Journal of Experimental Botany

Fennimore, Steven A.; Foley, Michael E.

doi: 10.1093/jxb/49.318.89pmid: N/A

Abstract Genetic and physiological data indicate that gibberellic acid does not have a primary role in the regulation of seed dormancy in wild oat (Avena fatua L.). The gibberellic acid sensitivity threshold of dormant caryopses imbibed for 7 d was 1 µM. Intact dormant seeds were after-ripened for 0, 2, 4, 8, 12, 16, and 20 weeks at 40 °C and imbibed in H2O, 100 nM or 1 µM gibberellic acid. The length of the after-ripening interval was inversely related to the mean base gibberellic acid concentration (the concentration resulting in 50% germination). Thus, after-ripening, not gibberellic acid, is the principal factor that regulates the release of seed dormancy in wild oat. F2 caryopses (dormant×non-dormant) classified by germination response to progressively higher gibberellic acid concentrations, were pooled according to their gibberellic acid requirement: low, medium and high. Germination responses of the F3 progeny from the low, medium, and high gibberellic acid requirement pools were regressed on to the F2 parent values, and a heritability for germination response to gibberellic acid, h2=0.24, was calculated. Random amplified polymorphic DNA analysis of DNA samples from F2 pools requiring low and high gibberellic acid concentrations were screened with 200 decamer primers and no polymorphisms were found. The findings of this investigation demonstrate that gibberellic acid is not the primary regulator of seed dormancy in wild oat. Seed dormancy, wild oat, genetic analysis, gibberellic acid This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Smart, David R.; Bloom, Arnold J.

doi: 10.1093/jxb/49.318.95pmid: N/A

Abstract Root NO3− absorption was examined under steady state conditions in the presence and absence of NH4+ using intact tomato plants (Lycopersicon esculentum cv. T-5). Plants grown under a low-salt regime showed much higher rates of NO3− absorption than plants grown under a high-salt regime, but the presence of NH4+ at concentrations less than 200 µM increased the capacity for net NO3− uptake for both the low- and high-salt conditions. Simultaneous changes in net NO3− , K+, and H+ exchanges were continuously monitored for 3 h prior to and up to 7 h following exposure to NH4+ . Upon first exposure to 50 or 100 µM NH4+, NO3− absorption remained constant; but during the subsequent 6 to 7 h, NO3− absorption continually increased. Net K+ absorption decreased iµMediately following its first exposure to NH4+ , but gradually recovered during the 7 h following first exposure. Changes in K+ absorption were not correlated with changes in NO3− absorption. Proton efflux gradually increased under NH4+ exposure and was significantly correlated with the observed increase in NO3− absorption. When roots absorbing NO3− were exposed to 5000 µM NH4+, NO3− absorption declined throughout the entire observation period. Ammonium, nitrate, proton, absorption, tomato This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Björkman, Thomas; Pearson, Karen J.

doi: 10.1093/jxb/49.318.101pmid: N/A

Abstract High temperature causes unevenly-sized flower buds on broccoli inflorescences. This deformity limits production of broccoli to areas where summer temperatures rarely exceed 30 °C. The stage of development sensitive to heat was determined by exposing plants of ‘Galaxy’ broccoli at varying developmental stages to 35 °C day temperature for 1 week, and subsequently analysing the head structure. During the high temperature exposure, the development of certain flower buds was arrested. There was no corresponding cessation of bud initiation at the apex. No injury resulted if heat was applied before the reproductive induction, nor was there injury to differentiated flower buds. Meristems were affected only if heat was applied during inflorescence production or the floral initiation process. Shorter heat exposures produced little injury, and longer exposures were lethal. The plant's development at this sensitive period still appeared vegetative externally, but the youngest leaves had just begun to reorientate as a consequence of the reduced stem elongation rate. The meristem was less than 1 mm wide, and floral primordia were just forming, still subtended by leaf primordia. The injury was fully expressed by the time the head was first exposed (approximately 5–10 mm wide), though it became more apparent as the head matured. The buds that were delayed in development by the high temperature developed into normal flowers. Brassica oleracea, broccoli, flowering, heat injury, developmental arrest This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Gilbert, Glena A.; Gadush, Michelle V.; Wilson, Clyde; Madore, Monica A.

doi: 10.1093/jxb/49.318.107pmid: N/A

Abstract The purpose of this study was to analyse the accumulation of amino acid in source and sink tissues of variegated Coleus blumei Benth. leaves during an extended exposure to salinity stress. The imposed stress resulted in a reduction in shoot height and leaf size, as well as a reduction in total protein and nitrogen content in both the sink and source tissues. At the same time, accumulation of low molecular weight nitrogen-containing compounds in Coleus leaves was observed, which peaked within the first 10 d of exposure to salinity, and then declined, but remained slightly elevated for the remainder of the study. A number of amino acids were found to accumulate in both the sink and source tissues, including arginine, asparagine, and serine. A larger proportion of asparagine and less arginine was observed in the sink tissue than the source tissue of the salinity-stressed plants. This difference may reflect the mobility of these compounds in the phloem. No proline was found to accumulate in either the source or sink tissue during the exposure to salinity. From the pulse-chase labelling of stressed Coleus leaves it can deduced that some of the observed accumulation of amino acids and amides observed is due to de novo synthesis and not simply the result of protein degradation. Salinity stress, Coleus blumei, carbon partitioning, amino acids, compatible solutes This content is only available as a PDF. Author notes 4 Current address: University of Texas, Protein Microanalysis Facility, Austin, TX 78712, USA. © Oxford University Press 1998 © Oxford University Press 1998

Stoke, N.J.;Terry, G.M.;Hewitt, C.N.

doi: 10.1093/jxb/49.318.115pmid: N/A

Abstract Four-week-old velvet beans (Mucuna pruriens L.) were fumigated with ozone, isoprene and propene both singly and in combination (hydrocarbon+oxidant) in controlled-environment chambers for a 4 week period. Measurements were made of total soluble protein, ascorbate, dehydroascorbate, lipid peroxidation, and glutathione reductase activity in mature and young velvet bean leaves. Significant increases in soluble protein concentration with respect to the controls were found in plants fumigated with propene and isoprene+ozone for young leaves, and ozone only for mature leaves. The analysis of ascorbate concentrations in young leaves showed a significant increase in total ascorbate for propene-fumigated plants, a significant decrease in the level of the oxidized form (dehydroascorbate) for ozone and isoprene+ozone-treated plants, and a significant increase in the reduced form for plants fumigated with propene, propene+ozone and isoprene+ozone. The analysis of ascorbate levels in mature leaves showed no significant effect from any fumigation regime. When compared to control material the specific activity of the enzyme glutathione reductase was found to be significantly reduced in young leaves treated with propene, isoprene+ozone and ozone alone. However, in mature leaves this effect is lost and there are no significant differences with respect to the control. Ozone, hydrocarbons, velvet bean, Mucuna pruriens, antioxidants © Oxford University Press 1998

Roberts, J.A.

doi: 10.1093/jxb/49.318.125pmid: N/A

This content is only available as a PDF. © Oxford University Press 1998