Reduction In Leaf Water Potential Research Articles

PHYSIOLOGICAL RESPONSES OF THREE WOODY SPECIES SEEDLINGS UNDER WATER STRESS, IN SOIL WITH AND WITHOUT ORGANIC MATTER

ABSTRACT The low availability of water in the soil is one of the limiting factors for the growth and survival of plants. The objective of this study was to evaluate the responses of physiological processes in early growth of guanandi (Calophyllum brasilense Cambess), African mahogany (Khayai vorensis A. Chev) and oiti (Licaniato mentosa Benth Fritsch) over a period of water stress and other of rehydration in the soil with and without addition of organic matter. The study was conducted in a greenhouse and the experimental design was completely randomised into a 3 x 2 x 2 factorial scheme, comprising three species (guanandi, African mahogany, and oiti), two water regimes (with and without water restriction) and two levels of organic fertilisation (with and without the addition of organic matter). Irrigation was suspended for 15 days in half of the plants, while the other half (control) continued to receive daily irrigation, the soil being maintained near field capacity for these plants. At the end of the stress period, the plants were again irrigated for 15 days to determine their recovery. Water restriction reduced leaf water potential and gas exchange in the three species under study, more severely in soil with no addition of organic matter. The addition of this input increased soil water retention and availability to the plants during the suspension of irrigation, reducing the detrimental effects of the stress. During the period of rehydration, there was strong recovery of water status and leaf gas exchange. However recovery was not complete, suggesting that some of the effects caused by stress irreversibly affected cell structures and functions. However, of the species being studied, African mahogany displayed a greater sensitivity to stress, with poorer recovery.

Physiological and ultrastructural responses of sour orange (Citrus aurantium L.) clones to water stress

Water stress is a major abiotic constraint leading to serious crop losses. Recently, in the Mediterranean region, water stress has become markedly sensed, especially in Citrus orchards. This study investigated the physiological responses of local sour orange (Citrus aurantium L.) clones to severe water stress. Water stress was applied by withholding irrigation during weeks, followed by a rewatering phase during three months. Under water stress, sour orange clones decreased their stomatal conductance, net photosynthetic rate, and transpiration rate. On the contrary, biomass was stable, especially in the Kliaa clone. In addition, reduced leaf water potentials (-3 MPa) and water contents were measured in most of the clones, except Kliaa which kept the highest water potential (-2.5 MPa). After rewatering, all clones recovered except of the Ghars Mrad (GM) clone. Ultrastructural observations of leaf sections by transmission electron microscopy did not reveal marked alterations in the mesophyll cells and chloroplast structure of Kliaa in comparison to the sensitive clone GM, in which palisade parenchyma cells and chloroplasts were disorganized. This contrasting behavior was mainly attributed to genetic differences as attested by molecular analysis. This study highlighted GM as the drought-sensitive clone and Kliaa as the tolerant clone able to develop an avoidance strategy based on an efficient stomatal regulation. Although a high percentage of polyembryony characterizes C. aurantium and justifies its multiplication by seeds, heterogeneous water-stress responses could be observed within sour orange plants in young orchards.

Nitrogen Sustains Seed Yield of Quinoa Under Intermediate Drought

AbstractQuinoa (Chenopodium quinoa Willd.) is a promising crop for food security in dry areas. Studies have been conducted to define nitrogen (N) fertilization levels and to understand the responses of quinoa to drought, but little is known about the response of this crop to N fertilization under drought stress. The aim of this study was to investigate whether N fertilization could improve quinoa yield and physiology under limited water. A greenhouse experiment was carried out with quinoa grown at four N fertilization levels (0, 0.2, 0.4 and 0.6 g N pot−1) and two watering treatments (progressive drought and full irrigation; 10 and 98 % of pot water holding capacity, respectively). Results of this experiment showed that N may confer a certain degree of drought tolerance to quinoa as seed quality and yield of N‐fertilized plants were not affected by drought stress. Responses such as faster stomatal closure, reduced leaf water potential, higher leaf abscisic acid (ABA) concentration and particularly an improved N remobilization in N‐fertilized plants may have played a role in sustaining seed yield in the drought‐stressed treatment. These results under controlled conditions serve as a basis to elucidate drought tolerance mechanisms activated with N fertilization and to define the use of N in management practices under semi‐arid environments.

Salt tolerance of Beta macrocarpa is associated with efficient osmotic adjustment and increased apoplastic water content.

The chenopod Beta macrocarpa Guss (wild Swiss chard) is known for its salt tolerance, but the mechanisms involved are still debated. In order to elucidate the processes involved, we grew wild Swiss chard exposed to three salinity levels (0, 100 and 200mm NaCl) for 45days, and determined several physiological parameters at the end of this time. All plants survived despite reductions in growth, photosynthesis and stomatal conductance in plants exposed to salinity (100 and 200mm NaCl). As expected, the negative effects of salinity were more pronounced at 200mm than at 100mm NaCl: (i) leaf apoplastic water content was maintained or increased despite a significant reduction in leaf water potential, revealing the halophytic character of B.macrocarpa; (ii) osmotic adjustment occurred, which presumably enhanced the driving force for water extraction from soil, and avoided toxic build up of Na(+) and Cl(-) in the mesophyll apoplast of leaves. Osmotic adjustment mainly occurred through accumulation of inorganic ions and to a lesser extent soluble sugars; proline was not implicated in osmotic adjustment. Overall, two important mechanisms of salt tolerance in B.macrocarpa were identified: osmotic and apoplastic water adjustment.

Genotypic variation in N uptake and assimilation estimated by 15N tracing in water deficit-stressed Brassica napus

To investigate varietal difference in nitrogen-use efficiency and water-deficit tolerance among eight Brassica napus cultivars, direct quantification of the amount of newly absorbed N and its incorporation to amino acids and proteins was performed by tracing 15N for 7 days of well-watered (control) and water-deficit conditions. Water deficit leads to reduction of leaf water potential (Ψw), biomass, chlorophyll content and nitrogen concentration with cultivar variation. The amount of newly absorbed N for the given time significantly decreased in water-deficit plants, which can be classified into three groups; high N uptake [Saturnin, Tamra (>6.5mgplant−1)], medium [Colosse, Sparta, Capitol, Akela (4–6mgplant−1)], and low [Youngsan, Pollen (<4mgplant−1)]. Water deficit significantly decreased overall the amount of N assimilated into amino acids and proteins. Significant cultivar variation for the inhibition of de novo protein synthesis caused by water deficit was found, being the highest in Pollen (−42.2% compared to control) versus the lowest in Saturnin (−31.2%). By an estimation of nitrogen-use efficiency based on N uptake (NUpE) and N assimilation (NUaE), Saturnin and Tamra could be identified as N-efficient genotypes, while Youngsan and Pollen as inefficient ones. It was found that cultivar variation in NUpE and NUaE was significantly associated with the change in Ψw as affected by water deficit. The present study suggests that the Ψw can be used as an easy and sensitive determinant predictive for assessing NUpE which is a preliminary factor for NUaE under water deficit.

Kaolin influences tomato response to salinity: physiological aspects

Environmental stress as salinity can negatively affect the physiology of tomato plants. Conditions leading to a reduction of transpiration can contribute to greater tolerance to salinity. Use of kaolin-based particle film technology (PFT) may be an effective tool to control stomatal conductance and transpiration rate, thus mitigating the detrimental effect of salinity. The present three-year study has investigated the effects of kaolin application on leaf gas exchange, leaf water potential, leaf and canopy temperature of field-grown tomato, irrigated with brackish water by drip method, in southern Italy. Treatments were: (1) three salinity levels of irrigation water (electrical conductivity of water = 0.5, 5 and 10 dS m−1); (2) tomato plants treated or not with kaolin; and (3) two cultivars in each year. The increase in salinity caused the reduction of leaf water potential, stomatal conductance, net photosynthesis and transpiration rate, and the increase of leaf and canopy temperature. Kaolin has resulted in an improvement of leaf water potential, and the reduction in gas exchange variables in low-salinity conditions. Under high salinity, kaolin was effective in limiting the reductions in net photosynthesis and reducing leaf and canopy temperature. These latter variables were slightly affected by kaolin, in different ways in respect to the saline treatments; while in non-saline conditions were 0.2–0.5°C higher in the kaolin-treated plants, the situation was reversed in more saline treatment. The variation of leaf and canopy temperature shows that kaolin influences the thermal balance mainly for the dual effect of reflection of the incident radiation and partial occlusion of the stomata. Kaolin mitigated detrimental effects of salinity also on yield, contributing to the improvement of income for the farmers. The use of kaolin-based PFT may be an effective tool to alleviate salinity stress in tomato production under arid and semi-arid conditions.

Desempenho ecofisiológico de milho, sorgo e braquiária sob déficit hídrico e reidratação

O presente estudo avaliou o desempenho ecofisiológico das espécies Zea mays (milho), Sorghum bicolor (sorgo) e Brachiaria decumbens (braquiária) sob condições de déficit hídrico em casa de vegetação. O potencial hídrico foliar, trocas gasosas, fluorescência da clorofila a e variáveis bioquímicas do metabolismo fotossintético foram avaliados no máximo estresse e na reidratação. Aos 90 dias após a emergência e sob 21 dias com suspensão da irrigação o milho apresentou a maior redução do potencial hídrico (248%), condutância estomática (87%) e fotossíntese (53%) quando comparado às plantas bem hidratadas. O sorgo apresentou redução de 212%, 42% e 26%, enquanto a braquiária mostrou valores menores em 105%, 36% e 31%, respectivamente para os mesmos parâmetros. Entretanto, dois dias de reidratação foram o suficiente para todas as espécies recuperarem os valores apresentados pelos respectivos controles. A espécie que apresentou a menor queda relacionada aos parâmetros avaliados foi o sorgo, com redução em apenas 4 das 14 variáveis avaliadas, enquanto braquiária e milho reduziram 9 variáveis quando sob seca. O presente estudo destaca que, além da questão econômica, a tomada de decisão por parte de técnicos e pequenos agricultores de quais espécies devem ser utilizadas, sob baixa disponibilidade de tecnologia e alto risco de ocorrência de falta de água, deve-se levar em conta também o desempenho ecofisiológico.

Association of Nodule Performance Traits with Shoot Performance Traits of Common Bean Under Drought Stress

Although symbiotic nitrogen fixation (SNF) and nodule characteristics have been evaluated before, their use as phenotypic markers for drought tolerance in beans (Phaseolus vulgaris L.) and their association with aboveground traits under water deficiency have not been quantified widely. Therefore, the effect of drought stress on the association of nodule performance traits with shoot performance traits was investigated using six common bean lines with contrasting differences in their adaptation to drought and low phosphorus (P) availability in soil. Drought stress reduced leaf water potential and gas-exchange characteristics (CO2 assimilation, stomatal conductance) in all lines tested, but two drought-tolerant lines, BAT 477 and BT_34-1,-1, were superior in their ability to adjust their leaf water status under drought. These two lines were also superior in root growth, rate of CO2 assimilation, vegetative biomass production, and nitrogen-fixing ability under drought stress. A direct relation of SNF and nodule fresh weight with gas-exchange traits and biomass production existed, suggesting that relative growth of shoot vs. root depends on the provision of nitrogen by SNF and photosynthetic carbon assimilation. Overall, differences found in nodule, root, and shoot performance traits indicated that the P-efficient bean line (BT_34-1-1) was superior to the other lines in adaptation to drought. Marked association of nodule performance traits with shoot performance traits under drought stress was detected. We suggest that nodule characteristics and SNF ability should be included with above- and below-ground traits as phenotypic markers in germplasm evaluation and breeding programs aimed at improving drought tolerance in common bean.

Anatomic and physiological modifications in seedlings of Coffea arabica cultivar Siriema under drought conditions

Due to the weather changes prognostic for the coming years, the understanding of water deficit and physiological responses of plants to drought becomes an important requirement in order to develop technologies such as mechanisms to assist plants to cope with longer drought periods, which will be essential to maintenance of Brazilian and worldwide production. This study aimed to evaluate ecophysiological and anatomical aspects as well as the nitrate reductase activity in Siriema coffee seedlings subjected to four treatments: Daily irrigated, non-irrigated, re-irrigated 24 hours and re-irrigated 48 hours after different stress periods. Non-irrigation promoted a reduction in leaf water potential being accented from the ninth day of evaluation onwards. Re-irrigation promoted a partial recovery of the plant water potential. Non-irrigated plants showed an increase in stomatal resistance and reduction of transpiration and nitrate reductase activity. In the roots, there was a decrease in nitrate reductase activity under water stress. Leaf anatomical modifications were significant only for the adaxial surface epidermis and palisade parenchyma thickness, this latter characteristic being higher in control plants. Stomatal density and polar and equatorial diameter ratios showed the highest values in plants under water stress. In the roots, differences only in the cortex thickness being bigger in the non-irrigated treatment could be observed. Therefore, Siriema coffee plants under water stress show physiological, biochemical and anatomical modifications that contribute to the tolerance of this genotype to these conditions.

Integrating transcriptional, metabolomic, and physiological responses to drought stress and recovery in switchgrass (Panicum virgatum L.).

BackgroundIn light of the changes in precipitation and soil water availability expected with climate change, understanding the mechanisms underlying plant responses to water deficit is essential. Toward that end we have conducted an integrative analysis of responses to drought stress in the perennial C4 grass and biofuel crop, Panicum virgatum (switchgrass). Responses to soil drying and re-watering were measured at transcriptional, physiological, and metabolomic levels. To assess the interaction of soil moisture with diel light: dark cycles, we profiled gene expression in drought and control treatments under pre-dawn and mid-day conditions.ResultsSoil drying resulted in reduced leaf water potential, gas exchange, and chlorophyll fluorescence along with differential expression of a large fraction of the transcriptome (37%). Many transcripts responded differently depending on time of day (e.g. up-regulation pre-dawn and down-regulation mid-day). Genes associated with C4 photosynthesis were down-regulated during drought, while C4 metabolic intermediates accumulated. Rapid changes in gene expression were observed during recovery from drought, along with increased water use efficiency and chlorophyll fluorescence.ConclusionsOur findings demonstrate that drought responsive gene expression depends strongly on time of day and that gene expression is extensively modified during the first few hours of drought recovery. Analysis of covariation in gene expression, metabolite abundance, and physiology among plants revealed non-linear relationships that suggest critical thresholds in drought stress responses. Future studies may benefit from evaluating these thresholds among diverse accessions of switchgrass and other C4 grasses.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-527) contains supplementary material, which is available to authorized users.

Contrasting Hydraulic Strategies during Dry Soil Conditions in Quercus rubra and Acer rubrum in a Sandy Site in Michigan

Correlation analyses were carried out for the dynamics of leaf water potential in two broad-leaf deciduous tree species in a sandy site under a range of air vapor pressure deficits and a relatively dry range of soil conditions. During nights when the soil is dry, the diffuse-porous, isohydric and shallow-rooted Acer rubrum does not recharge its xylem and leaf water storage to the same capacity that is observed during nights when the soil is moist. The ring-porous, deep-rooted Quercus rubra displays a more anisohydric behavior and appears to be capable of recharging to capacity at night-time even when soil moisture at the top 1 m is near wilting point, probably by accessing deeper soil layers than A. rubrum. Compared to A. rubrum, Q. rubra displays only a minimal level of down-regulation of stomatal conductance, which leads to a reduction of leaf water potential during times when vapor pressure deficit is high and soil moisture is limiting. We determine that the two species, despite typically being categorized by ecosystem models under the same plant functional type—mid-successional, temperate broadleaf—display different hydraulic strategies. These differences may lead to large differences between the species in water relations, transpiration and productivity under different precipitation and humidity regimes.

The effects of throughfall exclusion on xylogenesis of balsam fir

A 20-40% reduction in soil moisture is projected for the boreal forest of Eastern Canada for the period 2070-99 relative to 1971-2000. In order to better predict the effects of a reduced water supply on the growth of balsam fir (Abies balsamea (L.) Mill.), a dominant tree species of the boreal forest, we simulated 2 consecutive years of summer droughts (starting in July) by means of throughfall exclusion. Four 100-m(2) plots were established in 2010 with polyethylene sheets maintained 1.3-2 m aboveground and redirecting the water outside the plots. Wood microcores were extracted weekly from mature trees from April to October 2011 to analyse the time dynamics of wood formation in that year. The number of tracheids formed during and before treatment and their anatomical characteristics were determined through microscopic analyses. The growth of lateral and terminal branches and the water potential of balsam fir seedlings were also monitored. Throughfall exclusion significantly reduced soil water content by 5.8% in 2010 and 10.5% in 2011. Xylogenesis was affected significantly by the treatment. Tracheids were 16.1% smaller in diameter and their cell wall was 14.1% thicker during both years. The treatment delayed by more than a week the start of the tracheid differentiation process in the second year with a concomitant decrease (26%) in the number of tracheids produced. The seedlings displayed a 32% reduction in growth and a 40% reduction in leaf water potential. Our results suggest that a future regime of increased frequency and intensity of droughts could have negative effects on the duration of xylogenesis and the production of xylem cells in balsam fir.

EXOGENOUS APPLICATION OF POTASSIUM NITRATE TO ALLEVIATE SALT STRESS IN RICE SEEDLINGS

□ Overall growth characteristics of many plant species cultivated in soil affected by salinity could be alleviated by the application of potassium nitrate (KNO3) to the soil. The aim of this research was to investigate salt-tolerance in a salt-sensitive rice cultivar, ‘Pathumthani 1’ (PT1), in response to the exogenous application of 11.8 mM KNO3, in comparison to ‘Homjan’ (HJ), a salt tolerant cultivar. Water potential (ψw) in both the roots and leaves of PT1 seedlings under salt stress dropped significantly, while it was maintained in PT1 pretreated with KNO3, and similarly in HJ. The reduction of leaf water potential was positively related to total chlorophyll degradation, leading to diminished chlorophyll fluorescence, directly affecting growth in plants exposed to salt stress. In salt-sensitive PT1, the application of 11.8 mM KNO3 improved salt-tolerance via the conservation of water use efficiency, the maintenance of photosynthetic pigments, enhancement of chlorophyll a fluorescence, and stimulation of growth characters.

Adaptation to High Temperature and Water Deficit in the Common Bean (Phaseolus vulgarisL.) during the Reproductive Period

This paper reviews the adaption to heat and drought stresses inPhaseolus vulgaris, a grain and vegetable crop widely grown in both the Old and New World. Substantial genotypic differences are found in morphophysiological characteristics such as phenology, partitioning, plant-water relations, photosynthetic parameters, and shoot growth, which are related to reproductive responses. The associations between (a) days to podding and leaf water content and (b) the number of pods per plant and seed yield are consistent across different environments and experiments. Leaf water content is maintained by reductions in leaf water potential and shoot extension in response to heat and drought stress. Heat-tolerant cultivars have higher biomass allocation to pods and higher pod set in branches. These traits can be used as a marker to screen germplasm for heat and drought tolerance. In this paper, we briefly review the results of our studies carried out on heat and drought tolerance in the common bean at the Tropical Agriculture Research Front, Ishigaki, Japan.

The response of aphids to plant water stress – the case of Myzus persicae and Brassica oleracea var. capitata

AbstractThe possible repercussions of decreasing water availability in plant–insect interactions largely remain unclear. To study this, we designed two factorial studies applying two levels of water stress to Brassica oleraceae var. capitata L. (Brassicaceae) plants inoculated with the aphid Myzus persicae Sulzer (Hemiptera: Aphididae: Macrosiphini). One study investigated the effect of aphids and water stress on leaf water potential components, aphid population size, aphid intrinsic rate of increase (rm), and fecundity. The other investigated the effect of aphids and water stress on gas exchange, leaf fluorescence yield, estimation of leaf chlorophyll, and above‐ground dry weight. Drought treatment reduced the size of the M. persicae population. Aphid numbers were strongly and positively correlated with soil moisture and negatively correlated with leaf temperature. Aphids on droughted plants had lower rm and lower fecundity per aphid. Under aphid stress, plants showed reduced maximum photosynthetic rate (Amax), lower leaf chlorophyll as estimated by soil plant analysis development (SPAD) values, higher osmotic potential, and reduced final above‐ground dry weight compared with control plants. Aphid infestation also led to significantly higher leaf water potentials and reduced light‐adapted fluorescence yield. Compared with control plants, water‐stressed plants showed reduced Amax, lower SPAD values, reduced leaf water potential, lower turgor, and reduced final above‐ground dry weight. Osmotic potential was lower in droughted plants when aphids were not present. Plants under combined aphid and water stress showed significantly reduced SPAD and final above‐ground dry weight, with comparatively higher leaf water potentials. These results show that aphid infestation limits solute accumulation in the vacuole of drought stressed cabbage. Aphid infestation reduced the host’s ability to photosynthesise optimally and led to reduced growth. Plant stress hypotheses propose that a senescence feeder such as M. persicae would show higher rates of growth in response to the increasing ‘quality’ of the phloem sap under water shortage. In the case of M. persicae, our results do not support the hypothesis that drought leads to improved aphid population growth and survival.

Trocas gasosas e balanço de carboidratos em plantas de cana-de-açúcar sob condições de estresses radiculares

Embora a resposta da fotossíntese de plantas de cana-de-açúcar a estresses ambientais seja conhecida, o acúmulo de fitomassa e a dinâmica de carboidratos de reserva diante da exposição simultânea ao frio e à seca são pouco conhecidos. Este trabalho objetiva investigar o efeito do déficit hídrico e da baixa temperatura radicular, isolados e simultaneamente, no genótipo de cana-de-açúcar IACSP94-2094, considerado tolerante à seca. Como hipótese, consideramos que este genótipo também é tolerante à baixa temperatura radicular, já que baixas temperaturas e déficit hídrico ocorrem simultaneamente no campo. A imposição da restrição hídrica de forma isolada ou simultaneamente à baixa temperatura radicular causou redução do potencial da água na folha e da assimilação de CO2, o que não foi observado nas plantas submetidas apenas à baixa temperatura do substrato. Os teores foliares de carboidratos não estruturais, de sacarose e de amido aumentaram nas plantas sob frio radicular. Nos tratamentos com déficit hídrico, apenas o teor de amido foliar diminuiu. Os estresses radiculares causaram aumento nos teores de açúcares solúveis totais e diminuição no teor de amido nas raízes. Como o acúmulo de fitomassa das plantas não foi afetado, mesmo com a restrição no crescimento radicular nos tratamentos com baixa temperatura do substrato, conclui-se que o genótipo de cana-de-açúcar IACSP94-2094 contém indícios de tolerância à baixa temperatura radicular. A manutenção do crescimento da planta deve estar associada à degradação das reservas de amido foliares e radiculares.

Foliar Damage, Ion Content, and Mortality Rate of Five Common Roadside Tree Species Treated with Soil Applications of Magnesium Chloride

Sensitivity to magnesium chloride (MgCl2) was assessed on five common roadside tree species by maintaining soil concentrations at 0-, 400-, 800-, or 1,600-ppm chloride via MgCl2 solution over four growing seasons. Evaluations of growth, leaf retention, foliar damage, and ion concentrations were conducted. Water potentials were measured on two species. Foliar chloride and magnesium concentrations were positively correlated with foliar damage in all species. Conifers exhibited mild damage during the first growing season but moderate to severe damage during the first winter and second growing season. The two highest MgCl2 treatments caused leaf loss, severe damage, or mortality of Douglas-fir, lodgepole, and ponderosa pines after two seasons of treatments and of limber pine after four seasons. Aspen also displayed foliar damage and crown loss but abscised damaged leaves and flushed asymptomatic leaves throughout the growing seasons. The highest treatment caused mortality of aspen in 4 years. Approximately 13,000–17,000-ppm foliar chloride was associated with severe damage in conifers but ranged from 13,000- to 33,000-ppm in fully necrotic leaves. Aspen foliage contained the highest concentrations of chloride (24,000–36,000-ppm), and limber pine leaves had the lowest (<14,200-ppm). Although MgCl2 caused reductions in leaf water potential, aspen and ponderosa pine did not appear to be under substantial moisture stress and continued to take up ions. Mortality of common roadside tree species in 2 to 4 years can occur due to high MgCl2 soil concentrations, and transportation officials should consider these implications in their management plans.

Water stress before harvest of pepper-rosmarin

The objective of this work was to assess the effect of different periods of water stress before harvest of pepper-rosmarin (Lippia sidoides) on the contents of essential oil and flavonoids. The experiment was carried out during 270 days of cultivation, with drainage lysimeters, in a completely randomized block design with five treatments: 0, 2, 4, 6, and 8 days of water suppression before harvest, with four replicates. Fresh and dry matter yield, essential oil content, total flavonoids content, and water potential and temperature of leaves were determined. There was a decrease of approximately 50% in oil content and of 60% in total flavonoid content with the reduction of leaf water potential in 0.3 MPa. Essential oil is more sensitive to water stress than total flavonoids.

Identification and expression analysis of CjLTI, a novel low temperature responsive gene from Caragana jubata

Using rapid amplification of cDNA ends, a full length cDNA (CjLTI) was cloned from apical buds of Caragana jubata, a plant species that grows under extreme cold. The cDNA obtained was 573 bp long consisting of an open reading frame of 351 bp encoding 116 amino acids. Homology analysis did not exhibit significant similarity with any sequence at NCBI database, therefore it was deduced as a novel gene. Secondary structure analysis suggested that the deduced CjLTI contained 25.86% α-helices, 4.31% β-turns, 6.90% extended strands, and 62.93% random coils. The hydropathy profile suggested CjLTI to be a hydrophobic protein having characteristic features of signal peptides at N-terminus. The gene exhibited down-regulation at 5 min of exposure to low temperature (LT, 4 ± 3 °C) followed by a strong up-regulation after 15 min and onwards. Methyl jasmonate (MJ) lead to up-regulation of CjLTI starting at 5 min onwards. The gene exhibited up- and down-regulation of expression pattern in response to abscisic acid (ABA) and salicylic acid (SA). Mild drought stress slightly up-regulated gene expression and at severe drought (up to 115% reduction in leaf water potential) slight down-regulation of gene expression was observed. These results suggested CjLTI to be a LT responsive gene wherein MJ, ABA and SA pathways might be involved in regulating the gene expression.

Hydraulic conductance as well as nitrogen accumulation plays a role in the higher rate of leaf photosynthesis of the most productive variety of rice in Japan

An indica variety Takanari is known as one of the most productive rice varieties in Japan and consistently produces 20–30% heavier dry matter during ripening than Japanese commercial varieties in the field. The higher rate of photosynthesis of individual leaves during ripening has been recognized in Takanari. By using pot-grown plants under conditions of minimal mutual shading, it was confirmed that the higher rate of leaf photosynthesis is responsible for the higher dry matter production after heading in Takanari as compared with a japonica variety, Koshihikari. The rate of leaf photosynthesis and shoot dry weight became larger in Takanari after the panicle formation and heading stages, respectively, than in Koshihikari. Roots grew rapidly in the panicle formation stage until heading in Takanari compared with Koshihikari. The higher rate of leaf photosynthesis in Takanari resulted not only from the higher content of leaf nitrogen, which was caused by its elevated capacity for nitrogen accumulation, but also from higher stomatal conductance. When measured under light-saturated conditions, stomatal conductance was already decreased due to the reduction in leaf water potential in Koshihikari even under conditions of a relatively small difference in leaf–air vapour pressure difference. In contrast, the higher stomatal conductance was supported by the maintenance of higher leaf water potential through the higher hydraulic conductance in Takanari with the larger area of root surface. However, no increase in root hydraulic conductivity was expected in Takanari. The larger root surface area of Takanari might be a target trait in future rice breeding for increasing dry matter production.