Functional Plant Biology

This special issue presents key papers for plant scientists on the quest to further address and improve flood tolerance of terrestrial plants. The papers address low O₂ responses in roots, shoots or whole plants in controlled laboratory conditions or in the field situation using natural wetland plants as models as well as economically important crops, such as rice, wheat and barley.

A barrier to radial oxygen loss (ROL) in roots is an important adaptation of many wetland plants growing in waterlogged, anoxic soils; however, knowledge of the nature of the barrier is sparse. The ROL barrier enhances longitudinal oxygen diffusion through aerenchyma to the root tip. Our comparison of two Hordeum marinum accessions differing in ROL barrier strength showed that the deposition of suberin into walls of the root exodermis is associated with reduction in loss of oxygen from basal root zones to the external medium.

Flooding generally poses a threat to terrestrial plants, but wetland species display adaptations that prevent damage by the adverse conditions imposed by floods. One of these adaptations – formation of adventitious roots that replace the original non-adapted root system – may be severely constrained if insufficient light or contact of leaves with the atmosphere is present during the flooding event. This results in significantly fewer adventitious roots growing out of the stem, and thus poor performance in these stressful conditions.

Halophytes represent extraordinary strategies of flooding tolerance, most of them poorly understood. Traits associated with internal tissue aeration are often essential to submergence tolerance but the present study shows that other traits may also be relevant in order to sustain growth under recurrent submergence. Understanding traits that confer flooding tolerance is important in times with global climate changes that worldwide are predicted to result in more frequent flooding events.

Some terrestrial plants, including wheat (Triticum aestivum), possess superhydrophobic leaf surfaces that retain a thin gas film when submerged. We tested gas film retention time of 14 different wheat cultivars and found that wheat could retain the gas films for a minimum of 2 days. We suggest that leaf gas film is a relevant trait to use as a selection criterion to improve the flood tolerance of crops that become temporarily submerged.

Climate changes result in more floods also in regions where the mean precipitation is predicted to decline. Dryland crops such as wheat and barley are particularly vulnerable to submergence stress. Here, we show that superhydrophobic leaf surfaces enhance survival of completely submerged wheat by formation of thin leaf gas films that helps wheat to ‘breathe’ under water.

Elongation-induced leaf emergence (escape strategy) is hypothesised to be more beneficial under single long-term submergence than under repeated short-term submergence. We tested this idea in Chloris gayana Kunth. grass. We found that under a single 2-week submergence event, plants accumulated a 2.9-fold higher dry mass than when experiencing the same submergence duration in separate events along 1 week, validating our hypothesis.

Potassium (K) is one of the limiting factors that influenced rice growth and yield in submergence prone soils. Here we show that application of K at a higher dose (40 kg K₂O ha^–1 (basal) + one foliar spray at 0.5% K at panicle initiation stage) was beneficial in improving rice survival and grain yield. This finding will aid in boosting rice productivity in submergence prone rainfed ecology of Eastern Indo-Gangetic Plain.

Rice seeds are able to germinate under water, also thanks to their ability to produce α-amylase under O₂ shortage, thus allowing starch degradation. Calcineurin B-like interacting protein kinase 15 (CIPK15) was previously identified as a positive regulator of α-amylase induction during anaerobic germination. In this study, we describe calcineurin B-like proteins 4 (CBL4) as a CIPK15 partner under low O₂.

Leaf gas exchange is commonly manipulated using low O₂ to suppress photorespiration but the detailed effects of this condition on leaf metabolism have often been disregarded. In this study, we used metabolomics to show metabolic alterations typical of a hypoxic response and that the aspartate pathway, including methionine synthesis, is sensitive to the O₂ mole fraction. These results provide evidence that, contrary to common belief, leaf catabolism and biosyntheses are sensitive to gaseous conditions.

This work investigated physiological mechanisms conferring barley adaptation to combined waterlogging and salinity stress. Plants exposed to combined stress showed a negative correlation between shoot Na⁺ accumulation and the extent of salinity damage. Overall, the reported results indicated that K⁺ reduction in the plants but not stress-induced Na⁺ accumulation in the shoot was the most critical feature determining the overall plant performance under combined stress conditions.

It is uncertain how elevated CO₂ will affect photosynthesis during extreme events. Seven genotypes of Eucalyptus camaldulensis var. camaldulensis were grown in 400 or 640 parts per million CO₂, and photosynthetic electron transport, stomatal conductance and net CO₂ uptake were measured before, during and after a 4-day heatwave. The correlations between climate of origin and physiological responses depend on growth CO₂, which makes it difficult to predict species responses to episodic aspects of climate change.

Leaf respiration is an integral component of plant growth and the global carbon cycle, and it is typically lower during the day than at night. We investigated leaf respiration in Mediterranean holm oak woodland, and found that light inhibition was not strongly related to changes in soil water content or ambient temperature. The findings have implications for predictive models that seek to calculate plant carbon balance.

Horn-shaped gall is of great value in food, medicine and the industrial field, so the control of its formation will be helpful to increase the products. Vacuolar invertase is related to the rapid expansion of the galls, but ionically bound cell wall invertase is involved in the rapid growth of tissues. This might also be found in other kinds of galls.

Soil water availability is a key factor limiting rates of carbon assimilation in plants. However, we found that as water availability declined, investment in foliar nitrogen, photosynthetic capacity and intrinsic water-use efficiency increased across eight co-occurring tree species in semiarid Australia. We conclude that differential access to water is an important factor driving variability of traits related to carbon gain.

The stable co-existence of a diversity of plant species within a single biome is possible if the species access different resources. In semiarid Australia we found that co-occurring tree species had differing access to water, resulting in multiple plant water-use strategies in this water-limited environment. These differing strategies have important implications for the survival of these species under drought.

The mechanism by which flowers regulate their function and structure to maintain water balance is unclear. We found that flowers of two Magnolia species consumed less than half the water that leaves did, and explored different hydraulic strategies in flowers and leaves to sustain hydraulic safety. This study contributes new knowledge to the field of floral hydraulics.

Understanding morphophysiological variations in plant leaf traits on tropical dry forests is essential for studying global climate changes. We was investigated the effect of rainfall on the morphophysiological features of Croton blanchetianus. We argue that C. blanchetianus has a remarkable ability to adapt to global climate changes. Consequently, this species may be important in reforestation programs.

Rice is a staple food in many countries and local production is carried out under unfavourable conditions, so effective and affordable alternatives to enhance local production are mandatory to palliate hunger. The underlying hypothesis is that certain beneficial bacterial strains can boost plant’s adaptive metabolism to overcome environmental limitations, so this study aimed to identify bacterial genes involved in beneficial effects on plants by creating random mutants of an effective Pseudomonas strain by evaluating loss of protection against salt stress in rice, and growth of tomato. Mutants were mapped and putative responsible genes sequenced. This study reveals the effectiveness of beneficial bacteria on two relevant crops, phylogenetically distant, so it appears as a challenging alternative to meet food security.

Leaf respiration (R) is an important determinant of tree and forest function, yet the impacts of rising atmospheric CO₂ on leaf R remain poorly understood. We found that leaf respiration is largely unaffected by elevated CO₂, and is relatively similar across seedlings of geographically and climatically diverse populations of Eucalyptus grandis. We conclude that elevated CO₂ is unlikely to change leaf R in E. grandis.

Although Ca²⁺ is transported by Ca²⁺-ATPase into root nodule cell symbiosomes, surprisingly little is known on its role in their functioning. An attempt to solve the problem was made using the data on calcium behaviour in prokaryotes and endosymbiosis role in its signalling. The data outlined indicate that Ca²⁺ signalling in bacteroids is putatively its key functional role in symbiosomes.

A new approach to monitoring leaf photosynthesis in situ using 30 ms chlorophyll fluorescence transients at ~ 2 s intervals at distances up to 2 m is described. By monitoring fluorescence with near full reduction of Q_A (the primary quinone acceptor of PSII) these transients deliver parameters not directly available from other methods (relative functional absorption cross section of photosystem II, rates of intersystem electron transport and relative oxidation state the plastoquinone (PQ) pool). These permit non-intrusive evaluation of brief sun flecks in shade canopies whereas calibration against traditional PAM methods is obtained in longer protocols achieving full reduction of PQ.

Ozone has been proposed as a convenient elicitor against pathogens. We hypothesised that ozone treatment may elicit defence against Blumeria graminis f. sp. tritici (Bgt) by inducing ROS signalling or other defence routes in wheat. We found that ozone treatment was effective in diminishing Bgt invasion in the susceptible cultivar, which was plausibly related to the SA pathway.

Mineral transport in plants is typically studied using chemical tracer compounds. However, after grape berries begin to ripen, xylem mobile tracers are often constrained to the vasculature near the proximal end. Here we show it is possible to observe the transport of important minerals, such as Mn, using magnetic resonance imaging.

Floranthene (FLT), a polycyclic aromatic hydrocarbons (PAH) poses a potential ecological risk to plants by damaging their photosynthetic machinery. It inhibits PSII while PSI protects itself from the damaging effects of FLT by initiating cyclic electron flow. This important information was provided using a very quick, noninvasive and simple technique of chlorophyll a fluorescence measurement.

Both phosphatidic acid (PA) and guanine nucleotide exchange factors (GEFs) are essential signalling molecules in adaptive response to various external stresses. Here we show that PA binds specifically to GEF8, thus regulating the activity of small GTPase ROPs in Arabidopsis. Our findings identify a direct functional regulation of lipid-mediation of GEFs activity and small GTPase signalling in cells.

Signalling is a central phenomenon in biology. It is crucial to all aspects of plant physiology including growth, development and interactions with the environment. Here, novel hypotheses and experimental data regarding signalling hubs, second messengers, programmed cell death and autophagy are presented from the Fourth Plant Signalling and Behaviour Symposium in Sankt Petersburg, Russia, June 2016).

Drought and cold are two major factors limiting the growth of cool-season grasses and cause declines in grassland and forage quality. This study investigated the physiological and biochemical responses of one native grass species – Festuca sinensis – in China to temperature and water stress. Our results showed this grass could adapt to certain changes in the ecological environment by regulating their physiological and biochemical reactions.

Arabidopsis myotubularins AtMTM1 and AtMTM2 control stomata movements via reactive oxygen species (ROS) homeostasis under drought stress. Acting as a secondary messenger in the ABA-induced ROS production in guard cells, PtdIns5P emerges as an evolutionarily conserved signalling molecule downstream of AtMTMs calibrating cellular ROS levels under stress. AtMTM1 and AtMTM2 activities balance ABA-induced ROS and cellular homeostasis under dehydration stress.

Aluminium (Al) toxicity is a significant problem for plant growth and production on acidic soils, which cover over 40% of the world’s arable land. In this study, we investigated the role of melatonin in soybean resistance to Al toxicity. The application of melatonin alleviated Al toxicity through enhancement of antioxidant enzymes activities and organic acid anions exudation.

Peroxisomes balance the cellular levels of reactive oxygen species (ROS) and therefore should modulate ROS-regulated programs like autophagy or cell death. We used tobacco suspension cultures to show that degradation of peroxisomes via autophagy was a prerequisite for cell death and depended on the levels of the major peroxisomal protein, catalase. This suggests a role of plant catalase in the regulation of peroxisome turnover and autophagic cell death.

The electrophysiological response pattern of Nitellopsis obtusa cell can be assessed to evaluate the effect of many biologically active compounds. We illustrate a variety of electrophysiological approaches for the investigations of electrical signaling after chemical treatment in vivo. The insights about the Characean model system are likely to hold for plants in general and even deepen the understanding of the plant evolution.

Although many studies established nitric oxide (NO) as a signaling molecule in plants, the identification of target molecules of NO has remained elusive due to the lack of in depth molecular studies. Our quantitative proteome analysis suggests the differential regulation of 248 proteins and dynamic regulation of metabolic pathways by exogenous NO donor in chickpea. This is the first report in legumes pointing at the potential candidates that attribute the reported functions of NO in plants.

We studied the dynamics of photochemical activity in seed coats and cotyledons during development of yellow- and green-seeded pea cultivars by using the pulse amplitude modulation fluorometric analysis. The fast transients of the chlorophyll a fluorescence revealed higher photochemical activity in the coats of yellow-seeded cultivar at the early- and middle cotyledon stages of seed development in comparison to those observed in the green-seeded ones. Photochemical activity in the cotyledons of both cultivars could not be any more detected at the late cotyledon stage. This process was triggered by dehydration of seed tissues.

Root growth is controlled by phytohormones, but what cellular processes are regulated and how it occurs is still an open question. Here it is shown that cytokinin affects root growth mainly through its effect on cell proliferation, and does not initiate the transition of cells to differentiation as previously thought. Cellular analysis performed could be applied for the analysis of how any plant hormone influences developmental processes in plant roots.

Intracellular communications in plant cells of large dimensions rely primarily on cytoplasmic streaming, because diffusion is too slow for the transport on mm-scale distances. Illumination of a small cell spot at a various distances from the point of chlorophyll fluorescence measurements revealed the wave-like propagation of the fluorescence response along the cell length. The results show that the photosynthetic function of immobile chloroplasts under constant light can be affected by long-distance transmission of a photosynthetically active metabolite from the remote cell parts.

Understanding the molecular mechanisms of plant development constitutes an important field of investigations in the current era of plant biology research. Nitric oxide signalling regulates a variety of biochemical processes in plants. Present review provides an in-depth analysis of our current understanding on the subject, particularly with reference to plant growth under stress conditions.

Melatonin is an important hormone and signalling molecule in all forms of life including humans, plants and bacteria. Recent plant physiology and genomic experiments have described the redirection of plant growth and metabolism, and demonstrated a diversity of genes involved in response to melatonin, however, the exact metabolic cascades that translate melatonin signals into physiological responses is not fully understood. This review provides an overview of melatonin mediated signalling manifested as behaviours and its roles in basic and industrial research.

Memristors, or resistors with memory, exist in vivo as components of plasma membranes in plants, fruits, roots and seeds. Authors found memristors in an androecium, spur, petals and pedicel in Sunpatiens flowers. The discovery of memristors in Sunpatiens (Impatiens spp.) creates a new direction in the modelling and understanding of electrophysiological phenomena and memory elements in flowers.

Plant fibres with a tertiary cell wall (G-layer) may function as plant ‘muscles’. Large-scale transcriptome profiling of isolated flax phloem fibres permitted to identify the major players and regulatory elements that operate during graviresponce specifically in the fibres of the pulling stem side. The suggested mechanisms of phloem fibre involvement in tropisms may considerably renew the concept of herbaceous plant behaviour upon gravistimulation.

Clarifying herbivory-induced plant cellular signalling is a critical step to push the research of plant-herbivore interaction forward. We review the role of ion channels/transporters in modulating herbivory-induced early signalling events and rapid systemic signal transmission in plants. This work provides a comprehensive source of information about plant defensive strategies upon attack.

Cytokinin is an important plant hormone and its mode of action has been extensively studied; however, to date, the subcellular localisation of cytokinin perception and signal transduction remains a matter of debate. This study describes cytokinin receptor–phosphotransmitter interaction and its subcellular localisation in living plant cells and it provides several experimental evidences for receptor activity at the endoplasmic reticulum (ER) membrane. It is concluded that intracellular cytokinins within the ER lumen may play an important role in cytokinin signalling, at least in some cell types.

Rhizobium bacteria, which live within the root nodules of legumes, allow plants to capture nitrogen gas from the atmosphere and use it for their own growth. Central to this symbiosis is an intracellular structure, called the symbiosome, in which nitrogen-fixing bacterial cells exchange components with the host cells that harbor them. Recent research on the differentiation of symbiosomes and of the infected cells that accommodate them has helped to decipher some general molecular mechanisms of cell differentiation.

Plants, like animals, produce electrical signals in response to various external influences. In this study we raised a question whether the electrical signals transmit information about the nature of the stimulus, and found out that different stimuli induce signals of varied parameters. The obtained results explain how plants adapt to changing environment.

Environmental stresses are main causes for low agricultural productivity. At the cellular level, stresses induce generation of reactive oxygen species (ROS), ion disequilibrium, autophagy and programmed cell death (PCD). Here we propose that these processes interact and that ROS and ion disequilibrium are triggers of autophagy and PCD. Overall, presented data contribute to understanding plant stress physiology.

Transient elevation of cytosolic Ca²⁺, also referred as a Ca²⁺signal, is as central phenomenon of plant signalling. Plants evolved sophisticated systems to initiate, amplify and terminate Ca²⁺ signals. Structure and properties of these systems, including Ca²⁺-permeable ion channels, Ca²⁺-ATPases, Ca²⁺/H⁺ exchangers and ‘ROS-Ca²⁺ hub’ are discussed here. They provide a fine-tuned mechanism for encoding diverse external and internal stimuli.

Focussed ion bean scanning electron microscopy (FIB-SEM) is a technique that can be used to generate 3D renderings of cells and their contents. Although FIB-SEM has been regularly used to investigate animal cells and tissues, it has rarely been deployed to study plant structures. Here we demonstrate that FIB-SEM can easily be used to study plant samples and have discovered previously unknown arrangements of organelles and membranes in those samples.

Photosynthetic electron transport chain is not only source of ATP and NADPH for photosynthesis; it is a sensor, informing adaptation systems of plant about environmental changes. An important transmitter of this information is hydrogen peroxide whose mechanisms of formation are presented, laying special emphasis on the formation outside and within thylakoid membrane. It is discussed, that the formation place can ensure definite signal about the specific environmental change.

Although plant proteases of the phytaspase family are important contributors to stress-induced plant cell death, phytaspase of a classical model plant Arabidopsis thaliana has escaped identification thus far. We identified the Arabidopsis phytaspase-encoding gene and characterised the recombinant enzyme. Substrate specificity and properties of the Arabidopsis phytaspase display both important similarities with and distinctions from the already characterised phytaspases.

Cyclic GMP (cGMP) signalling in plants is crucial for many physiological processes. Recent analytical and genomic developments now allow detailed studies into the biochemistry and physiological role of cGMP in plants, and the latest findings are reviewed in this article.

Large conductance SV/TPC1 channels are ubiquitously and abundantly expressed in the vacuolar membranes of higher plants. They are unique established Ca²⁺-permeable channels in vacuoles, but their activity is strongly negatively controlled, so that they were believed to be inactive or to act only locally. Recent evidence suggests the key role of SV/TPC1 channels in the long-distance Ca²⁺ signalling.

Plants adapt to environmental light conditions with the use of the sophisticated phytochrome system. In this work, polymorphism of its major component – phytochrome A– was investigated. With the use of transgenic Arabidopsis and fluorescence technique, it was shown that two molecular types of the photoreceptor differ by the state of phosphorylation and their existence accounts for its complex functions.

The ABA-deficient barley mutant Az34 and wild type (WT) were exposed to air warming. Although transpiration rate of both genotypes increased, leaf water potential decreased in the mutant but was maintained in WT plants. Only WT plants showed increased root ABA accumulation, which increased root hydraulic conductivity and aquaporin abundance, which seems important in maintaining leaf hydration.