Leaf Expansion Growth Research Articles

Hormonal Balance, Photosynthesis, and Redox Reactions in the Leaves of Caragana korshinskii Kom. under Water Deficit.

To evaluate the physiological responses of Korshinsk peashrub (Caragana korshinskii Kom.) to water deficit, photosynthetic gas exchange, chlorophyll fluorescence, and the levels of superoxide anion (O2•-), hydrogen peroxide (H2O2), malondialdehyde (MDA), antioxidant enzymes, and endogenous hormones in its leaves were investigated under different irrigation strategies during the entire growth period. The results showed that leaf growth-promoting hormones were maintained at a higher level during the stages of leaf expansion and vigorous growth, and zeatin riboside (ZR) and gibberellic acid (GA) gradually decreased with an increase in water deficit. At the leaf-shedding stage, the concentration of abscisic acid (ABA) dramatically increased, and the ratio of ABA to growth-promoting hormones increased to a high level, which indicated that the rate of leaf senescence and shedding was accelerated. At the stages of leaf expansion and vigorous growth, the actual efficiency of photosystem II (PSII) (ΦPSii) was downregulated with an increment in non-photochemical quenching (NPQ) under moderate water deficit. Excess excitation energy was dissipated, and the maximal efficiency of PSII (Fv/Fm) was maintained. However, with progressive water stress, the photo-protective mechanism was inadequate to avoid photo-damage; Fv/Fm was decreased and photosynthesis was subject to non-stomatal inhibition under severe water deficit. At the leaf-shedding stage, non-stomatal factors became the major factors in limiting photosynthesis under moderate and severe water deficits. In addition, the generation of O2•- and H2O2 in the leaves of Caragana was accelerated under moderate and severe water deficits, which caused an enhancement of antioxidant enzyme activities to maintain the oxidation-reduction balance. However, when the protective enzymes were insufficient in eliminating excessive reactive oxygen species (ROS), the activity of catalase (CAT) was reduced at the leaf-shedding stage. Taken all together, Caragana has strong drought resistance at the leaf expansion and vigorous growth stages, but weak drought resistance at the leaf-shedding stage.

Shoot Emergence, Leaf Expansion, and Corm Growth in Amorphophallus muelleri Blume Treated with Hydropriming and Shading

A bulbil, as planting material, is difficult to stimulate to grow in a dormant state. This study examines the hydropriming effect on shoot emergence and the shading treatments on leaf and cormel growth during the vegetative stage. The priming was carried out by soaking the bulbils in distilled water for 0, 3, 6, 12, and 24 hours and the shading treatments at 0, 40, and 80 percent. The results show that the imbibition occurred immediately during the first 3 hours and continued to increase up to 24 hours. The bulbil re-drying process reached the pre-treatment water content in less than three days. Significantly the earlier emergence was observed in the plants exposed to the 80% shading. The petiole sheath breakup was not affected by the hydropriming and shading. The konjac planted in the shading treatment produced more sprouts, longer but slender petioles, larger but thinner leaves, and larger cormel size. The differences in fresh and dry weight were more related to tuber moisture content than the direct effect of the shading treatment. The SPAD value of konjac leaves immediately increased within a few days after the application of the NPK fertilizer and consistently lasted for four weeks.

Plant mitochondrial FMT and its mammalian homolog CLUH controls development and behavior in Arabidopsis and locomotion in mice.

Mitochondria in animals are associated with development, as well as physiological and pathological behaviors. Several conserved mitochondrial genes exist between plants and higher eukaryotes. Yet, the similarities in mitochondrial function between plant and animal species is poorly understood. Here, we show that FMT (FRIENDLY MITOCHONDRIA) from Arabidopsis thaliana, a highly conserved homolog of the mammalian CLUH (CLUSTERED MITOCHONDRIA) gene family encoding mitochondrial proteins associated with developmental alterations and adult physiological and pathological behaviors, affects whole plant morphology and development under both stressed and normal growth conditions. FMT was found to regulate mitochondrial morphology and dynamics, germination, and flowering time. It also affects leaf expansion growth, salt stress responses and hyponastic behavior, including changes in speed of hyponastic movements. Strikingly, Cluh± heterozygous knockout mice also displayed altered locomotive movements, traveling for shorter distances and had slower average and maximum speeds in the open field test. These observations indicate that homologous mitochondrial genes may play similar roles and affect homologous functions in both plants and animals.

Central rib and the nutritive value of leaves in forage grasses

In grasses, leaf expansion and central rib growth occur in a non-proportional manner, with potential implications to the nutritive value of leaves. The objective of this study was to evaluate the relationship among blade length, percentage of central rib, anatomical characteristics and the nutritive value along the length of leaf blades of different sizes and hierarchical order of insertion on the tiller axis of Napier elephant grass (Pennisetum purpureum Schum. cv. Napier). Two experiments were carried out with isolated growing plants during the summer of 2017 (January to March). Central rib mass increased linearly with the increase in leaf blade mass and its percentage relative to blade mass decreased from the base to the tip of the leaf. There were no significant variations in anatomical characteristics along the length of leaf blades when central rib was not taken into account. The central rib showed negative relationship with nutritive value. The apical portions of long leaves showed similar digestibility to short leaves. The multivariate analysis of Cluster and Principal Components grouped the response variables according to leaf hierarchical order, final blade length and percentage of structural tissues, highlighting the relationship between leaf size, structural tissues and nutritive value.

Differential growth response of green and variegated Ficus benjamina to exogenous cytokinin and shade

Abstract Benjamin fig (Ficus benjamina) is an important foliage and landscape crop species comprising green and variegated genotypes. The latter develop leaves with yellow and white leaf areas which may impose lower photosynthetic activity, thus resulting in slower growth than green genotypes. In many species, the exogenous supply of cytokinin to pot-grown plants promotes growth, mainly due to enhanced carbon fixation. In this work, we analyze the effect of spraying the cytokinin 6-benzylaminopurine (BAP) on growth and development of green and variegated Ficus benjamina genotypes. Two experiments were carried out in a greenhouse, in which either different number of BAP applications (Experiment 1) or different BAP concentrations (Experiment 2) were tested. In Experiment 2, plants were grown under three different light intensities. BAP sprays promoted rate of leaf appearance, leaf expansion and whole-plant growth, and the effect was stronger in variegated than in green plants. The relative growth rate promotion by BAP was associated with increased net assimilation rate rather than with variation in the leaf area ratio. On the other hand, shading had a more negative impact on growth and development of variegated plants than in green ones. Variegated plants, unlike green ones, developed leaves with high specific leaf area under the lowest light intensity. This led to high leaf area ratio values, which helped to maintain relative growth rates close to those of plants under moderate shading.

K对能源植物杂交狼尾草耐盐性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 钾对能源植物杂交狼尾草耐盐性的影响 DOI: 10.5846/stxb201301220127 作者: 作者单位: 山东师范大学生命科学学院,山东师范大学生命科学学院,山东师范大学生命科学学院,山东师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家科技支撑计划项目（2009BADA7B05）；山东省博士基金项目（BS2011SW048）；山东省科技发展计划项目（2013GNC11310） The effect of K on the salt tolerance of the bioenergy plant hybrid Pennisetum Author: Affiliation: Key Laboratory of Plant Stress,College of Life Science,Shandong Normal University,Key Laboratory of Plant Stress,College of Life Science,Shandong Normal University,Key Laboratory of Plant Stress,College of Life Science,Shandong Normal University,Key Laboratory of Plant Stress,College of Life Science,Shandong Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以盆栽的杂交狼尾草（Pennisetum americanum ×P. purpureum）为实验材料，在不同浓度NaCl（0%，0.5%）条件下，用含有不同钾浓度（0.1，3，6，9 mmol/L）的营养液处理4周后，测定植株高度、分蘖数、干重、叶片净光合速率、不同部位的离子含量、MDA（丙二醛）含量和细胞质膜透性等生理指标，以确定缓解盐害的适宜钾浓度。结果表明：0.5% NaCl明显抑制了杂交狼尾草幼苗的生长和光合。在0.5% NaCl处理下，随着钾素浓度增加，杂交狼尾草的生物量显著增加，其中6 mmol/L的钾显著降低杂交狼尾草所受盐害，即6 mmol/L的钾素处理缓解了NaCl对杂交狼尾草株高、分蘖数、干重、光合速率的抑制；降低了杂交狼尾草叶片的MDA含量和质膜透性；降低了功能叶的Na+含量，增加了K+含量，从而增加了功能叶的K+/Na+。以上结果表明，适宜的钾浓度（6 mmol/L）能明显缓解NaCl对能源植物杂交狼尾草生长和光合的抑制。这些结果为在盐碱地上大面积种植杂交狼尾草时合理施用钾肥提供了理论依据。 Abstract:More than 6% of the world's total land area is impacted by salt. Most cultivated plants are sensitive to salt stress, and NaCl salinity, which results in ionic disturbance, osmotic and toxic effects, and which usually causes a great reduction in vegetative growth, rate of photosynthesis and an imbalance in plant nutrient uptake. Potassium (K) deprivation resulting from NaCl salinity, is expected to have a large and rapid negative effect on the rate of leaf expansion and final growth. Potassium (K), as one of 17 essential elements required for plant growth, participates in an array of processes, for example, potassium ions can be used as an activator for 60 different enzymes, promote photosynthesis, facilitate the transport of photosynthetic products, regulate the water potential of plant cells and stomatal movement. Plants subjected to salt stress are particularly prone to K deciency as within saline soils there may be less available K due to reduced K diffusion and poor root uptake. Therefore, K is frequently the main limiting element for plant growth and development during the ecological transformation of saline impacted land. Hence, the reasonable application of K fertilizers is the recommended treatment for enhancing soil K availability, stimulating plant yields and avoiding the deterioration of saline land. Hybrid pennisetum (Pennisetum americanum×P. Purpureum) is now widely regarded to have substantial potential as a bioenergy plant and a forage source for livestock production. It has been characterized by good stress resistance, fast growth and high yields. Hence, hybrid pennisetum is a suitable energy plant candidate for the transformation of coastal areas, which are considered as suitable sites for cultivation of energy plants, since they are widespread and cannot usually be used as farmland due to the high soil salinity. Therefore, in order to better guide the establishment of the bio-transformation of the Yellow River Delta saline lands using this potential energy plant, the effects of K nutrition on growth, photosynthesis and ion accumulation of the energy plant hybrid pennisetum, seedlings were examined under saline conditions. In a pot experiment, we investigated the effects of K+ level on seedling growth, ion concentrations in leaves and roots, photosynthetic characteristics, MDA (malondialdehyde) concentration and membrane permeability in the leaves of the hybrid pennisetum, under 0.5% NaCl to determine suitable levels of potassium supply to alleviate the salt damage of the studied species. The results showed the growth and photosynthesis of hybrid pennisetum seedlings were significantly inhibited under 0.5% NaCl conditions. However, the dry weight of shoots and roots, plant height and tillering number were significantly increased with the addition of K+, especially for 6 mmol/L of K+ under 0.5% NaCl. K+ supply significantly reduced the inhibitive effect of NaCl on plant height, tillering number, dry weight of shoot and root, and photosynthesis. The K+ supply also decreased the MDA concentration and membrane permeability, decreased the concentration of Na+ and increased the concentration of K+, markedly improving the K+/Na+ ratio of functional leaves. The results indicated that a supply of suitable concentrations of K+ (6 mmol/L) can significantly alleviate the inhibition of growth and photosynthesis caused by salinity in hybrid pennisetum. These findings would provide a theoretical basis for practical application when large-scale cultivation of hybrid pennisetum occurs on saline land. 参考文献 相似文献 引证文献

Regulation of leaf hydraulics: from molecular to whole plant levels.

The water status of plant leaves is dependent on both stomatal regulation and water supply from the vasculature to inner tissues. The present review addresses the multiple physiological and mechanistic facets of the latter process. Inner leaf tissues contribute to at least a third of the whole resistance to water flow within the plant. Physiological studies indicated that leaf hydraulic conductance (Kleaf) is highly dependent on the anatomy, development and age of the leaf and can vary rapidly in response to physiological or environmental factors such as leaf hydration, light, temperature, or nutrient supply. Differences in venation pattern provide a basis for variations in Kleaf during development and between species. On a short time (hour) scale, the hydraulic resistance of the vessels can be influenced by transpiration-induced cavitations, wall collapses, and changes in xylem sap composition. The extravascular compartment includes all living tissues (xylem parenchyma, bundle sheath, and mesophyll) that transport water from xylem vessels to substomatal chambers. Pharmacological inhibition and reverse genetics studies have shown that this compartment involves water channel proteins called aquaporins (AQPs) that facilitate water transport across cell membranes. In many plant species, AQPs are present in all leaf tissues with a preferential expression in the vascular bundles. The various mechanisms that allow adjustment of Kleaf to specific environmental conditions include transcriptional regulation of AQPs and changes in their abundance, trafficking, and intrinsic activity. Finally, the hydraulics of inner leaf tissues can have a strong impact on the dynamic responses of leaf water potential and stomata, and as a consequence on plant carbon economy and leaf expansion growth. The manipulation of these functions could help optimize the entire plant performance and its adaptation to extreme conditions over short and long time scales.

Xylem ionic relations and salinity tolerance in barley

Control of ion loading into the xylem has been repeatedly named as a crucial factor determining plant salt tolerance. In this study we further investigate this issue by applying a range of biophysical [the microelectrode ion flux measurement (MIFE) technique for non-invasive ion flux measurements, the patch clamp technique, membrane potential measurements] and physiological (xylem sap and tissue nutrient analysis, photosynthetic characteristics, stomatal conductance) techniques to barley varieties contrasting in their salt tolerance. We report that restricting Na(+) loading into the xylem is not essential for conferring salinity tolerance in barley, with tolerant varieties showing xylem Na(+) concentrations at least as high as those of sensitive ones. At the same time, tolerant genotypes are capable of maintaining higher xylem K(+)/Na(+) ratios and efficiently sequester the accumulated Na(+) in leaves. The former is achieved by more efficient loading of K(+) into the xylem. We argue that the observed increases in xylem K(+) and Na(+) concentrations in tolerant genotypes are required for efficient osmotic adjustment, needed to support leaf expansion growth. We also provide evidence that K(+)-permeable voltage-sensitive channels are involved in xylem loading and operate in a feedback manner to maintain a constant K(+)/Na(+) ratio in the xylem sap.

Spectral and Dose Dependence of Light-Induced Ion Flux Responses from Maize Leaves and their Involvement in Leaf Expansion Growth

Two types of segments (intact leaf tissue and isolated mesophyll tissue respectively) were isolated from basal (still growing) and tip (non-growing) maize leaf regions. The leaf segments were exposed to different light qualities (blue or red light) and quantities, and net fluxes of K+, Ca2+ and H+ were measured non-invasively using ion-selective vibrating microelectrodes (the MIFE technique). A clear dose dependency of all ion flux responses on both red (RL) and blue (BL) light fluence rate was found. We provide evidence that light-induced K+ flux kinetics are different between growing and non-growing tissues and attribute this difference to the direct involvement of RL-induced K+ flux in turgor-driven leaf expansion growth controlled by the epidermis, as well as to the charge-balancing role of K+ in the leaf mesophyll. Generally, BL was much more efficient in stimulating K+ uptake in the growing basal region compared with RL. We also show a much stronger influence of RL on Ca2+ fluxes in the basal region compared with BL, which argues in favor of the importance of RL in Ca2+ signaling during leaf growth.

Interspecific Competition for Soil N and its Interaction with N2 Fixation, Leaf Expansion and Crop Growth in Pea–Barley Intercrops

Field experiments were carried out during three successive years to study through a dynamic approach the competition for soil N and its interaction with N2 fixation, leaf expansion and crop growth in pea–barley intercrops. The intensity of competition for soil N varied between experiments according to soil N supply and plant densities. This study demonstrates the key role of competition for soil N which occurs early in the crop cycle and greatly influences the subsequent growth and final performance of both species. Relative yield values for grain yield and N accumulation increased with the intensity of competition for soil N. Barley competed strongly for soil N in the intercrop. Its competitive ability increased steadily during the vegetative phase and remained constant after the beginning of pea flowering. The period of strong competition for soil N (500–800 degree-days after sowing) also corresponded to the period of rapid growth in leaf area for both species and therefore an increasing N demand. For each species, the leaf area per plant at the beginning of pea flowering was well correlated with crop nitrogen status. Barley may meet its N needs more easily in intercrops (IC) and has greater leaf area per plant than in sole crops (SC). Barley having a greater soil N supply results in an even higher crop N status and greater competitive ability relative to pea in intercrop. Competition by barley for soil N increased the proportion of pea N derived from fixation. The nitrogen nutrition index (NNI) values of pea were close to 1 whatever the soil N availability in contrast to barley. However N2 fixation started later than soil N uptake of pea and barley and was low when barley was very competitive for soil N. Due to the time necessary for the progressive development and activity of nodules, N2 fixation could not completely satisfy N demand at the beginning of the crop cycle. The amount of N2 fixed per plant in intercrops was not only a response to soil N availability but was largely determined by pea growth and was greatly affected when barley was too competitive.

How periodic growth pattern and source/sink relations affect root growth in oak tree seedlings

Seedlings of Quercus pubescens were grown in root boxes to study the growth pattern of the root system in relation to shoot development. Shoot growth was typically rhythmic. Root elongation was also periodic, in contrast to several previous reports on other Quercus species. Both taproot and lateral root elongation were depressed during expansion of the second leaf flush, with a more pronounced response of lateral root growth. Apical diameter of the taproot followed comparable but less prominent trends than taproot elongation. Modifying source/sink relationships through various defoliation treatments altered the root growth pattern. Ablation of source organs (mature leaves or cotyledons) amplified the decrease in root growth concomitant with leaf expansion. Root growth recovery was even more difficult when both cotyledons and mature leaves had been removed. Ablation of sink aerial organs (young leaves) initially suppressed competition for growth between the shoot and the root, and then caused a gradual decrease in lateral root growth. Antagonism between maximum leaf expansion and root growth reduction during the second flush, and various responses of seedlings with modified source/sink relationships, raise an hypothesis of mutual competition for carbohydrates. The gradual decrease in lateral root growth after ablation of young leaves suggests a long-term carbohydrate limitation, or auxin limitation as auxin sources have been removed.

Effects of cadmium hyperaccumulation on physiological characteristics of Sedum alfredii Hance (Crassulaceae)

Sedum alfredii is a newly found cadmium (Cd)-hyperaccumulator, but there have been no detailed studies on its physiological responses when Cd is hyperaccumulated. Leaf expansion and root growth were inhibited significantly at high Cd concentrations, and Cd was suggested to suppress cell expansion and induce senescence. Chlorophyll fluorescence analysis indicated that its photosynthesis appeared to be unaffected. Decreased F v/ F m correlated well with decreased water content of leaves. Cd treatments were demonstrated to result in an increase of chlorophyll content. The chlorophyll a/ b ratio showed a reduction with increasing Cd concentrations. The Cd content peaked and reached a maximum of 11,000 mg kg −1 in leaves at 600 μM Cd. It was almost saturated at 600 μM Cd in stems and roots, and then was, respectively, up to a maximum of 5300 and 3100 mg kg −1 at 800 μM Cd. Fe concentrations in leaves, stems and roots increased significantly in the presence of Cd. Increasing Cd concentration might induce the expression of Fe transporter. This could have important implications both for human nutrition and for phytoremediation of metal contamination. Other elements (K, Ca, Zn and P) were distributed differently. Taking together, these results suggested that S. alfredii could be a good new model to investigate the mechanism of metal hyperaccumulation.

Tolerance and physiological responses of Phragmites australis to water deficit

The water stress tolerance of Phragmites australis (Cav.) Trin ex. Steud. grown in the laboratory were investigated by examining effects of different levels of imposed water deficits on growth, photosynthesis and various physiological traits related to water stress. Individual plants were grown under conditions of unrestricted water supply and compared with groups of plants receiving 60, 30, 15 or 5% of previous daily water requirements, respectively. Water deficit was found to reduce the leaf area and the leaf biomass per plant due to decreased production of new leaves, increased leaf shedding and reduced average leaf size. Leaf production and leaf expansion growth were very sensitive to water availability and were reduced when plants were subjected to fairly mild water deficit. Osmolality in sap expressed from leaves and the concentration of proline in leaves were only significantly increased in severely stressed plants, indicating that osmotic adjustment was of minor importance until a critical stress level was reached. Photosynthetic parameters were rather unaffected until the water availability was very low and led to the assertion that reduced CO 2 assimilation was mainly due to stomatal closure and not biochemical changes. Water stress had no effect on the activity of Rubisco. The CO 2 assimilation rate and stomatal conductance decreased in such a way that the intrinsic water use efficiency ( A/ g s) increased, indicating efficient CO 2 utilization in water stressed plants. The apparent quantum yield ( φ i ) was reduced in leaves of the most stressed plants, probably due to a decrease in the CO 2 molar fraction in the chloroplasts following stomatal closure. The initial response of P. australis to water deficit is a reduction in leaf area, the remaining leaves staying physiological rather well functioning until they are severely stressed. A high intrinsic water use efficiency and the ability to maintain some capacity for photosynthesis under severe water stress can undoubtedly contribute to the survival of P. australis under dry conditions. Taken together with its well-developed adaptations to flooding, P. australis seems very well adapted to grow in wetland areas with a widely fluctuating hydroperiod. P. australis grows very well in rather deep water, but can also tolerate extensive periods of drought with reduced availability of water.

Light‐induced transient ion flux responses from maize leaves and their association with leaf growth and photosynthesis

Net fluxes of H+, K+ and Ca2+ ions from maize (Zea mays L.) isolated leaf segments were measured non-invasively using ion-selective vibrating microelectrodes (the MIFE technique). Leaf segments were isolated from the blade base, containing actively elongating cells (basal segments), and from non-growing tip regions (tip segments). Ion fluxes were measured in response to bright white light (2600 micromoles m-2 s-1) from either the leaf segments or the underlying mesophyll (after stripping the epidermis). Fluxes measured from the mesophyll showed no significant difference between basal and tip regions. In leaf segments (epidermis attached), light-induced flux kinetics of all ions measured (H+, Ca2+ and K+) were strikingly different between the two regions. It appears that epidermal K+ fluxes are required to drive leaf expansion growth, whereas in the mesophyll light-induced K+ flux changes are likely to play a charge balancing role. Light-stimulated Ca2+ influx was not directly attributable either to leaf photosynthetic performance or to leaf expansion growth. It is concluded that light-induced ion flux changes are associated with both leaf growth and photosynthesis.

Distinctive diel growth cycles in leaves and cladodes of CAM plants: differences from C3 plants and putative interactions with substrate availability, turgor and cytoplasmic pH

Distinct diel rhythms of leaf and cladode expansion growth were obtained in crassulacean acid metabolism (CAM) plants under water-limited conditions, with maxima at mid-day during phase III of CO2 assimilation. This pattern coincided with the availability of CO2 for photosynthesis and growth during the decarboxylation of malic acid, with maximum cell turgor due to the nocturnally accumulated malic acid, and with the period of low cytoplasmic pH associated with malic acid movement from vacuole to cytosol. Maximum growth rates were generally only 20% of those in C3 plants and were reached at a different time of the day compared with C3 plants. The results suggest that malic acid, as a source of carbohydrates, and a determinant of turgor and cytoplasmic pH, plays a major role in the control of diel growth dynamics in CAM plants under desert conditions. The observed plasticity in phasing of growth rhythms under situations of differing water availability suggests that a complex network of factors controls the diel growth patterns in CAM plants and needs to be investigated further.

Functional diversity of photosynthesis during drought in a model tropical rainforest – the contributions of leaf area, photosynthetic electron transport and stomatal conductance to reduction in net ecosystem carbon exchange

ABSTRACTThe tropical rainforest mesocosm within the Biosphere 2 Laboratory, a model system of some 110 species developed over 12 years under controlled environmental conditions, has been subjected to a series of comparable drought experiments during 2000–2002. In each study, the mesocosm was subjected to a 4–6 week drought, with well‐defined rainfall events before and after the treatment. Ecosystem CO2 uptake rate (Aeco) declined 32% in response to the drought, with changes occurring within days and being reversible within weeks, even though the deeper soil layers did not become significantly drier and leaf‐level water status of most large trees was not greatly affected. The reduced Aeco during the drought reflected both morphological and physiological responses. It is estimated that the drought‐induced 32% reduction of Aeco has three principal components: (1) leaf fall increased two‐fold whereas leaf expansion growth of some canopy dominants declined to 60%, leading to a 10% decrease in foliage coverage of the canopy. This might be the main reason for the persistent reduction of Aeco after rewatering. (2) The maximum photosynthetic electron transport rate at high light intensities in remaining leaves was reduced to 71% for three of the four species measured, even though no chronic photo‐inhibition occurred. (3) Stomata closed, leading to a reduced ecosystem water conductance to water vapour (33% of pre‐drought values), which not only reduced ecosystem carbon uptake rate, but may also have implications for water and energy budgets of tropical ecosystems. Additionally, individual rainforest trees responded differently, expressing different levels of stress and stress avoiding mechanisms. This functional diversity renders the individual response heterogeneous and has fundamental implications to scale leaf level responses to ecosystem dynamics.

Effects of NaCl salinity and water stress on growth and leaf water relations of Asteriscus maritimus plants

Potted plants of Asteriscus maritimus (L.) Less were submitted to water stress (during two consecutive cycles, irrigation water was withheld for 5 days followed by a recovery period of 25 days) and saline stress (150 days of exposure to 0, 70 and 140 mM NaCl daily irrigation) in order to assess the effect on leaf water relations and growth parameters. Plants under saline and water stress conditions showed lower biomass and an early reduction in leaf expansion growth. Both stresses promoted a substantial degree of stomatal regulation; but, in spite of this, the plants showed signs of leaf tissue dehydration, decreases in RWC and Ψ pd values. However, salt-treated plants, developed a NaCl inclusion mechanisms, underwent osmotic adjustment, which was able to maintain leaf turgor. Under both stress conditions g l was independent to plant water status in the range between –0.8 and 1.0 MPa. Under water stress conditions, midday leaf water potential showed a threshold value (around −1.1 MPa), below which leaf conductance remained constant. In the salt-treated plants, the gradual closure of the stomata over a wide range of Ψ md may be important in maintaining some level of photosynthesis.

Temperature effects on leaf properties, resin content, and composition in Grindelia chiloensis (Asteraceae)

Grindelia chiloensis (Asteraceae) is a shrub native to the Patagonia and Monte regions of Argentina, presently under investigation as a resin crop. The rate of production of diterpene resin–acids is, in part, determined by environmental conditions and can be manipulated changing water, nitrogen, and radiation availability. Although the theory predicts that resin content should increase with low temperature, this response has not been tested, yet. The objective of this work was to test whether the response of resin production to temperature predicted by the Growth-Differentiation-Balance Hypothesis (GDBH) is found in G. chiloensis. Cloned plants of G. chiloensis were grown in greenhouses under different temperature regimes. Structural and functional characters were measured. Leaf resin and stem total non-structural carbohydrate content (TNC) were higher in plants grown at sub-optimal temperature (low temperature) for growth, whereas assimilation rate was not affected, in accordance with predictions. Under low temperature, specific leaf weight (SLW) and leaf–stem ratio were higher due to reductions in leaf expansion and stem growth, whereas individual leaf mass was not affected. Resin composition was slightly affected by temperature, suggesting that it is under strong genetic control. The stimulant effect of restrictive environmental conditions (low temperature in our study) required to compensate for the short growing season found in cooler environments such as Patagonia, appears insufficient to compensate for the reductions in aboveground biomass, thus resulting in lower resin production per plant.

Characterization of Vegetative Growth of a Supernodulating Soybean Genotype, Sakukei 4

ArticleThe supernodulating soybean cultivar Sakukei 4 was previously characterized by its superior ability to maintain a high leaf nitrogen (N) content and high photosynthetic rate. Despite these desirable traits, the growth performance of Sakukei 4 was inferior to that of its normally nodulating parental cultivar, Enrei. The physiological basis for the unique growth characteristics of Sakukei 4 remains unclear. The objective of the present study was to characterize in further detail thevegetative growth of Sakukei 4, particularly during the period before pod expansion. In the first experiment, the growth of Sakukei 4 was compared with that of its parental cultivar Enrei under various rates of N fertilizer. The dry weight of tops, roots and nodules of the plants grown at lower rates of N application was greater in Enrei than in Sakukei 4, but it was vice versa at higher rates of N application. The number and weight of nodules were far greater in Sakukei 4 than in Enrei at any rate of N application. These genotypic differences were significant on 39 days after sowing (DAS) and became greater at the flowering stage. In the second experiment, therefore, more detailed growth analysis was made during an earlier growth stage (DAS 31-46). During this period, relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) were lower in Sakukei 4 than in Enrei and the related non-nodulating line En1282, whereas the leaf photosynthetic rate was higher in Sakukei 4 at all leaf positions. The dry-matter partitioning to each plant part excluding nodules was similar in all three genotypes. The rate of leaf expansion in Sakukei 4 during this period was significantly slower than that in the other genotypes. These results suggest that the inferior growth of Sakukei 4 prior to flowering is probably due to excessive dry-matter partitioning to nodules and depressed capability of leaf expansion and root growth, which might limit dry-matter production of the whole plant during pre-flowering stage.

Response of Cassava to Water Deficit: Leaf Area Growth and Abscisic Acid

Cassava (Manihot esculenta Crantz) responds to decreases in water status by pronounced stomatal closure and decreased leaf area growth. Many water deficit responses are thought to be regulated by abscisic acid (ABA). To evaluate the extent to which ABA accumulated in a temporal pattern related to water deficit and leaf area growth, five cassava genotypes were grown in greenhouse conditions and subjected to water deficit and recovery treatments during the vegetative‐growth stage. Young and mature leaves were sampled for analysis of area growth and ABA. Under water deficit, leaves from all genotypes rapidly accumulated large amounts of ABA in both mature and young leaves. Correspondingly, young leaves halted leaf expansion growth and transpiration rate decreased. Young leaves accumulated more ABA than mature leaves in both the control and stressed treatments. The high ABA levels under water deficit were completely reversed to control levels after 1 d of rewatering. This rapid return to control ABA levels corresponded with a rapid recovery of leaf area growth rates. We postulate that the rapid reduction in leaf area growth and stomatal closure observed in our study may be due to cassava's ability to rapidly synthesize and accumulate ABA at an early phase of a water deficit episode.