates, preferent allocation of carbohydrates to roots for maintenance of osmotic homeostasis and finally, reduction of protein synthesis caused growth inhibition in pistachio.     

Proline biosynthesis in winter plants due to exposure to low temperatures

The content of bound proline sharply increased in proteins of different organs of young plants of winter rape and winter wheat exposed for 72 h to temperatures from 0 to 2 °C while it decreased only in root tips of wheat plants. Free proline which at 20 °C occurs in all plant organs only in trace amounts, accumulated considerably after 72 h exposure to low temperatures in the above-ground organs and only slightly in the roots. Free proline did not accumulate during the first 24 h at 0 to 2 °C in detached leaves of winter wheat but it was incorporated into newly synthetized proteins in which proline content increased after 6 h incubation to its maximum ( + 11.75% in comparison to control); the content of free glutamate sharply decreased during the first 6 h of incubation and the accumulation of bound glutamate was belated in comparison to that of bound proline. Sucrose infiltrated into detached leaves of winter wheat strongly stimulated proline incorporation into proteins at low temperatures, but it did not influence glutamate incorporation. The results suggest that the main reason for thede novo proline biosynthesis during the first six hours of hardening of the plants is the synthesis of proteins rich in proline; free proline accumulates later predominantly in the above-ground organs as a surplus. The above-ground organs are dehydrated in the course of the hardening process approximately to the same extent both in the light and in the dark, but proline content increases much less in the dark than in tho light.     

Changes in photosynthesis caused by adaptation of maize seedlings to short-term drought

Detached leaf is in the state of increasing water deficit; it is a good experimental model for looking into the hardening effect of adaptation of eight-day-old maize (Zea mays L.) seedlings to short-term drought (five days without watering). The light stage of photosynthesis and photosynthetic CO₂/H₂O exchange in detached leaves were studied. Specific surface density of leaf tissue (SSDL), the content of chlorophylls a and b, proline, MDA as well as photosynthetic parameters: quantum yield of photosystem II fluorescence, assimilation of CO₂, and transpiration at room temperature and light saturation (density of PAR quantum flux of 2000 μmol/(m² s)) at normal and half atmospheric CO₂ concentration were determined. The leaves of seedlings exposed to short-term drought differed from control material by a greater SSDL and higher content of proline. The hardening effect of the stress agent on the dark stage of photosynthesis was detected; it was expressed in the maintenance of the higher photosynthetic CO₂ assimilation against control material due to the elevation of stomatal conductance for CO₂ diffusing into the leaf. Judging from the lack of differences in the MDA content, short-term drought did not injure photosynthetic membranes. In detached leaves of experimental maize seedlings, photosynthesis was maintained on a higher level than in control material.     

Distribution and biosynthesis of theanine in Theaceae plants

The theanine content of the leaves of 27 species or varieties of Theaceae plants was investigated. Theanine was present in 21 species or varieties, but in much lower amounts (<0.2 μmol/g fresh weight) than the quantity detected in Camellia sinensis var. sinensis. The major free amino acids in leaves of four species belonging to the genera Schima and Eurya, were glutamic acid, aspartic acid, glutamine, asparagine, alanine and proline and content of these amino acids is similar to or higher than theanine. Accumulation of free amino acids in these plants was generally lower than in C. sinensis var. sinensis. The biosynthetic activity of theanine, assessed by the incorporation of radioactivity from [¹⁴C]ethylamine, was detected in seedlings of two species of Schima. The theanine biosynthetic activity in roots was higher than that of leaves.     

Induction of salt tolerance in salicylate-deficient <Emphasis Type="Italic">NahG</Emphasis> Arabidopsis transformants using the nitric oxide donor

The effects of treatment with nitric oxide donor sodium nitroprusside (SNP, 0.5 mM) on salt tolerance of wild type (Col–0) Arabidopsis thaliana plants and Arabidopsis thaliana plants transformed with the bacterial salicylate hydroxylase gene (NahG) were compared. Basic salt tolerance level (200 mM NaCl) was higher in NahG transformants. Under salt stress conditions, these plants showed higher activity levels for antioxidant enzymes as well as higher content of sugars and anthocyanins. The treatment with NO donor induced salt tolerance in the plants of both genotypes, which could be observed as less strong growth inhibition, reduced oxidative damage, and preservation of chlorophyll pool in leaves. After the exposure to salt stress, the activity of both superoxide dismutase and guaiacol peroxidase was higher in SNP-treated wild type plants and NahG transformants than in the nontreated plants. After the imposition of salt stress, proline content in leaves of the wild type plants treated with the nitric oxide donor was lower than in the leaves of the nontreated plants. In contrast, SNP treatment of NahG transformants led to a significant increase in the proline content in leaves under the salt stress conditions. Conclusions have been made that wild type Col-0 plants and NahG transformants differ in how their systems of protection against salt stress are activated and that nitric oxideinduced mobilization of protection systems in A. thaliana may not require the presence of salicylate.     

ABA and proline accumulation in leaves and roots of wild (<Emphasis Type="Italic">Hordeum spontaneum</Emphasis>) and cultivated (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> ‘Maresi’) barley genotypes under water deficit conditions

The purpose of the study was to examine water stress-induced changes in the ABA and proline contents in roots and leaves of a potentially more resistant wild accession of Hordeum spontaneum and the modern cultivar Maresi (Hordeum vulgare). Leaves of H. spontaneum had higher contents of constitutive ABA and proline in comparison to those of ‘Maresi’. A moderate water deficit resulted only in root dehydration, which was higher in ‘Maresi’. Increases of water deficit in roots coincided with an increase of ABA content in roots, followed by that in leaves. The level of proline increased only in leaves and only in the case of H. spontaneum. Under conditions of severe water stress, the root dehydration levels were similar in the both genotypes, whereas leaf dehydration was higher in ‘Maresi’. H. spontaneum, as compared to ‘Maresi’ showed an earlier increase of ABA content in the roots and accumulated more ABA in the leaves. Free proline levels in the roots increased in both genotypes but H. spontaneum exhibited a 2-fold higher proline accumulation than ‘Maresi’. In H. spontaneum the accumulation of proline in the leaves occurred noticeably earlier and to a higher extent than in ‘Maresi’. A possible connection of these modifications with water stress resistance of the investigated genotypes is discussed in this paper.     

植物叶片脯氨酸的变化及其对亚硫酸伤害的防护作用

 在特定污染条件下,植物叶脯氨酸含量与K+渗出量(％)呈负相关变化,并因树种和叶片成熟度而异、脯氨酸含量为成叶>老叶,K+渗出量则是老叶>成叶,外施脯氨酸对植物亚硫酸伤害具有一定的防护作用。     

Different responses of young and expanded lettuce leaves to fungicide Mancozeb: chlorophyll fluorescence,lipid peroxidation,pigments and proline content

This work aimed to study the effects of commercial doses of the fungicide, Mancozeb, on the photosynthetic apparatus of lettuce young leaves (YL) and expanded leaves (EL). Seven days after Mancozeb application, chlorophyll a fluorescence, pigment contents, lipid peroxidation, and proline content were evaluated. Independently of leaf age, Mancozeb treatment reduced the efficiency of photosystem II photochemistry, increased the nonphotochemical quenching and proline content, decreased pigment contents, and induced lipid peroxidation. Moreover, EL showed a more stable photosynthetic apparatus, less prone to oxidative damages compared with YL. The parameters measured proved to be good markers for the rapid and preliminary diagnosis of fungicide toxicity.     

Effect of Drought Stress on Lipid Peroxidation,Osmotic Adjustment and Antioxidant Enzyme Activity of Leaves and Roots of <Emphasis Type="Italic">Lycium ruthenicum</Emphasis> Murr. Seedling

Seedling stage is a critical period for survival and growth under drought stress. In the current study, we determined effects of drought stress on physiological and biochemical parameters of leaves and roots of Lycium ruthenicum Murr. seedling. The variables measured were lipid peroxidation (in terms of malondialdehyde (MDA) content), osmotic substances (free proline, soluble protein, and soluble sugar), and antioxidative enzymes (peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT)). Free proline, soluble sugar, and MDA of leaves and roots increased with increasing stress level. Leaves displayed higher accumulations of free proline and MDA than roots. However, roots showed higher total soluble sugar than leaves. Under drought stress, soluble proteins in leaves and roots decreased initially and then increased. Meanwhile, measured proteins were higher in leaves. Under drought stress, SOD, POD, and CAT activities in leaves increased initially and then decreased but increased with increasing drought stress level in roots. Under drought the level of accumulation of osmotics was higher in the leaves than in the roots, while increased activity of antioxidant enzymes persisted in the stressed roots longer that in the leaves.     

兴安鹿蹄草（Pyrola dahurica (H.Andr.) Kom.）雪盖前后丙二醛及渗透调节物质含量的变化

研究了自然生境下生长的兴安鹿蹄草（Pyrola dahurica (H.Andr.) Kom.）根状茎及叶片中渗透调节物质、膜脂过氧化产物在雪盖前后的变化。结果表明,在雪盖前期（10月1日~12月15日）兴安鹿蹄草根状茎及叶片中丙二醛（MDA）含量先增高,尔后下降,翌年春季雪盖后期（3月1日~4月15日）MDA含量明显低于雪盖前期,雪盖前期根状茎的丙二醛（MDA）含量低于叶片,雪盖后期高于叶片。可溶性糖、可溶性蛋白质含量在雪盖前期随着温度的下降而升高,11月中旬达到最大,尔后下降,脯氨酸含量先下降尔后升高。雪盖后期渗透调节物质含量高于雪盖前期,可溶性糖含量随气温的升高而下降,可溶性蛋白质与脯氨酸含量随气温升高而大幅度升高,而且成明显正相关。根状茎的可溶性糖含量在雪盖前期、雪盖后期低于叶片,可溶性蛋白质与脯氨酸含量在雪盖前期、雪盖后期高于叶片。兴安鹿蹄草主要通过渗透调节物质含量的变化来适应雪盖前期及雪盖后期低温环境而安全越冬。     

Girdling induces oxidative damage and triggers enzymatic and non-enzymatic antioxidative defences in Citrus leaves

The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old ‘Loretina’ mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (F_o) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms.     

Girdling induces oxidative damage and triggers enzymatic and non-enzymatic antioxidative defences in Citrus leaves

The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old ‘Loretina’ mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (F_o) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms.     

Evaluation of Polyamine and Proline Levels during Low Temperature Acclimation of Citrus

The polyamines (PA) putrescine (Put), spermidine (Spd), and spermine (Spm) were measured during 3 weeks exposure to cold hardening (15.6°C day and 4.4°C night) and nonhardening (32.2°C day and 21.1°C night) temperature regimes in three citrus cultivars: sour orange (SO) (Citrus aurantium L.), `valencia' (VAL) (Citrus sinensis L. Osbeck), and rough lemon (RL) (Citrus jambhiri Lush). The changes in PA were compared to the amount of free proline, percent wood kill and percent leaf kill. A 2- to 3-fold increase in Spd concentrations were observed in hardened RL, SO, and VAL leaves compared to nonhardened leaves. Spermidine reached its highest level of approximately 200 nanomoles per gram fresh weight after 1 week of acclimation in both SO and VAL leaves, while RL spermidine content continued to increase up to the third week of acclimation. Spm levels in acclimated VAL and RL leaves increased 1- to 4-fold. However, SO leaves Spm content decreased with acclimation. Putrescine levels in SO and VAL increased 20 to 60% during the first 2 weeks of acclimation then declined after 3 weeks. RL putrescine content was not affected by cold acclimation. The data presented here provided direct relationship between increased Spd concentration and citrus cold hardiness. Free proline was 3- to 6-fold higher in acclimated than in nonacclimated trees. Results also demonstrate that in acclimated versus nonacclimated citrus trees the absolute amount rather than the ratio of increase in free proline is more important in predicting their ability to survive freezing stress.     

Leaf orientation,photorespiration and xanthophyll cycle protect young soybean leaves against high irradiance in field

In order to fully understand the adaptive strategies of young leaves in performing photosynthesis under high irradiance, leaf orientation, chloroplast pigments, gas exchange, as well as chlorophyll a fluorescence kinetics were explored in soybean plants. The chlorophyll content and photosynthesis in young leaves were much lower than that in fully expanded leaves. Both young and fully expanded leaves exhibited down-regulation of the maximum quantum yield (F_V/F_M) at noon in their natural position, no more serious down-regulation being observed in young leaves. However, when restraining leaf movement and vertically exposing the leaves to 1200 μmol m⁻² s⁻¹ irradiance, more pronounced down-regulation of F_V/F_M was observed in young leaves; and the actual photosystem II (PS II) efficiency (Ф_PSII) drastically decreased with the significant enhancement of non-photochemical quenching (NPQ) and ‘High energy’ quenching (q_E) in young leaves. Under irradiance of 1200 μmol m⁻² s⁻¹, photorespiration (P_r) in young leaves measured by gas exchange were obviously lower, whereas the ratio of photorespiration/gross photosynthetic rate (P_r/P_g) were higher than that in fully expanded leaves. Compared with fully expanded leaves, young leaves exhibited higher xanthophyll pool and a much higher level of de-epoxidation components when exposure to high irradiance. During leaf development, the petiole angle gradually increased all the way. Especially, the midrib angle decreased with the increasing of irradiance in young leaves; however, no distinct changes were observed in mature leaves. The changes of leaf orientation greatly reduced the irradiance on young leaf surface under natural positions. In this study, we suggested that the co-operation of leaf angle, photorespiration and thermal dissipation depending on xanthophyll cycle could successfully prevent young leaves against high irradiance in field.     

Proline and functioning of the antioxidant system in Thellungiella salsuginea plants and cultured cells subjected to oxidative stress

The effects of proline on the functioning of antioxidant enzymes — superoxide dismutase (SOD) and ascorbate peroxidase (APO) — in Thellungiella salsuginea plants and cultured cells under normal conditions of culturing and under the influence of hydrogen peroxide (500 μM) were studied. Proline addition (0.2, 2, or 5 mM) to the medium for suspension culture or nutrient medium for plant growing resulted in the increase in the content of intracellular proline in both cultured cells and intact plant leaves and also in the activation of proline dehydrogenase, i.e., the enzyme degrading proline. Under normal conditions, treatment with proline exerted prooxidant action on both cellular and organismal levels. This was manifested in MDA accumulation and changes in APO and SOD activities. The amino acid alanine, used as a control, did not exert similar strong effect as proline. Application of 500 μM H₂O₂ on plant leaves resulted in the development of oxidative stress, whereas hydrogen peroxide addition into the culture medium — to the death of 50% of suspension cells. When plants and cultured cells were treated with 2 mM proline and than with H₂O₂, the number of dead cells in suspension was 35%, the content of MDA was decreased, APO was activated, and SOD activity was decreased in both cell culture and plant leaves. Thus, an increase in the intracellular proline concentration changed the redox balance and induced functioning of APO and SOD at both normal conditions of plant growing and cell culturing and under stress.