Recurrent water deficit causes alterations in the profile of redox proteins in citrus plants

Drought tolerance memory transmission by citrus buds

Plants face recurrent drought events, and previous stresses can influence their responses to subsequent stress episodes. Studies on drought stress memory are recent in citriculture, although they show promise as a tool for crop improvement. Here, we investigated whether stress memory mechanisms can be detected in citrus plants grafted with buds from plants subjected to recurrent water deficit. Three rootstock varieties, namely 'Rangpur Santa Cruz' lime, 'Sunki Maravilha' mandarin and 'Sunki Tropical' mandarin, in combination with 'Valencia' orange, were either maintained under full irrigation or subjected to one, two, or three water deficit cycles. Buds from 'Valencia' orange were grafted onto 'Swingle' citrumelo rootstocks and were evaluated. This combination displayed improved physiological and biochemical performance under water limitation, especially 'Valencia' buds grafted onto 'Sunki Maravilha', with better photosynthetic performance under water deficit. These findings indicate that genotype-dependent epigenetic memory is a key factor in restoring citrus plants' capacity to rely on previous stress experiences to restore better photosynthetic and physiological responses when undergoing new water deficit events. Therefore, epigenetic marks can be stored and transmitted to new citrus plants and are a promising alternative to enable increased water deficit tolerance when plants are then challenged by drought-prone environments.

Drought stress memory in rice guard cells: Proteome changes and genomic stability of DNA

Drought is one of the major threats for crop plants among them rice, worldwide. The effects of drought vary depending on the plant growth phase and the occurrence of a previous stress, which can leave a memory of the stress. Stomata guard cells perform many essential functions and are highly responsive to hormonal and environmental stimuli. Therefore, information on how guard cells respond to drought might be useful for selecting drought tolerant plants. In this work, physiological analysis, comparative proteomics, gene expression and 5 - methylcytosine (%) analysis were used to elucidate the effects of drought in single stress event at vegetative or reproductive stage or recurrent at both stages in guard cells from rice plants. Photosynthesis and stomatal conductance decreased when drought was applied at reproductive stage in single and recurrent event. Twelve drought-responsive proteins were identified, belonging to photosynthesis pathway, response to oxidative stress, stress signalling and others. The expression of their encoding genes showed a positive relation with the protein abundance. Drought stress increased the total DNA methylation when applied at vegetative stage in single (35%) and recurrent event (18%) and decreased it in plants stressed at reproductive stage (9.8%), with respect to the levels measured in well-watered ones (13.84%). In conclusion, a first drought event seems to induce adaptation to water-deficit conditions through decreasing energy dissipation, increasing ATP energy provision, reducing oxidative damage in GC. Furthermore, the stress memory is associated with epigenetic markers.

Drought resistance in Harumi tangor seedlings grafted onto different rootstocks

In this study we analysed the influence of drought stress on the leaf morphological characteristics, osmotic adjustment substances, antioxidant enzymes, and resistance-related photosynthetic physiological indices of Harumi tangor plants grafted onto Poncirus trifoliata (Pt), Citrus junos (Cj), and Citrus tangerine (Ct). The leaf relative water content and leaf area of the three rootstocks decreased with increasing drought stress, with the smallest decrease in Cj. The relative conductivity and malondialdehyde content increased with increasing drought stress. Proline, total soluble sugar, soluble protein, and activities of superoxide dismutase, ascorbate peroxidase, and catalase increased with drought stress but decreased under severe drought stress, with Cj exhibiting the greatest increase in enzyme activity. The net photosynthetic rate, stomatal conductance, transpiration rate, and chlorophyll a and b content were all lower than those of the control, whereas intercellular CO2 concentration increased with increasing drought stress. The initial fluorescence and maximal quantum yield of PSII were approximately equal for all rootstocks but increased with increasing drought stress severity. The combined analysis of physiological indicators, membership function, and principal components indicated that the drought resistance of grafted H. tangor decreased in the order Cj > Ct > Pt.

Proteomic and metabolomic analysis of desiccation tolerance in wheat young seedlings

Young wheat seedlings are desiccation tolerant and have the capacity to withstand long dehydration period. In this study, we characterized the proteome and metabolome of wheat seedlings during desiccation and after recovery. Functional classification of differentially identified proteins revealed dynamic changes in the number and abundance of proteins observed during stress and recovery. Desiccation resulted in a decline in the abundance of proteins associated with photosynthesis and carbohydrate reserves, along with an increase in the presence of proteins associated with stress and defense response, such as peroxiredoxins and antioxidant enzymes. Following recovery, the abundance of stress-responsive proteins returned either partially or completely to their baseline level, confirming their importance to the seedling's desiccation response. Furthermore, proteins involved in carbohydrate metabolism, as well as fructose-bisphosphate aldolase and fructokinase-2 and phosphorylated metabolites as the substrate or the end-product, showed the inverse pattern during desiccation and after re-watering. This may reflect the fact that plants maintained energy supply during stress to protect seedlings from further damage, and for use in subsequent recovery after rewatering period. This study provides novel insights into the molecular mechanisms underlying the desiccation tolerance of wheat seedlings, and paves the way for more detailed molecular analysis of this remarkable phenomenon.

HVA22 from citrus: A small gene family whose some members are involved in plant response to abiotic stress

The HVA22 gene has been isolated for the first time from the aleurone layer of barley (Hordeum vulgare). Here, we characterized the HVA22 family from citrus (C. clementina and C. sinensis). Twelve genes, 6 in each species, were identified as well as duplication events for some of them. The ORF size ranged from 235 to 804 bp and the protein molecular weight from 94 to 267 kDa. All the citrus HVA22 protein presented transmembrane location and conserved TB2/DP1/HVA22 region. Phylogenetic and gene expression analyses suggested that some citrus HVA22 play a role in flower and fruit development, and that gene expression may be regulated by hormone or environmental conditions. Other regulation levels were also predicted, such as alternative splicing and post-translational modifications. The overall data indicated that citrus HVA22 may be involved in vesicular traffic in stressed cells, and that CcHVA22d could be involved in dehydration tolerance.