Physiological and biochemical adaptations of Cynodon dactylon (L.) Pers. from the Salt Range (Pakistan) to salinity stress

Naturally adapted salt tolerant populations provide a valuable material for exploring the adaptive components of salt tolerance. Under this aspect, two populations of Cynodon dactylon (L.) Pers. were subjected to salt stress in hydroponics. One was collected from a heavily salt-affected soil in the vicinity of a natural salt lake, Uchhali Lake, in the Salt Range of the Punjab province of Pakistan, and the other from a normal non-saline habitat from the Faisalabad region. The NaCl treatments in Hoagland's nutrient solution were: Control (no salt), 50, 100, 150 and 200 mM of NaCl. After 8 weeks of growth in hydroponics produced biomass, ion relations, and photosynthetic capacity were measured in the differently adapted ecotypes. In the ecotype of C. dactylon from the Salt Range, shoot dry weight was only slightly affected by varying levels of salt. However, in contrast, its root weight was markedly increased. On the other hand, the ecotype from Faisalabad (non-saline habitat) showed a marked decrease in shoot and root dry weights under saline regimes. The ecotype from the Salt Range accumulated relatively less amount of Na⁺ in the shoot than did that from Faisalabad, particularly at higher salt levels. Shoot or root K⁺ and Ca²⁺ contents varied inconsistently in both ecotypes under salt stress. All the photosynthetic parameters, leaf water potential and osmotic potential, and chlorophyll content in both ecotypes were adversely affected by salt stress, but all these physiological attributes except turgor potential and soluble sugars were less affected at high salinities in the salt tolerant ecotype from Salt Range. This ecotype accumulated significantly higher organic osmotica (total free amino acids, proline, total soluble proteins, and total soluble sugars) under saline conditions than its intolerant counterpart. Overall, the salt tolerant ecotype of C. dactylon from the Salt Range showed high salt tolerance due to its restricted uptake of Na⁺ accompanied by an increased uptake of K⁺ and Ca²⁺ in the roots as well as shoot due to its higher photosynthetic capacity and accumulation of organic osmotica such as free amino acids and proline under saline conditions.     

Effect of Pb on leaf antioxidant enzyme activities and ultrastructure of the two ecotypes of <Emphasis Type="Italic">Sedum alfredii</Emphasis> Hance

Hydroponic experiments were conducted to study the effect of Pb on growth, leaf antioxidant enzyme activities, and ultrastructure of the accumulating ecotype (AE) and non-accumulating ecotype (NAE) of Sedum alfredii Hance. AE was found to be more tolerant to excessive Pb levels in growth medium. Concentrations of Pb in the shoots of the AE were 1.98 times higher than those in the NAE when 0.2 mM Pb was supplied. Both chlorophyll a and b did not decrease significantly in AE plants after Pb treatment, while a significant decrease was noted in chlorophyll a and b of NAE plants treated with Pb concentrations greater than 0.05 mM. The results showed that activities of superoxide dismutase (SOD) and catalase (CAT) were elevated in the leaves of AE under Pb stress. However in NAE, Pb-caused enhancement was noticed only in the activity of SOD while activity of CAT was declined as compared to the control plants. With increased Pb level, malondialdehyde (MDA) content increased significantly in both ecotypes of S. alfredii, indicating that Pb toxicity led to lipid peroxidation and membrane damage, but MDA content in the leaves of NAE was always higher than in AE plants. The ultrastructural analysis of the spongy mesophyll cells revealed that excessive Pb concentrations obviously damaged the cell membrane, chloroplasts, and mitochondria of both the ecotypes but damage was more severe in NAE. Although growth, leaf physiology, and ultrastructure of both the ecotypes were affected by Pb treatment, deleterious effects were more pronounced in NAE. This text was submitted by the authors in English.     

Growth and Differentiation of Seedlings of an Aquatic Plant,Trapella sinensis OLIV II. Photosynthesis and Respiration of Seedling in Early Stages

Trapella sinensis seedlings were examined to determine whether the effect of growth regulators such as gibberellin (GA₃), kinetin and the extract of Chlorella cells on chlorophyll formation, photosynthetic activity and cytochrome oxidase activity depend upon the developmental stage. Each addition promoted the growth on both the basis of dry weight and of fresh weight. Among these regulators, only Chlorella extract promoted growth as a result of an activated rate of photosynthesis through increased chlorophyll formation. There also was an increased respiratory rate through increased cytochrome oxidase activity.     

Light-dependent Synthesis of δ-aminolaevulinic Acid Dehydratase During the Developmental Period of Trapella Seedlings

Mature seeds of Trapella sinensis, after removal of receptacles, were germinated for 10 days at 23°C in the dark and then were illuminated. After illumination, the activity of δ-aminolaevulinic acid (ALA) dehydratase was determined in relation to chlorophyll synthesis, and increases in dry weight of the whole or of parts of a developing seedling. Internal programming of development was related to changes in ALA dehydratase activity on the basis of porphobilinogen synthesis. Exogenously added ALA as well as an extract of Chlorella cells promoted this activity. There was an enhancement of chlorophyll formation resulting in an enhancement of the photosynthetic rate and in an increase of growth promotion by addition of Chlorella extract.     

Differential responses of Arabidopsis ecotypes to cold, chilling and freezing temperatures

Arabidopsis plants show an increase in freezing tolerance in response to exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. In the present study, we evaluated the physiological and morphological responses of various Arabidopsis ecotypes to continuous growth under chilling (14°C) and cold (6°C) temperatures and evaluated their basal freezing tolerance levels. Seedlings of Arabidopsis plants were extremely sensitive to low growth temperatures: the hypocotyls and petioles were much longer and the angles of the second pair of true leaves were much greater in plants grown at 14°C than in those grown at 22°C, whereas just intermediate responses were observed under the cold temperature of 6°C. Flowering time was also markedly delayed at low growth temperatures and, interestingly, lower growth temperatures were accompanied by longer inflorescences. Other marked responses to low temperatures were changes in pigmentation, which appeared to be both ecotype specific and temperature dependent and resulted in various visual phenotypes such as chlorosis, necrosis or enhanced accumulation of anthocyanins. The observed decreases in chlorophyll contents and accumulation of anthocyanins were much more prominent in plants grown at 6°C than in those grown at 14°C. Among the various ecotypes tested, Mt‐0 plants markedly accumulated the highest levels of anthocyanins upon growth at 6°C. Freezing tolerance examination revealed that among 10 ecotypes tested, only C24 plants were significantly more sensitive to subzero temperatures. In conclusion, Arabidopsis ecotypes responded differentially to cold (6°C), chilling (14°C) and freezing temperatures, with specific ecotypes being more sensitive in particular traits to each low temperature.     

Difference in capacity of physiological integration between two ecotypes of Leymus chinensis underlies their different performance

Background and aims

Physiological integration can enhance the performance of clonal plants, but whether this differs between ecotypes and whether such difference is underlying their distribution have scarcely been addressed. We aimed to determine whether physiological integration differs between ecotypes and whether an ecotype with a wider distribution shows a greater capacity of physiological integration.

Methods

A garden experiment was conducted with ramet pairs of both ecotypes (grey-green and yellow-green ecotype) of a typical rhizomatous clonal plant, Leymus chinensis, using rhizome connection (connected vs. disconnected) and ecotype as factors. Physiological and biomass features were measured and compared to assess the effects of physiological integration for both ecotypes.

Results

Physiological integration enhanced the maximum net photosynthetic rate, apparent quantum efficiency, respiration rate, water use efficiency, and chlorophyll content of ramets no matter whether they were subject to nutrient-poor or -rich soil, as long as they were connected to other ramets. Moreover, such an effect on photosynthetic capacity and water use efficiency was larger for the grey-green ecotype than for the yellow-green ecotype.

Conclusions

The results suggested that grey-green ecotype has significantly greater capacity of physiological integration than yellow-green ecotype, which was assumed to be one of the underlying mechanisms of the wider distribution of the former in nature.     

The effect of Chinese tallow tree (Sapium sebiferum) ecotype on soil–plant system carbon and nitrogen processes

The EICA hypothesis predicts that shifts in allocation of invasive plants give rise to higher growth rates and lower herbivore defense levels in their introduced range than conspecifics in their native range. These changes in traits of invasive plants may also affect ecosystem processes. We conducted an outdoor pot experiment with Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) seedlings from its native (Jiangsu, China, native ecotype) and introduced ranges (Texas, USA, invasive ecotype) to compare their relative performances in its native range and to examine ecotype effects on soil processes with and without fertilization. Consistent with predictions, plant (shoot and root) mass was significantly greater and leaf defoliation tended to be higher, while the root:shoot ratio was lower for the invasive ecotype relative to the native ecotype. Seasonal amounts of soil–plant system CO₂ and N₂O emissions were higher for the invasive ecotype than for the native ecotype. Soil respiration rates and N₂O emission increases from fertilization were also greater for the invasive ecotype than for the native ecotype, while shoot-specific respiration rates (g CO₂–C g⁻¹ C day⁻¹) did not differ between ecotypes. Further, soil inorganic N (ammonium and nitrate) was higher, but soil total N was lower for soils with the invasive ecotype than soils with the native ecotype. Compared with native ecotypes, therefore, invasive ecotypes may have developed a competition advantage in accelerating soil processes and promoting more nitrogen uptake through soil–plant direct interaction. The results of this study suggest that soil and ecosystem processes accelerated by variation in traits of invasive plants may have implications for their invasiveness.     

Photosynthesis in relation to D1, PsaA and Rubisco in marine and brackish water ecotypes of Fucus vesiculosus and Fucus radicans (Phaeophyceae)

The aim of this study was to investigate photosynthetic differences between the marine, Norwegian Sea ecotype and the brackish, Bothnian Sea ecotype of F. vesiculosus and F. radicans and to see whether photosynthetic differences could be connected with the relative amounts of D1 protein (PSII), PsaA (PSI) protein and/or Rubisco. For this purpose, we tested if a higher photosynthetic maximum (P _max) in the Atlantic Ocean ecotype of F. vesiculosus relative to the Baltic Sea ecotype, and an increase of the P _max in Baltic Sea ecotype of F. vesiculosus at higher salinity, could be due to an increase in the relative amounts of Rubisco. The proteins have been evaluated on a relative basis. Immunoblot signals showed that the amount of Rubisco was higher in both ecotypes of F. vesiculosus than in F. radicans, but no differences could be detected between the two ecotypes of F. vesiculosus. The results suggest an uneven photosystem protein stoichiometry in Fucus, with more of the PSI protein PsaA relative to the PSII protein D1. The difference in P _max between the two ecotypes of F. vesiculosus might be related to the difficulties for the algae to adapt to the environment in Bothnian Sea.     

How do changes in temperature during growth affect leaf pigment composition and photosynthesis in Zea mays genotypes differing in sensitivity to low temperature?

The changes in photosynthetic activity and composition of pigments induced by changes in temperature were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of maize (Zea mays L.). The plants were grown under a controlled environment at a photon flux density of 550 mol m^-2 s^-1, a 12 h photoperiod and at a suboptimal temperature of 14/12 C (day/night) until the full expansion of the third leaf. After this treatment, the chilling-tolerant genotypes, when compared with the sensitive ones, displayed a higher photosynthetic activity, a higher content of chlorophyll (Chl) a+b, a higher Chl a/b ratio, a larger total carotenoid pool size as well as a different carotenoid composition. When temperature was subsequently increased to 24/22 C for 3 d the composition of the pigments changed, but the chilling-sensitive genotypes, while adjusting their lower Chl a/b ratio and their different carotenoid composition, were unable to adjust their lower content of chlorophyll, their smaller total carotenoid pool size or their lower photosynthetic performance. Moreover, while the chilling-tolerant genotypes converted the most part of zeaxanthin to violaxanthin in the xanthophyll cycle, the chilling-sensitive genotypes retained high amounts of zeaxanthin. The changes in pigment composition that occurred over the 3 d at 24/22 °C were largely conserved when the plants were returned to 14/12 °C, but photosynthetic activity decreased and zeaxanthin accumulated again. The results suggest that the capability of the chilling-tolerant genotypes, when compared with the sensitive ones, to retain high amounts of pigments and to form a competent photosynthetic apparatus at low temperature is the basis for their more vigorous growth in cool climates.     

Factors that Control the Species Composition of Freshwater Phytoplankton,with Special Attention to Nutrient Concentrations

Variations of species composition and population size of planktonic algae were studied in relation to the different nutrient levels in a eutrophic pond and an oligotrophic lake. The results obtained were discussed in comparison with the changes in photosynthesis and chlorophyll of several algal populations cultured under different nutrient conditions. As based on unialgal culture experiments two types of algae (the Chlorella-type and the Melosira-type) could be distinguished with regard to variations of photosynthesis and chlorophyll in response to different nutrient levels. Distribution of the Chlorella-type algae may be confined to eutrophic waters, while the Melosira-type algae can be distributed widely in waters from oligotrophic to eutrophic.     

Correlation of alpha-Linolenate to Photosynthetic O(2) Production in Chlorella

Photosynthetic oxygen evolution per milligram of chlorophyll in Chlorella vulgaris varies with the age of the culture. The rate of oxygen evolution is low in the starting cells, it rises to a maximum after 24 hours of growth and then declines to the initial low value after 72 to 90 hours. These changes in photosynthetic competence of chlorophyll in Chlorella are paralleled by changes in α-linolenate per milligram of chlorophyll. In general the magnitude of the photosynthetic competence of chlorophyll is directly proportional to the magnitude of the ratio of α-linolenate to chlorophyll, regardless of whether high ratios are due to high α-linolenates or low chlorophyll values. This relationship holds when the cultures are grown either under continuous or intermittent illumination.     

Physiological homeostasis for ecological success of Typha (Typha domingensis Pers.) populations in saline soils

The natural capacity of plants to endure salt stress is largely regulated by multifaceted structural and physio-biochemical modulations. Salt toxicity endurance mechanism of six ecotypes of Typha domingensis Pers. was evaluated by analyzing photosynthesis, ionic homeostasis, and stomatal physiology under different levels of salinity (0, 100, 200 and 300 mM NaCl). Typha populations were collected across different areas of Punjab, an eastern province in Pakistan. All studied attributes among ecotypes presented differential changes as compared to control. Different salt treatments not only affected gas exchange attributes but also shown significant modifications in stomatal anatomical changes. As compared to control, net photosynthetic rate, transpiration rate, total chlorophyll contents and carotenoids were increased by 111%, 64%, 103% and 171% respectively, in Sahianwala ecotype among all other ecotypes. Similarly, maximum water use efficiency (WUE), sub stomatal CO₂ concentration, sodium (Na⁺) and chloride (Cl⁻) contents were observed in Sahianwala (191%, 93%, 168%, 158%) and Knotti (162%, 75%, 146%, 182%) respectively, as compared to the others ecotypes. Adaxial and abaxial stomatal areas remained stable in Sahianwala and Knotti. The highest abaxial stomatal density was observed in Gatwala ecotype (42 mm²) and maximum adaxial stomatal density was recorded in Sahianwala ecotype (43 mm²) at 300 mM NaCl salinity. The current study showed that Typha ecotypes responded varyingly to salinity in terms of photosynthesis attributes to avoid damages due to salinity. Overall, differential photosynthetic activity, WUE, and changes in stomatal attributes of Sahianwala and Knotti ecotypes contributed more prominently in tolerating salinity stress. Therefore, Typha domingensis is a potential species to be used to rehabilitate salt affected lands for agriculture and aquatic habitat.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-00963-x.     

Natural variation in the regulation of leaf senescence and relation to other traits in Arabidopsis

Leaf senescence results in the recycling of nutrients, thereby providing resources required for growth and reproduction. In this study, the effect of day-length on leaf senescence in eight different Arabidopsis thaliana ecotypes was determined and the relationship between senescence and other morphological and life history traits was analysed. A significant variation in the start and extent of leaf senescence depending on the genetic background and the response to day-length was found. Whereas senescence of early flowering ecotypes was accelerated by long days, no effect of day-length on senescence could be found in late flowering Kas-1 plants. Senescence in the different ecotypes was associated with other traits, such as floral transition, the total number of fruits, the total number of leaves and the maximum chlorophyll content. Plants that bolted early also senesced early, produced fewer leaves, accumulated less chlorophyll, but produced more fruits. The present results indicate that senescence may be a key component in the trade-off between investment in photosynthetic capacity and reproduction. The relationship between senescence and other traits was maintained independent of whether differences in senescence were caused by genetic (ecotype) or environmental (day-length) variation, suggesting that genetic and environmental factors affect these traits through common regulatory pathways.     

Leaf structural dynamics associated with adaptation of two Ebenus cretica ecotypes

Morphological and anatomical features of Ebenus cretica leaflet, such as lanceolate shape, reduced size, dense cover with non-glandular hairs, epidermis of small cells, compact mesophyll, amphipleurous presence of palisade parenchyma, thick cuticle, development of numerous mesophyll phenol-storing cells and the amphistomatic type, disclose the xeromorphic character of the plant. In the island of Crete two ecotypes of E. cretica, ecotype A and ecotype C, are greatly extended. In ecotype A leaflets, the above features are more prominent than in ecotype C. This fact accomplished by physiological data favours the suggestion that plants of ecotype A are better adapted to the xerothermic environment of the island of Crete. This may be the reason that ecotype A occupies the major portion of the island and is predominant in the western and central regions. The distinction of ecotypes A and C, by evaluating the strategies these plants used in order to better adapt and the characteristics of their inflorescences may be used as a criterion for the selection of the most appropriate ecotype for application in floriculture and ornamental horticulture.     

CHARACTERIZATION OF BLEACHING IN CHLORELLA INDUCED BY SUBOPTIMAL GROWTH TEMPERATURES1

Incubation of cultures of a high-temperature strain of chlorella at 10 C stopped growth and bleached all chlorophyll in the cells in 24 hr. Optimal conditions of light (3.0 mw/cm²), gas (1% CO₂-in-air), and inorganic medium for maximal growth at 39 C were maintained in the transfer from 39 to 12, 10, or 5 C. The bleaching process at 10 C is characterized by a lag period for the first few hours followed by a linear decrease in chlorophyll content of cultures. The amounts of time required to bleach half of the chlorophyll initially present (effective half-times) at 10 C were 14 hr for chlorophyll a and 17 hr for chlorophyll b. Effective half-times of bleaching for total chlorophyll were 47 hr at 12 C and 6 hr at 5 C. Addition of glucose to inorganic medium delayed but did not prevent bleaching. Use of argon gas instead, of 1% CO₂-in-air prevented cells from bleaching in both inorganic and glucose media, and indicated an oxygen requirement for bleaching. Incubation of 6 additional strains of Chlorella at 10 C resulted in responses ranging from bleaching to no growth to growth.     

Respiration for maintenance and growth inReynoutria japonica ecotypes from different altitudes on Mt Fuji

Respiration for maintenance and growth ofReynoutria japonica ecotypes from altitudes of 700 and 2420 m on Mt Fuji were measured in two controlled thermal conditions. The maintenance respiration of the high-altitude ecotype at both 15 and 25°C was significantly (1.7-fold) higher than that of the low-altitude ecotype, whereas growth respiration was independent of both ecotype and temperature. The temperature coefficient (Q₁₀) of the maintenance respiration was about 1.9 in both ecotypes. The results show that there is ecotypic differentiation in the performance of maintenance respiration. It is suggested that the high maintenance respiration of the high-altitudeR. japonica ecotype is advantageous in severe upland environments but disadvantageous in a warm lowland climate in terms of carbon economy.     

Differential responses of two Stellaria longipes ecotypes to ultraviolet-B radiation and drought stress

Enhanced ultraviolet-B (UVB) radiation and water deficit affect plant growth and development. We determined the effects of UVB and drought stress on growth parameters and chemical attributes of two ecotypes (alpine and prairie) of Stellaria longipes under controlled-environment conditions. Clonal ramets of these ecotypes were grown under three UVB levels (0, 5, and 10 kJ m⁻² d⁻¹) and exposed to two watering regimes (well watered and drought stressed) for 21 days. Compared to the alpine, the prairie ecotype was taller, had higher number of nodes, and greater leaf area and specific leaf weight (leaf dry weight: leaf area), which resulted in increased dry matter in this ecotype. Overall, ‘prairie’ was higher in total chlorophyll (Chl), but lower in Chla:b ratio, flavonoids, and ethylene, than ‘alpine’. In both ecotypes, UVB and drought stress reduced growth and dry matter, whereas UVB increased carotenoids and flavonoids. Drought stress decreased ethylene evolution. These characteristics were also determined in plants growing in the field. In the field-growing plants, ‘prairie’ had higher growth and dry matter, but lower Chla:b ratio and flavonoids, than ‘alpine’. The two ecotypes responded differentially to UVB and watering regime, as ‘prairie’ appeared to be more sensitive to UVB and drought stress than ‘alpine’.     

Effects of Prolonged UV-B Enhanced Fluorescent Radiation on Some Marine Microalgae

The eukaryotic unicellular microalgae Chlorella salina, Dicrateria inornata, and Isochrysis galbana were grown under control (fluorescent 20 W m^–2) and UV-B enhanced (UV-B^E, 0.5 W m^–2) fluorescent radiation. The growth rate showed marginal increase under UV-B^E. Decrease in protein content was observed in Dicrateria cells but in Chlorella an initial increase up to 4 d and in Isochrysis an increase at days 4 and 5 was noted. The chlorophyll a content showed marked increase in Chlorella and Isochrysis but in Dicrateria a decline was found. UV-B^E reduced the photosynthetic activity in all three species, but the reduction was larger in Chlorella and Dicrateria. Fluorescence excitation spectra for F₆₈₂ in Chlorella cells grown for 5 d under UV-B^E showed reduction in all peaks. In contrast to this, in Dicrateria and Isochrysis cells, the 530 and 590 nm excitation peaks increased with an appreciable decrease in the 466 nm peak. SDS-PAGE analysis revealed significant decrease in the contents of 47, 33, and 23 kDa polypeptides in Chlorella cells. In Dicrateria cells, significant loss in the content of 55, 38, and 18 kDa polypeptides was observed. The content of low molecular mass polypeptides (15 kDa) remained unaffected. Isochrysis cells were more stable in preserving the content of thylakoid polypeptides.     

Growth temperature affects O2 consumption rates and plasticity of respiratory flux to support shoot growth at various growth temperatures

The temperature dependence of respiration rates and their acclimation to growth temperature vary among species/ecotypes, but the details remain unclear. Here, we compared the temperature dependence of shoot O₂ consumption rates among Arabidopsis thaliana ecotypes to clarify how the temperature dependence and their acclimation to temperature differ among ecotypes, and how these differences relate to shoot growth. We examined growth analysis, temperature dependence of O₂ consumption rates, and protein amounts of the respiratory chain components in shoots of twelve ecotypes of A. thaliana grown at three different temperatures. The temperature dependence of the O₂ consumption rates were fitted to the modified Arrhenius model. The dynamic response of activation energy to measurement temperature was different among growth temperatures, suggesting that the plasticity of respiratory flux to temperatures differs among growth temperatures. The similar values of activation energy at growth temperature among ecotypes suggest that a similar process may determine the O₂ consumption rates at the growth temperature in any ecotype. These results suggest that the growth temperature affects not only the absolute rate of O₂ consumption but also the plasticity of respiratory flux in response to temperature, supporting the acclimation of shoot growth to various temperatures.