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Gibberellins A1, A3, As, A1*, A20, and A29 were identified by full scan gas chromatography-mass spectrometry in leaf sheath segments of 7-day-old barley (Hordeum vulgare L. cv Golden Promise) seedlings grown at 200C under long days. In a segregating population of barley, cv Herta (Cb 3014), containing the recessive slender allele, (sin 1) the concentration of GA, and GA3 was reduced by 10-fold and 6-fold, respectively, in rapidly growing homozygous slender, compared with normal, leaf sheath segments. However, the concentration of the C20 precursor, GA19, was nearly 2-fold greater in slender than in normal seedlings. There was little difference in the ABA content of sheath segments between the two genotypes. The gibberellin biosynthesis inhibitor, paclobutrazol, reduced the final sheath length of normal segregants (50% inhibition at 15 micromolar) but had no effect on the growth of slender seedlings at concentrations below 100 micromolar. There was a 15-fold and 4-fold reduction in GA, and GA3, respectively, in sheath segments of 8-day-old normal seedlings following application of 10 micromolar paclobutrazol. The same treatment also reduced the already low concentrations of these gibberellins in slender segregants. The results show that the pool sizes of gibberellins A1 and A3 are small in slender barley and that leaf sheath extension in this genotype appears to be gibberellin-independent. The relationship between gibberellin status and tissue growth-rate in slender barley is contrasted with other gibberellin nonresponsive, but dwarf, mutants of wheat (Triticum aestivum) and maize (Zea mays).

Chlorophyll levels in 1-cm sections of the youngest fully expanded leaves of normal (Y) Festuca pratensis L. declined almost to zero over a period of 6 days after excision. Chlorophyll in a mutant genotype (NY) remained near the initial level for the whole of this period. Abscisic acid promoted pigment loss in Y but had no significant effect on chlorophyll in NY. Kinetin retarded pigment loss in Y but was ineffective in NY. Other biochemical changes associated with leaf senescence-reduction in protein content and the appearance of novel isoenzymes of a-naphthyl acetate esterases-occurred in both genotypes. Abscisic acid accelerated protein breakdown, whereas kinetin inhibited the loss of protein in both genotypes. The mutation thus appears to be expressed as a highly specific lesion in pigment metabolism. We concluded that pigment breakdown, which is widely used as an index of leaf senescenice, may not be an inevitable part of the aging process.Leaf senescence is a syndrome, comprising a number of biochemical and physiological changes. In many species, the most obvious symptom is yellowing of the leaves resulting from the degradation of photosynthetic pigments. In consequence, Chl content is employed widely as an index of leaf senescence, not only in the study of senescence per se, but also in the bioassay of gibberellins (15), cytokinins (6), and other growth regulators which influence senescence. In herbage plant breeding programs concerned with selection for winter greenness and extension of the climatic limits of the productive phase of leaf development (3), a subjective assessment of pigment content is often employed as a selection criterion. In such studies, it is commonly assumed that Chl degradation is linked in an obligate fashion to all the other components of the senescence process, such as protein degradation, changes in enzyme activity, and in isoenzyme patterns (2,11,13 Plants were glasshouse-grown in shallow boxes of John Innes No. 1 compost under normal daylight supplemented as necessary with high pressure mercury vapor lighting to give a daylength of 17 hr. The youngest fully expanded leaves of plants at the 5-or 6-leaf stage were cut into 1-cm sections and kept on moist filter paper in Petri dishes (13) in complete darkness at 20 C. Before incubation, leaf sections were surface sterilized as described by von Abrams (14) and aseptic conditions were maintained throughout the incubation period.Tissue Extraction. Each sample consisted of 10 leaf sections. After weighing, the sections were homogenized in 1 ml of buffer (0.05 M tris, 0.01 M MgSO4, 2 mm GSH, 0.25 mM EDTA; pH 7.4) using a pestle and mortar. The resultant paste was centrifuged for 6 min at 12,000g to give a supernatant for soluble protein and isoenzyme determinations.Determination of Soluble Protein and Chlorophyll. Protein was determined by the Lowry procedure (9) after precipitation with 10% trichloroacetic acid. Changes in specific leaf protein components were followed by disc electrophoresis according to the methods of Davis...

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Leaf f^rowth rate and the turgor pressure ot" cells in the e.xpanding zone of lea\-es of Lolium temulentum were measured simultaneously. Growth rate was reduced o\'er a range from 30//m min ' to zero by reducing the temperature of the expanding zone from 20 to 2 °C. Turgor pressure remained constant at 05 MPa. This implies tliat growth reduction by low temperature is due to changes in cell wall rheology. Cell membrane hydraulic eonducti\ ity (L^J was reduced with temperature as expected, but this was not sufficient to influence growth rate detectably.Key words: l^oliuin teinulcnluin, growth rate, turgor pressure, wall rheology, pressure probe, chill stress. JNTHOnUCTlONThe annual growth cycle of perennial temperate grasses involves substantial exposure to sub-optimal temperatures. These plants do not possess a true winter dormancy mechanism, but respond directly to prevailing temperatue conditions. An understanding ot the nature of tbese responses is important m impro\ing performance at low temperatures and tbence overall annual productivity (Pollock & Eagles, 1988). Grasses also provide an ideal system for studying cell expansion since, in common with other monocots, they possess a locahzed intercalary meristem and extension zone (Pollock & Eagles, 1988) allowing uneqtii\ocal identification of the position of the expanding cells. Stoddart el al., (1986) have described an instrument that allou.s the continuous and direct measurement of growth of graminaceous seedlings whilst the temperature of the leaf meristem is altered. Using seedlings of Lolium temulentum it was found that temperature perception and response occur within the extension zone over a time scale that precludes eflects on the supply of nascent cells. It has been suggested tbat tbe sensiti\ ity of extension growtb to cbilling may represent some pbysical limitation to growtb based on cbanges in tbe water * .Address tor cori'L'spoiKlcnce. relations properties of tbe plants (Kleinendorst & Brouwer, 1970; Watts, 1971; Barlow, Boersma & Young, 1977). Current models of tbe water relations of growing cells are based on tbe Lockhart equation (Lockhart, 1965; Tomos, 1985). (1)This equation relates relative growth rate (\/V) (d V/At); where V = cell volume and / = time) to the wall rheological properties