Plant Physiology

Cosgrove, D. J.

doi: 10.1104/pp.102.1.1pmid: 11536544

Article PDF first page preview Close This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Scholthof, KBG.; Scholthof, H. B.; Jackson, A. O.

doi: 10.1104/pp.102.1.7pmid: 12231793

Article PDF first page preview Close This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Nonami, H.; Boyer, J. S.

doi: 10.1104/pp.102.1.13pmid: 12231794

Abstract When transpiration is negligible, water potentials in growing tissues are less than those in mature tissues and have been predicted to form gradients that move water into the enlarging cells. To determine directly whether the gradients exist, we measured water potentials along the radius of stems of intact soybean (Glycine max [L.] Merr.) seedlings growing in vermiculite in a water-saturated atmosphere. The measurements were made in individual cells by first determining the turgor with a miniature pressure probe, then determining the osmotic potential of solution from the same cell, and finally summing the two potentials. The osmotic potentials were corrected for sample mixing in the probe. The measurements were checked with a thermocouple psychrometer that gave average tissue water potentials. In the elongating region, the water potential was highest near the xylem and lowest near the epidermis and in the center of the pith. In the basal, more mature region of the same stems, water potentials were near zero next to the xylem and throughout the tissue. These basal potentials reflected mostly the potential of the xylem, which extended into the elongating tissues. Thus, the high basal potential confirmed the high potential near the xylem in the elongating tissues. The psychrometer measurements for each tissue gave average potentials that agreed with the average of the cell potentials from the pressure probe. We conclude that a radial gradient was present in the elongating region that formed a water potential field in three dimensions around the xylem and that confirmed the predictions of Molz and Boyer (F.J. Molz and J.S. Boyer [1978] Plant Physiol 62: 423–429). This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Sage, R. F.; Seemann, J. R.

doi: 10.1104/pp.102.1.21pmid: 12231795

Abstract The light-dependent regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity was studied in 16 species of C4 plants representing all three biochemical subtypes and a variety of taxonomic groups. Rubisco regulation was assessed by measuring (a) the ratio of initial to total Rubisco activity, which reflects primarily the carbamylation state of the enzyme, and (b) total Rubisco activity per mol of Rubisco catalytic sites, which declines when 2-carboxyarabinitol 1-phosphate (CA1P) binds to carbamylated Rubisco. In all species examined, the activity ratio of Rubisco declined with a reduction in light intensity, although substantial variation was apparent between species in the degree of Rubisco deactivation. No relationship existed between the degree of Rubisco deactivation and C4 subtype. Dicots generally deactivated Rubisco to a greater degree than monocots. The total activity of Rubisco per catalytic site was generally independent of light intensity, indicating that CA1P and other inhibitors are not major contributors to the light-dependent regulation of Rubisco activity in C4 plants. The light response of the activity ratio of Rubisco was measured in detail in Amaranthus retroflexus, Brachiaria texana, and Zea mays. In A. retroflexus and B. texana, the activity ratio declined dramatically below a light intensity of 400 to 500 [mu]mol of photons m-2 s-1. In Z. mays, the activity ratio of Rubisco was relatively insensitive to light intensity compared with the other species. In A. retroflexus, the pool size of ribulose bisphosphate (RuBP) declined with reduced light intensity except between 50 and 500 [mu]mol m-2 s-1, when the activity ratio of Rubisco was light dependent. In Z. mays, by contrast, the pool size of RuBP was light dependent only below 350 [mu]mol m-2 s-1. These results indicate that, in response to changes in light intensity, most C4 species regulate Rubisco by reversible carbamylation of catalytic sites, as commonly observed in C3 plants. In a few species, notably Z. mays, Rubisco is not extensively regulated in response to changes in light intensity, possibly because the activity of the CO2 pump may become limiting for photosynthesis at subsaturating light intensity. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Bilang, J.; Macdonald, H.; King, P. J.; Sturm, A.

doi: 10.1104/pp.102.1.29pmid: 8108497

Abstract We have used the photoaffinity label azido-[3H]IAA (5-N3- [7–3H]indole-3-acetic acid), a biologically active analog of indole-3-acetic acid, to identify auxin-binding proteins (ABPs) in the soluble fraction of Hyoscyamus muticus. A 25-kD polypeptide previously described (H. Macdonald, A.M. Jones, P.J. King [1991] J Biol Chem 266: 7393–7399) has now been purified to homogeneity by conventional methods. Binding of azido-[3H]IAA to the purified protein was reduced by active auxins but not by inactive indoles. Partial amino acid sequences of the purified protein showed high homology to glutathione S-transferase (GST) from tobacco (ParB) and from maize (GT32). The conclusion that the 25-kD ABP is a GST is further supported by high GST activity in fractions highly enriched in the 25-kD polypeptide and recognition of the ABP by antibodies against GST from wheat and maize. Furthermore, purification of a protein from a soluble protein extract from H. muticus by affinity chromatography on glutathione-agarose also yielded a 25-kD polypeptide that was indistinguishable in its N-terminal amino acid sequence and biochemical characteristics from the protein purified by conventional methods. Possible functions of GST in auxin action are discussed. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Adam, Z.; Hoffman, N. E.

doi: 10.1104/pp.102.1.35pmid: 8108505

Abstract CAB-7p is a chlorophyll a/b binding protein of photosystem I (PSI). It is found in light-harvesting complex I 680 (LHCI-680), one of the chlorophyll complexes produced by detergent solubilization of PSI. Two types of evidence are presented to indicate that assembly of CAB-7p into PSI proceeds through a membrane inter-mediate. First, when CAB-7p is briefly imported into chloroplasts or isolated thylakoids, we initially observe a fast-migrating membrane form of CAB-7p that is subsequently converted into PSI. The conversion of the fast-migrating form into PSI does not require stroma or ATP. Second, trypsin treatment of thylakoids containing radiolabeled CAB-7p indicates that there are at least two membrane forms of the mature 23-kD protein. The predominant form is completely resistant to proteolysis; a second form of the protein is cleaved by trypsin into 12- and 7-kD polypeptides. We interpret this to mean that the intermediate is a cleavable form that becomes protease resistant during assembly. This notion is supported by the observation that CAB-7p in LHCI-680 is largely cleaved by trypsin into 12- and 7-kD polypeptides, whereas CAB-7p in isolated PSI particles is trypsin resistant. In vitro, we generated a mutant form of CAB-7p, CAB-7/Bgl2p, that was able to integrate into thylakoid membranes but was unable to assemble into PSI. The membrane form of CAB-7/Bgl2p, like LHCI-680, was predominantly cleaved by trypsin into 12- and 7-kD fragments. We suggest that the mutant protein is arrested at an intermediate stage in the assembly pathway of PSI. Based on its mobility in nondenaturing gels and its susceptibility to protease cleavage, we suggest that the intermediate form is LHCI-680. We propose the following distinct stages in the bio-genesis of LHCI: (a) apoprotein is integrated into the thylakoid, (b) chlorophyll is rapidly bound to apoprotein forming LHCI-680, and (c) LHCI-680 assembles into the native PSI complex. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Guo, Zj.; Nakagawara, S.; Sumitani, K.; Ohta, Y.

doi: 10.1104/pp.102.1.45pmid: 12231796

Abstract To produce phytoalexin, 6-methoxymellein (6-MM) was induced in suspension cultures of carrot (Daucus carota) by buthionine sulfoximine (BSO) and CuCl2. Addition of BSO (a specific inhibitor of glutathione [GSH] synthesis) to the cultures lowered the cellular GSH levels. This depletion of GSH was BSO-concentration dependent, and the extent of 6-MM accumulation was dependent on the GSH depletion. The accumulation of 6-MM induced by BSO was suppressed by exogenous GSH. Exogenous H2O2 stimulated the production of 6-MM when added 1 d after BSO treatment, whereas H2O2 added at time zero or on the 4th d of BSO treatment did not. Moreover, a synergistic effect of simultaneous addition of BSO and CuCl2 was observed. These results suggest that active oxygen species may be involved in the triggering of 6-MM synthesis. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Coleman, G. D.; Englert, J. M.; Chen, THH.; Fuchigami, L. H.

doi: 10.1104/pp.102.1.53pmid: 12231797

Abstract In poplar (Populus deltoides Bartr. ex Marsh), a 32-kD bark storage protein (BSP) accumulates in the bark during autumn and winter and declines during spring shoot growth. We investigated the physiological and environmental factors necessary for the degradation of poplar BSP. Poplar plants were exposed to short-day (SD) photoperiods for either 28 or 49 d. Plants exposed to short days for 28 d formed a terminal bud but were not dormant, whereas exposure to short days for 49 d induced bud dormancy. BSP accumulated in bark of plants exposed to both SD treatments. The level of BSP declined rapidly when nondormant plants were returned to long days. BSP levels did not decline in dormant plants that were exposed to long-day (LD) conditions. If dormant plants were first treated with either low temperatures (0[deg]C for 28 d) or with 0.5 M H2CN2 to overcome dormancy and then returned to long days, the level of BSP declined. Removal of buds from non-dormant or dormant plants in which dormancy had been overcome inhibited the degradation of BSP in LD conditions. BSP mRNA levels rapidly declined in plants exposed to long days, irrespective of the dormancy status of the plants or the presence or absence of buds. These results indicate that the buds of poplars are somehow able to communicate with bark storage sites and regulate poplar BSP degradation. These results further support an association of BSP mRNA levels with photoperiod because short days stimulate BSP mRNA accumulation, whereas long days result in a decline of BSP mRNA abundance. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Rosenberg, N.; Shimoni, Y.; Altschuler, Y.; Levanony, H.; Volokita, M.; Galili, G.

doi: 10.1104/pp.102.1.61pmid: 12231798

Abstract Following their sequestration into the endoplasmic reticulum (ER), wheat storage proteins may either be retained and packaged into protein bodies within this organelle or transported via the Golgi to vacuoles. We attempted to study the processes of transport and packaging of wheat storage proteins using the heterologous expression system of yeast. A wild-type wheat [gamma]-gliadin, expressed in the yeast cells, accumulated mostly within the ER and was deposited in protein bodies with similar density to natural protein bodies from wheat endosperm. This suggested that wheat storage proteins contain sufficient information to initiate the formation of protein bodies in the ER of a heterologous system. Only a small amount of the [gamma]-gliadin was transported to the yeast vacuoles. When a deletion mutant of the [gamma]-gliadin, lacking the entire N-terminal repetitive region, was expressed in the yeast cells, the mutant was unable to initiate the formation of protein bodies within the ER and was completely transported to the yeast vacuole. This strongly indicated that the information for packaging into dense protein bodies within the ER resides in the N-terminal repetitive region of the [gamma]-gliadin. The advantage of using yeast to identify the signals and mechanisms controlling the transport of wheat storage proteins and their deposition in protein bodies is discussed. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Subramaniam, R.; Reinold, S.; Molitor, E. K.; Douglas, C. J.

doi: 10.1104/pp.102.1.71pmid: 8108506

Abstract A heterologous probe encoding phenylalanine ammonia-lyase (PAL) was used to identify PAL clones in cDNA libraries made with RNA from young leaf tissue of two Populus deltoides x P. trichocarpa F1 hybrid clones. Sequence analysis of a 2.4-kb cDNA confirmed its identity as a full-length PAL clone. The predicted amino acid sequence is conserved in comparison with that of PAL genes from several other plants. Southern blot analysis of popular genomic DNA from parental and hybrid individuals, restriction site polymorphism in PAL cDNA clones, and sequence heterogeneity in the 3[prime] ends of several cDNA clones suggested that PAL is encoded by at least two genes that can be distinguished by HindIII restriction site polymorphisms. Clones containing each type of PAL gene were isolated from a poplar genomic library. Analysis of the segregation of PAL-specific HindIII restriction fragment-length polymorphisms demonstrated the existence of two independently segregating PAL loci, one of which was mapped to a linkage group of the poplar genetic map. Developmentally regulated PAL expression in poplar was analyzed using RNA blots. Highest expression was observed in young stems, apical buds, and young leaves. Expression was lower in older stems and undetectable in mature leaves. Cellular localization of PAL expression by in situ hybridization showed very high levels of expression in subepidermal cells of leaves early during leaf development. In stems and petioles, expression was associated with subepidermal cells and vascular tissues. This content is only available as a PDF. Copyright © 1993 by American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)