Rapid changes in root HvPIP2; 2 aquaporins abundance and ABA concentration are required to enhance root hydraulic conductivity and maintain leaf water potential in response to increased evaporative demand

To address the involvement of abscisic acid (ABA) in regulating transpiration and root hydraulic conductivity (Lp(Root)) and their relative importance for maintaining leaf hydration, the ABA-deficient barley mutant Az34 and its parental wild-type (WT) genotype (cv. Steptoe) were grown in hydroponics and exposed to changes in atmospheric vapour pressure deficit (VPD) imposed by air warming. WTplants were capable of maintaining leaf water potential (psi(L)) that was likely due to increased Lp(Root) enabling higher water flow from the roots, which increased in response to air warming. The increased Lp(Root) and immunostaining for HvPIP2; 2 aquaporins (AQPs) correlated with increased root ABA content of WT plants when exposed to increased air temperature. The failure of Az34 to maintain psi(L) during air warming may be due to lower Lp(Root) than WT plants, and an inability to respond to changes in air temperature. The correlation between root ABA content and Lp(Root) was further supported by increased root hydraulic conductivity in both genotypes when treated with exogenous ABA (10(-5) M). Thus the ability of the root system to rapidly regulate ABA levels (and thence aquaporin abundance and hydraulic conductivity) seems important to maintain leaf hydration

The Influence of Hydrocarbon-Oxidizing Auxin-Producing Bacteria on the Growth, Biochemical Parameters, and Hormonal Status of Barley Plants in the Process of Bioremediation of Oil-Contaminated Soil

Взаимосвязи бактерий и растений в процессе биоремедиации почв, загрязненных нефтью, уделяется много внимания, однако воздействие бактерий-деструкторов нефти, синтезирующих фитогормоны, на содержание и распределение этих соединений в самих растениях, исследовано слабо. Целью полевого опыта было изучение влияния углеводородокисляющих бактерий, продуцирующих ауксины, на ростовые, биохимические показатели и гормональный статус растений ячменя в присутствии нефти и перспективы применения их ассоциаций для очистки почвы, содержащей нефть (в среднем 2,7 %). Обработка растений штаммами Enterobacter sp. UOM 3 и Pseudomonas hunanensis IB C7 приводила к увеличению длины и массы корней и побегов, индекса листовой поверхности и улучшению показателей элементов структуры урожая, которые были угнетены под воздействием поллютанта. В результате бактеризации повышалось содержание хлорофилла, флавоноидов и снижалось количество пролина. Наиболее заметным проявлением влияния бактерий на гормональную систему растений было уменьшение накопления абсцизовой кислоты. Полученные данные свидетельствуют о том, что интродукция микроорганизмов ослабляла для растений негативные последствия абиотического стресса, вызванного присутствием нефти. Совместное применение бактерий-нефтедеструкторов и растений эффективнее снижало содержание углеводородов в почве и увеличивало ее микробиологическую активность по сравнению с использованием их по отдельности. Изученные микробно-растительные комплексы признаны перспективными для биоремедиации нефтезагрязненных почвExtensive research has been done to investigate the relationship between bacteria and plants in the process of bioremediation of soils contaminated with oil, but the effect of oil-degrading bacteria that synthesize phytohormones on the content and distribution of these compounds in plants has been poorly studied. The aim of the field experiment was to study the effect of hydrocarbon-oxidizing bacteria producing auxins on the growth, biochemical parameters, and hormonal status of barley plants in the presence of oil and the prospects for using bacterial-plant associations for treating soil that contains oil (2.7 %, on average). Treatment of plants with cultures of Enterobacter sp. UOM 3 and Pseudomonas hunanensis IB C7 led to an increase in the length and mass of roots and shoots and the leaf surface index and an improvement in the parameters of the components of the crop structure that were suppressed by the pollutant. As a result of bacterization, the contents of chlorophyll and flavonoids increased, and the amount of proline decreased. The most noticeable effect of bacteria on the hormonal system of plants was a decrease in the accumulation of abscisic acid. The data obtained indicate that the treatment of plants with bacterial cultures alleviated the negative consequences of abiotic stress caused by the presence of oil for plants. The use of oil-degrading bacteria and plants in combination rather than separately more effectively reduced the content of hydrocarbons in the soil and increased its microbiological activity. The microbial-plant combinations studied in this work are regarded as promising for the bioremediation of oil-contaminated soil

Effect of partial rootzone drying on the concentration of zeatin-type cytokinins in tomato (Lycopersicon esculentum Mill.) xylem sap and leaves.

Effect of partial rootzone drying on the concentration of zeatin-type cytokinins in tomato (Solanum lycopersicum L.) xylem sap and leaves Guzel R. Kudoyarova1, Lidia B. Vysotskaya1, Alla Cherkozyanova1 and Ian C. Dodd2,* 1Institute of Biology of the Russian Academy of Sciences, Ufa Research Centre, Oktyabrya str. 69, 450054, Ufa, Russian Federation 2Department of Biological Sciences, The Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK * To whom correspondence should be addressed. E-mail: [email protected] Decreased cytokinin (CK) export from roots in drying soil might provide a root-to-shoot signal impacting on shoot physiology. Although several studies show that soil drying decreases the CK concentration of xylem sap collected from the roots, it is not known whether this alters xylem CK concentration ([CKxyl]) in the leaves and bulk leaf CK concentration. Tomato (Solanum lycopersicum L.) plants were grown with roots split between two soil columns. During experiments, water was applied to both columns (well-watered; WW) or one (partial rootzone drying; PRD) column. Irrigation of WW plants aimed to replace transpirational losses every day, while PRD plants received half this amount. Xylem sap was collected by pressurizing detached leaves using a Scholander pressure chamber, and zeatin-type CKs were immunoassayed using specific antibodies raised against zeatin riboside after separating their different forms (free zeatin, its riboside, and nucleotide) by thin-layer chromatography. PRD decreased the whole plant transpiration rate by 22% and leaf water potential by 0.08 MPa, and increased xylem abscisic acid (ABA) concentration 2.5-fold. Although PRD caused no detectable change in [CKxyl], it decreased the CK concentration of fully expanded leaves by 46%. That [CKxyl] was maintained and not increased while transpiration decreased suggests that loading of CK into the xylem was also decreased as the soil dried. That leaf CK concentration did not decline proportionally with CK delivery suggests that other mechanisms such as CK metabolism influence leaf CK status of PRD plants. The causes and consequences of decreased shoot CK status are discussed

ABA mediation of shoot cytokinin oxidase activity: assessing its impacts on cytokinin status and biomass allocation of nutrient deprived wheat.

Although nutrient deprivation alters the concentrations of several plant hormones, the role of each in decreasing shoot-to-root ratio is not clear. A 10-fold dilution of the nutrient concentration supplied to hydroponically-grown 7-day-old durum wheat (Triticum turgidum L. ssp. durum Desf.) plants decreased shoot growth, shoot-to-root ratio and shoot and root cytokinin concentrations, increased shoot ABA concentration and shoot cytokinin oxidase activity, but had no effect on xylem sap ABA and cytokinin concentrations. Nutrient deprivation also increased xylem concentrations of conjugated ABA. The role of ABA in these responses was addressed by adding 11.4 µm ABA to the nutrient solution of well fertilised plants, or 1.2 mm fluridone (an inhibitor of ABA biosynthesis) to the nutrient solution of nutrient-deprived plants. The former induced similar changes in shoot-to-root ratio (by inhibiting shoot growth), shoot ABA concentration, shoot and root cytokinin concentrations and shoot cytokinin oxidase activity as nutrient deprivation. Conversely, fluridone addition to nutrient-deprived plants restored shoot-to-root ratio (by inhibiting root growth), shoot ABA concentration, shoot and root cytokinin concentrations to levels similar to well fertilised plants. Although root growth maintenance during nutrient deprivation depends on a threshold ABA concentration, shoot growth inhibition is independent of shoot ABA status. Although fluridone decreased shoot cytokinin oxidase activity of nutrient-deprived plants, it was still 1.7-fold greater than well fertilised plants, implying that nutrient deprivation could also activate shoot cytokinin oxidase independently of ABA. These data question the root signal basis of cytokinin action, but demonstrate that changes in ABA status can regulate shoot cytokinin concentrations via altering their metabolism

Common and specific responses to availability of mineral nutrients and water

Changes in resource (mineral nutrients and water) availability, due to their heterogeneous distribution in space and time, affect plant development. Plants need to sense these changes to optimize growth and biomass allocation by integrating root and shoot growth. Since a limited supply of water or nutrients can elicit similar physiological responses (the relative activation of root growth at the expense of shoot growth), similar underlying mechanisms may affect perception and acquisition of either nutrients or water. This review compares root and shoot responses to availability of different macronutrients and water. Attention is given to the roles of root-to-shoot signalling and shoot-to-root signalling, with regard to coordinating changes in root and shoot growth and development. Involvement of plant hormones in regulating physiological responses such as stomatal and hydraulic conductance is revealed by measuring the effects of resource availability on phytohormone concentrations in roots and shoots, and their flow between roots and shoots in xylem and phloem saps. More specific evidence can be obtained by measuring the physiological responses of genotypes with altered hormone responses or concentrations. We discuss the similarity and diversity of changes in shoot growth, allocation to root growth, and root architecture under changes in water, nitrate, and phosphorus availability, and the possible involvement of abscisic acid, indole-acetic acid, and cytokinin in their regulation. A better understanding of these mechanisms may contribute to better crop management for efficient use of these resources and to selecting crops for improved performance under suboptimal soil conditions

Accumulation of cytokinins in roots and their export to the shoots of durum wheat plants treated with the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP)

Cytokinin flow from roots to shoots can serve as a long-distance signal important for root-to-shoot communication. In the past, changes in cytokinin flow from roots to shoots have been mainly attributed to changes in the rate of synthesis or breakdown in the roots. The present research tested the possibility that active uptake of cytokinin by root cells may also influence its export to shoots. To this end, we collapsed the proton gradient across root membranes using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to inhibit secondary active uptake of exogenous and endogenous cytokinins. We report the impact of CCCP on cytokinin concentrations and delivery in xylem sap and on accumulation in shoots of 7-day-old wheat plants in the presence and absence of exogenous cytokinin applied as zeatin. Zeatin treatment increased the total accumulation of cytokinin in roots and shoots but the effect was smaller for the shoots. Immunohistochemical localization of cytokinins using zeatin-specific antibodies showed an increase in immunostaining of the cells adjacent to xylem in the roots of zeatin-treated plants. Inhibition of secondary active cytokinin uptake by CCCP application decreased cytokinin accumulation in root cells but increased both flow from the roots and accumulation in the shoots. The possible importance of secondary active uptake of cytokinins by root cells for the control of their export to the shoot is discussed

Secondary Active Transporters Decrease Cytokinin Flow into Barley Shoots and Inhibit their Growth under Phosphate Deficit

Исследование посвящено изучению роли вторично активного транспорта как одного из важных механизмов перераспределения цитокининов между побегом и корнем, обеспечивающего приспособительную к дефициту фосфора ростовую реакцию растений ячменя. Определяли концентрацию (нг/г сырой массы) и содержание (нг в целом органе) разных форм цитокининов в побегах и корнях растений ячменя методом иммуноферментного анализа (ИФА). Показано, что при дефиците фосфора поддержание массы корней, подавление их ветвления и снижение массы побегов растений ячменя сорта Прерия были обусловлены снижением концентрации цитокининов в побеге и повышением их содержания в корнях. Применение ингибитора вторично активного транспорта протонофора карбонилцианид-м- хлорфенилгидразона нивелировало гормональную реакцию на дефицит фосфора: предотвращало накопление цитокининов в корне и повышало их содержание в побеге, а также изменяло долю зеатина и его производных в суммарном содержании цитокининов в побегах и корнях. Анализ этих данных показал, что в корнях содержание зеатиннуклеотида и зеатинрибозида изменялось незначительно, в то время как максимально снижалось содержание зеатина, на поглощение которого клетками корней протонофор оказывал существенное влияние в отличие от рибозида. В работе обсуждается важная роль вторично активного трансмембранного переноса в регуляции транспорта цитокининов из корней в побеги при дефиците фосфатовSecondary active transport is one of the most important mechanisms controlling cytokinin distribution between shoots and roots which enables the adaptive growth reaction of barley. Concentrations (ng/g of fresh mass) and contents (ng/organ) of different forms of cytokinins were determined in shoots and roots of barley plants by immunoassay. It was shown that under phosphate deficit the maintenance of root growth, inhibition of root branching and decline in shoot mass of barley plants (Hordeum vulgare 'Prairie') was due to decline in shoot cytokinins and their accumulation in the roots. Protonophore carbonyl cyanide-m-chlorophenylhydrazone as an inhibitor of secondary active transport leveled off hormonal reaction to phosphate deficit: it prevented accumulation of cytokinins in roots, increased their content in shoots and changed the percentage of zeatin and its derivatives in total cytokinin content in roots and shoots. A data analysis showed that in roots, protonophore did not change significantly the content of ribosides and nucleotides of zeatin, while uptake of free zeatin by cells was significantly affected by the protonophore and its content decreased dramatically. The role of secondary active trans-membrane transfer is discussed in the context of cytokinins transport from roots to shoots under phosphate defici

Влияние дефицита фосфора на рост корней, продукцию активных форм кислорода и содержание гормонов в растениях ячменя

The article presents the results of research into the effect of removing phosphate from a nutrient medium on the content of auxins and cytokinins in roots, root elongation and content of reactive oxygen species in root tips of the barley ‘Steptoe’. In our experiments, the growth response was detected as root elongation after a 4-day exposure to a phosphate-free medium. Activation of linear root growth was preceded by changes in hormonal balance and in the level of reactive oxygen species. Auxin content in the roots increased after 6 h of phosphate starvation and a two-fold increase in the concentration of auxins in roots was detected by the end of the first day of the exposure to the phosphate deficit conditions. Staining with diaminobenzidine revealed an increased level of reactive oxygen species in the root tips of phosphate-starved plants after 6 h of exposure. However, after one day (24 h), a reverse pattern was observed: the level of staining was higher in the plants supplied with phosphates. Immunolocalisation of cytokinins in the root tips, where the zones of cell division and extension determining root elongation are located, showed a decreased content of zeatin in the cells under the effect of phosphorus deficit. The obtained data suggest that the detected rise in the amount of reactive oxygen species was due to the increased concentration of auxins accumulated as a result of the phosphate deficit effect on the barley plants. The increase in ROS and auxins contents could in turn influence the level of cytokinins and, in the end, affect root elongation. Further experiments are needed to test this hypothesisВ работе представлены результаты изучения влияния удаления фосфатов из питательного раствора на содержание ауксинов и цитокининов в корнях, удлинение корней и содержание активных форм кислорода в кончиках корней растений ячменя. Ростовая реакция, проявившаяся в наших экспериментах в удлинении корней растений ячменя сорта Steptoe, была отмечена после 4 суток воздействия бесфосфатной среды. Активации линейной скорости роста корней предшествовали изменения гормонального баланса и уровня реактивных форм кислорода. C помощью метода иммуноферментного анализа через 6 часов воздействия дефицита фосфора было отмечено достоверное возрастание, а к концу первых суток – двукратное увеличение концентрации ауксинов в корне. На фоне фосфатного голодания окрашивание корней диаминобензидином позволило выявить повышенный уровень реактивных форм кислорода в кончиках корней через 6 часов; по истечении первых суток (24 ч) наблюдали обратную картину – уровень окрашивания корней снабженных фосфатами растений был выше. Результаты иммунолокализации цитокининов в кончиках корней, где и находятся определяющие рост корней в длину зоны деления и растяжения, показали снижение содержания зеатина в клетках, находящихся под влиянием дефицита фосфора. Полученные данные позволяют предположить, что выявленное накопление в корнях активных форм кислорода может быть обусловлено повышенной концентрацией ауксинов, накопившихся в результате воздействия дефицита фосфора на растения ячменя. Повышение уровня ауксинов и реактивных форм кислорода в свою очередь могло повлиять на уровень цитокининов и, в конечном счете, на удлинение корней. Требуются дальнейшие исследования для проверки этого предположени

Rhizobacteria Inoculation Effects on Phytohormone Status of Potato Microclones Cultivated In Vitro under Osmotic Stress

Water deficits inhibit plant growth and decrease crop productivity. Remedies are needed to counter this increasingly urgent problem in practical farming. One possible approach is to utilize rhizobacteria known to increase plant resistance to abiotic and other stresses. We therefore studied the effects of inoculating the culture medium of potato microplants grown in vitro with Azospirillum brasilense Sp245 or Ochrobactrum cytisi IPA7.2. Growth and hormone content of the plants were evaluated under stress-free conditions and under a water deficit imposed with polyethylene glycol (PEG 6000). Inoculation with either bacterium promoted the growth in terms of leaf mass accumulation. The effects were associated with increased concentrations of auxin and cytokinin hormones in the leaves and stems and with suppression of an increase in the leaf abscisic acid that PEG treatment otherwise promoted in the potato microplants. O. cytisi IPA7.2 had a greater growth-stimulating effect than A. brasilense Sp245 on stressed plants, while A. brasilense Sp245 was more effective in unstressed plants. The effects were likely to be the result of changes to the plant’s hormonal balance brought about by the bacteria