Growth Responses of Alaska Pea Seedlings to Visible Radiation and Gibberellic Acid.

Relative growth rate determinations on 5-millimeter regions of cucumber (Cucumis sativus L.) hypocotyls show that dim-red lightgrown seedlings have an even distribution of growth along the stem axis. This contrasts with the apical to basal graded decline in growth rate seen in dark-grown seedlings, including dark-grown cucumber seedlings used as controls in this study. Dark-grown seedlings convert to the nongradient pattern when transferred to dim-red light. The small amount of light required suggests that the change in developmental pattern may happen in the natural light environment.A consensus characteristic of stem elongation is a gradient of elongation rates along the stem axis, with high rates of elongation near the apex and a graded decline toward the base. Etiolation is characterized by rapid stem elongation exhibiting a graded pattern (8,9,23,25,28), whereas stem elongation following deetiolation is relatively slow but still exhibits the apical to basal gradient of extension rates (9,10,25). The hypothesis that changes in cell structure and function follow the gradient in growth rate has been tested for several developmental processes (23,25,28).Germinating cucumber (Cucumis sativus L.) seedlings in continuous DRL3 (21) MATERIALS AND METHODSCucumber seedlings (Cucumis sativus L. cv Burpee's pickler) were germinated in moist vermiculite and grown under DRL as described previously (21) or in a similar dark room at 24 ± 10C. Experiments were carried out in growth rooms at two locations (Berkeley, CA, and San Antonio, TX). For both locations, the DRL field in the growth room had fluence rates ranging from 0.3 to 0.5 ,Imol m-2 s-'. The light source for DRL emitted 90% of its total output between 600 and 700 nm, with peaks at 638 and 648 nm (13; data not shown).For determination of RGRs (18, 22), marks (carborundum chips, 100 ,um diameter) were placed at 5-mm intervals along hypocotyls of 3.5-to 4-d-old seedlings for total length of 40 to 60 mm. Seedlings were allowed to recover from handling for 2 h before data were taken. Video images were obtained from a Panasonic WV-1850 video camera (Matsushita Electronics, Seacaucus, NJ) that has a high sensitivity to red and IR light. Images of DRL-grown seedlings were obtained using light available in the DRL growth room. DG seedlings were imaged under photomorphogenetically inactive IR illumination (12). For marking and placement for imaging, DG seedlings were exposed to 1 to 2 min of green work light, which was previously shown not to affect growth in this cultivar (8). The images were processed by a personal computer running video digitizer board (Video-Van-Gough, Tekmatic Systems, Ben Lomond, CA) and programs used previously (18). The digitizer located the marks and recorded their position in x and y coordinates on an arbitrary scale. Region lengths were determined by calculating distances between marks and converting numbers from computer units to millimeters using a conversion factor established by measuring known distances. Marks were tracked for 2 h, ...

Section: Resultssupporting

confidence: 73%

“…A 10-fold higher fluence rate resulted in a permanent reduction in elongation rate in peas (15), and a 300-fold higher fluence rate had this effect in cucumber (26). High-fluence red light also caused a more rapid suppression of elongation than did DRL (8; data not shown).…”

Section: Resultsmentioning

confidence: 99%

Adaptation to Dim-Red Light Leads to a Nongradient Pattern of Stem Elongation in Cucumis Seedlings

Shinkle

Sooudi²,

Jones³

1992

“…These hypotheses require further investigation. They are consistent with observations that light-mediated inhibition of stem growth can be reversed by application of GA3 or GA, to pea plants (3,(7)(8)(9). They also reconcile apparently conflicting data (1, 1 [1][2][3][4][5][6][7][8][9][10][11][12][13]17) pertaining to the mechanism of control of GA1 3f-hydroxylase activity and GA, production in lightand dark-grown pea plants.…”

Section: Discussionsupporting

confidence: 76%

Gibberellin A₁ Biosynthesis in Pisum sativum L.

Smith¹

1992

A comparative study of the metabolism of radiolabeled gibberellin (GA) 1, 19, and 20 in isolated vegetative tissues of isogenic Le and le pea (Pisum sativum) plants incubated in vitro with the appropriate GA substrate is described. The results of this study provide evidence that the enzymes involved in the latter stages of GA biosynthesis are spatially separated within the growing pea plant. Apical buds were not apparently involved in the production of bioactive GA1 or its immediate precursors. The primary site of synthesis of GA2o from GA1, was immature leaflets and tendrils, and the synthesis of bioactive GA, and its inactive catabolite GAs occurred predominantly in stem tissue. GA29, the inactive catabolite of GA20, was produced to varying extents in all the tissues examined. Little or no difference was observed in the ability of corresponding Le and le tissues to metabolize radiolabeled GA,, GA19, or

“…The difference in internode elongation in light-and darkgrown pea seedlings has been described for several cultivars and genotypes (2,(8)(9)(10)14 There are two reports in the literature that the dwarf cv Progress No. 9 responded to GA20 in the dark, even though this GA elicited no growth response in red light when applied in the same manner and at the same dosages (1, 19).…”

Section: Introductionmentioning

confidence: 99%

“…The difference in internode elongation in light-and darkgrown pea seedlings has been described for several cultivars and genotypes (2,(8)(9)(10)14). Etiolation is so great in some dwarf cultivars, e.g.…”

mentioning

confidence: 99%

Use of an Acylcyclohexanedione Growth Retardant, LAB 198 999, to Determine Whether Gibberellin A₂₀ Has Biological Activity per se in Dark-Grown Dwarf (le⁵⁸³⁹) Seedlings of Pisum sativum

Sponsel

Reid

1992

Dwarf (le5839) seedlings of Pisum sativum respond to gibberellin A20 (GA20) in the dark, although the same dosage of GA20 applied to light-grown le5839 seedlings elicits no growth response. The acylcyclohexanedione growth retardant, LAB 198 999, which is known to inhibit gibberellin oxidation and in particular 30-hydroxylation such as the conversion of GA20 to GA1, also inhibits the growth response of dark-grown dwarf (/e5839) seedlings to GA20.Thus, the biological activity of GA20 in the dark appears to be a consequence of its conversion to GA1, even though it is known from studies with light-grown seedlings that the le mutation reduces the conversion of GA20 to GA1.The biochemical basis of the Le/le gene difference in Pisum sativum L. was determined by Ingram et al. (5,6). Lightgrown shoots of the wild type converted GA203 to GA,, whereas the conversion of GA20 to GA1 was greatly reduced in shoots of the dwarf le genotype. Wild-type seedlings responded as well to GA20 as to GA1, whereas in dwarf le seedlings the response to GA20 was much less than that to GA1 (5, 7). It was concluded from this work that the activity of GA20 in light-grown stems is due to its conversion to GA,. GA, is purported to be the primary GA that controls internode growth in pea (5). The observation that the le allele is a leaky mutation accounts for the small response of lightgrown shoots to high doses of GA20 (5).The difference in internode elongation in light-and darkgrown pea seedlings has been described for several cultivars and genotypes (2,(8)(9)(10)14 There are two reports in the literature that the dwarf cv Progress No. 9 responded to GA20 in the dark, even though this GA elicited no growth response in red light when applied in the same manner and at the same dosages (1, 19). It was postulated that the conversion of GA20 to GA, is increased in the dwarf in the dark, although an alternative suggestion, namely that GA20 may have biological activity per se in the dark, was also made in both papers. The results were later rationalized in terms of enhanced sensitivity of dark-grown tissue to GA, (15), although the magnitude of this enhancement does not appear to be sufficient to explain the activity of low dosages of GA20 in the dark.In this study, the possibility that GA20 may have biological activity per se in dark-grown dwarf pea seedlings was investigated by comparing its activity in dark-and light-grown Le and le5839 seedlings in the presence of one of the new acylcyclohexanedione growth retardants (3, 11). These retardants have as their primary mode of action the inhibition of 3f-hydroxylation of GA20 to GA, (12