Internode length and anatomical changes in Pisum genotypes crys and cryc in response to extended daylength and applied gibberellin A1

Dwarf pea (Pisum sativum L.) plants with genotypes cry^c and cry^s responded differently when an 8 h photoperiod (8 h daylight, 16 h dark) was extended to 24 h (8 h daylight, 16 h incandescent light). Genotype cry^c showed up to a 4-fold increase in internode length, sustained by increases in both cell length (particularly of epidermal cells) and cell number (particularly of cortical cells) while cry^s plants showed up to a 2-fold increase in internode length sustained mostly by an increase in cell number. Under an 8 h (daylight) photoperiod the two genotypes did not differ in their sensitivity to applied gibberellin A₁ (GA₁) and they showed a similar pattern of response. GA₁ significantly increased internode length, cell length and cell number in both genotypes. Incandescent light did not increase the size of the response to GA₁ except for cry^s plants at high dose rates of GA₁ (29–58 nmol). At saturating doses of GA₁ the two genotypes attained a similar peak internode length; incandescent light increased the peak by about 40%. GA₁ increased the rate of leaf appearance by up to 33% while incandescent light reduced the rate by 4–7%. The elongation response of the more mature internodes of cry^c plants to GA₁ or incandescent light was due primarily to an increase in cell length whereas increased cell number made a significant contribution in the case of internodes which were relatively immature at the time the stimulus was applied. The progressive increase in internode length of both genotypes during ontogeny was due primarily to an increase in cell number. In conclusion, alleles cry^c and cry^s (background le La) do not confer a difference in sensitivity to GA₁ and the increase in internode length in response to incandescent light is probably not the result of a real or perceived increase in GA₁ level. Allele cry^s may partially block a phytochrome mediated response to light and the key difference between genotypes cry^s and cry^c may lie in the greater elongation (extensibility?) of cry^c epidermal cells in incandescent light.     

nif Gene expression in a Nif+, Fix−Bradyrhizobium japanicum variant

Abstract Bradyhizobium japonicum USDA 110 has been shown to contain several genetically similar, naturally occurring colony morphology variants. One of these variants, L2-110, although devoid of symbiotic nitrogen fixation, retains significant levels of explanta nitrogen fixation ability relative to other symbiotically competent USDA 110 variants (MN-110 and I-110). Interestingly, Northern blot analyses revealed that L2-110 nodules, despite their lack of symbiotic nitrogen fixation, contained 65% the level of mRNA for dinitrogenase ( nif DK) and 64% the level of dinitrogenase reductase ( nif H) mRNA relative to MN-110 nodules. Western blot analyses of tissue from the same nodules detected 32% the level of dinitrogenase and 31% the level of dinitrogenase reductase in L2-110 relative to MN-110. L2-110 appears to be a new class of mutant based on the complete absence of symbiotic nitrogen fixation (Fix⁻ and the presence of significant exanta nitrogen fixation (Nif⁺).     

Ca++ antagonists distinguish different requirements for cAMP-mediated gene expression in the cellular slime mold, Dictyostelium discoideum

Cyclic AMP is essential for the accumulation of many prespore mRNAs and can advance the time of appearance of mRNAs specifically enriched in prestalk cells. Additionally, when late-developing cells are washed free of cAMP, a number of growth phase mRNAs reaccumulate. This reaccumulation can be suppressed by cAMP. These effects of cAMP are all mediated through the cell surface cAMP receptor and can occur under conditions where the receptor-associated adenylate cyclase is inactive, indicating that the initial intracellular transduction event necessary for expression of these mRNAs does not depend upon cAMP synthesis. The dihydropyridine derivatives, nifedipine and nitrendipine, are highly specific Ca++ channel blockers. They are shown here to prevent the influx of Ca++ from the external medium that occurs in response to cAMP binding to the cell surface receptor during development. These two compounds as well as another Ca++ antagonist, 8-N,N-diethylamino)octyl-3,4,5-trimethoxy-benzoate (TMB-8) and a calmodulin inhibitor, N-(6-amino-hexyl)-5-chloro-1-naphthalene sulfonamide (W7), all specifically decrease cAMP-mediated prespore mRNA accumulation in a dose-dependent manner. They also prevent cAMP from suppressing the expression of the growth phase genes. The growth phase mRNAs reaccumulate in cAMP-treated cells in the presence of increasing concentrations of these drugs. By contrast, cAMP induction of the pre-stalk-enriched mRNA is not as significantly affected by these agents. These results raise the possibility that the cell surface cAMP receptor can couple to different signal transduction systems and thereby induce or suppress the expression of different sets of cAMP-regulated genes during development.     

Role of the response regulator RssB in σS recognition and initiation of σS proteolysis in Escherichia coli

In growing Escherichia coli cells, the master regulator of the general stress response, sigmaS (RpoS), is subject to rapid proteolysis. In response to stresses such as sudden carbon starvation, osmotic upshift or shift to acidic pH, sigmaS degradation is inhibited, sigmaS accumulates and numerous sigmaS-dependent genes with stress-protective functions are activated. sigmaS proteolysis is dependent on ClpXP protease and the response regulator RssB, whose phosphorylated form binds directly to sigmaS in vitro. Here, we show that substitutions of aspartate 58 (D58) in RssB, which result in higher sigmaS levels in vivo, produce RssB variants unable to bind sigmaS in vitro. Thus, RssB is the direct substrate recognition factor in sigmaS proteolysis, whose affinity for sigmaS depends on phosphorylation of its D58 residue. RssB does not dimerize or oligomerize upon this phosphorylation and sigmaS binding, and RssB and sigmaS exhibit a 1:1 stoichiometry in the complex. The receiver as well as the output domain of RssB are required for sigmaS binding (as shown in vivo and in vitro) and for complementation of an rssB null mutation. Thus, the N-terminal receiver domain plays an active and positive role in RssB function. Finally, we demonstrate that RssB is not co-degraded with sigmaS, i.e. RssB has a catalytic role in the initiation of sigmaS turnover. A model is presented that integrates the details of RssB-sigmaS interaction, the RssB catalytic cycle and potential stress signal input in the control of sigmaS proteolysis.     

Changes in NO3− and K+ uptake by four species in flowing solution culture in response to increased irradiance

Net rates of NO₃^? and K⁺ uptake were compared for oilseed rape (Brassica napus L. cv. Jet neuf), perennial ryegrass (Lolium perenne L. cv. S23), Italian ryegrass (Lolium multiflorum Lam. cv. Augusta) and wheat (Triticum aestivum L. cv. Fen-man) in flowing solution culture during a 4-day sequence of low-low-high-high natural irradiance. Concentrations of NO₃^? (10 μM) and K⁺ (2.5 μM) in solutions were maintained automatically and hourly variation in net uptake of these ions was measured. During the 2 days of low irradiance (<1 MJ m^?2 day^?1) the uptake rates of both ions by all species were low at <1 mmol NO₃^?, m^?2 h^?1 and <0.4 mmol K⁺ m^?2 h^?1. Uptake increased in each species during the first day of high irradiance (7.90 MJ m^?2 day^?1) to >4 mmol NO₃^? m^?2 h^?1 and >1.4 mmol K⁺ m^?1 h^?1. These higher rates were maintained throughout the following night. The lag-time between maximum irradiance and the onset of the highest acceleration in uptake was greater for NO₃^? (5–8 h) than for K⁺ (≤1 h) in rape, wheat and Italian ryegrass. Uptake of NO₃^?, by perennial ryegrass showed an almost constant acceleration for 18 h following maximum irradiance. In all species the measured maximum inflows (uptake rate per unit root length) of both ions were greater than theoretical maximum potential inflows to a non-competing infinite-sink root in soil, by factors of 7 and 36, respectively, for NO₃^? and K⁺, averaged over all species.     

Back to log phase: σS as a global regulator in the osmotic control of gene expression in Escherichia coli

It is now well established that the σ^S subunit of RNA polymerase is a master regulator in a complex regulatory network that governs the expression of many stationary-phase-inducible genes in Escherichiacoli. In this review, more recent findings will be summarized that demonstrate that σ^S also acts as a global regulator for the osmotic control of gene expression, and actually does so in exponentially growing cells. Thus, many σ^S-dependent genes are induced during entry into stationary phase as well as in response to osmotic upshift. K⁺ glutamate, which accumulates in hyperosmotically stressed cells, seems to specifically stimulate the activity of σ^S-containing RNA polymerase at σ^S-dependent promoters. Moreover, osmotic upshift results in an elevated cellular σ^S level similar to that observed in stationary-phase cells. This increase is the result of a stimulation of rpoS translation as well as an inhibition of the turnover of σ^S, which in exponentially growing non-stressed cells is a highly unstable protein. Whereas the RNA-binding protein HF-I, previously known as a host factor for the replication of phage Qβ RNA, is essential for rpoS translation, the recently discovered response regulator RssB, and ClpXP protease, have been shown to be required for σ^S degradation. The finding that the histone-like protein H-NS is also involved in the control of rpoS translation and σ^S turnover, sheds new light on the function of this protein in osmoregulation. Finally, preliminary evidence suggests that additional stresses, such as heat shock and acid shock, also result in increased cellular σ^S levels in exponentially growing cells. Taken together, σ^S function is clearly not confined to stationary phase. Rather, σ^S may be regarded as a sigma factor associated with general stress conditions.     

Phosphorus status determines biomass response to elevated CO2 in a legume : C4 grass community

Thirty-six mesocosms, each containing a two-species community of Trifolium repens (C₃ legume) and Stenotaphrum secundatum (C₄ grass), were grown in sand with three nutrient regimes, zero N low P, zero N high P and supplied N high P, under ambient (aCO₂) and twice ambient CO₂ (eCO₂) for 15 months in two greenhouses. Aboveground annual production in the P limited mesocosms did not respond to eCO₂ and was reduced by 50% relative to mesocosms with an adequate P supply, where dry-matter production was increased by 12–24% under eCO₂. The stimulation of production by eCO₂ occurred throughout the year despite a clear seasonality in growth. There was no effect of eCO₂ on leaf area index (LAI), which was larger under high P than low P. Live root mass at the end of the experiment was higher under eCO₂ in all nutrient treatments, but the response of total belowground C (root+soil) to eCO₂ depended on P treatment. Under limiting P, belowground C was not significantly changed by eCO₂ (2–2.3 t belowground C ha⁻¹). Under high P supply, both root and soil C pools increased under eCO₂. Under aCO₂, low P supply increased belowground C by 0.7–1 t C ha⁻¹ above that added by the high P treatment. P is commonly limiting in Australian ecosystems and the majority of ecosystem N input is provided by biological N fixation. Consequently, the response of legumes to eCO₂ is of particular importance. These results demonstrate that at low P availability, there is likely to be only a limited response of biomass production by T. repens to eCO₂, which in turn may constrain any ecosystem response.     

Involvement of Ca2+ signalling in the sugar-inducible expression of genes coding for sporamin and β-amylase of sweet potato

Genes coding for sporamin and β-amylase of sweet potato are inducible not only by high levels of metabolizable sugars, such as sucrose, but also by a low concentration of polygalacturonic acid (PGA). Calmodulin inhibitors and EGTA inhibited both the PGA-inducible and the sucrose-inducible accumulation of mRNAs for sporamin and β-amylase in sweet potato. Calmodulin inhibitors, EGTA and La³⁺, also inhibited the sucrose-inducible expression, in leaves of transgenic tobacco, of a fusion gene, β-Amy:GUS, which consists of the promoter of the β-amylase gene and the coding sequence for β-glucuronidase. The sucrose-inducible expression of the β-Amy:GUS fusion gene was also inhibited by two inhibitors of Ca²⁺ channels, diltiazem and nicardipine. These results suggest that the sugar-inducible expression of genes for sporamin and β-amylase involves, at least in part, Ca²⁺-mediated signalling, and that the cytosolic free Ca²⁺ may mediate cross-talk between signals related to carbohydrate metabolism and other stimuli. Treatment of coelenterazine-loaded leaf discs of tobacco expressing a Ca²⁺-binding photoprotein, aequorin, with 0.2 M sucrose for 24 h significantly reduced the level of luminescence that could be induced by cold shock, as compared to cold shock-induced luminescence in coelenterazine-loaded leaf discs treated with water. Repression of cold shock-induced luminescence was due to the conversion of holoaequorin to apoaequorin during the treatment with sucrose. Treatment of coelenterazine-loaded leaf discs with a 0.2 M solution of glucose or fructose, but not of mannitol or sorbitol, also reduced the cold shock-induced luminescence. It is suggested that non-synchronous increases in cytosolic level of free Ca²⁺ occur in leaf discs during treatment with high levels of metabolizable sugars.     

Antioxidant status of the potato tuber and Ca2+ deficiency as a physiological stress

The antioxidant status of potato ( Solanum tuberosum L.) tubers of two genotypes, cv. Désirée and clone 10337de40 was investigated in relation to susceptibility to internal rust spot (IRS), a Ca²⁺-related physiological disorder. Concentrations of total calcium within the perimedulla tissue of tubers, grown with a restricted (1 m M CaCl₂) Ca²⁺ supply, were similar in cv. Désirée (IRS resistant) and clone 10337de40 (IRS susceptible). A range of antioxidants was assayed in order to assess antioxidant status in both genotypes under the two Ca²⁺ treatments. Although no appreciable differences were detected between low Ca²⁺ and control treatments, certain antioxidants were present at significantly higher levels in the IRS resistant genotype, cv. Désirée. These included dehydroascorbate reductase (EC 1.8.5.1) activity (more than 100% higher), total glutathione content (ca 40% higher), glutathione reductase (EC 1.6.4.2) activity (almost 50% higher), peroxidase (EC 1.11.1.7) activity (ca 60% higher) and superoxide dismutase (EC 1.15.1.1) activity (almost 80% higher). There was no difference in ascorbate content, ascorbate free radical reductase activity (EC 1.6.5.4), α-tocopherol levels and catalase activity (EC 1.11.1.6) between the two genotypes. The possible relationship between resistance to IRS and a superior antioxidant status, found in cv. Désirée, is discussed.     

Regulation of K+ and NO3− fluxes in roots of sunflower (Helianthus annuus) after changes in light intensity

Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K⁺ and NO₃⁻ uptake by roots, both uptake of K⁺ and NO₃⁻ and secretion into the xylem of young sunflower plants ( Helianthus annuus L.) were measured after changes in light intensity.
No close correlation was observed between the uptake of NO₃⁻ and that of K⁺; an increase in light intensity produced a much greater stimulation of NO₃⁻ uptake than of K⁺ uptake. On the other hand, secretion of NO₃⁻ into the xylem was tightly coupled to that of K⁺, and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K₂-malate shuttle on the regulation by the shoot of K⁺ and NO₃⁻ secretion in the xylem, which is linked to NO₃⁻ uptake, while K⁺ uptake is independent of this regulation mechanism.     

Bovine haemoglobin βA Zebu, βA43(CD3)Ser Thr: an intermediate globin type between the βA and βD Zambia is present in Indian zebu cattle

Two bovine haemoglobin beta chains, electrophoretically identical with the beta A chain of Herefords, were obtained from Ongole and Banteng, Bos javanicus, cattle. The amino acid residue differences of the two beta chains were compared by electrophoresis, cation-exchange and reverse-phase chromatography, amino acid analyses, and Edman degradation in comparison with beta A chain. The results showed that two beta chains differed from the beta A chain of the Hereford breed by the substitution of serine with threonine at the beta 43 position. No other difference was found between the two chains and beta A. This new beta chain type was termed beta A Zebu, which forms a possible evolutionarily transitional type between the beta A and the rare variant beta D Zambia found previously in African zebu cattle. The beta A Zebu differentiates from the previous beta B by at least four amino acid substitutions involving five codon-base changes.