Physical Basis for Altered Stem Elongation Rates in Internode Length Mutants of Pisum
48
Citation
29
Reference
10
Related Paper
Citation Trend
Abstract:
Biophysical parameters related to gibberellin (GA)-dependent stem elongation were examined in dark-grown stem-length genotypes of Pisum sativum L. The rate of internode expansion in these genotypes is altered due to recessive mutations which affect either the endogenous levels of, or response to, GA. The GA deficient dwarf L181 (ls), two GA insensitive semierectoides dwarfs NGB5865 and NGB5862 (Ika and Ikb, respectively) and the `slender' line L197 (la cry[ill]), which is tall regardless of GA content, were compared to the wild-type tall cultivar, Torsdag. Osmotic pressure, estimated by vapor pressure osmometry, and turgor pressure, measured directly with a pressure probe, did not correlate with the differences in growth rate among the genotypes. Mechanical wall properties of frozen-thawed tissue were measured using a constant force assay. GA deficiency resulted in increased wall stiffness judged both on the basis of plastic compliance and plastic extensibility normalized for equal stem circumference. Plastic compliance was not reduced in the GA insensitive dwarfs, though Ika reduced circumference-normalized plasticity. In contrast, in vivo wall relaxation, determined by the pressure-block technique, differed among genotypes in a manner which did correlate with extension rates. The wall yield threshold was 1 bar or less in the tall lines, but ranged from 3 to 6 bars in the dwarf genotypes. The results with the ls mutant indicate that GA enhances stem elongation by both decreasing the wall yield threshold and increasing the wall yield coefficient. In the GA-insensitive mutants, Ika and Ikb, the wall yield threshold is substantially elevated. Plants possessing Ika may also possess a reduced wall yield coefficient.Keywords:
Elongation
Turgor pressure
Osmotic pressure
Abstract Measurements were made of the growthof the sub‐apical region of decapitated, etiolated epicotyls of Pisum sativum L. cv. Alaska after treatments with indoleacetic acid (IAA), gibberellic acid (GA) and triiodobenzoic acid (TIBA). Growth was measured either at the end of a 2‐day period, at short intervals during growth, or was monitored continuously for 2–3 h using a position‐sensing transducer. In experiments measuring growth after 2 days, high levels (0.1–10 μg/plnat) of IAA caused expansion, whereas similar levels of GA caused elongation. When both hormones were applied together, the effects of IAA were dominant and expansion ensued, even when GA was present at 100 times the amount of IAA. Very low amounts of IAA (0.5–5 ng/plant), however, caused elongation. The elongation elicited by high GA or low IAa was inhibited to a similar extent by TIBA and this inhibition of elongation was associated with an increased expansion at the extreme tip. When application of the hormones was delayed, GA‐induced elongation was reduced considerably, IAA‐induced elongation was lessened somewhat and IAA‐induced expansion was partially converted into elongation. In experiments measuring elongation at short intervals, high levels of IAA caused rapid elongation followed after 3 to 6 h by expnasion. Both GA and low levels of IAA extended the duration of elongation with little apparent effect on the rate of growth. In fast‐growth experiments, low, intermediate and high levels of IAA doubled the rate of elongation with a lag period of about 20 min, whereas GA had at most a very slight stimulatory effect on the growth rate. It is concluded that the main role of GA in this system is to maintain physiological levels of IAA in the growing zone and that the level of IAA present determines whether elongation or expansion will take place.
Elongation
Etiolation
Gibberellic acid
Epicotyl
Cite
Citations (7)
Etiolation
Cite
Citations (23)
The highly active, polar gibberellin‐like substance found in the apical region of shoots of tall (genotype Le ) peas ( Pisum sativum L.) is shown by combined gas chromatography‐mass spectrometry (GC/MS) to be GA 1 . This substance is either absent or present at only low levels in dwarf ( le ) plants. Multiple ion monitoring (MIM) tentatively suggests that GA 8 may also be present in shoot tissue of tall peas. Gibberellin A 1 is the first 3 β‐hydroxylated gibberellin positively identified in peas, and its presence in shoot tissue demonstrates the organ specificity of gibberellin production since GA 1 has not been detected in developing seeds. Application of GA 1 can mask the Le/le gene difference. However, whilst Le plants respond equally to GA 20 and GA 1 , le plants respond only weakly to GA 20 , the major biologically active gibberellin found in dwarf peas. These results suggest that the Le gene controls the production of a 3 β‐hydroxylase capable of converting GA 20 to GA 1 . Further support for this view comes from feeds of [ 3 H] GA 20 to Le and le plants. Plants with Le metabolise [ 3 H] GA 20 to three major products whilst le plants produce only one major product after the same time. The metabolite common to Le and le plants co‐chromatographs with GA 29 . The additional two metabolites in Le peas co‐chromatograph with GA 1 and GA 8 .
Gibberellic acid
Cite
Citations (57)
Pretreatment effects of different gibberellins, helminthosporic acid, cyclic AMP and Kinetin on subsequent IAA-induced elongation were tested in cucumber hypocotyl sections. Gibberellin A7 was more active than GA3, while gibberellin A3 was almost inactive. Both helminthosporic acid and cyclic AMP mimicked GA3-action, though the degree of their activity was less. Kinetin pretreatment resulted in marked inhibition of IAA-induced elongation. The pretreatment effect of GA3 was also reflected in a greater responce of the sections to synthetic auxins.
Elongation
Kinetin
Cite
Citations (2)
Cite
Citations (23)
In shoots of the garden pea ( Pisum sativum L.), the main bioactive gibberellin (GA) is GA 1 , which is synthesised from GA 20 by 3 β ‐hydroxylation. Gibberellin A 20 is produced from GA 19 , as part of the process known as GA 20‐oxidation. Because these steps are thought to be negatively regulated by GA 1 , we compared the metabolism of labelled GA 19 and GA 20 in mutants deficient in GA 1 , with that observed in isogenic wild‐type (WT) plants. There was a large and specific increase in the 3 β ‐hydroxylation of labelled GA 20 in the GA 1 ‐deficient (dwarf) mutants, compared with the WT. Metabolism experiments did not provide convincing evidence for feedback regulation of 20‐oxidation, possibly because GA 19 akppears to be metabolised rapidly, even in WT pea shoots. Both 3 β ‐hydroxylase and 20‐oxidase transcript levels were markedly higher in the mutants than in isogenic WT lines. The results sukpport previous suggestions that both biosynthetic steps are feedback‐regulated by GA 1 in pea.
Hydroxylation
Wild type
Cite
Citations (33)
The elongation of etiolated stem segments in Pisum sativum L. was promoted by both exogenous IAA and GA3. The effect of IAA on the segment elongation could be blocked by gibberellin biosysthesis inhibitor S-3307, meanwhile, the effect of GA3 was inhibited by auxin transport inhibitor TIBA. These inhibitions could be relieved by reusing GA3 and IAA respectively. The observation of split halves of the apical segments indicated that IAA promoted the elongation of cortical cell, while GA3 promoted the elongation of inward tissue cells primarily.
Elongation
Etiolation
Cite
Citations (0)
Abstract The process of leaf elongation in grasses is characterized by the creation and transformation of distinct cell zones. The prevailing turgor pressure within these cells is one of the key drivers for the rate at which these cells divide, expand and differentiate, processes that are heavily impacted by drought stress. In this article, a turgor‐driven growth model for grass leaf elongation is presented, which combines mechanistic growth from the basis of turgor pressure with the ontogeny of the leaf. Drought‐induced reductions in leaf turgor pressure result in a simultaneous inhibition of both cell expansion and differentiation, lowering elongation rate but increasing elongation duration due to the slower transitioning of cells from the dividing and elongating zone to mature cells. Leaf elongation is, therefore, governed by the magnitude of, and time spent under, growth‐enabling turgor pressure, a metric which we introduce as turgor‐time. Turgor‐time is able to normalize growth patterns in terms of varying water availability, similar to how thermal time is used to do so under varying temperatures. Moreover, additional inclusion of temperature dependencies within our model pioneers a novel concept enabling the general expression of growth regardless of water availability or temperature.
Turgor pressure
Elongation
Cite
Citations (17)
Cite
Citations (7)