Inhibition Of Leaf Growth Research Articles

Long-term inhibition by auxin of leaf blade expansion in bean and Arabidopsis.

The role of auxin in controlling leaf expansion remains unclear. Experimental increases to normal auxin levels in expanding leaves have shown conflicting results, with both increases and decreases in leaf growth having been measured. Therefore, the effects of both auxin application and adjustment of endogenous leaf auxin levels on midrib elongation and final leaf size (fresh weight and area) were examined in attached primary monofoliate leaves of the common bean (Phaseolus vulgaris) and in early Arabidopsis rosette leaves. Aqueous auxin application inhibited long-term leaf blade elongation. Bean leaves, initially 40 to 50 mm in length, treated once with alpha-naphthalene acetic acid (1.0 mm), were, after 6 d, approximately 80% the length and weight of controls. When applied at 1.0 and 0.1 mm, alpha-naphthalene acetic acid significantly inhibited long-term leaf growth. The weak auxin, beta-naphthalene acetic acid, was effective at 1.0 mm; and a weak acid control, benzoic acid, was ineffective. Indole-3-acetic acid (1 microm, 10 microm, 0.1 mm, and 1 mm) required daily application to be effective at any concentration. Application of the auxin transport inhibitor, 1-N-naphthylphthalamic acid (1% [w/w] in lanolin), to petioles also inhibited long-term leaf growth. This treatment also was found to lead to a sustained elevation of leaf free indole-3-acetic acid content relative to untreated control leaves. Auxin-induced inhibition of leaf growth appeared not to be mediated by auxin-induced ethylene synthesis because growth inhibition was not rescued by inhibition of ethylene synthesis. Also, petiole treatment of Arabidopsis with 1-N-naphthylphthalamic acid similarly inhibited leaf growth of both wild-type plants and ethylene-insensitive ein4 mutants.

Leaf growth and stomatal sensitivity to ABA in droughted pepper plants

The role of xylem sap abscisic acid (ABA) in regulating leaf growth and stomatal conductance was investigated on droughted pepper cultivars. Two pepper cultivars Capsicum annuum var. grossum, Bellboy and Capsicum annuum var. annuum ‘Cili Padi’ were established in growth chamber in soil compost mixture-filled polyvinyl-chloride tubes, 200 mm long and of an internal diameter of 105 mm. Soil was fertilized and wet to field capacity during plant establishment. One group of plants was given one last watering and left unwatered for 9 days and another group of plants was watered daily. Under gradually decreasing soil moisture content, C. annuum var. grossum ‘Bellboy’ and C. annuum var. annuum ‘Cili Padi’ differed in their leaf water status, stomatal conductance, leaf growth and xylem sap ABA concentrations. The reduction in stomata and leaf growth was independent to the changes in the internal water relations as soil drying progressed. Stomatal conductance of ‘Bellboy’ began to decline within 2 days of cessation of watering, while ‘Cili Padi’ showed a reduction in this variable approximately 2 days later. Leaf growth of well watered ‘Bellboy’ was more rapid than that of ‘Cili Padi’. When watering was stopped, ‘Bellboy’ showed an earlier inhibition of leaf growth. There were differences in the sensitivity of stomata and leaf growth to leaf and soil water status. Leaf growth was apparently responsive to variation in soil water availability in a range where leaf water status did not change. Both cultivars showed the same responses in stomatal conductance and leaf growth when expressed as a function of ABA concentration in the xylem. The study showed that under gradual water stress condition, any production of ABA from roots to be ineffective in triggering early stomatal closure and cessation of leaf growth.

Does high bicarbonate supply to roots change availability of iron in the leaf apoplast

The role of the leaf apoplast in iron (Fe) uptake into the leaf symplast is insufficiently understood, particularly in relation to the supposed inactivation of Fe in leaves caused by elevated bicarbonate in calcareous soils. It has been supposed that high bicarbonate supply to roots increases the pH of the leaf apoplast which decreases the physiological availability of Fe in leaf tissues. The study reported here has been carried out with sunflower plants grown in nutrient solution and with grapevine plants grown on calcareous soil under field conditions. The data obtained clearly show that the pH of the leaf apoplastic fluid was not affected by high bicarbonate supply in the root medium (nutrient solution and field experiments). The concentrations of total, symplastic and apoplastic Fe were decreased in chlorotic leaves of both sunflower (nutrient solution experiment) and grapevine plants in which leaf expansion was slightly inhibited (field experiment). However, in grapevine showing severe inhibition of leaf growth, total Fe concentration in chlorotic leaves was the same or even higher than in green ones, indicative to the so-called `chlorosis paradox'. The findings do not support the hypothesis of Fe inactivation in the leaf apoplast as the cause of Fe deficiency chlorosis since no increase was found in the relative amount of apoplastic Fe (% of total leaf Fe) either in the leaves of sunflower or grapevine plants. It is concluded that high bicarbonate concentration in the soil solution does not decrease Fe availability in the leaf apoplast.

Abscisic acid is correlated with the leaf growth inhibition of four genotypes of maize differing in their response to salinity.

In this paper we tested the hypothesis that the leaf growth reduction of salt-stressed maize is regulated by the abscisic acid (ABA) concentrations in the growing zone of the leaf. Leaf elongation rate (LER) of maize (Zea mays L.) was rapidly inhibited by salinity (80 mM NaCl), and the (+)-ABA concentration increased significantly in the growing zone of the leaf. Upon removal of salinity, ABA concentrations decreased rapidly in the growing zone and LER increased to control levels. Four maize genotypes differing in their responses to salinity were compared over a range of leaf ABA concentrations. (+)-ABA concentrations in the growing zone of the leaf were highly correlated with LER inhibition for all four genotypes. However, the sensitivity of LER to leaf ABA concentrations differed amongst the genotypes. Thus, for each genotype, ABA concentrations in the growing zone of the leaf were a good predictor of maize LER response to salinity.

Corrigendum to: Abscisic acid is correlated with the leaf growth inhibition of four genotypes of maize differing in their response to salinity

In this paper we tested the hypothesis that the leaf growth reduction of salt-stressed maize is regulated by the abscisic acid (ABA) concentrations in the growing zone of the leaf. Leaf elongation rate (LER) of maize (Zea mays L.) was rapidly inhibited by salinity (80 mM NaCl), and the (+)-ABA concentration increased significantly in the growing zone of the leaf. Upon removal of salinity, ABA concentrations decreased rapidly in the growing zone and LER increased to control levels. Four maize genotypes differing in their responses to salinity were compared over a range of leaf ABA concentrations. (+)-ABA concentrations in the growing zone of the leaf were highly correlated with LER inhibition for all four genotypes. However, the sensitivity of LER to leaf ABA concentrations differed amongst the genotypes. Thus, for each genotype, ABA concentrations in the growing zone of the leaf were a good predictor of maize LER response to salinity.

Salinity-induced inhibition of leaf elongation in maize is not mediated by changes in cell wall acidification capacity.

The physiological mechanisms underlying leaf growth inhibition under salt stress are not fully understood. Apoplastic pH is considered to play an important role in cell wall loosening and tissue growth and was demonstrated to be altered by several growth-limiting environmental conditions. In this study we have evaluated the possibility that inhibition of maize (Zea mays) leaf elongation by salinity is mediated by changes in growing cell wall acidification capacity. The kinetics of extended apoplast pH changes by leaf tissue of known expansion rates and extent of growth reduction under stress was investigated (in vivo) and was found similar for non-stressed and salt-stressed tissues at all examined apoplast salinity levels (0.1, 5, 10, or 25 mM NaCl). A similar rate of spontaneous acidification for the salt and control treatments was demonstrated also in in situ experiments. Unlike growing cells that acidified the external medium, mature nongrowing cells caused medium alkalinization. The kinetics of pH changes by mature tissue was also unchanged by salt stress. Fusicoccin, an enhancer of plasmalemma H(+)-ATPase activity level, greatly stimulated elongation growth and acidification rate to a similar extent in the control and salt treatments. That the ability of the growing tissue to acidify the apoplast did not change under same salt stress conditions that induced inhibition of tissue elongation rate suggests that salinity does not inhibit cell growth by impairing the acidification process or reducing the inherent capacity for cell wall acidification.

Assessment of barium toxicity in bush beans.

External and internal lowest observed effect concentrations (LOECs) for Ba in bean plants (Phaseolus vulgaris) were established using a nutrient solution culture system where BaSO(4) precipitation in the growth medium was avoided. This was achieved by alternating every 24 h with a nutrient solution containing Ba (0, 50, 500, or 5000 microM) and all essential elements except S, with another containing S and all other nutrients but no Ba. The external LOEC for acute toxicity symptoms in the form of leaf withering and leaf growth inhibition was 481 microM of free Ba(2+). This was also the LOEC for the complete inhibition of elongation of secondary roots, while for the elongation of the primary root the external LOEC was 4,821 microM. Barium interfered with both the sulfate transport from roots to shoots and the import of Ca into leaves. However, K was the most Ba-sensitive nutrient. External LOEC for reduced leaf K concentrations was 48 microM free Ba(2+); the corresponding internal LOECs for primary and trifoliolate leaves were 700 and 460 mg kg(-1) DW, respectively.

The Effect of Superovulation of Javanese Thin-Tail Ewes Prior to Mating on Lamb Birth Weight and Preweaning Growth

There is little information on optimum management of fodder tree legumes for maximum leaf production. The type of management depends on both their morphology and form of utilisation, which varies between species. As differences exist in relative growth rates and ability to persist over longer periods, their management is influenced by cutting height and cutting frequency (Horne et al., 1986). This study was undertaken at the University of Queensland to observe the responses of commonly used fodder tree legumes to cutting management. Four cutting treatments (60 cm, 100 cm, 150 cm and lopped) commencing in August, 1987 were imposed on five established tree legume species (Acacia angustissimus, Calliandra calothrysus, Albizia chinensis, Gliricidia sepium and Leucaena leucocephala). Each row of species contained five trees per treatment. Two months later the trees were cut at their respective heights and coppiced material lopped and subsequent harvests made at 1.5 monthly intervals until March. Materials harvested were separated into leaf (including flowers and pods) and stems (>6 mm diameter) and oven dried at 60C. The low spring temperatures reduced and inhibited leaf growth of all species and G. sepium respectively, but improved during summer. At 150 cm, L. leucocephala was better during spring and all species produced similar yields during summer. The overall mean leaf yields (%) at the respective heights over the period were 19, 26, 36, 19; 13, 24, 43, 19; 14, 22, 44 and 20. When lopped, leaf yield of C. calothrysus was high during spring and summer but similar to A. chinensis and G. sepium respectively in terms of forage quality. The overall mean leaf yields over the period were 7, 16, 10 and 65%. As cutting height increased, the number of remaining shoots, leaves and buds in the bottom canopy also increased from which regrowth was rapid. However, the proportion of leaves removed either by cutting, lopping or loss through leaf fall removed most photosynthetic tissues and reduced current photosynthate, resulting in reduced leaf yield. Regrowth and plant survival then depended on the reserve carbohydrate in the stem and rate of dry-matter accumulation, which varied between species. The different responses to cutting management provided some options for their use as reserve fodder in grazing systems. Horne, PM Catchpole D W and Ella A 1986 ACIAR

Rapid effects of nitrogen form on leaf morphogenesis in tobacco.

Ammonium (NH4+) instead of nitrate (NO3-) as the nitrogen (N) source for tobacco (Nicotiana tabacum L.) cultivated in a pH-buffered nutrient solution resulted in decreased shoot and root biomass. Reduction of shoot fresh weight was mainly related to inhibition of leaf growth, which was already detectable after short-term NH4+ treatments of 24 h, and even at a moderate concentration level of 2 mM. Microscopic analysis of the epidermis of fully expanded leaves revealed a decrease in cell number (50%) and in cell size (30%) indicating that both cell division and cell elongation were affected by NH4+ application. Changes in various physiological parameters known to be associated with NH4(+)-induced growth depression were examined both in long-term and short-term experiments: the concentrations of total N, soluble sugars and starch as well as the osmotic potential, the apparent hydraulic conductivity and the rate of water uptake were not reduced by NH4+ treatments (duration 1-12 d), suggesting that leaf growth was neither limited by the availability of N and carbohydrates, nor by a lack of osmotica or water supply. Although the concentration of K+ in leaf press sap declined in expanding leaves by approximately 15% in response to NH4+ nutrition, limitation of mineral nutrients seems to be unlikely in view of the fast response of leaf growth at 24 h after the start of the NH4+ treatment. No inhibitory effects were observed when NH4+ and NO3- were applied simultaneously (each 1 mM) resulting in a NO3-/NH4+ net uptake ratio of 6:4. These findings suggest that the rapid inhibition of leaf growth was not primarily related to NH4+ toxicity, but to the lack of NO3(-)-supply. Growth inhibition of plants fed solely with NH4+ was associated with a 60% reduction of the zeatine + zeatine riboside (Z + ZR) cytokinin fraction in the xylem sap after 24 h. Furthermore Z + ZR levels declined to almost zero within the next 4 d after start of the NH4+ treatment. In contrast, the concentrations of the putative Z + ZR precursors isopentenyl-adenine and isopentenyl-adenosine (i-Ade + i-Ado) were not affected by NH4+ application. Since cytokinins are involved in the regulation of both cell division and cell elongation, it seems likely that the presence of NO3- is required to maintain biosynthesis and/or root to shoot transfer of cytokinins at a level that is sufficient to mediate normal leaf morphogenesis.

Spatial distributions and net deposition rates of Fe, Mn and Zn in the elongating leaves of wheat under saline soil conditions

In this study, we quantified the spatial distributions of Fe, Mn and Zn and their net deposition rates in the elongating and mature zones of leaf 4 on the main stem of spring wheat (Triticum aestivum L.) on a millimetre scale during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty loam with 0 and 120 mМ NaCl in growth chambers. The sampling was conducted on the 3rd day after leaf 4 emerged during the photoperiod. The patterns of spatial distributions of Fe, Mn and Zn concentrations (mmol kg–1 FW) in the growing leaves were distinct. Salinity affected the distri-bution pattern of Fe concentration on the FW basis, whereas it did not affect those of the Zn and Mn. The distribution patterns of Fe and Mn differed from those for N, P, K, Ca and Mg found in a previous study, whereas the distribution pattern of Zn was similar to those of Mg, P and N. The spatial distribution of the net deposition rates (mmol kg–1 FW h–1) in both treatments demonstrated the strongest sink for the micronutrients in the elongation zone, and their net deposition rates were enhanced by 120 mМ NaCl at the middle of the elongation zone. From the results, we conclude that the inhibition of leaf growth of wheat is probably not due to the effect of salinity on Fe, Mn and Zn in leaves.

Spatial distributions and net deposition rates of Fe, Mn and Zn in the elongating leaves of wheat under saline soil conditions

In this study, we quantified the spatial distributions of Fe, Mn and Zn and their net deposition rates in the elongating and mature zones of leaf 4 on the main stem of spring wheat (Triticum aestivum L.) on a millimetre scale during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty loam with 0 and 120 mМ NaCl in growth chambers. The sampling was conducted on the 3rd day after leaf 4 emerged during the photoperiod. The patterns of spatial distributions of Fe, Mn and Zn concentrations (mmol kg–1 FW) in the growing leaves were distinct. Salinity affected the distri-bution pattern of Fe concentration on the FW basis, whereas it did not affect those of the Zn and Mn. The distribution patterns of Fe and Mn differed from those for N, P, K, Ca and Mg found in a previous study, whereas the distribution pattern of Zn was similar to those of Mg, P and N. The spatial distribution of the net deposition rates (mmol kg–1 FW h–1) in both treatments demonstrated the strongest sink for the micronutrients in the elongation zone, and their net deposition rates were enhanced by 120 mМ NaCl at the middle of the elongation zone. From the results, we conclude that the inhibition of leaf growth of wheat is probably not due to the effect of salinity on Fe, Mn and Zn in leaves.

Effects of salinization on nutrient transport to lettuce leaves: consideration of leaf developmental stage

Most recent reviews of plant salinity response have included the concept of a nutritional disturbance as one likely mechanism by which shoot growth might be inhibited. None the less, few studies of dicotyledonous plants have presented data on nutrient transport into the most intensively growing shoot tissues. In this paper net nutrient deposition was followed for 3 d in 8 sequential, growing leaves of Lactuca sativa, which were grown either in conditions of moderate salinization, or in a growth‐stimulating concentration of NaCl. The nutrient deposition was studied from 0.7 to 3.7 d following completion of stepwise salinization. This deposition was followed in immature leaves, which had attained only 1–2% of ultimate leaf mass by the completion of the study. In such young leaves development is still dominated by cell division. The transport of Ca2+ specifically to the youngest leaves was reduced by more than twice as much as was K+ transport. Transport of the other major divalent cationic nutrient, Mg2+, was not decreased for these leaves. The factors of increase for Na+ and Cl− after 3.7 d after completion of salinization averaged 152 and 62% over control levels for the three youngest leaves (for Na+ and Cl−, respectively). Though significant, these increases were only 27 and 14% as great as increases in three leaf sets of more developed growing leaves. Decreases in net K+ deposition and leaf K+ concentration were not greater for the youngest than they were for the oldest leaves. Net S deposition was reduced 44% more in younger than older growing leaves, but for most leaves not beyond the level expected due to reduced sink strength. The reduction in net P deposition also seemed more related to reduced sink strength, but was reduced to approx. 50% in both younger and more developed growing leaves. While Fe concentration was not reduced by salinization at any developmental stage, Zn2+ net transport and Zn concentration were both reduced in the two youngest leaves (57 and 70%, respectively). Given the moderate treatment imposed (Na:Ca ratio of 22) the results suggest that Ca2+ transport to the youngest leaves is probably highly sensitive to salinization of the root medium and is perhaps a key physiological response in the inhibition of leaf growth.

Evidence and characterization of a virus of St John's Wort (Hypericum perfora tum L.)

Vein yellows, necrotic leaf spots and growth inhibition were observed on St John's wort plants (Hypericum perforatum L.) growing in a field in northern Thuringia. A virus was isolated from diseased plants and mechanically transmitted to several species of the genera Antirrhinum, Chenopodium, Cucurbita, Datura, Gomphrena, Lathyrus, Malva, Nicotiana, Ocimum, Petunia, Phaseolus and Spinacia. After retransmitting the virus to H. perforatum it developed symptoms similar to those observed in the field and was reisolated from experimentally infected H. perforatum plants. High concentrations of the virus were found in Nicotiana clevelandii Gray and N. occidentalis Wheeler. The thermal inactivation point was 52°C. The virus remained infectious in frozen and dried leaves of N. clevelandii for at least 3 months, but lost its infectivity in crude sap of N. clevelandii plants already after 3 days, in crude sap of H. perforatum plants even after 1 day. The virus has isometric particles with a diameter of 27 nm. It is highly immunogenic and an antiserum was produced with a titre of 1/2 048. The virus is serologically not identical or related with 10 other viruses investigated. It is not transmissible by the aphid species Myzus persicae (Sulz.), but it seems easily transmissible by leaf contact and by cutting of leaves or stalks. The contents of valuable active compounds in diseased plants differ partly from those in healthy plants. According to the first preliminary studies different varieties of St John's wort respond the virus infection in a distinct manner.

Water stress inhibits hydraulic conductance and leaf growth in rice seedlings but not the transport of water via mercury-sensitive water channels in the root

The mechanisms by which moderate water stress (adding polyethylene glycol 6000 to the root medium) induces a sustained inhibition of growth in emerging first leaves of intact rice (Oryza sativa) seedlings was investigated under growth-chamber conditions. Early (24 h) inhibition of leaf growth was not related to changes in root size or in osmotic potential gradients and cell wall-yielding characteristics in the leaf-expansion zone of stressed seedlings. However, reductions in root-to-leaf hydraulic conductance (L) were measured in two rice cultivars after 4 or 24 h at various levels of water stress, and these reductions correlated well with the inhibition of leaf growth. We assayed L by a psychrometric method and, in intact seedlings, by a novel osmotic-jump method. The addition of 0.5 mM HgCl2 to the root medium to inhibit water transport through Hg-sensitive water channels in the roots did not inhibit leaf growth in unstressed seedlings. However, both leaf growth and L were additionally reduced (by 49% and 43%, respectively) within minutes of adding HgCl2 to roots of water-stressed seedlings. Water stress therefore appeared to increase the transport of water via Hg-sensitive water channels. Other mechanisms were apparently involved in inhibiting overall L and leaf growth.

Does Salinity Inhibit Alfalfa Leaf Growth by Reducing Tissue Concentration of Essential Mineral Nutrients?

The increased salinity of arid and semi‐arid lands has become a problem of great concern in agriculture. The possibility that the inhibition of leaf growth in alfalfa (Medicago sativa) growing under saline conditions may be associated with a reduction in ion concentration in the leaf was investigated. Seeds of alfalfa cv. Buraimi were sown in PVC cylinders filled with loamy sand and arranged in large pots embedded in the soil with the rim just above the soil surface. This arrangement simulated plants grown under field conditions. Seedlings were irrigated with saline (12.2 dS m−1) and nutrient solutions (full strength or 20 times dilution) twice weekly. After 6 weeks the plants were harvested and separated into roots, stem and leaves. The leaves were further separated into lamina and petioles and analysed for the major and minor nutrient elements. Salinization significantly reduced the fresh weights of the roots, stem and leaves as well as the concentration of N, K, Ca and Mg in the leaf tissue. With the exception of Cu concentration, which was enhanced by salinity, all the micronutrients (B, Zn, Mn and Fe) had reduced concentrations in the leaves of salinized alfalfa. The application of an external nutrient solution, especially the full‐strength solution, produced an increase in leaf growth and leaf nutrient element concentration. On the basis of these results it was concluded that reduced leaf nutrient concentration may be one of the primary causes of the inhibition of leaf growth that was characteristic of alfalfa growing under salinity stress.

Water-stressed maize, barley and rice seedlings show species diversity in mechanisms of leaf growth inhibition

The possible occurrence of species diversity in mechanisms underlying leaf-growth inhibition by water stress, was investigated in related cereal plants. Water stress was generated by additions of the osmoticum polyethylene glycol 6000 to the root medium. Effects of external water potentials ranging from 0 to -0.6 MPa, on early growth parameters of emerging leaves were measured under controlled environment conditions, using pairs of maize, barley or rice genotypes with differing resistance to water stress under field conditions. Water potentials of -0.4 MPa for 24 h, similarly reduced leaf growth, comparative production rates of leaf epidermal cells and cell size in all genotypes. These reductions did not appear to be caused by reductions in the osmotic potential gradients between the expanding leaf cells and their external water source. However, growth inhibition in maize and barley, was accompanied by significant reductions in comparative leaf and cell wall extensibility. Moreover, regression plots revealed good linear correlations (r=0.83 ** for maize and r=0.77 ** for barley) between the reductions in leaf growth induced by a series of water potentials and associated reductions in leaf extensibility. In contrast, the reduction in growth of rice leaves, was not accompanied by any significant changes in leaf or cell wall extensibility. Similarly, regression plots revealed poor correlations between leaf growth and leaf extensibility in both paddy and upland rice (r=0.17 and r=0.07, respectively). Thus, despite numerous inter-species similarities, biophysical changes associated with stress-induced leaf growth inhibition in maize and barley, differed from those in rice.

Water-stressed maize, barley and rice seedlings show species diversity in mechanisms of leaf growth inhibition

Water-stressed maize, barley and rice seedlings show species diversity in mechanisms of leaf growth inhibition

Role of sodium in the ABA‐mediated long‐term growth response of bean to salt stress

Long‐term salt effects on plant growth have often been related to direct ion toxicity due to the accumulation of high ion concentrations in plant tissue. This work examines the relative importance of endogenous ABA, as well as Na+ and Cl− toxicity, in the inhibition of leaf growth and photosynthesis, in bean plants grown at 1, 25, 50 and 75 mM NaCl until the fruit‐bearing stage. All salt‐treated plants showed very high leaf Cl− concentrations, with little difference between plants exposed to 50 or 75 mM NaCl. The 25 and 50 mM salt‐treated plants were able to successfully exclude Na+ from their leaves, and only suffered an initial decline in the rate of leaf growth. Plants exposed to 75 mM NaCl showed an increase in Na+ leaf concentrations with an accompanying decrease in growth and photosynthesis as salt exposure progressed. A high correlation was found between leaf Na+ and leaf growth. Leaf ABA significantly increased with salt supply, and was highly correlated with both leaf Na+ and leaf growth. Our results suggest that in bean plants under long‐term salt stress, leaf ABA may participate in the regulation of leaf growth, and leaf Na+ would be at least partly responsible for increased ABA levels.

The influence of phosphate deficiency on photosynthesis, respiration and adenine nucleotide pool in bean leaves

The decrease in inorganic phosphate (Pi) content of 10-d-old Phaseolus vulgaris L. plants did not affect rates of photosynthesis (PN) and respiration (RD), leaf growth, and adenylate concentration. Two weeks of phosphate starvation influenced the ATP content and leaf growth more than PN and RD. The ATP concentration in the leaves of 15- and 18-d-old phosphate deficient (-P) plants after a light or dark period was at least half of that in phosphate sufficient (+P, control) plants. Similar differences were found in fresh and dry matter of leaves. However, PN declined to 50 % of control in 18-d-old plants only. Though the RD of -P plants (determined as both CO2 evolution and O2 uptake) did not change, an increased resistance of respiration to KCN and higher inhibition by SHAM (salicylhydroxamic acid) suggested a higher engagement of alternative pathway in respiration and a lower ATP production. The lower demand for ATP connected with inhibition of leaf growth may influence the ATP producing processes and ATP concentration. Thus, the ATP concentration in the leaves depends stronger on Pi content than on PN and RD.

Endogenous abscisic acid levels are linked to decreased growth of bush bean plants treated with NaCl

This paper studies the relative importance of endogenous ABA and ion toxicity in the leaf growth inhibition caused by NaCl in salt‐adapted and unadapted bush beans. Adaptation to salt‐stress was achieved by germination of seeds in 75 mM NaCl, while unadapted plants were germinated in tap water. The adaptation process caused a transitory increase in leaf ABA, Na+ and Cl− concentrations, while leaf expansion was inhibited. However, when grown for 8 or 13 days in 75 mM NaCl‐containing nutrient solution, primary and first trifoliolate leaves of salt‐adapted plants had greater areas than those of unadapted plants. Concentrations of ABA, Na+ and Cl− in these leaves were lower in adapted plants, and a strong negative correlation between leaf expansion growth and either leaf Na+, Cl− or ABA concentrations could be established. However, in the second trifoliolate leaves only the ABA, but not the Na+ or Cl−, concentrations were significantly correlated with leaf expansion. Our results suggest that salt‐induced inhibition of leaf expansion growth in bush beans is mediated by ABA rather than Na+ or Cl− toxicity. Moreover, the increase of ABA, induced by the salt‐pretreatment, seems to play an important role in limiting the accumulation of Na+ and Cl− in the leaves, leading to adaptation of bush beans to salt‐stress.