Plant metabolic response to stress in an arid ecosystem is mediated by the presence of neighbors.

Plant neighbors in arid environments can ameliorate abiotic stress by reducing insolation, but they also attract herbivores and pathogens, especially when neighbors are close relatives that share similar antagonists. Plants' metabolic profiles provide a chemical fingerprint of the physiological processes behind plant responses to different environmental stresses. For example, abscisic acid and proline, mainly involved in stomatal closure and osmotic adjustment, can induce plant responses to abiotic stress, while jasmonic acid and salicylic acid primarily regulate plant defense to herbivory or pathogens. Neighbor plants can generate contrasting ecological contexts, modulating plant responses to abiotic and biotic stresses. We hypothesize that plant metabolic profile is modulated by its neighbors in a vegetation patch, expecting a higher investment in metabolites related to biotic-stress tolerance (i.e., herbivory or pathogens) when growing associated with other plants, especially to phylogenetically close relatives, compared to plants growing alone. We show that plants from five species growing with neighbors invest more in biotic-stress tolerance while their conspecifics, growing alone, invest more in abiotic-stress tolerance. This tendency in plants' metabolic profiles was not affected by the phylogenetic diversity of their neighborhood. Linking physiological snapshots with community processes can contribute to elucidating metabolic profiles derived from plant-plant interactions.

Abscisic acid promotes plant acclimation to the combination of salinity and high light stress.

Plants encounter combinations of different abiotic stresses such as salinity (S) and high light (HL). These environmental conditions have a detrimental effect on plant growth and development, posing a threat to agricultural production. Metabolic changes play a crucial role in enabling plants to adapt to fluctuations in their environment. Furthermore, hormones such as abscisic acid (ABA), jasmonic acid (JA) and salicylic acid (SA) have been previously identified as regulators of plant responses to different abiotic stresses. Here we studied the response of Arabidopsis wild type (Col and Ler) plants and mutants impaired in hormone biosynthesis (aba2-11 and aba1-1 in ABA, aos in JA and sid2 in SA) to the combination of S and HL (S + HL). Our findings showed that aba2-11 plants displayed reduced growth, impaired photosystem II (PSII) function, increased leaf damage, and decreased survival compared to Col when subjected to stress combination. However, aos and sid2 mutants did not display significant changes in response to S + HL compared to Col, indicating a key role for ABA in promoting plant tolerance to S + HL and suggesting a marginal role for JA and SA in this process. In addition, we revealed differences in the metabolic response of plants to S + HL compared to S or HL. The analysis of altered metabolic pathways under S + HL suggested that the accumulation of flavonoids is ABA-dependent, whereas the accumulation of branched-chain amino acids (BCAAs) and proline is ABA-independent. Therefore, our study uncovered a key function for ABA in regulating the accumulation of different flavonoids in plants during S + HL.

Morphological, physiological, and molecular scion traits are determinant for salt-stress tolerance of grafted citrus plants.

Introduction: Citrus productivity has been decreasing in the last decade in the Mediterranean basin as a consequence of climate change and the high levels of salinity found in the aquifers. Citrus varieties are cultivated grafted onto a rootstock, which has been reported as responsible for plant tolerance to adverse situations. However, other important factors for stress tolerance relying in the scion have been less studied. The aim of this study was to evaluate the effect of the grafted scion on citrus tolerance to salt stress. Methods: Four different citrus rootstock/scion combinations were subjected to salt stress for 30 days, using Carrizo citrange (CC) or Citrus macrophylla (CM) as rootstocks, and Navelina orange (NA) or Oronules mandarin (OR) as scions. CM-OR was the most tolerant combination, whereas CC-NA was the most sensitive one. Results and discussion: Our results support the idea that the rootstock plays an important role in salt stress tolerance, but scion is also crucial. Thus, photosynthesis and transpiration, processes regulated by abscisic acid and jasmonic acid, are determinant of plant performance. These photosynthetic parameters were not affected in plants of the salt-tolerant combination CM-OR, probably due to the lower intoxication with Cl- ions, allowing a better performance of the photosynthetic machinery under stress conditions. The different stomatal density of the two citrus scions used in this work (higher in the sensitive NA in comparison to the tolerant OR) also contributes to the different tolerance of the grafted plants to this adverse condition. Additionally, CsDTX35.1 and CsDTX35.2, genes codifying for Cl- tonoplast transporters, were exclusively overexpressed in plants of the salt-tolerant combination CM-OR, suggesting that these transporters involved in Cl- compartmentalization could be crucial for salt stress tolerance. It is concluded that to improve citrus tolerance to high salinity, it is important that scions have a versatile photosynthetic system, an adequate stomatal density, and a proper modulation of genes coding for Cl- transporters in the tonoplast.

Appraisal of Abelmoschus esculentus L. Response to Aluminum and Barium Stress.

Trace metal element (TME) pollution is a major threat to plants, animals and humans. Agricultural products contaminated with metals may pose health risks for people; therefore, international standards have been established by the FAO/WHO to ensure food safety as well as the possibility of crop production in contaminated soils. This study aimed to assess the accumulating potential of aluminum and barium in the roots, shoots and fruits of Abelmoschus esculentus L., and their effect on growth and mineral nutrition. The content of proline and some secondary metabolites was also evaluated. After treating okra plants with aluminum/barium (0, 100, 200, 400 and 600 µM) for 45 days, the results showed that Al stimulated the dry biomass production, whereas Ba negatively affected the growth and the fructification yield. The okra plants retained both elements and exhibited a preferential accumulation in the roots following the sequence: roots > shoots > fruits, which is interesting for phytostabilization purposes. Al or Ba exposure induced a decline in mineral uptake (K, Ca, Mg, Zn and Fe), especially in roots and shoots. In order to cope with the stress conditions, the okra plants enhanced their proline and total phenol amounts, offering better adaptability to stress.

Assessing of growth, antioxidant enzymes, and phytohormone regulation in Cucurbita pepo under cadmium stress.

One of the major problems worldwide is soil pollution by trace metal elements, which limits plant productivity and threatens human health. In this work, we have studied the effect of different concentrations of cadmium on Cucurbita pepo plants, evaluating different physiological and biochemical parameters: hormone signaling, metabolite concentration (malondialdehyde and hydrogen peroxide) and, in addition, the antioxidant enzyme activities of catalase and superoxide dismutase were evaluated. The production of biomass decreased under the Cd-stress. The results showed that C. pepo accumulates higher amounts of Cd2+ in roots than in shoots and fruits. Cd2+ differently affected the content of endogenous phytohormones. Furthermore, data suggest an essential involvement of roots in the regulation of tolerance to trace elements. As a result, indole acetic acid content increased in roots of treated plants, indicating that this phytohormone can stimulate root promotion and growth under Cd-stress. Similarly, salicylic acid content in roots and shoots increased in response to Cd2+, as well as abscisic acid levels in roots and fruits. In roots, the rambling accumulation pattern observed for jasmonic acid and salicylic acid suggests the lack of a specific regulation role against trace element toxicity. The activity of catalase and superoxide dismutase decreased, disrupted by the metal stress. However, the proline, malondialdehyde and hydrogen peroxide content significantly increased in Cd2+in all the analyzed tissues of the stressed plants. All these data suggest that C. pepo plants are equipped with an effective antioxidant mechanism against oxidative stress induced by cadmium up to a concentration of 500 µM.

Barium effect on germination, plant growth, and antioxidant enzymes in Cucumis sativus L. plants.

Barium (Ba) is a nonessential element that can cause several deleterious effects in most organisms. Elevated Ba concentrations can be toxic for plants and may affect growth and disturbances in homeostasis. This study aimed to evaluate the Ba stress, the plant-tolerance limits, and the detoxification strategy adopted by Cucumis sativus L. The effect of Ba on seed's germination and vegetative development of this species was evaluated. For germination test, different Ba concentrations were used (0, 200, 500, 1,000, and 2,000 µM). Results showed that germination was stimulated with 500 and 2,000 µM of Ba. The toxicity effect on plant development was studied by treating the plants with increasing doses of Ba (100, 200, 300, and 500 µM) during 45 days. Shoot and root dry biomass production decreased significantly with elevated Ba concentrations, although water content enhanced in the roots. The concentration of Ba, 500 µM, induced high Ba accumulation in shoots and roots (9 times higher than in the control plants). Moreover, results showed that catalase, guaiacol peroxidase, and ascorbate peroxidase activities were stimulated in the different tissues of cucumber plants which highlight the occurring of an oxidative damage through Ba treatments and the involvement of the plant enzymatic antioxidant defense system.

Root exudates: from plant to rhizosphere and beyond.

KEY MESSAGE: This article describes the composition of root exudates, how these metabolites are released to the rhizosphere and their importance in the recruitment of beneficial microbiota that alleviate plant stress. Metabolites secreted to the rhizosphere by roots are involved in several processes. By modulating the composition of the root exudates, plants can modify soil properties to adapt and ensure their survival under adverse conditions. They use several strategies such as (1) changing soil pH to solubilize nutrients into assimilable forms, (2) chelating toxic compounds, (3) attracting beneficial microbiota, or (4) releasing toxic substances for pathogens, etc. In this work, the composition of root exudates as well as the different mechanisms of root exudation have been reviewed. Existing methodologies to collect root exudates, indicating their advantages and disadvantages, are also described. Factors affecting root exudation have been exposed, including physical, chemical, and biological agents which can produce qualitative and quantitative changes in exudate composition. Finally, since root exudates play an important role in the recruitment of mycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR), the mechanisms of interaction between plants and the beneficial microbiota have been highlighted.

Hormonal and metabolic responses of Mexican lime plants to CTV infection.

Plant viral infections alter gene expression and metabolism in infected host. To study the molecular responses of Mexican lime to CTV infection, an analysis of plant metabolome in response to infection with severe (T318) or mild (T385) isolates of CTV was performed. Healthy plants and those infected with any of the two virus strains showed different metabolite profiles, at different stages of new sprout development. Proline content increased in plants infected with CTV, proportionally to the virulence of the virus strain. Abscisic acid content decreased after virus infection whereas jasmonic and salicylic acid levels increased. CTV infection had an impact on plant secondary metabolism, by stimulating the synthesis of different metabolites such as l-methylhistidine, phenylpropanoid derivatives. These metabolites are common responses of different organisms, including higher mammals, to viral diseases, and its presence in this system points to the existence of universal responses to virus infection among different kingdoms.

Salt stress alleviation in citrus plants by plant growth-promoting rhizobacteria Pseudomonas putida and Novosphingobium sp.

KEY MESSAGE: This work reveals the protective role of two rhizobacteria, Pseudomonas putida and Novosphingobium sp., on citrus plants subjected to salt stress conditions. Detrimental salt stress effects on crops are likely to increase due to climate change reducing the quality of irrigation water. Plant growth-promoting rhizobacteria (PGPRs) can mitigate stress-induced damage in plants cultivated under high salinity conditions. In this work, Citrus macrophylla (alemow) plants inoculated with the rhizobacteria Pseudomonas putida KT2440 or Novosphingobium sp. HR1a were subjected to salt stress for 30 days. Results showed that in absence of salt stress, Novosphingobium sp. HR1a induced a decrease of transpiration (E) and stomatal conductance (gs). Both rhizobacteria reduced salt stress-induced damage. Levels of abscisic acid (ABA) and salicylic acid (SA) were lower in inoculated plants under salt stress conditions. Similarly, under stress conditions maximum efficiency of photosystem II (Fv/Fm) in inoculated plants decreased to a lower extent than in non-inoculated ones. In stressed plants, Novosphingobium sp. HR1a also induced leaf accumulation of 3-indole acetic acid (IAA) and a delay in the decrease of quantum yield (ΦPSII). P. putida KT2440 inhibited root chloride and proline accumulation in response to salt stress. Although both bacterial species had beneficial effects on salt-stressed citrus plants, Novosphingobium sp. HR1a induced a better plant performance. Therefore, both strains could be candidates to be used as PGPRs in programs of inoculation for citrus protection against salt stress.

Root exudates from citrus plants subjected to abiotic stress conditions have a positive effect on rhizobacteria.

Plants are constantly releasing root exudates to the rhizosphere. These compounds are responsible for different (positive or negative) interactions with other organisms, including plants, fungi or bacteria. In this work, the effect of root exudates obtained from in vitro cultured citrus plants on two rhizobacteria (Pseudomonas putida KT2440 and Novosphingobium sp. HR1a) was evaluated. Root exudates were obtained from two citrus genotypes differing in their sensitivity to salt and heat stress and differentially affected the growth of both rhizobacteria. Root exudates from salt-stressed plants of C. macrophylla (salt tolerant) induced an increase in bacterial growth higher than that obtained from Carrizo citrange exudates (salt sensitive). Root exudates from heat-stressed plants also had a positive effect on bacterial growth, which was more evident in the heat-sensitive C. macrophylla. These results reveal that the growth of these rhizobacteria can be modulated through citrus root exudates and can change depending on both the stress conditions as well as the genotype. Biosensors P. putida KT2442 (pMIS5) and Novosphingobium sp. HR1a (pPAH) were used to test the presence of proline and salicylates in root exudates by measuring ß-galactosidase activity. This activity increased in the presence of root exudates obtained from stressed plants to a higher extent in the case of exudates obtained from the genotype resistant to each particular stress, indicating that those root exudates contain larger quantities of proline and salicylates, as it has been described previously. Our data reveals that both P. putida KT2442 (pMIS5) and Novosphingobium sp. HR1a (pPAH), could be used as biosensors of plant stress.

Citrus plants exude proline and phytohormones under abiotic stress conditions.

KEY MESSAGE: This article describes the root exudation of proline and phytohormones in citrus and their involvement in salt- and heat-stress responses. Plants are constantly releasing several compounds to the rhizosphere through their roots, including primary and secondary metabolites. Root exudation can be affected by growth conditions, including pH, nutrient availability, soil salinity, or temperature. In vitro-cultured plants of two citrus genotypes with contrasting tolerance to salt- and heat-stress conditions were used as plant material. Proline and phytohormone contents in root exudates from plants subjected to salt or high-temperature conditions were evaluated. In addition, tissue damage and lipid peroxidation together with endogenous levels of chloride, proline, and phytohormones were determined in roots and shoots. Proline was released in larger quantities to the rhizosphere when plants were subjected to salt or heat stress. In each stress condition, the concentration of this amino acid was higher in the exudates obtained from plants tolerant to this particular stress condition. On the other hand, root exudation of phytohormones salicylic acid, indole acetic acid, abscisic acid, and jasmonic acid generally increased under both adverse conditions. Results confirm a phytohormone exudation in citrus plants, which had not been described previously and can have an important role in the rhizosphere communication. Moreover, stress conditions and the different tolerance of each genotype to the particular stress significantly modify the exudation pattern both quantitatively and qualitatively.

Social cognition makes an independent contribution to peer relations in children with Specific Language Impairment.

BACKGROUND: Language is important for developing and maintaining social relationships, and also for understanding others minds. Separate studies have shown that children with Specific Language Impairment (SLI) present difficulties in both abilities, although the role of social cognition (SC) on peers' perception remains unexplored. AIMS: The present study aims to assess specific sociometric features of children with SLI through peer nominations of liking and disliking, and also to explore their relationship to the children's SC. METHODS AND PROCEDURES: Thirty-five children with SLI attending ordinary schools (3;10 to 8;00 years old) and thirty-five age-matched children (AM) were assessed with language, SC and sociometric measures. RESULTS: SLI group received more disliked nominations and had lower scores on SC tasks compared to the AM group. After controlling for age and language, SC made an independent contribution to disliked nominations within the SLI group. CONCLUSIONS: Difficulties with peers of children with SLI are related to their language level but also with their SC abilities. Consequently, only resolving language impairments will not necessarily improve early peer acceptance in children with SLI. IMPLICATION: This finding stresses the importance of early intervention programmes aimed at reducing deleterious effects in later development and socialization with peers.

Abscisic Acid: a versatile phytohormone in plant signaling and beyond.

As sessile organisms, plants cannot escape from adverse conditions and, therefore, they have developed complex responses to the changing environment. Plant responses to abiotic cues involve changes in metabolism, photosynthesis, gene expression, ion levels, etc., and must be perfectly coordinated by phytohormones. The abscisic acid (ABA) is the main phytohormone involved in abiotic stress responses although it is nowadays clear that its signaling pathways are not isolated but interconnected with other hormone signals in complex networks. This article revises molecular mechanisms involved in the crosstalks of ABA with other phytohormones in response to different physiological processes. Moreover, ABA is not a molecule exclusive from plants but it can be found in many other organisms including bacteria, algae, fungi, animals, etc. Interestingly, it can be synthesized and secreted by a variety of human cells. These aspects that confer to the ABA a range of ubiquitous molecule will be also revised in this article.

Apical dominance in saffron and the involvement of the branching enzymes CCD7 and CCD8 in the control of bud sprouting.

BACKGROUND: In saffron (Crocus sativus), new corms develop at the base of every shoot developed from the maternal corm, a globular underground storage stem. Since the degree of bud sprouts influences the number and size of new corms, and strigolactones (SLs) suppress growth of pre-formed axillary bud, it was considered appropriate to investigate SL involvement in physiology and molecular biology in saffron. We focused on two of the genes within the SL pathway, CCD7 and CCD8, encoding carotenoid cleavage enzymes required for the production of SLs. RESULTS: The CsCCD7 and CsCCD8 genes are the first ones isolated and characterized from a non-grass monocotyledonous plant. CsCCD7 and CsCCD8 expression showed some overlapping, although they were not identical. CsCCD8 was highly expressed in quiescent axillary buds and decapitation dramatically reduced its expression levels, suggesting its involvement in the suppression of axillary bud outgrowth. Furthermore, in vitro experiments showed also the involvement of auxin, cytokinin and jasmonic acid on the sprouting of axillary buds from corms in which the apical bud was removed. In addition, CsCCD8 expression, but not CsCCD7, was higher in the newly developed vascular tissue of axillary buds compared to the vascular tissue of the apical bud. CONCLUSIONS: We showed that production and transport of auxin in saffron corms could act synergistically with SLs to arrest the outgrowth of the axillary buds, similar to the control of above-ground shoot branching. In addition, jasmonic acid seems to play a prominent role in bud dormancy in saffron. While cytokinins from roots promote bud outgrowth. In addition the expression results of CsCCD8 suggest that SLs could positively regulate procambial activity and the development of new vascular tissues connecting leaves with the mother corm.

Which are the best predictors of theory of mind delay in children with specific language impairment?

BACKGROUND: The relationship between language and theory of mind (ToM) development in participants with specific language impairment (SLI) it is far from clear due to there were differences in study design and methodologies of previous studies. AIMS: This research consisted of an in-depth investigation of ToM delay in children with SLI during the typical period of acquisition, and it studied whether linguistic or information-processing variables were the best predictors of this process. It also took into account whether there were differences in ToM competence due to the degree of pragmatic impairment within the SLI group. METHODS & PROCEDURES: Thirty-one children with SLI (3;5-7;5 years old) and two control groups (age matched and language matched) were assessed with False Belief (FB) tasks, a wide battery of language measures and additional information-processing measures. OUTCOMES & RESULTS: The members of the SLI group were less competent than their age-matched peers at solving FB tasks, but they performed similarly to the language-matched group. Regression analysis showed that overall linguistic skills of children with SLI were the best predictor of ToM performance, and especially grammar abilities. No differences between SLI subgroups were found according to their pragmatic level. CONCLUSIONS & IMPLICATIONS: A delay in ToM development in children with SLI around the critical period of acquisition is confirmed more comprehensively, and it is shown to be more strongly related to their general linguistic level than to their age and other information-processing faculties. This finding stresses the importance of early educational and clinical programmes aimed at reducing deleterious effects in later development.

Biotechnological approaches to study plant responses to stress.

Multiple biotic and abiotic environmental stress factors affect negatively various aspects of plant growth, development, and crop productivity. Plants, as sessile organisms, have developed, in the course of their evolution, efficient strategies of response to avoid, tolerate, or adapt to different types of stress situations. The diverse stress factors that plants have to face often activate similar cell signaling pathways and cellular responses, such as the production of stress proteins, upregulation of the antioxidant machinery, and accumulation of compatible solutes. Over the last few decades advances in plant physiology, genetics, and molecular biology have greatly improved our understanding of plant responses to abiotic stress conditions. In this paper, recent progresses on systematic analyses of plant responses to stress including genomics, proteomics, metabolomics, and transgenic-based approaches are summarized.

Carrizo citrange plants do not require the presence of roots to modulate the response to osmotic stress.

The study of the effects of a specific stress condition on the performance of plants grown under field conditions is difficult due to interactions among multiple abiotic and biotic factors affecting the system. In vitro tissue-culture-based techniques allow the study of each adverse condition independently and also make possible to investigate the performance of genotypes of interest under stress conditions avoiding the effect of the root. In this paper, the response of Carrizo citrange, a commercial citrus rootstock, to osmotic stress was evaluated by culturing in vitro intact plants and micropropagated shoots. The osmotic stress was generated by adding two different concentrations of polyethyleneglycol to the culture media. Different parameters such as plant performance, organ length, antioxidant activities, and endogenous contents of proline, malondialdehyde, and hormones were determined. Differently to that observed under high salinity, when subjected to osmotic stress conditions, Carrizo citrange showed increased endogenous levels of MDA, proline, and ABA. These results evidence that the mechanisms of response of Carrizo citrange to saline or osmotic stress are different. The presence of roots was not necessary to activate any of the plant responses which indicates that the organs involved in the stress perception and signaling depends on the type of adverse condition to which plants are subjected.

Modulation of the antioxidant system in Citrus under waterlogging and subsequent drainage.

Soil flooding induces an impairment of the photosynthetic system that often leads to an accumulation of reactive oxygen species (ROS) in plant tissues. Moreover, flooding release by drainage can cause a sudden oxygen burst that exacerbates oxidative damage. To examine the influence of different anoxic and post-anoxic periods on citrus physiology, citrumelo CPB4475, a moderate flood-tolerant genotype, was subjected to three different periods of soil flooding followed by drainage. Plant performance in terms of visible damage, photosynthetic activity, malondialdehyde (MDA) and hydrogen peroxide accumulation was examined together with the plant antioxidant response. The results indicated that coordinated antioxidant activity, involving increased activities of superoxide dismutase (SOD) (EC 1.15.1.1) and catalase (CAT) (EC 1.11.1.6), together with a modulation of the ascorbate-glutathione cycle, allowed plants to cope with flooding-induced oxidative stress up to a certain point. Elevated ascorbate peroxidase (APX) (EC 1.11.1.11) activity or discrete increases in AsA or glutathione concentrations seemed inefficient in maintaining low levels of oxidative damage. Waterlogging stress release by soil drainage did not improve plant performance but, on the contrary, enhanced oxidative stress and even accelerated plant injury. This appears to be the result of sudden oxygen burst soon after release of water.

Antioxidant enzymatic activity is linked to waterlogging stress tolerance in citrus.

Soil flooding constitutes a seasonal factor that negatively affects plant performance and crop yields. In this work, the relationship between oxidative damage and flooding sensitivity was addressed in three citrus genotypes with different abilities to tolerate waterlogging. We examined leaf visible damage, oxidative damage in terms of malondialdehyde (MDA) concentration, leaf proline concentration, leaf and root ascorbate and glutathione contents and the antioxidant enzyme activities superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6) and glutathione reductase (EC 1.8.1.7). No differences in the extent of oxidative damage relative to controls were found among genotypes. However, a different ability to delay the apparition of oxidative damage was associated to a higher tolerance to waterlogging. This ability was linked to an enhanced activated oxygen species' scavenging capacity in terms of an increased antioxidant enzyme activity and higher content in polar antioxidant compounds. Therefore, the existence of a direct relationship between stress sensitivity and the early accumulation of MDA is proposed. In addition, data indicate that the protective role of proline has to be considered minimal as its accumulation was inversely correlated with tolerance to the stress. The positive antioxidant response in Carrizo citrange (Poncirus trifoliata L. Raf. x Citrus sinensis L. Osb.) and Citrumelo CPB 4475 (Poncirus trifoliata L. Raf. x Citrus paradisi L. Macf.) might be responsible for a higher tolerance to flooding stress, whereas in Cleopatra mandarin (Citrus reshni Hort. Ex Tan.), the early accumulation of MDA seems to be associated to an impaired ability for H2O2 scavenging.

Mothers' use of cognitive state verbs in picture-book reading and the development of children's understanding of mind: a longitudinal study.

Mothers read stories to their children (N=41) aged between 3.3 years and 5.11 years old, and children then completed two false-belief tasks. One year later, mothers read a story to 37 of those children who were also given four tasks to assess their advanced understanding of mental states. Mothers' early use of cognitive verbs in picture-book reading correlated with their children's later understanding of mental states. Some pragmatic aspects of maternal input correlated with children's later outcomes. Two different factors in mothers' cognitive discourse were identified, suggesting a zone of proximal development in children's understanding of mental states.