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Sample Lab Report

Gibberellin Absorption at the Seed Stage of the Brassica Mutant – rosette 
Increases Internodal Elongation 
Cynthia O. Kholos Huntington Library and Botanical Garderns’ Grounding In Botany 

Abstract

 A single-gene mutant (rosette [ros/ros]) was soaked in a Gibberellin Acid (GA) aqueous solution and incubated at 3°C for a period of 14 hours prior to potting – to prevent premature sprouting – to observe the effects of shoot elongation in comparison to a control group.  The effects of the GA treatment retarded growth on all but 9 of the 200 seedlings.  The GA soaking treatment appeared to decrease the likelihood of successful sprouting and revealed no significant, observable effects on stem elongation. 

Introduction

 A range of genotypes of the Brassica mutants, which yield a faster growth development, have been subject to experiments that involve the exogenous application of Gibberellin Acid (GA).  Data from several studies have revealed a positive correlation between the exogenous application of GA, at varied concentrations, on shoot elongation (Rood, Pearce, Williams and Pharis 1989) and internodal elongation (Rood, Williams, Pearce, Murofushi, Mander, and Pharis 1990).  The effects of exogenous GA on the rosette plant spinach (Spinacia oleracea L.) was investigated and found to inhibit the effects of growth retardants, as well as increase the   endogenous GA1, evidenced by stem elongation (Zeevaart, Gage, and Talon 1993).  The exogenous application via the soil, foliar spray, and shoot tip indicate a direct relation to growth development.  In this study, we explore the response to exogenous application of rosette mutant seeds, incubated in a and 0.1% GA(aq.) solution, to stem elongation. 

Tools and Methods

 Materials:  100 fast plant (Brassica Mutant – rosette) seeds incubated for in a 20mL DI and 20mL 0.1% GA(aq.) solution for 14 hours at 3°C prior to planting has been compared to a control group of 100 non-incubated fast plant seeds.  Standard fast planting procedure was followed for both groups.  All 200 seeds were exposed to a 24hour fluorescent light period of14 days.  Measurements were conducted at two 7-day intervals from soil level to the tip of the last bifurcating stems. Methods:  Data measurements have been quantified and means have been compared, taking into consideration standard deviation.  A one-tail P(T<=t) value has been computed according to the following null hypothesis: Mean plant height for both groups equal at the second 7-day interval measurement. 

Quantitative Analysis

 
Average
Controls
 0.661
GA Treated
0.348
Standev0.3471.269
   
t-Test: Paired Two Sample for Means
   
 Variable 1Variable 2
Mean0.66090.3478
Variance0.12071.6097
Observations4646
Pearson Correlation0.0265 
Hypothesized Mean Difference0 
df45 
t Stat1.6251 
P(T<=t) one-tail0.0556 
t Critical one-tail1.6794 
P(T<=t) two-tail0.1111 
t Critical two-tail2.0141 
  

Results

 Seeds treated with GA showed no observable growth on day 5 except for 4 seedlings in one tray and 3 on the second tray with an average height of 3.5mm for all seven.  On day 8, no significant growth on GA treated seeds was noted.  By day 16 only 9 seedlings had germinated and heights were as follows:  1cm, 1cm, 8cm, 1cm for the first tray, and 1cm, 1cm, and 3cm for the second tray.  All 25 cells of trays one and two of the untreated control plants had at least one successful germination with the averages noted in the chart below. 

Discussion

 Measurements from all 50 control plants remaining after thinning were averaged (.66mm) with a calculated standard deviation of .347.  GA treated seeds resulting in 9 successful germination and sub-sequent growth were averaged together with the 41 non-sprouting seeds occupying remaining cells in the tray (.348), which yielded a standard deviation of 1.269.  The  P(T<=t) one tail test revealed a 95% confidence that the variances were not comparably similar.   Results were contradictory to the original hypothesis that germination and shoot elongation would be faster and greater in the GA soaked seeds.  Next steps will be to redesign an experimental set-up that takes into consideration the length of incubation and future research will reflect the use of various concentration levels of GA in the treatment of the rosette seeds.   

Literature Cited

 Rood, Pearce, Williams and Pharis (1989) A Gibberllin-Deficient Brassica Mutant – rosette.  Plant Physiol. (1989)89, 482-487 Rood, Williams, Pearce, Murofushi, Mander, and Pharis (1990) A Mutant Gene That Increases Gibberellin Production in Brassica.  Plant Physiol. (1990)93, 1168-1174 Zeevaart, Gage, and Talon (1993)  Gibberellin A is required for stem elongation in spinach.  Proc. Natl. Acad. Sci. USA Vol. 90, 7401-7405  

Acknowledgements

 The assistance of Martha Kirouac, Ph.D. and Mike Kerkman is gratefully acknowledged.  The fast plant (Brassica Mutant – rosette) seeds and the 0.1% GA(aq.) solution was provided by the Huntington Library and Botanical Garden’s “Grounding In Botany” course grant, 1151 Oxford Road, San Marino, CA 91108 
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