Water deficit is one of the most important abiotic stresses constraining crop production in rapeseed. Understanding the mechanisms of adaptation to this stress is essential for the development and production of drought-tolerant genotypes. For this reason, this research study aims to investigate the importance of genetic diversity in identifying genotypes with a high degree of drought tolerance through assessing effectiveness of inter simple sequence repeat (ISSR) markers on 14 genotypes of rapeseed in a factorial design. Morphological and physiological characteristics were studied after the early stages of growth; in order to evaluate the genetic diversity among genotypes, 18 different ISSR markers were used. A total of 106 clear and scalable loci were amplified, of which 60 bands (56.6%) were polymorphic. The highest polymorphism information content belonged to marker number 9 with the amount of 0.365 (85.7%). Gene variation ranged from 0.081 to 0.365 and the rapeseed genotypes were divided into three groups by cluster analysis (unweighted pair group method with arithmetic mean method). The analysis of molecular variance showed that 70% of the total variation was observed within populations and 30% of this variation occurred among populations. In addition, t-test was used for comparing oil content percentage among different genotypes in control and stress levels. Adriana had the highest amount of seed oil with 36.47%, whereas Karaj 2 had the lowest amount with 27.28 and Cooper had the highest decrease in oil content percentage under stress conditions. Overall, the genotypes Likord, Hyola 401 and Sarigol 32 were identified as the most drought-tolerant.

This study was designed to understand how drought stress impact on the physiological and molecular status of genetically diverse Lolium perenne L. (perennial ryegrass) populations. The sensitivities of the 36 perennial ryegrass populations were checked against PEG-6000-simulated drought stress by analysing physiological status. Afterward, drought-related gene expressions were evaluated under normal and stressed conditions. The drought stress significantly up-regulated the drought-related genes in P6, P10, P15 and P30, while no difference was observed in drought-sensitive ones. The results collectively showed that four populations (P6, P10, P15, P30) are tolerant to drought stress and activate drought-related genes. Genetic similarities of the populations were also monitored using microsatellite (SSR) markers. The ten SSR primers detected 38 alleles. Surprisingly, the drought-tolerant populations were classified into different groups by principal component (PCA) and cluster analysis, showing that they are genetically different. Moreover, four unique alleles were identified by two SSR primers (P-07, and P-08) in P6, P10 and P15. In addition, the drought-tolerant populations (P6, P10, P15, P30) can be used to develop new perennial ryegrass cultivars for areas having drought problems.

Date palm is a relatively salt- and drought-tolerant plant and more recent efforts have been focused on recognizing genes and pathways that confer stress tolerance in this species. The cDNA start codon targeted marker (cDNA–SCoT) technique is a novel, simple, fast and effective method for differential gene expression investigation. In the present study, this technique was exploited to identify differentially expressed genes during several stress treatments in date palm. A total of 12 SCoT primers combined with oligo-dT primers amplified differentially expressed fragments among the stress treatments and control samples. Differentially expressed fragments were highly homologous to known genes or encoded unclassified proteins with unknown functions. The expression patterns of the genes that had direct or indirect relationships with salinity and drought stress response were identified and their possible roles were discussed. This study suggests that the cDNA-SCoT differential display method is a useful tool to serve as an initial step for characterizing transcriptional changes induced by abiotic stresses and provide gene information for further study and application in genetic improvement and breeding in date palm.

We explored the seed-associated bacterial endophytic microbiome in seeds of the endemic holoparasitic species Cistanche armena from a saline and arid habitat in Armenia. A combination of culture-dependent and molecular techniques was employed for identifying the seed endomicrobiome (culturable and unculturable). From surface-sterilized seeds, 10 phyla, comprising 256 endophytic bacterial genera, were identified. Of the culturable strains, we also investigated the plant growth-promoting (PGP) traits. Most of the isolates were spore forming, halotolerant and alkaliphile Bacillus spp., indicating that the endophytic bacteria of C. armena seeds own traits related to the natural habitat of their host plant. Our results confirm that Bacillus species are common and dominated endophytes from plants growing on saline and arid soils. Pantoea spp. and Stenotrophomonas spp. are more favourable PGP endophytes in seeds of C. armena. The PGP traits of these bacteria, such as production of indole, a precursor of auxin, ACC-deaminase and organic acids have the potential to improve the tolerance of their host plants against the abiotic stresses present in their natural habitat. To the best of our knowledge, this is the first report concerning bacterial seed endophytes of the C. armena.

Low-quality water and soil salinization are increasingly becoming limiting factors for food production, including olive – a major fruit crop in several parts of the world. Identifying putative salinity-stress tolerance in olive would be helpful in the future development of new tolerant varieties. In this study, novel salinity-responsive biomarkers (SRBs) were characterized in the species, namely, monooxygenase 1 (OeMO1), cation calcium exchanger 1 (OeCCX1), salt tolerance protein (OeSTO), proteolipid membrane potential modulator (OePMP3), universal stress protein (OeUSP2), adaptor protein complex 4 medium mu4 subunit (OeAP-4), WRKY1 transcription factor (OeWRKY1) and potassium transporter 2 (OeKT2). Unique structural features were highlighted for encoded proteins as compared with other plant homologues. The expression of olive SRBs was investigated in leaves of young plantlets of two cultivars, ‘Nabali’ (moderately tolerant) and ‘Picual’ (tolerant). At 60 mM NaCl stress level, OeMO1, OeSTO, OePMP3, OeUSP2, OeAP-4 and OeWRKY1 were up-regulated in ‘Nabali’ as compared with ‘Picual’. On the other hand, OeCCX1 and OeKT2 were up-regulated at three stress levels (30, 60 and 90 mM NaCl) in ‘Picual’ as compared to ‘Nabali’. Salinity tolerance in olive presumably engages multiple sets of responsive genes triggered by different stress levels.

Seed priming with water (hydropriming or HP) has been shown to be beneficial for seed germination and plant growth. However, there is little information on the effects of seed priming with amino acids and casein hydrolysate (CH) compared with HP, particularly in relation to early post-germinative seedling growth under salinity stress. In this study, Italian ryegrass seeds (Lolium multiflorum L.) were primed with 1 mM of each of the 20 protein amino acids and CH (200 mg l−1) before they were germinated in 0, 60 and 90 mM NaCl in Petri dishes for 4 d in darkness. Germination percentage (GP), radicle length (RL) and peroxidase (POD) activity in the root of 4-d-old Italian ryegrass seedlings were investigated. Generally, when the seeds were germinated in 0, 60 and 90 mM NaCl, there was no significant difference in GP of seeds among various priming treatments, except that a higher GP was observed in seeds of HP treatment compared with the non-primed seeds when incubated in 60 mM NaCl. When incubated in 60 and 90 mM NaCl, seedlings from seeds primed with L-methionine or CH exhibited greater RL (greater protection against salinity stress) and higher root POD activity than those from non-primed and hydro-primed seeds. Under salinity stress, there were higher levels of malondialdehyde (MDA) in the root of 4-d-old Italian ryegrass seedlings, a marker of oxidative stress, but seed priming with CH was effective in reducing the salinity-triggered increase in MDA content. These results suggest that priming with L-methionine or CH would be better than HP for the protection of seedling root growth under salinity stress and might be associated with enhanced antioxidative defence against salinity-induced oxidative stress.

Cytochrome P450 monooxygenases (P450s) play significant roles in protecting organisms from abiotic stress damage. Here, we report the sequence and characterization of a P450s gene (AccCYP4AV1), isolated from Apis cerana cerana Fabricius. The open reading frame of AccCYP4AV1 is 1506 base pairs long and encodes a predicted protein of 501 amino acids and 57.84 kDa, with an isoelectric point of 8.67. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis indicated that AccCYP4AV1 is more highly expressed in the midgut than in other tissues. In addition, the highest expression occurs in newly emerged adult workers, followed by the first instar of the larval stage. In addition, the expression of the AccCYP4AV1 was upregulated by low temperature (4 °C), ultraviolet radiation, hydrogen peroxide, paraquat, and dichlorvos treatments. In contrast, AccCYP4AV1 transcription was downregulated by other abiotic stress conditions: exposure to increased temperature (44 °C), deltamethrin, cadmium chloride, and mercury (II) chloride. Moreover, when AccCYP4AV1 was knocked-down by RNA interference, the results suggested that multiple antioxidant genes (AccsHSP22.6, AccSOD2, AccTpx1, and AccTpx4) were downregulated and antioxidant genes AccGSTO1 and AccTrx1 were upregulated. The activity levels of peroxidase and catalase were upregulated in the AccCYP4AV1-knocked-down samples, compared with those in the control groups. These findings suggest that the AccCYP4AV1 protein might be involved in the defense against abiotic stress damage.

A major drawback of avocado (Persea americana Mill.) is susceptibility to frosts, which reduces yields and limits its geographic distribution and market growth. Whereas the frost-susceptible cultivar ‘Hass’ leads the global avocado market, cv. ‘Ettinger’, although commercially less important, is considered frost-tolerant. The mechanism behind the greater frost tolerance of ‘Ettinger’ has not yet been elucidated; therefore, the aim of the current study was to evaluate the differences between the frost responses of the two cultivars. The results showed that detached ‘Ettinger’ branches had greater tolerance than ‘Hass’ to controlled frost stress. Tissue browning caused by methyl viologen oxidative cell damage, superoxide accumulation in leaf discs following wounding and browning of cut surfaces in branches were much lower in ‘Ettinger’ than in ‘Hass’, suggesting greater antioxidant activity (AA) in the former. In leaf extracts, AA was significantly higher in ‘Ettinger’ than in ‘Hass’, but osmolarity was similar in the two cultivars. Total phenolics content was significantly higher in ‘Ettinger’ but addition of a protein mask did not significantly reduce AA in either cultivar. Interestingly, following the freezing treatment, AA increased in ‘Ettinger’ and remained almost unchanged in ‘Hass’, while osmolarity was unaffected in either cultivar. These results suggest that the greater frost-tolerance of ‘Ettinger’ than ‘Hass’ is due largely to its greater AA, which springs mainly from a non-enzymatic source, i.e. accumulation of phenolic compounds. Based on the current study, future applications may be developed to minimize frost damage in avocado orchards.

Mosses have adapted to the Antarctic environment and are an ideal medium for studying plant resistance to abiotic stress. Chalcone synthase is the first committed enzyme in the flavonoid metabolic pathway, which plays an indispensable role in plant resistance to adversity. In this study, six genes (Pn021, PnCHS088, Pn270, PnCHS444, PnCHS768 and Pn847) were identified in the Antarctic moss Pohlia nutans Lindberg transcriptome by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). Sequence alignment and three-dimensional structure analysis revealed the conserved amino acid residues of the enzymes of the chalcone synthase family, including three catalytic residues (Cys164, His303 and Asn336) and two substrate recognition residues (Phe215 and Phe265). Phylogenetic analysis indicated that PnCHS088, PnCHS444 and PnCHS768 might be chalcone synthase but that Pn021 is more like stilbenecarboxylate synthase. These genes were located at the transition between fungi and advanced plants in the phylogenetic tree. In addition, real-time PCR analysis revealed that the expression profiles of the six P. nutans genes were influenced by diverse abiotic stresses as well as by abscisic acid and methyl jasmonate. The results presented here contribute to the study of the CHS gene family in polar mosses and further reveal the mechanisms underlying the adaptation of mosses to extreme environments.

Here we review the potential of ILB 938 (IG 12132 – doi: 10.18730/60FD2), a unique faba bean accession originating from the Andean region of Colombia and Ecuador, maintained at ICARDA – International Center for Agricultural Research in the Dry Areas, with resistance to multiple biotic and abiotic stresses and carrying some useful morphological markers. It has been used as a donor of leaf-related drought adaptation traits and chocolate spot (Botrytis fabae) resistance genes in faba bean breeding programmes worldwide. From generated populations of recombinant inbred lines, quantitative traits loci associated with these useful traits have been mapped. Other markers, such as a lack of stipule-spot pigmentation and clinging pod wall, show the presence of unusual changes in biochemical pathways that may have economic value in the future.

Drought is the major abiotic constraint to the rice production in the rain-fed areas across Asia and sub-Saharan Africa. Wild species of Oryza offer a wide spectrum of adaptive traits and can serve as potential donors of biotic and abiotic stress tolerance. At the Punjab Agricultural University, we are maintaining an active collection of 1630 accessions of wild species germplasm (AA, CC, BBCC and CCDD) of rice. These accessions were screened to assess genetic variation for drought tolerance under field conditions. Severe water stress was imposed at the late vegetative stage by withholding water initially for 25 d and then extended further to 35 d during kharif season in the years 2013–14 and 2015–16. The tolerance score for drought stress was based on the extent of leaf rolling and leaf drying. Based on the 2 years’ data, seven accessions from Oryza rufipogon, four from Oryza longistaminata and one each from Oryza officinalis and Oryza latifolia were found tolerant to drought stress. These selected accessions were further phenotype for root morphology. The average root length among the selected accessions ranges between 36 and 80 cm and the number of primary roots vary from 30 to 87 cm. The O. rufipogon accession IRGC 106433, O. longistaminata accession IRGC 92656A, O. officinalis accession IRGC 101152 and O. latifolia accession IRGC 80769 showed approximately 2–2.5 times longer root length and number than the indica rice elite cultivar PR121. The results indicated potentiality of selected wild species germplasm for conferring drought tolerance to the elite cultivars.

Weeds represent a major cause of agricultural losses worldwide. Most weeds share a common set of life history characteristics that predispose them to weediness, two of which are self-compatibility, which allows for ease of colonization through reproductive assurance, and high trait plasticity, which allows for tolerance of a wide variety of environments and abiotic conditions. However, self-fertilization typically comes at the cost of inbreeding depression. This study investigates the role of inbreeding depression and trait plasticity under abiotic stress in the tall morningglory, a widespread self-compatible agricultural weed in the southeastern United States. Results show very little inbreeding depression in this species, likely due to purging of deleterious alleles through repeated founder events in agricultural landscapes. In contrast, abiotic stress induced substantial plasticity in ecophysiological traits, reproductive traits, and biomass allocation. In terms of performance, drought sharply impacted reproduction but not vegetative growth, and nitrogen limitation sharply impacted both. These findings are applicable to the control of weedy morningglory and underscore the usefulness of evolutionary ecology to weed management.

Common ragweed is a troublesome allergenic invader and noxious weed of several crops. Despite extensive research to understand the factors affecting its invasion, the role of environmental stresses and soil types on survival and growth is poorly understood. The objective of this study was to determine the effects of drought, salinity, and soil types on survival, growth, and nutrient uptake of ragweed in greenhouse experiments to predict its invasiveness in Turkey. Three separate experiments, with five drought intensities (100, 75, 50, 25, and 12.5% of field capacity [FC]), four levels of salinity (0, 3, 6, and 12 dS m−1), and five soil types varying in sand, silt, and clay content were performed. Severe drought and salinity levels reduced seedling survival, while soil type had no effect. Increasing drought and salinity negatively affected growth and nutrient uptake; the poorest growth was observed under severe drought intensity. Ragweed exhibited intensive tolerance to drought, even severe levels, while it tolerated salinity up to 6 dS m−1 for seedling survival. Growth was negatively affected above 3 dS m−1. The highest and lowest nutrient accumulations were recorded under moderate and extreme drought intensities, respectively. Similarly, the highest Na accumulation was observed under extreme saline conditions, whereas the highest P uptake and K/Na ratio were achieved under nonsaline conditions (0 dS m−1). Variation of soil texture had no effect on growth and nutrient uptake. The highest Ca, Mg, and Na accumulations were recorded on clay soil, while higher P accrued on sandy-loam soil. Increased tolerance of ragweed to severe drought and moderate salinity and its nonselective nature for soil type indicate that semiarid and partially arid regions in Turkey have plenty of vacant niches for ragweed invasion.

We report the determination of abscisic acid (ABA) and its metabolites, phaseic acid (PA), dihydrophaseic acid (DPA) and ABA glucose ester (ABA-GE), in non-dormant dry and imbibed seeds of tomato (Solanum lycopersicum Mill.) cv. Moneymaker (wild type), and its tss1, tss2 and tos1 mutants. High ABA in dry seeds may originate from ABA accumulation in the sheath tissue, which was in contact with an ABA-containing medium, the endocarpus. The highest germination percentages at 72 h, observed in tss1 and tss2, coincided with minimal ABA content. Wild-type and mutant seeds showed different ABA and catabolic patterns, and these were correlated with their sensitivity to abiotic stress. Whereas dry seeds showed a high basal ABA, imbibed seeds showed higher ABA metabolite content, particularly DPA. The dramatic decrease of ABA following seed imbibition suggests an activation of ABA catabolism during the early stages of the germination process. The observed variation of ABA metabolites among dry and imbibed seeds of Solanum lycopersicum cv. Moneymaker and its tss1, tss2 and tos1 mutants shows that ABA metabolism is differentially regulated in these genotypes.

Summary 221

I. Introduction 221

1. The role of sucrose in plants 221

2. C4photosynthesis 222

II. Pathway of sucrose synthesis in C4plants 223

III. Control of sucrose synthesis in C4plants 225

1. The diurnal cycle in C3plants 225

2. The diurnal cycle in C4plants 227

3. Abiotic stress and sucrose synthesis 230

4. Integration of sucrose synthesis with other metabolic pathways 232

IV. Future prospects 233

Acknowledgements 234

References 234

Sucrose has a central role in the metabolism of all higher plants. Here we discuss the location of sucrose synthesis in the leaves of C4 plants, the control of flux through the pathway and its response to environmental conditions, and finally some of the prospects for the genetic manipulation of sucrose metabolism in C4 plants. Much of our knowledge about sucrose synthesis in plants comes from C3 species; it is evident, from those studies of C4 species that are available, that there are many similarities between sucrose synthesis in C3 and C4 plants. However, some of the basic regulatory mechanisms common to both C3 and C4 plants seem to have been adapted for the specialized photosynthetic metabolism of C4 plants. There are also some other important differences: for example, some C4 species possess photosynthetic cells with little or no capacity for sucrose synthesis. For these reasons it is not always appropriate to extrapolate directly from C3 to C4 plants. Even where data are available from one C4 species, usually maize, it should not be assumed that all C4 plants are necessarily the same in every respect. Although C4 plants constitute a small fraction of the plant kingdom as a whole, they include a disproportionate number of agriculturally important species. C4 plants also have some advantages over C3 plants for studies of the regulation of cell-specific gene expression and the control of metabolism. For these reasons we suggest that they are worthy of more attention by researchers.

This paper reviews the results of several years' study by a multidisciplinary team comprising geneticists, physiologists, ecologists and statisticians of abiotic stress tolerance in barley. The strategy involves genetic fingerprinting of wild barley lines (Hordeum spontaneum C. Koch) from a range of habitats and testing these for responses to abiotic stresses under controlled conditions. Multiple regression analysis is used to identify genetic markers associated with experimentally determined stress responses. These data are related to site-of-origin ecogeographic data and used to identify areas of useful wild variation. Markers associated with traits of interest can be mapped in genetic mapping populations, revealing areas of the barley genome carrying genes controlling stress responses. This paper highlights our work on associations of amplied fragment length polymorphisms with salt tolerance and describes some initial results of the use of SSRs in studying drought tolerance in barley.