Regulatory roles of sugars in plant growth and development

In recent years, several studies have focused on the factors and mechanisms that regulate plant growth and development, as well as the functioning of signaling pathways in plant cells, unraveling the involvement of sugars in the processes regulating such growth and development. Saccharides play an important role in the life of plants: they are structural and storage substances, respiratory substrates, and intermediate metabolites of many biochemical processes. Sucrose is the major transport form of assimilates in plants. Sugars can also play an important role in the defense reactions of plants. However, it has been shown that glucose, sucrose, or trehalose-6-phosphate (Tre6P) can regulate a number of growth and metabolic processes, acting independently of the basal functions; they can also act as signaling molecules. Changes in the concentration, qualitative composition, and transport of sugars occur continuously in plant tissues, during the day and night, as well as during subsequent developmental stages. Plants have developed an efficient system of perception and transmission of signals induced by lower or higher sugar availability. Changes in their concentration affect cell division, germination, vegetative growth, flowering, and aging processes, often independently of the metabolic functions. Currently, the mechanisms of growth regulation in plants, dependent on the access to sugars, are being increasingly recognized. The plant growth stimulating system includes hexokinase (as a glucose sensor), trehalose-6-phosphate, and TOR protein kinase; the lack of Tre6P or TOR kinase inhibits the growth of plants and their transition to the generative phase. It is believed that the plant growth inhibition system consists of SnRK1 protein kinases and C/S1 bZIP transcription factors. The signal transduction routes induced by sugars interact with other pathways in plant tissues (for example, hormonal pathways) creating a complex communication and signaling network in plants that precisely controls plant growth and development

The effects of diversified phosphorus nutrition on the growth of oat (Avena sativa L.) and acid phosphatase activity

We studied the effect of differential phosphorus (P) supply on the development of oat seedlings (Avena sativa L. ‘Arab’) as well as localization and activity of acid phosphatases in tissues and root exudates. Plants were grown for 1–3 weeks on nutrient media with inorganic phosphate (+P, control), reduced Pi (0.1 P), phytic acid (PA) as organic P source, and without P addition (−P), in standard conditions or in a split-root culture system. Phosphate starvation reduced shoot growth but increased root elongation and root/shoot ratio, whereas 0.1 P and PA oat plants had similar growth parameters to +P plants. The growth on −P medium significantly decreased Pi content in all tissues, but only a slight Pi decrease was observed in plants grown on 0.1 P and PA media or various split-root system conditions. Pi starvation led to an increase in acid phosphatase (APase) activity in root exudates when compared to +P, 0.1 P, and PA plant samples. APase activity was especially intensive in root cross sections in rhizodermis and around/in vascular tissues of −P plants. For plants grown on 0.1 P medium and on phytic acid, APase activity did not change when compared to the control. Three major isoforms of APases were detected in plant tissues (similar in all studied conditions, with a higher activity of one isoform under Pi deficit). Generally, lowered Pi content (0.1 P) was not stressful to oat plants for up to 3 weeks of culture. Oat plants grew equally well on nutrient media with Pi and on media with phytate, although phytate was considered not available for other plants. The oat plants activated mainly extracellular APases, but also intracellular enzymes, rather via nonlocal signals, to acquire Pi from external/internal sources under Pi deficiency

Sucrose metabolism control in plants as response to changes of environmental conditions

Sucrose is a final product of photosynthesis; it is transported to the sink organs of a plant where it is used as substrate, metabolized to other organic compounds or stored. Besides, sucrose has a nonnutritive role — controlling plant growth, development and regulation of cell metabolism. This review summarizes information on the key enzymes of sucrose synthesis and breakdown, and regulations of their activity (transcriptional, translational control or posttranslational modifications) under unfavourable conditions. Changes of carbohydrate concentration in tissues have been frequently shown to be involved in plant responses to different stresses. Changes in sugar content influence the expression of various genes via a variety of signal transduction pathways. The regulatory role of sucrose, e.g. control of its own metabolism, and possible interactions of sugarresponse pathways with other signalling events are discussed

Can the uptake of phosphates by plants be improved?

Phosphorus is an important nutrient but usually it is at low availability in the soil - thus, it can limit plant growth and agricultural production. Plants have evolved various responses to adapt to low phosphorus nutrition - which is shortly summarized in this review. for example, roots secrete organic acids and different enzymes to rhizosphere, or can induce the transport system to improve the release (from the soil) and uptake of inorganic phosphate (Pi). Plants might control Pi nutrition by induction of mycorrhizae or by developing specific root structures - proteoid roots. attempts to generate plants which may more efficiently acquire Pi from the soil have recently been made by several scientific groups. the usefulness of such transgenic plants, with improved Pi uptake and enhanced Pi mobilization, and possible application of these plants in agriculture are discussed

Chlorophyll a fluorescence - history of discovery and practical application in environmental plant science

Fluorescencja chlorofilu a jest czułą, nieinwazyjną i szybką metodą pomiaru wydajności fotosystemu II (PSII). Artykuł przedstawia wprowadzenie teoretyczne, historię odkrycia fenomenu, opis najczęściej używanych technik oraz praktyczne zastosowanie pomiarów fluorescencji chlorofilu a w badaniach. Scharakteryzowano trzy główne metody pomiaru fluorescencji chlorofilu a tj. szybką, modulowaną oraz jej obrazowanie. Analiza parametrów fotoluminescencji chlorofilu a dostarcza wielu informacji o funkcjonowaniu PSII roślin rosnących w warunkach stresu abiotycznego i biotycznego, jest powszechnie wykorzystywana przez fizjologów roślin oraz ekofizjologów. Przedstawiono najnowsze wyniki badań wpływu wybranych niekorzystnych warunków środowiska (promieniowanie świetlne, wysoka temperatura, przechłodzenie, susza, zalanie, uszkodzenie mechaniczne) na zmiany parametrów fluorescencji chlorofilu a. Artykuł jest wprowadzeniem do tematyki pomiarów fluorescencji chlorofilu a i jest przeznaczony dla osób zainteresowanych wykorzystaniem jej w swoich badaniach.Chlorophyll a fluorescence is a sensitive, non-invasive fast tool for measuring photosynthetic efficiency mainly of photosystem II (PSII). We present description of basic photoluminescence mechanism, history of chlorophyll fluorescence discovery and review of main chlorophyll fluorescence measurement techniques with practical issue. In this article, we focus on methods of a fast chlorophyll fluorescence, pulse-amplitude modulated chlorophyll fluorescence and chlorophyll fluorescence imaging technique. Described techniques are powerful and widely use tools, available for plant physiologists and ecophysiologists. Analysis of the chlorophyll fluorescence parameters, which are good indicators or biomarkers of plant tolerance, provides many information about efficiency of PSII during abiotic and biotic stress. We describe how environmental stress conditions (irradiance, heat, cold, drought, flood and mechanical wounding) influence to most popular chlorophyll a fluorescence parameters and how to interpret them. The aim of this review is to provide a simple, practical guide to chlorophyll fluorescence for beginners

Mechanisms of oat (Avena sativa L.) acclimation to phosphate deficiency

Background Deficiency of available forms of phosphorus is common in most soils and causes reduction of crop plants growth and yield. Recently, model plants responses to phosphate (Pi) deficiency have been intensively studied. However, acclimation mechanisms of cereals like oat (Avena sativa L.), to low Pi stress remains not fully understood. Oat plants have been usually cultured on poor soils, with a low nutrient content, but their responses to such conditions are not well known, therefore the main goal of the study was to investigate the mechanisms that enable oat plants to grow under low Pi conditions. Methods Four oat cultivars (A. sativa, cv. Arab, Krezus, Rajtar and Szakal) were grown for three weeks in a nutrient media with various P sources: inorganic—KH2PO4 (control), organic—phytate (PA) and with no phosphate (−P). The effects of Pi deficiency on the level of P, oat growth parameters, intensity of photosynthesis, plant productivity, root exudation ability, localization, activity and isoforms of acid phosphatases, enzymes involved in Pi mobilization, were estimated. In addition, the effect of mycorrhization on plant growth was also observed. Results All studied oat cultivars grown on Pi-deficient media had significantly decreased Pi content in the tissues. Pi deficiency caused inhibition of shoot growth, but generally it did not affect root elongation; root diameter was decreased, root/shoot ratios increased, whereas PA plants showed a similar growth to control. Photosynthesis rate and productivity parameters decreased under low Pi nutrition, however, sugar content generally increased. Studied oat cultivars did not respond to low Pi via increased exudation of carboxylates from the roots, as pH changes in the growth media were not observed. Pi starvation significantly increased the activity of extracellular and intracellular acid phosphatases (APases) in comparison to the control plants. Three major APase isoforms were detected in oat tissues and the isoform pattern was similar in all studied conditions, usually with a higher level of one of the isoforms under Pi starvation. Generally no significant effects of mycorrhizal colonization on growth of oat cultivars were observed. Discussion We postulated that acid phosphatases played the most important role in oat cultivars acclimation to Pi deficiency, especially extracellular enzymes involved in Pi acquisition from soil organic P esters. These APases are mainly located in the epidermis of young roots, and may be released to the rhizosphere. On the other hand, intracellular APases could be involved in fast Pi remobilization from internal sources. Our study showed that oat, in contrast to other plants, can use phytates as the sole source of P. The studied oat cultivars demonstrated similar acclimation mechanisms to Pi deficiency, however, depending on stress level, they can use different pools of acid phosphatases

Mitochondria Are Important Determinants of the Aging of Seeds

Seeds enable plant survival in harsh environmental conditions, and via seeds, genetic information is transferred from parents to the new generation; this stage provides an opportunity for sessile plants to settle in new territories. However, seed viability decreases over long-term storage due to seed aging. For the effective conservation of gene resources, e.g., in gene banks, it is necessary to understand the causes of decreases in seed viability, not only where the aging process is initiated in seeds but also the sequence of events of this process. Mitochondria are the main source of reactive oxygen species (ROS) production, so they are more quickly and strongly exposed to oxidative damage than other organelles. The mitochondrial antioxidant system is also less active than the antioxidant systems of other organelles, thus such mitochondrial ‘defects’ can strongly affect various cell processes, including seed aging, which we discuss in this paper