Water Deficit Treatments Research Articles

EFFECTS OF SEED PRIMING ON SEED GERMINATION AND EARLY SEEDLING GROWTH OF CHILI (CAPSICUM ANNUM L.) UNDER WATER DEFICIT CONDITION

Seed priming may improve seed germination and early seedling growth of plants under water deficit condition. The present study was conducted to investigate the effects of seed priming on the germination and early seedling growth of chili under water deficit condition and to identify the optimum rate of seed priming for higher seed germination and early seedling growth. The water deficit stress level towards early seedling growth also been identified. The priming treatments involved were non-priming as control, and priming with gibberellic acid (GA3) at 5 mg/L, 10 mg/L and 15 mg/L. Seed germination experiment was conducted using wet-tissue method for seven days duration. Germination percentage, germination index and seedling vigour index were recorded in the seed germination experiment. The germinated seeds were then sown and grown under five different levels of water deficit treatment in accordance with the frequency of watering mainly watering 8 times (S1), 4 times (S2), 2 times (S3), once (S4), and not watered (S5), in a duration of 14 days. The early seedling growth performance was based on plant height, and root length. Seed germination and early seedling growth performance of 5 mg/L GA3 primed seeds was significantly better as compared to other seed priming treatments. In addition, the S1 and S2 could be regarded as non-stress condition, S3 and S4 as mild to moderate stress and S5 as severe stress since all seedlings were not survived under S5 condition. In general, S2 was found to be the optimum watering treatment as it recorded the highest plant height and root length of the seedlings.

Chemical composition and reproductive functionality of contrasting faba bean genotypes in response to water deficit

Water deficit (WD), a major contributor to yield reductions in faba bean (Vicia faba), is a complex phenomenon that varies across daily to seasonal cycles. Several studies have identified various morphological and physiological indicators of WD tolerance, which generally show limited water use during WD. Limited information is available on the impact of WD on nutrient content and reproductive biology of the faba bean. We studied carbohydrates, amino acids, mineral nutrients and the abundance of naturally occurring carbon isotopes (δ13 C) in leaf and grain tissues of faba bean genotypes grown under well-watered (WW) and WD conditions. δ13 C of leaf tissues were found to indicate changes in water use due to WD but this was not reflected in grain tissues. Nutrient concentrations with regard to amino acids and minerals were not influenced by WD. However, carbohydrate accumulation was found to be significant for WD, specifically through the presence of a higher concentration of myo-inositol in WD leaf tissues. Alternatively, sucrose concentration in grain tissues was reduced under WD treatment. WD hampered reproductive functionality by reducing pollen viability and germination with the severity and duration of stress and this reduction was less prominent in the drought-tolerant genotype (AC0805#4912) compared to the sensitive one (11NF010c-4). It was also demonstrated that WD caused developmental impairment in the stamen and pistil, where the pistil appeared more sensitive than stamen. These findings suggest that WD impairs pollen viability and pistil function reducing yield volume, but the nutrient content of the resulting yield is not significantly affected.

Morphological, Physiological, and Biochemical Impacts of Different Levels of Long-Term Water Deficit Stress on Linum album Ky. ex Boiss. Accessions

Linum album (Ky. ex Boiss.) is an important medicinal plant that produces compounds such as the well-known anticancer lignan podophyllotoxin and fatty acids. Despite its high medicinal value, it has not yet been studied in detail under agricultural conditions. This study was conducted to evaluate the morphological, phenological, and physiological responses of six L. album accessions under different levels of water deficit treatments (100%, 75%, 50%, and 25% available water) in pot conditions. Based on the results, some of the morphological characteristics of the response to water deficit were established. Accessions UTLA7, UTLA9, and UTLA10 showed a higher seed yield and dry weight of the vegetative part. There was a substantial difference in the occurrence of phenological stages in the accessions. The maturation process was accelerated in plants under stress conditions, and accession UTLA9 completed its complete growth cycle faster than the other accessions. The physiological responses of the different accessions did not show the same pattern on the basis of the characteristics studied, and significant differences were observed depending on the trait and accession. Among the most important results of this study was the diversity of responses in different accessions. Based on these results, it is recommended that morphological features (such as seed yield per plant, plant height, number of inflorescences per plant, shoot and root dry weight) be used to select tolerant accessions for the desired product.

Effect of Regulated Deficit Irrigation on Potato under-Mulched Drip Irrigation

In order to study the effects of water deficit on potato under-mulched drip irrigation, the paper interpreted the effects of water deficit at different growth stages on growth characteristics, yield, quality and the water use of potato under-mulched drip irrigation. The results showed that mild water deficit treatment in potato tuber forming period can effectively reduce excessive plant branches and contribute to the increase of crop yield. Meanwhile, the total sugar content, protein and starch content can be improved, and the content of organic acids was significantly reduced, which is conducive to the improvement of potato quality. Tuber growth period is a period with large water demand for crops, so that enough moisture should be guaranteed during this period. Finally, the current problems in potato planting were analysed, and the future research directions were prospected.

Determining optimal deficit irrigation and fertilization to increase mango yield, quality, and WUE in a dry hot environment based on TOPSIS

Rational application of water and fertilizer management practices can not only improve mango (Mangifera indica L.) yield and quality but also improve irrigation water-use efficiency (IWUE). However, few studies have addressed the use of water and fertilizer management practices in hot, dry environments with the aim of achieving relatively favorable levels of these parameters concurrently. We used the technique for order preference by similarity to an ideal solution (TOPSIS) method to identify optimal water and fertilizer management practices that resulted in high fruit yields and high IWUE in Southwest China. A randomized block design study with four irrigation levels [full irrigation throughout the growth period (FI), regulated deficit irrigation during flowering (RDIFS), regulated deficit irrigation during fruit expansion (RDIES), and regulated deficit irrigation at maturity (RDIMS)] and three fertilization levels [FH, a water-soluble compound fertilizer (N:P2O5:K2O = 12:8:40) applied at 129.0 kg ha−1; FM, 103.2 kg ha−1; and FL, 77.4 kg ha−1] was implemented in 2018 and 2019 to investigate these relationships. The net photosynthesis rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) of mango under the different water deficit treatments were significantly lower than those under the FI treatment with the same fertilization conditions, but the instantaneous water-use efficiency (WUEi) of the leaves increased. The fresh fruit yield, solids:acid ratio (SOAR), sugar:acid ratio (SUAR), and IWUE under the RDIFS treatment were significantly lower than those under the FI treatment at the same fertilization rates. Averaged over all fertilization rates, the fruit yield under RDIES was 8.6–22.3% lower than that under FI in both years, but the IWUE significantly increased from 3.7% to 18.6%. Compared with the FI treatment, the RDIMS treatment had no significant effect on fruit yield but significantly increased the IWUE (35.5–44.7%), total sugar (TS) content (3.7–8.5%), and carotenoid content (CC) (1.5–13.1%) in both years. At the same irrigation level, the Pn, Gs and Tr increased with an increasing fertilization rate, while the fruit yield, IWUE, TS, and vitamin C (VC) content of fresh fruit first decreased but then increased with increasing fertilization rate. IWUE was more closely related to photosynthesis characteristics at the flowering stage than at the mature stage, but fruit quality was more closely related to photosynthesis characteristics at the mature stage than at the flowering stage. Compared with the FIFH treatment, the RDIMSFM treatment significantly increased the fruit yield by 10.1% and 6.6% in 2018 and 2019, respectively, and increased the IWUE by 28.1% and 35.6%, respectively. On the basis of the TOPSIS method, the multi-target optimum scheduling of mango was achieved under the RDIMSFM treatment. The identified optimum combination of water and fertilizer can provide a scientific basis for irrigation and fertilization optimization and management in the hot, dry environment of Southwest China.

Interaction Effects of Dust and Water Deficit Stresses on Growth and Physiology of Persian Oak (Quercus Brantii Lindl.)

ABSTRACT Understanding the relationship between factors affecting the decline of Zagros forests can elucidate many challenges associated with sustainable and effective forest management. Therefore, this study aimed to investigate the interaction effects of simulated dust (0, 20, 40 and 60 g/m2) using dust simulator at three times (April, July and October 2016) and irrigation regimes (−0.3 and −0.9 MPa of soil water potential as control and water deficit treatments) on morpho-physiological characteristics of one- and three-year-old seedlings of Persian Oak (Quercus brantii Lindl) in the Research Field of Isfahan University of Technology in Iran. Results showed that dust stress significantly increased physical damage at 15 and 30 days, proline content and concentration of soluble carbohydrates under both irrigation regimes. Dust stress at 60 g/m2 level significantly decreased relative water content, leaf area, membrane stability index, plant height and consequently shoot fresh and dry weights under both irrigation regime. Under water deficit stress, corresponding reduction in shoot dry weight was 37.9%, 51.6% and 67.2% in one-year-old seedlings and 38.3%, 53.2% and 63.3% in three-year-old seedlings at 20, 40, and 60 g/m2dust treatments, respectively. In general, the results revealed that water stress exacerbated the stress caused by dusting.

Qualitative characterization of secondary metabolites of Paspalum virgatum weed under different water conditions

The presence of weeds amid pastures has caused significant damage to cattle farmers due to the difficulty in controlling these species. Paspalum virgatum stands out as an aggressive weed in Amazonian agroecosystems. Proper management of weed species is threatened by their aggressiveness, adaptation to low fertility soils and morphological, physiological and biochemical similarities with the grasses used as fodder. It is also possible that part of these characteristics of aggressiveness occur due to the ability of weeds to produce allelochemicals, resulting in damage to surrounding plants. The objective of this study was to qualitatively verify the presence of secondary metabolites in P. virgatum species under different water availability. The analyzed species were initially grown separately under three conditions of water availability: water deficit, field capacity and flooded environment. The water deficit treatment was conducted to verify weed ability to develop under conditions of extreme water shortage. This is a characteristic related to its rusticity, as found in grasses in the Amazon region. Excess water treatments were also conducted, since this is a common condition found in areas with partial flooding of a few months during the rainy season in the Amazon. After 120 days, weeds were collected and separated into roots, stems and leaves. The material was subsequently dried, ground and subjected to procedures to determine secondary metabolites. Phenolic compounds, flavonoids and alkaloids were identified in all conditions of plant development. The flavonoid detection test presented an intense yellow color. This is a strong indication of the presence of this class in stems and leaves of plants under flood and in leaves of plants under field capacity soil conditions. An intense presence of phenolic compounds was verified in stems and leaves, regardless of treatment. General alkaloids were found in great intensity in all samples. Saponins were found in leaves of P. virgatum under water stress (flooding and water deficit). All the metabolites were found in the plants, diverging between treatments and parts of the plant. It was concluded that the species presented higher steroid content in the roots when growing in places with excess of water. In conditions of full water supply, the presence of steroid was less intense in the roots, leaves and stems, result also found in roots and leaves of plants under water deficit. Alkaloids were less intensely present in the roots, regardless of the water treatment in which the plant was submitted. Results demonstrated that there are secondary metabolites responsible for some physiological ability of the weed to withstand excess or water deficit, indicating the need for further studies

DcABF3, an ABF transcription factor from carrot, alters stomatal density and reduces ABA sensitivity in transgenic Arabidopsis

Abscisic acid-responsive element (ABRE)-binding factors (ABFs) are important transcription factors involved in various physiological processes in plants. Stomata are micro channels for water and gas exchange of plants. Previous researches have demonstrated that ABFs can modulate the stomatal development in some plants. However, little is known about stomata-related functions of ABFs in carrots. In our study, DcABF3, a gene encoding for ABF transcription factor, was isolated from carrot. The open reading frame of DcABF3 was 1329 bp, encoding 442 amino acids. Expression profiles of DcABF3 indicated that DcABF3 can respond to drought, salt or ABA treatment in carrots. Overexpressing DcABF3 in Arabidopsis led to the increase of stomatal density which caused severe water loss. Expression assay indicated that overexpression of DcABF3 caused high expression of stomatal development-related transcription factor genes, SPCH, FAMA, MUTE and SCRMs. Increased antioxidant enzyme activities and higher expression levels of stress-related genes were also found in transgenic lines after water deficit treatment. Changes in expression of ABA synthesis-related genes and AtABIs indicated the potential role of DcABF3 in ABA signaling pathway. Under the treatment of exogenous ABA, DcABF3-overexpression Arabidopsis seedlings exhibited increased root length and germination rate. Our findings demonstrated that heterologous overexpression of DcABF3 positively affected stomatal development and also reduced ABA sensitivity in transgenic Arabidopsis.

Responses to Increased Salinity and Severe Drought in the Eastern Iberian Endemic Species Thalictrum maritimum (Ranunculaceae), Threatened by Climate Change

Thalictrum maritimum is an endangered, endemic species in East Spain, growing in areas of relatively low salinity in littoral salt marshes. A regression of its populations and the number of individuals has been registered in the last decade. This study aimed at establishing the causes of this reduction using a multidisciplinary approach, including climatic, ecological, physiological and biochemical analyses. The climatic data indicated that there was a direct negative correlation between increased drought, especially during autumn, and the number of individuals censused in the area of study. The susceptibility of this species to water deficit was confirmed by the analysis of growth parameters upon a water deficit treatment applied under controlled greenhouse conditions, with the plants withstanding only 23 days of complete absence of irrigation. On the other hand, increased salinity does not seem to be a risk factor for this species, which behaves as a halophyte, tolerating in controlled treatments salinities much higher than those registered in its natural habitat. The most relevant mechanisms of salt tolerance in T. maritimum appear to be based on the control of ion transport, by (i) the active transport of toxic ions to the aerial parts of the plants at high external salinity—where they are presumably stored in the leaf vacuoles to avoid their deleterious effects in the cytosol, (ii) the maintenance of K+ concentrations in belowground and aboveground organs, despite the increase of Na+ levels, and (iii) the salt-induced accumulation of Ca2+, particularly in stems and leaves. This study provides useful information for the management of the conservation plans of this rare and endangered species.

Wild Relatives of Wheat Respond Well to Water Deficit Stress: A Comparative Study of Antioxidant Enzyme Activities and Their Encoding Gene Expression

Previous studies have revealed that some wild wheat accessions respond well to water deficit treatments and have a good potential in terms of photosynthetic parameters, root system architecture, and several physiological properties. However, the biochemical responses and molecular mechanisms of antioxidant-encoding genes remain to be elucidated. Herein, we investigated the most tolerant accessions from A. crassa, Ae. tauschii, and Ae. cylindrica previously identified from a core collection in previous studies, along with a control variety of bread wheat (T. aestivum cv. Sirvan) through measuring the shoot fresh and dry biomasses; the activities of antioxidant enzymes (including ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (GPX), and peroxidase (POD)); and the relative expression of CAT, superoxide dismutase (MnSOD), and GPX and APX genes under control and water deficit conditions. Water deficit stress caused a significant decrease in the shoot biomasses but resulted in an increase in the activity of all antioxidant enzymes and relative expression of antioxidant enzyme-encoding genes. Principal component analysis showed a strong association between the shoot dry biomass and the activity of CAT, POD, and APX, as well as MnSOD gene expression. Thus, these traits can be used as biomarkers to screen the tolerant plant material in the early growth stage. Taken together, our findings exposed the fact that Ae. tauschii and Ae. crassa respond better to water deficit stress than Ae. cylindrica and a control variety. Furthermore, these accessions can be subjected to further molecular investigation.

Characterization of raffinose metabolism genes uncovers a wild Arachis galactinol synthase conferring tolerance to abiotic stresses

Raffinose family oligosaccharides (RFOs) are implicated in plant regulatory mechanisms of abiotic stresses tolerance and, despite their antinutritional proprieties in grain legumes, little information is available about the enzymes involved in RFO metabolism in Fabaceae species. In the present study, the systematic survey of legume proteins belonging to five key enzymes involved in the metabolism of RFOs (galactinol synthase, raffinose synthase, stachyose synthase, alpha-galactosidase, and beta-fructofuranosidase) identified 28 coding-genes in Arachis duranensis and 31 in A. ipaënsis. Their phylogenetic relationships, gene structures, protein domains, and chromosome distribution patterns were also determined. Based on the expression profiling of these genes under water deficit treatments, a galactinol synthase candidate gene (AdGolS3) was identified in A. duranensis. Transgenic Arabidopsis plants overexpressing AdGolS3 exhibited increased levels of raffinose and reduced stress symptoms under drought, osmotic, and salt stresses. Metabolite and expression profiling suggested that AdGolS3 overexpression was associated with fewer metabolic perturbations under drought stress, together with better protection against oxidative damage. Overall, this study enabled the identification of a promising GolS candidate gene for metabolic engineering of sugars to improve abiotic stress tolerance in crops, whilst also contributing to the understanding of RFO metabolism in legume species.

Physiological, biochemical and transcriptional responses of Passiflora edulis Sims f. edulis under progressive drought stress

Water deficit stress is responsible for at least 40 % of crop losses worldwide, positioning itself as a strong threat to food security. Purple passion fruit (Passiflora edulis Sims f. edulis) is one of the most desirable exotic fruits on the world market mainly for its organoleptic properties. Information on the response to water deficit stress for purple passion fruit is scarce and in some cases contradictory. Therefore, the objective of the present work was to evaluate the morphological, physiological, biochemical and transcriptional response of purple passion fruit during water deficit and depict its strategy. The response of purple passion fruit plants to two water deficit treatments (T1: 50 % of irrigation, T2: 0% of irrigation compared to control) was evaluated during 40 days of stress, measuring changes in physiological variables related to growth and water relations, as well as the content of metabolites related to stress and the expression of genes associated with drought stress. Results show that the plant prevents water loss, by stomata closure, modulation of growth and accumulation of proline and sugars, while promoting root growth, features associated with tolerance to water deficit. At the expression level, early transcriptional activation of PeDREB2A and PeRD21A were detected in plants under the most severe stress, while PeGOLS1 and PeAFL1 upregulation were observed in plants under milder stress. These results suggest that purple passion fruit plants display an isohydric behavior and evade water deficit stress as a response strategy, where loss of water is avoided.

Phenotypic and molecular changes in cassava (Manihot esculenta Crantz.) genotypes as a response to water-deficit stress

Three local Indonesian cassava (Manihot esculenta Crantz) genotypes, Adira 4, Roti, and Ubi Kuning retained their growth under a water deficit environment. To understand the physiological and molecular responses of cassava plants under such stress, we observed leaf stomata characteristics, i.e. stomata dimension (width and length) and density, and molecular expression of aquaporin (AQP) gene, respectively. The observation was performed on all genotypes on day 26 and 45 after water-deficit treatment. Quantification of gene expression was performed by comparing the threshold cycle (Ct) values of AQP with Ct values β-tubulin for each genotype. Results showed that water deficit treatment significantly affected both stomata density, length and width in all genotypes. On day 26 after treatment, the density of stomata in Roti and Ubi Kuning increased two times higher than the stomata density in plants under well-watered supply. Stomata length of Roti and Adira 4 under water stress was 0.4 times shorter than those under normal water supply. Relative expression of AQP, encoding AQP PIP2 proteins, in the Roti genotype showed that the gene transcripts have no significant elevation after experiencing water stress. In Adira 4, the expressions of AQP increased two-times at day 26 under water-deficit treatment compared with AQP expressions in well-watered treatment and continued to elevate up to three times higher at day 45 than those of expressed in Adira 4 plants under well-water treatment. In addition to stomata phenotypic changes, Ubi Kuning may regulate its water channel proteins AQP PIP2 to control turgor pressure in the beginning phase of water stress conditions. These results showed that three cassava genotypes responded differently under water deficit stress and these may serve as basic knowledge for further analysis.

Responses of Amygdalus pedunculata Pall. in the sandy and loamy soils to water stress

Amygdalus pedunculata Pall. is a major species that is widely planted in afforested soils with different textures in the transitional zone between Mu Us Desert and Loess Plateau, China. However, the responses of A. pedunculata to increasing intensity of water stress in different textural soils are not clear. Here, we conducted a soil column experiment to evaluate the effects of different textures (sandy and loamy) on water consumption, water use efficiency (WUE), biomass accumulation and ecological adaptability of A. pedunculata under increasing water stress, i.e., 90% (±5%) FC (field capacity), 75% (±5%) FC, 60% (±5%) FC, 45% (±5%) FC and 30% (±5%) FC in 2018. A. pedunculata grown in the sandy soil with the lowest (30% FC) and highest (90% FC) water contents had respectively 21.3%–37.0% and 4.4%–20.4% less transpiration than those with other water treatments (45%–75% FC). In contrast, A. pedunculata transpiration in the loamy soil decreased with decreasing water content. The magnitude of decrease in transpiration increased with increasing level of water deficit (45% and 30% FC). Mean daily and cumulative transpirations of the plant were significantly lower in the sandy soil than in the loamy soil under good water condition (90% FC), but the reverse was noted under water deficit treatments (45% and 30% FC). Plant height, stem diameter and total biomass initially increased with decreasing water content from 90% to 75% FC and then declined under severe water deficit conditions (45% and 30% FC) in the sandy soil. However, these plant parameters decreased with decreasing water content in the loamy soil. WUE in the sandy soil was 7.8%–12.3% higher than that in the loamy soil, which initially increased with decreasing water content from 90% to 75% FC and then declined under water deficit conditions (45% and 30% FC). The study showed that plant transpiration, biomass production and WUE responded differentially to increasing intensity of water stress in the sandy and loamy soils. The contrasting responses of A. pedunculata to water stress in different textural soils can guide future revegetation programs in the northern region of Chinese Loess Plateau by considering plant adaptability to varying soil and water conditions.

Altered Carbohydrate Allocation Due to Soil Water Deficit Affects Summertime Flowering in Meiwa Kumquat Trees

The summertime flowers of the ever-flowering Meiwa kumquat (Fortunella crassifolia Swingle) are the most useful for fruit production in Japan; however, summertime flowers bloom in three or four successive waves at approximately 10 day intervals, resulting in fruit of different maturity occurring on the same tree. Soil water deficit (SWD) treatment has been shown to reduce the flowering frequency and improve harvest efficiency; therefore, in this study, the effects of SWD treatment on the accumulation of soluble sugars in each tree organ above-ground were examined and it was discussed how SWD affects the whole-tree water relations and sugar accumulation by osmoregulation. The number of first-flush summertime flowers was higher in SWD-treated trees than non-treated control (CONT) trees (177.0 and 58.0 flowers, respectively), whereas the second- and third-flush flowers were only observed in CONT trees. The soluble sugar content was higher in SWD treated trees than CONT trees for all organs and tended to be higher in current-year organs than previous-year organs; however, when the sugar content of the current-year spring stems exceeded approximately 100 mg g−1 dry weight, the current-year leaf water potential decreased sharply and the rate of increase in the number of first-flush flowers also tended to decrease. SWD treatment significantly increased the total sugar content of the xylem tissue of the scaffold branches to three times the value in CONT trees (p = 0.001); however, the increase was observed even in sucrose, a disaccharide, similar to that in monosaccharides such as glucose and fructose. These results suggest that the increased sugar levels in the xylem tissue resulted from not only osmoregulation but also other factors as well; therefore, these sugars may affect whole-tree water relations as well as the development of flower buds.

A transcriptomic analysis reveals the adaptability of the growth and physiology of immature tassel to long-term soil water deficit in Zea mays L

Drought is a key threat to maize growth and yield. Understanding the mechanism of immature tassel (IT) response to long term drought is of paramount importance. Here, the maize inbred line PH6WC was tested under well-watered (CK) and two water deficit treatments (WD1 and WD2). The final IT length in the WD1 and WD2 treatments decreased by nearly 6.2% and 21.2% compared to the CK, respectively, and the average accumulation rate IT dry matter was 1.5-fold and 1.8-fold slower, respectively. Furthermore, RNA sequencing analysis was conducted on the IT sampled at 30 days after the WD treatments. In total, the cellular component in gene ontology (GO) analysis suggested that the differentially expressed genes were significantly enriched in three common terms (apoplast, plant-type cell wall, and anchored component of membrane) among the CK vs WD1, CK vs WD2, and WD1 vs WD2 comparisons. Next, a co-expression network analysis identified 44 modules that contained global expression genes. Finally, by combining the GO analysis with modules, nine genes involved in carbohydrate metabolism and the antioxidant system were screened out, and the six corresponding physiological parameters were all significantly increased under the WD treatments. These results showed that, although the IT length and dry matter decreased, the IT enhanced the adaptation to drought by regulating their own genetic and physiological changes.

Light and irrigation effects on chlorophyll fluorescence depend on seedling provenance in Magnolia pugana endemic of Mexico

In riparian forests, light and water are two important factors for plant acclimation to different environments. We evaluated the effect of different light and irrigation regimes on the effective quantum yield of photosystem II (фPSII), the maximum quantum efficiency of photosystem II (Fv/Fm), and the electron transfer rate (ETR) of Magnolia pugana seedlings that come from wild and cultivated plants, under greenhouse conditions. Rapid light curves (RLCs) were performed to obtain the maximum apparent electron transport rate and the saturating photosynthetic photon flux density for PSII. Effective quantum yield of PSII was higher at afternoon for cultivated and wild provenances, but in the latter decreased in longest water deficit treatment at noon. The combined water deficit and high light stress in the morning decreased фPSII; however, фPSII recovered in the afternoon, suggesting dynamic photoinhibition. Furthermore, фPSII of wild and cultivated seedlings in all irrigation levels showed dynamic photoinhibition as well. The electron transfer rate was higher for seedlings grown under high light than in shade. ETR results suggest that wild seedlings showed greater tolerance to water deficit conditions than cultivated ones. Rapid light curves indicate that photosystem II of M. pugana seedlings grown in high light conditions requires higher light intensities to reach saturation. In conclusion, wild and cultivated populations of Magnolia pugana seedlings showed photochemical adjustments to tolerate water deficit and light stress. This study offers new insights into the physiology of endangered plants and valuable guidance for conservation efforts designed at protecting in situ and ex situ wild Magnolia species.

Identification of genetic loci associated with forage quality in response to water deficit in autotetraploid alfalfa (Medicago sativa L.)

BackgroundAlfalfa has been cultivated in many regions around the world as an important forage crop due to its nutritive value to livestock and ability to adapt to various environments. However, the genetic basis by which plasticity of quality-relevant traits influence alfalfa adaption to different water conditions remain largely unknown.ResultsIn the present study, 198 accessions of alfalfa of the core collection for drought tolerance were evaluated for 26 forage quality traits in a field trial under an imposed deficit irrigation gradient. Regression analysis between quality traits and water stress revealed that values of fiber-related traits were negatively correlated with values of energy-related traits as water deficit increased. More than one hundred significant markers associated with forage quality under different water treatments were identified using genome-wide association studies with genotyping by sequencing. Among them, 131 markers associated with multiple traits in all the water deficit treatments. Most of the associated markers were dependent to the levels of water deficit, suggesting genetic controls for forage quality traits were dependent to the stress treatment. Twenty-four loci associated with forage quality were annotated to functional genes that may play roles in cell development or in response to water stress.ConclusionsThis study addressed the genetic base of phenotypic variation of forage quality traits under water deficit. The SNP markers identified in this study will be useful in marker-assisted selection for the genetic improvement of alfalfa with enhanced drought tolerance while maintaining forage quality.

Early events leading to water deficit responses in the liverwort Marchantia polymorpha

To understand the genetic and evolutionary basis of the responses to water deficit in plants, we turned to the basal liverwort Marchantia polymorpha, representing one of the most ancient plant lineages that first colonized land. Thalli exposed to water deficit showed a decreased growth rate and morphological modifications. In addition, water deficit led to relocation of cell organelles, mostly due to changes in volume of the central vacuole, which correlated with adjustments of osmotic potential. Abscisic acid (ABA) is a phytohormone that mediate responses to environmental stress in vascular plants. Consistently, we observed an increase in endogenous ABA levels upon water deficit in Marchantia, which correlated with the increased expression of genes encoding for LATE-EMBRYOGENESIS-ABUNDANT proteins, which are thought to protect cells from damage caused by water deficit. Transcriptome-level changes upon ABA and water deficit treatments revealed that several genes modify their expression under these conditions. Consistent with our cellular level observations, differentially expressed GO categories related to ion binding and transport may explain the changes in vacuole volume. Induction of stress-related genes, including several LEA genes, also points towards a possible conservation of ABA-dependent signaling pathways in M. polymorpha and defines a framework to understand the underlying molecular events.

Relationship between stable carbon isotope discrimination and water use efficiency under deficit drip irrigation of kiwifruit in the humid areas of South China

In order to explore the application value of the stable carbon isotope discrimination method in improving water use efficiency (WUE) and productivity of kiwifruit under deficit drip irrigation, five water deficit levels (55 %, 65 %, 75 %, 85 % and 100 % of full irrigation) with thirteen treatments were established at three growth stages in field-grown kiwifruit. The leaf stable carbon isotope discrimination (ΔL) at different growth stages and fruit stable carbon isotope discrimination (ΔF) at fruit maturation stage of kiwifruit were determined; the changes of WUE at leaf and yield levels were analyzed, and the indicating effect of carbon isotope discrimination (Δ13C) on the WUE of kiwifruit was also verified. The results showed that moderate water deficit improved the WUEi (photosynthesis rate/transpiration rate, Pn/Tr) and WUEn (photosynthesis rate/stomatal conductance, Pn/gs) of kiwifruit at each growth stage. Compared with full irrigation (CK), the yield (Y) and WUEy (yield/crop evapotranspiration, Y/ET) of low water deficit treatment (LD) at fruit maturation stage increased by 14.75 % and 23.74 %, respectively. There were significant relationships between ΔL and ΔF versus WUE, Ci/Ca (the specific value of intercellular CO2 concentration and ambient atmosphere CO2 concentration), CE (carboxylation rate), ET (crop evapotranspiration) and Y under deficit drip irrigation, respectively. ΔL was negatively correlated with WUEn (coefficient of determination, R2=0.4844, P<0.01) over the whole growth period, whereas ΔF was positively correlated with Y (R2=0.2805, P<0.05) and ET (R2=0.9267, P<0.01), respectively. Overall, this study verifies that ΔL can be used as a useful evaluation index of WUEn, and ΔF is an important indicator of quantifying Y and ET of kiwifruit under deficit drip irrigation.